FINAL REPORT OF THE
“AKSTAFA BLOCK” AND SURROUNDING
KURA-GABIRRY INTERFLUVE, AZERBAIJAN
PREPARED FOR
FRONTERA RESOURCES
HOUSTON, TEXAS
PREPARED BY
ARZU DJAVADOVA, CHIEF GEOLOGIST
FRONTERA RESOURCES AZERBAIJAN
BAKU, AZERBAIJAN
AND
DR. NED MAMULA
TECHNICAL EDITOR
NOVEMBER 1999
TABLE OF CONTENTS
REGIONAL SETTING........................................................................................................ 5
PREVIOUS GEOLOGICAL-GEOPHYSICAL INVESTIGATIONS................................ 12
TECTONICS AND STRUCTURE.................................................................................... 12
STRATIGRAPHY AND LITHOLOGY............................................................................. 19
Upper Cretaceous............................................................................................................... 22
Eocene................................................................................................................................ 26
Lower Eocene.............................................................................................................. 26
Middle Eocene............................................................................................................. 29
Upper Eocene.............................................................................................................. 40
Maykop Suite..................................................................................................................... 44
Tarkhanian Horizon............................................................................................................. 51
Chokrakian Horizon............................................................................................................ 53
Karaganian Horizon............................................................................................................. 56
Konkian Horizon................................................................................................................. 58
Sarmatian Stage.................................................................................................................. 59
Lower Sarmatian.......................................................................................................... 60
Middle Sarmatian......................................................................................................... 63
Cryptomactra Subhorizon.......................................................................................... 64
Upper Sarmatian.......................................................................................................... 67
Herson Horizon......................................................................................................... 70
Eldar Suite................................................................................................................ 71
Shirak Suite.................................................................................................................. 73
Upper Pliocene................................................................................................................... 74
Agchagilian Stage......................................................................................................... 75
Apsheronian Stage....................................................................................................... 78
Quaternary Deposits............................................................................................................ 80
OIL-GAS-WATER CONTENT......................................................................................... 82
Oil and Gas Seeps............................................................................................................... 82
Tarsdallar Area............................................................................................................. 85
Gyurzundag Area.......................................................................................................... 87
Akstafa Block.............................................................................................................. 87
SUMMARY AND PROPOSED FUTURE WORK........................................................... 96
Regional
Figure
1. Location map of the Akstafa Block, northwestern Azerbaijan
2. Tectonic map of the Caucasus region
3. Tectonic map of the lower structure stage of the Kura-Gabirry Interfluve (Jurassic-Paleogene)
4. Tectonic map of the upper structural stage of the Kura-Gabirry Interfluve (Miocene-Pliocene)
5. Location map of the uplifts of the Kura-Gabirry Interfluve
6. Seismo-geologic profile of the Djeiranchel Synclinorium-Chatma Anticlinorium (920607)
7. Seismo-geologic profile of the Djeiranchel-Chatma-Eldaroyugi region (86R110)
8. Stratigraphic column of Azerbaijan
9. Seismo-geologic profile location map for the Kura-Gabirry region
Cretaceous-Eocene
10. Electric log cross section of Upper Cretaceous (Sajdag-Mamadtepe-Tarsdallar)
11. Lithofacies and isopach map of Lower Eocene in the Kura-Gabirry Interfluve
12. Lithofacies and isopach map of Middle Eocene in the Kura-Gabirry Interfluve
13. Structure contour map of Middle Eocene in the Kura-Gabirry Interfluve
14. Electric log cross section of Middle-Upper Eocene (Damirtepe-Udabno)
15. Electric log cross section of Middle-Upper Eocene (Damirtepe-Udabno-Sajdag-Molladag)
16. Electric log cross section of Middle-Upper Eocene (Keyruk Keylan-Gyurzundag)
17. Electric log cross section of Middle-Upper Eocene (Gyurzundag-Beyuk Palantekan)
18. Lithofacies and isopach map of Upper Eocene in the Kura-Gabirry Interfluve
Maykop Suite (Oligocene-Lower Miocene)
19. Lithofacies and isopach map of Maykop in the Kura-Gabirry Interfluve
20. Structure contour map of Lower Maykop deposits in the Kura-Gabirry Interfluve
21. Electric log cross section of Maykop (Tarsdallar)
22. Electric log cross section of Maykop (Beyuk Palantekan-Keyruk Keylan)
23. Electric log cross section of Maykop (Mamadtepe-Molldag)
Tarkhanian and Chokrakian Horizons (Middle Miocene)
24. Lithofacies and isopach map of Tarkhanian Suite in the Kura-Gabirry Interfluve
25. Electric log cross section of Tarkhanian-Chokrakian suites in the Kura-Gabirry Interfluve
26. Lithofacies and isopach map of Chokrakian Suite in the Kura-Gabirry Interfluve
Karaganian and Konkian Horizons (Middle Miocene)
27. Lithofacies and isopach map of Karaganian Suite in the Kura-Gabirry Interfluve
28. Electric log cross section of Karaganian-Konkian in the Kura-Gabirry Interfluve
29. Lithofacies and isopach map of Konkian Suite in the Kura-Gabirry Interfluve
Sarmatian Stage (Upper Miocene)
30. Lithofacies and isopach map of Lower Sarmatian in the Kura-Gabirry Interfluve
31. Electric log cross section of Lower Sarmatian in the Chatma Anticlinorium
32. Lithofacies and isopach map of Middle Sarmatian in the Kura-Gabirry Interfluve
33. Structure contour map of Upper Sarmatian (basal) in the Kura-Gabirry Interfluve
34. Structure contour map of Upper Sarmatian (top) in the Kura-Gabirry Interfluve
35. Lithofacies and isopach map of Upper Sarmatian in the Kura-Gabirry Interfluve
36. Electric log cross section of Upper Sarmatian in the Chatma Anticlinorium
Akchagilian Stage (Upper Pliocene)
37. Lithofacies and isopach map of the Akchagilian Suite in the Kura-Gabirry Interfluve
Seismo-Geological Profiles
38. Tarsdallar structural high (91NP210)
39. Tarsdallar structural high (890310)
40. Damirtepe-Udabno region (920507)
41. Gyurzundag-Akhtepe structural high (830310)
42. Keyruk-Keylan-Gyurzundag-Beyuk Palantekan region (841710-871710)
43. W.Gyurzundag-Gyurzundag structural high (900410)
44. Djeiranchel-Beyuk Palantekan region (852510-844410)
45. Akhtepe-Palantekan-Tarsdallar structural high (863110)
46. Tarsdallar-Beyuk Palantekan region (845210-871610)
47. Lessor Caucasus-Chatma Anticlinorium regional line (842407)
Oil, Gas and Water Testing Results
Table
1. Oil-gas-water shows in fields of the Akstafa Block, Kura-Gabirry Interfluve
2. Well test results for the Tarsdallar Field, southeast Kura-Gabirry Interfluve
REGIONAL SETTING
The “Akstafa Block” occupies about 3500 km2 of the Kura-Gabirry Interfluve in northwestern Azerbaijan (Figure 1). The Kura-Gabirry Interfluve is situated between the Kura River to the south, the Gabirry River to the north, the Mingechevir Reservoir to the east and the Georgian border to the west. The Kura-Gabirry Interfluve is a major structural zone in the Transcaucasus intermontane Middle Kura Basin, which belongs to the system of intermontane downwarps in the Caucasus segment of the Alpine Fold Belt.
Figure 1. Location map of the Akstafa study block in northwestern Azerbaijan
The tectonic structure of the Interfluve is closely associated with the structure of the folded mountain systems of the surrounding Greater and Lesser Caucasus. Facies and thickness variations of Mesozoic and Cenozoic complexes appear to have been affected by offset of deep crustal faults along which subsidence of the Transacaucasus intermontane zone occurred within the broader Alpine geosynclinal belt (Figure 2). Tectonic uplift ceased by the close of Pliocene. The depth of the basement in the Kura Basin varies between 5 to 15 km. Along the entire 450 km length of the geosyncline, there are three distinctive, independent downwarped basins which differ by their size and time of subsidence: i.e. the Lower, Middle and Upper Kura basins.
Figure 2. Main tectonic units of the Caucasus. Legend symbols are as explained: 1=orogenic depressions, 2=outcrops of ophiolites, 3=possible location of the Paleotethys suture, 4=Mesotethys suture, 5=first order boundaries of tectonic units, 6=tectonic boundaries between zones, 7=tectonic boundaries between subzones, 8=zones of developing overthrust nappes, 9=outcrops of crystalline basement
The western-most of these basins, the Upper Kura Basin, extends east from the Dzirul downwarp, closes westward toward Georgia, and is separated from the Middle Kura Basin to the east by the Martkob transverse structure. The axis of the Middle Kura Basin extends 300 km eastward and the basin is 170 km wide at its maximum width. The basin axis terminates toward the east at a relatively wide transverse rise, which is delineated along the foot of the eastern slope by the West Caspian Fault. Further to the east lies the relatively small Lower Kura Basin.
The Middle Kura Basin, containing the Kura-Gabirry Interfluve, is the biggest and most structurally complex part of the Kura Basin system. This basin is defined by individual uplifts and downwarps within the Greater and Lesser Caucasus. The northwestern part of the basin is split into two parallel longitudinal downwarps by the Kakhrtin frontal rise of the Greater Caucasus, forming the Alazan subbasin to the north and the Iori subbasin to the south, the later containing the "Akstafa Block" as shown in Figure 1. The southwestern border of the Middle Kura Basin has a complex outline because the Shamkor, Allaverdin and Lok anticlinoriums intersect the basin axis at relatively high angles to the regional strike of the Kura-Gabirry Interfluve. These anticlinorial folds are cored by Jurassic rocks, and in some places by Precambrian-Lower Paleozoic metamorphic complexes. In addition, these anticlinoria are divided by the Ajaken, Kazakh and Lyalvar synclinoriums, which have been filled with Cretaceous and Paleogene deposits. Thus, the sinuous north and south borders of the basin coincide with the contact between the Mesozoic and Cenozoic complexes that outline the topographic relief and structural framework of the region (Figures 3 and 4).
Figure 3. Tectonic map of the lower structural stage of the Kura-Gabirry Interfluve
Figure 4. Tectonic map of the upper structural stage of the Kura-Gabirry Interfluve
There are three distinct structural zones within the Middle Kura Basin: an internal zone, which is located on a platform of Mesozoic basement, and two border zones which developed within Mesozoic-Paleogene geosynclines to the north and south of the Middle Kura Basin. The south Kura flexure (or deep-seated downwarp) serves as the boundary between the southern border zone and the internal zone. The internal zone is structurally complex. The geosynclines are relatively narrow, containing thin sedimentary deposits and frequent breaks in the sedimentary record. The “Akstafa Block” is actually located in the Lesser Caucasus, situated between the Kura and Gibirry rivers. Based upon gravity data the depth to basement there is 5-6 km.
The Lower Baykal and Upper Alpine structural complexes of the Chatma region dominate the sedimentary section. The pre-Alpine folded basement contains a Precambrian and lower Cambrian complex of faulted metamorphosed rocks. These rocks outcrop in a zone along the southern border of the basin as the Shamkhor, Lok, Khram and Dzirul massifs (Figure 2). These massifs are represented by gneisses, phyllites, slate, marble and intrusions of granitoid and ultrabasic rocks. These rocks are intensely deformed into roughly east-west trending isoclinal folds, however, within the Dzirul massif, the fold axes trend roughly north-south.
In the internal zone, including the area from the Kura River valley to Kahetia Mountain, the basement is deformed by a sequence of downwarps and uplifts. The deformation in this lower structural complex did not affect the upper sedimentary Alpine interval, as Mesozoic (Jurassic) sediments were deposited on an angular unconformity on upper Paleozoic. The upper structural complex that forms the Alpine Fold Belt has been divided into two subcomplexes: 1) a lower or Mesozoic-Neogene complex and 2) an upper or Pliocene-Quarternary complex. The Mesozoic-Neogene complex was involved in the development of the Caucasus geosyncline, while the Pliocene-Quarternary complex was involved in the orogenic or mountain building stage.
Lower Jurassic terrigenous sediments and volcanogenic deposits of Middle Jurassic were deposited in the geosynclinal stage of development in the border areas of the basin. These rocks were deformed into large folds which are also faulted. The total thickness of these complexes is roughly 300-350 m. The geosynclinal development occurred over a considerable period of geological time, i.e. from Upper Jurassic to the close of Miocene. The geosynclinal deposits, approximately 5-6 km thick, include:
· Upper Jurassic Lower Cretaceous volcanogenic-terrigenous sediments
· Upper Cretaceous through Paleocene volcanogenic-carbonate and pyroclastics
· Lower Eocene terrigenous sediments
· Middle Eocene volcanogenic-pyroclastic and carbonate rocks
· Lower Maykop (Lower-Middle Oligocene) molasse deposits
· Upper Miocene-Pliocene terrigenous sediments
The orogenic stage of development, in turn, consists of three substages: 1) Lower-Upper Miocene, consisting of offshore terrigenous sediments, continental molasse deposits, 2) Meotian-Middle Pliocene (Shirak Suite), which is characterized by a break in the sedimentary deposition within the Kura-Gabirry Interfluve, but is present in the central part of the basin (e.g. Southern Kahetia), and 3) transgressive deposits of the Akchagilian and Apsheronian stages, ending with regressive sediments of the Quaternary period.
The structural basement of this region has a sharply dissected surface. Relief on the basement surface is complicated and characterized by zones of strike-parallel and transverse faulting, and associated uplifts and downwarps. The basement has subsided 5-6 km in the border zone and subsided 10-11 km within the internal zone of the Kura-Gabirry Interfluve. The Kazakh-Signakh basement downwarp is in the west and the Shamkhor basement uplift is in the east of the Kura-Gabirry Interfluve.
Recent geological-geophysical investigations suggest that the Mesozoic-Neogene (Miocene) section in the northwest pre-Lesser Caucasus border monocline and in the basin located to the north is relatively undeformed. The pre-Lesser Caucasus southern monocline is a narrow zone of deformed Mesozoic rocks, overlain by Upper Pliocene-Quarternary shales. The Mesozoic deposits of this region plunge toward the northeast. Based upon drillhole data, these Mesozoic deposits are represented by fractured carbonate rocks of Santonian-Campanian-Maastrichtian (Upper Cretaceous) age, which are everywhere underlain by a sequence of pyroclastic rocks of Turonian age. Their thickness increases toward the northeast and they are gently folded into an undulating pre-Alpine basement. Locally, these fold axes trend north-south, gradually changing to southwest-northeast-trending folds in the neighboring Kazakh downwarp, which is filled by Cretaceous and Paleogene sediments.
Within the regional Shamkhor overthrust sheet, the local Dashsalakhlinsky, Kazakh, Akstafa, Tatly-Kedermin, Kyrykhlinsky, Shamkir-Dalimamdesky and Dzegamsky overthrusts were mapped by gravity surveys. Faulting along the southeast border of the Kazakh downwarp had a 400 m displacement in the Jurassic and a 200 m diplacement in the Cretaceous, however, these faults have not been mapped at the surface.
Finally, the physical geography of the Kura-Gabirry region has a significant influence on its climate and vegetation. A damp subtropical area lies to the west and a dry subtropical area with hot summers borders on the east. Annual rainfall ranges between 38-42 cm and snow is rare. The average annual temperature is 12-13 oC. Temperatures in the mountainous areas are roughly 2-3 degrees lower than in the plains. The maximum temperature recorded in the region was 50 oC. The prevailing winds are from the northwest and west. In the western and central parts of Kura-Gabirry Interfluve, the average annual wind speed is 3.4-4 m/second and 2-2.5 m/second.
Flora of the Kura-Gabirry Interfluve vary widely. The northern and southern areas of the interfluve, including the floodplain, are covered by forests consisting of poplar, karaagach (Ulmus globbra), pistachio (Pistacia mutica), barberry (Berberis orentalis), pomegranate (Punica granatus), mulberry (Morus alba), pear (Prunus), hawthorn (Crataegus) and wild grapes (Vitis). Relict pine trees named Eldar pines (Pinus eldarica) are cultivated in the sandy Eldar region. Dog roses and junipers grow on the northern slopes of the uplifts located in the north part of the region. Due to the lack of the moisture in the soil of the plains, long-term xerophytic and xerophile vegetation (e.g.wormwood (Artemisia) and goosefoot (salsolla dendroides) has developed extensively. Ephemeras and ephemeridaes grow in the valleys. In general, distribution of vegetation in the region is closely associated with local soil and climatic conditions. Agricultural planting also plays a significant role in the region.
PREVIOUS GEOLOGICAL-GEOPHYSICAL INVESTIGATIONS
The Kura-Gabirry Interfluve has long attracted the attention of the petroleum industry, because of the numerous natural oil and gas seeps which frequently create small streams and lakes of oil. These observations served as the basis for construction of primitive oil fields in Tulkutepe, Eldar and Bayda-Chatma. The first geologist/surveyors focused their attention on outcrops of the Neogene complex. The structure of older Paleogene and Mesozoic was investigated using drilling and geophysical methods.
The initial stage of geologic investigations in this area occurred between 1873 to 1920. These early studies were not systematic and tended to focus solely upon the existing oil and gas seeps. The first stratigraphic description of Miocene sediments in the Kura-Gabirry interfluve was conducted in the Chatma area in 1906-1907 by K. P. Kalitsin. The study suggested that all existing oil seeps were associated with the sand layers of Sarmatian horizon. During the period from 1920-1929, systematic regional investigations and semi-detailed surveys were carried out. During World War II, the scope of work was significantly reduced, however, in 1947, geological mapping resumed with plane table surveys at 1:10,000 and 1:25,000 scales. As a result of the 1:25,000 scale surveys, all of the interfluve and adjacent areas was mapped and much valuable geologic data acquired.
Prospect drilling commenced in 1948 and penetrated all basic structures at Mamadtepe (1948 and 1966-1967), B. Palantekan (1949-1950), Keyruk-Keilan and Gyurzundag (1951), Agtepe (1952-1953), Molladag (1954), Tauz-Kazakh, Armudlu (1961-1963), Khatunlu (1966-1967), Sajdag (1967-1971), Kirzan-Khuluf (1968-1971), Damirtepe-Udabno (1969-1971), Kaflandere-Ortagash (1979-1983), Tarsdallar-Palantekan (1984-1986), and Tarsdallar-Enikend (1986).
Regionally, a total of 265 prospecting wells were drilled, with 158 of the wells drilled to less than 500 m, 63 wells were drilled to roughly 1200 m and 38 wells were drilled to 1800 m. The total amount of drilling reported is approximately 190,101 m. Most of the wells were drilled with complete core samples, which proved to be extremely valuable for the identification of fauna, flora and for petrographic examination of the Neogene and Miocene-Paleogene rocks penetrated.
Both prospecting and parametric drilling was carried out in Sajdag, Armudlu, Mamadtepe, Demirtepe-Udabno, Gyurzundag, S. Palantekan, Keyruk-Keilan, Agtepe, Molladag, Beyuk Palantekan and Tarsdallar. A total of 52 prospecting/parametric wells were completed in these areas, with the cummulative amount of drilling reaching 180,500 m (Table 1).
Geophysical studies within Kura-Gabirry Interfluve have been conducted simultaneously with geological surveys and structural/prospecting drilling since 1929. The entire region has been covered by gravity, magnetic and aeromagnetic surveys at various levels of detail. Regional cross sections were also constructed using deep seismic surveys, complex vertical magnetic profiling and electric log profiling. Reflection and refraction seismic surveys cover most of the entire Kura-Gabirry Interfluve.
TECTONICS AND STRUCTURE
Based upon its geology and geomorphology, the “Akstafa Block” is divided into two zones: the Northern Zone or Chatma Anticlinorium and the Southern Zone or Djeiranchel Synclinorium. The Chatma Anticlinorium is characterized by hilly, high-relief terrain carved from heavily dissected Neogene and Sarmatian sediments. The Gabirry River forms the northern border of the Chatma Anticlinorium. The western border is located near the town of Udabno and the eastern border is the Mingechevir Reservoir. The southern Chatma Anticlinorium approximately coincides with the sinous geologic contact between Miocene and Pliocene deposits extending along the southern edge of the Beyuk Palantekan, Akhtakhtatepe, Molladag, Sajdag and Udabno uplifts (Figure 5).
Figure 5. Location map of the uplifts in the Kura-Gabirry Interfluve
Regionally, the Chatma Anticlinorium is comprised of a band of intensively deformed uplifts, approximately 10-15 km wide and 120 km long. These uplifts form a series of ridges that trend northwest to southeast toward the Mingechevir Reservoir, containing scattered peaks which exceed the average mountain top elevations. The highest peaks are located north of the Gabirry River, along the Chobandag uplift (892 m), which is the continuation of the Akhtakhtatepe (768 m) and Beyuk Palantekan (453) uplifts. Between the dissected uplifts of the Chatma region are deeply eroded ravines that widen toward the Gabirry Valley.
The southern part of the Chatma Anticlinorium appears to be less deformed, and contains the lessor peaks. Overall, the topography of the region appears to closely mirror local tectonic features. In most cases, elevated areas of relief correspond to anticlines formed by Miocene rocks, while low-lying areas have ben formed by younger sediments deposited in synclinal folds.
The northern part of the “Akstafa Block” is situated within the Chatma Anticlinorium. Based upon geological-geophysical data from this region and from the adjoining Greater and Lesser Caucasus, the sedimentary section across the Chatma Anticlinorium is in excess of 6-7 km thick, and considerably less thick across the Djeiranchel Synclinorium (Figures 6 and 7).
Figure 6. Seismo-geologic profile of the Djeiranchel Synclinorium-Chatma Anticlinorium
Figure 7. Seismo-geologic profile of the Djeiranchel-Chatma-Eldaroyugi region
In the northern Chatma region, the Eldaroyugi Uplift parallels the Akhtakhtatepe and Beyuk Palantekan uplifts. The Eldaroyugi Uplift extends eastward from Tulkitepe Mountain in the west, where at the 601 m elevation, the uplift abruptly changes to a northeast-southwest trend, and is separated from the adjacent Palantekan Uplift by the Eldar Steppe. Further east, near the village of Kesaman, the upift has been truncated by the Gabirry River Valley. Along its entire trace, the Eldaroyugi uplift is characterized by strongly dissected ridges, ravines, relatively flat northern slopes, and steep cliffs on the southern slopes.
The western part of the Eldaroyugi Uplift plunges in the direction of Chatma Valley, terminating at Alachig Mountain. Topographically, this mountain is a high plateau dotted with occasional mud volcanos. The steep north face of this ridge is dissected by many deep ravines that fall steeply toward the Gabirry River Valley. The Armudli Uplift stands to the south of Alachig Mountain in the western Chatma Valley.
South of and parallel to the Eldaroyugi Uplift stands another ridge crest of lesser elevation. In the west, this uplift appears to originate at Udabno Mountain (871 m) and extends parallel to the Sajdag and Molladag uplifts (709 m) along the southeast side of the Chobandag Ridge, where it intersects the Akhtakhtatepe Uplift.
The Southern Zone or Djeiranchel Synclinorium is a hilly semi-arid terrain that covers almost half of the Kura-Gabirry Interfluve, and is bordered by Udabno Mountain to the west, Mingechevir Reservoir to the east and the Kura River to the south. The Djeiranchel and Ortagash valleys located in this zone are floored by Pliocene Akchagylian and Apsheronian deposits.
The numerous ravines carved into the Djeiranchel Zone extend east-west toward the Kura River Plain. The deepest ravine within this zone gradually widens into the Gaflandere Valley. This east-west trending ravine originates on the south face of the Molladag uplift and has a maximum width of 80-90 m and a depth of 100-150 m. The relationship between the tectonics, lithology of the formations and topographic relief is readily apparent in this zone. For example, in most cases, positive topographic relief is directly associated with anticlinal folds, while negative topographic relief is located over synclinal folds. Only in rare cases is inverted topography observed, such as when anticlinal uplifts are underlain by Upper Pliocene shaley formations and the limbs of the fold are floored by competant rocks.
Structurally complex uplifts such as Mamadtepe, Kushkuna and Ortagash (545.2 m), Grdzelishvili-Gyurzundag (608.1 m), Keyruk-Keylan (642 m), Guyruhenchi (455 m) and Djeiranchel (413 m) occur in the central part of the Djeiranchel Synclinorium. These uplifts are capped by coarse gravel, sandstone and nonporous (tight) clays of Upper Pliocene age. Topographically, the northern slopes are flat and cover more surface area than the steep southern slopes which are highly dissected by deep ravines falling abruptly toward the Kura River.
In Georgia, the Kura River flows toward the east between the Kartlinsk Plain and Mzheti Mountain, where the river turns abruptly to the south and follows a stair-step-shaped course toward the southeast below the mouth of the Khrami River. Along its entire length, the Kura River has rather low banks. South of Tblisi, Georgia, the Kura branches into several distributaries, forming an extensive flood plain. There are smaller tributaries flowing into the Kura River from the east, i.e. the Khrami, Akstafa, Tauzchay, Dagamchay, Shamkhorchay and Gendjachay streams. The Kura River contains a large amount of suspended clays which are ultimately deposited in the Mingechevir Reservoir.
The stratigraphy and structure of the Kura-Gabirry Interfluve includes Upper Paleogene through Recent deposits. Exploratory wells within the region have penetrated at least to Cretaceous age materials. Upper Cretaceous and Jurassic rocks outcrop beyond the study area in the foothills of the Lesser Caucasus. Many of the observations in this section are based upon analyses of the results of petrophysical investigations of core samples and the interpretation of geophysical well logs obtained from prospecting wells. These lithologic and geophysical data were assembled in order to define stratigraphic boundaries and to develop regional stratigraphic correlations for Upper Cretaceous through Upper Sarmatian units (Figure 8).
Figure 8. Stratigraphic column of Azerbaijan
Figure 8 con’t. Stratigraphic column of Azerbaijan
Regional correlation schemes were also constructed using the orthogonally oriented seismo-geologic profiles shown in Figure 9. In addition to the seismo-geologic profiles, other important data used in building the regional correlation included: 1) results of microfauna studies in various wells, 2) lithologic description of core recovered from deep wells and 3) stratigraphic sections from exploratory wells.
Figure 9. Seismo-geologic profile location map for the Kura-Gabirry region
Collectively, these data have enabled identification of key marker horizons, directions of thickening and facies changes for some important stratigraphic units, including the assignment of: 1) the Tarkhanian Suite interval (Middle Miocene), which had previously been lumped together with the Chokrakianian Suite, 2) the Konkianian and Karaganianian Suite intervals (Middle Miocene), which were also previously lumped together as one suite, and 3) the Lower, Middle, and Upper Sarmatian subsuites, each of which has distinctive electric log characteristics.
On the basis of stratigraphic boundaries assigned from the above mentioned data, lithofacies- isopach maps were constructed for: 1) Lower, Middle and Upper Eocene, 2) Maykop Suite, 3) Tarkhanian Suite, 4) Chokrakian Suite, 5) Karaganian Suite, 6) Konkian Suite, 7) Lower, Middle and Upper Sarmatian and 8) Akchagylian Stage. In addition, structure contour maps have been compiled for key stratigraphic horizons, including: 1) Middle Eocene, 2) Lower Maykop and 3) the bottom and top of the Upper Sarmatian. Each of these stratigraphic units and the associated data are discussed below.
Upper Cretaceous
The maximum thickness of the Upper Cretaceous deposits drilled in Well Nos. 9 and 27 at Tarsdallar was 908 m and 912 m, respectively; 441 m in Well No. 4 at Sajdag Ridge; and 852 m in Well No. 1 on the Mamadtepe uplift (Figure 10). In addition, Well Nos. 5, 6, 11, and 20 at Tarsdallar had encountered much thinner Upper Cretaceous sediments.
Figure 10. Electric log of Upper Cretaceous section in the Sajdag-Mamadtepe-Tarsdallar region
Based upon the analysis of selected core samples, the Upper Cretaceous cross section of the Kura-Gabirry Interfluve is represented by three genetic types of rocks, i.e. effusive lava, tuffogenic rock, and carbonates. An attempt has been made to compare each of these rock intervals using electric log characteristics (i.e. no solid core or mud sampling was conducted during drilling).
For example, in the classic Well No. 9 at Tarsdallar, rock stratum have relatively low electrical resistivity, e.g. less than 1.0-1.08 ohm/m, and a relatively gentle SP curve characterizes the base of Upper Cretaceous from the 3928-4000 m interval (Figure 10). The only direct evidence of lithology from this interval is the montmorillonitic oil-stained sand brought up in the drilling mud of one well. This interval was not penetrated by other wells.
In the 3760-3928 m interval, the cross section consists of 45-50 m of altered sedimentary strata, including marl with 10-15 m of interbeded clay. The 3795-3800 m and 3816-3820 m intervals were rock cored. The electrical resistivity of these intervals approaches 16 ohm/m, while “normal” rock resistivity is less than 5-6 ohm/m. This interval was not penetrated by other wells.
The 3500-3760 m interval contains alternating layers of tuffites, pellitic tuff, sandstone-tuff, and gravels, based upon data from the core sampling. Xenoliths or rock inclusions within the layers of this interval consist of greenish-gray tuff-pelite with relatively low lime content and single forms of foraminfera. Also present are gray tuff-sandstones with a characteristically pinkish hue and globotruncana acra, gl. Calcaratu foraminifers, suggesting an age of Cenonian (lower Upper Cretaceous). This interval has a relatively lower electrical resistivity, i.e. 20 ohm/m.
The 3500-3760 m interval correlates with the 3290-4097 m interval at Mamadtepe Well No. 1 and the 3206-4097 m interval at Tarsdallar Well No. 27. Based upon the analysis of core material recovered from these wells, porphyrite and basalt comprise part of the total content of volcanic rocks. The 3300-3530 m interval in Well No. 9 and the 3350-3812 m interval in Well No. 27 (both at Tarsdallar) contain frequently alternating tuffogenic rocks (tuffs, tuff argillites, tuff marl, tuff gravels) and effusive rocks. However, it has high resistivity strata (50-100 ohm/m) in separate layers, which alternate with the low resistivity layers which are 5-10 ohm/m .
Based upon electric log data (Figure 10) the maximum high resistivity zones (3530-3554 m and 3811-3705 m intervals in Tarsdallar Well Nos. 9 and 27, respectively; and the 3290-3121 m interval in Mamadtepe Well No. 1) also have relatively higher permeability. This part of the Upper Cretaceous section, penetrated by Well No. 4 at Sajdag (3940-4440 m), has lower permeability, probably due to increasing rock density with depth. This section of Upper Cretaceous is represented by alternating tuffogenic rocks (tuff clay, volcanic ash, tuff siltstone, tuff shale) and associated limestone layers.
The fifth Upper Cretaceous suite in Well No. 9 (3168-3300 m) is characterized by relatively high electrical resistivity and comprised of carbonate rocks: gray, tough and fractured limestone, with marl (including shelly marl) and reddish-brown clay layers with high marl content. This carbonate suite was encountered by Well No. 27 in the 3135-3350 m interval (Tarsdallar) and at the Mamadtepe Well No. 1 in the 2590-2845 m interval, and is absent in Sajdag Well No. 4.
The Upper Cretaceous carbonate suite was also encountered in Well Nos. 5, 6 and 20 (Tarsdallar) in the 2866-2946 m, 3082-3150 m and 2798-2882 m intervals, respectively, and is represented by white limestone (polymorphs) with foraminifera and spherical fauna, i.e. globotruncana conica, gt. arca, Grunbelina tesoera, G. stiata. The presence of these fauna would suggest Maastrichtian age deposits.
According to well log data (Figure 10), these regional Upper Cretaceous deposits appear to be uniformly present except at Sajdag Well No. 4, where they are absent or are overlapped by a marly limestone suite that differs from the lower carbonate suite. The electrical resistivity of the strata is 10-20 ohm/m. Moreover, the marly limestone suite is comprised of marl with alternating limestone layers. Microfauna analysis of Globoconusa daubjegenesis (Bromu), Globigerina triloculinoides Plumm., suggests the age of the strata as Paleocene-Danian.
Paleocene
Paleocene-Danian deposits were encountered in Tarsdallar Well No. 5 in the 2780-2866 m interval (at 86 m), Well No. 6 in the 2993-3082 m interval (at 89 m), Well No. 9 (Figure 10) in the 3103-3168 m interval (at 65 m.), Well No. 11 in the 2673-2738 m interval (at 65 m), Well No. 20 in the 2748-2798 m interval (at 50 m), Well No. 27 (Figure 10) in the 3135-3211 m interval (at 76 m), Well No. 24 in the 4350-4452 m interval (at 102 m), Well No. 26 in the 3474-3536 m interval (at over 62 m). These deposits were also encountered at the Mamadtepe parametric Well No. 1 (Figure 10) in the 2550-2590 m interval (at 40 m). The Paleocene-Danian suite thickness varies between 40-102 m and increases toward the northeast.
Eocene
Eocene age sediments have been thoroughly investigated insofar as they have been encountered by numerous structural, prospecting and deep (parametric and prospecting) wells. These deposits are represented by complex sedimentary and volcanic rocks. Analysis of lithology, microfauna and resistivity logs from the wells has enabled Eocene sediments to be identified with respect to their particular paleogeographic distribution, facies changes and variations in thickness. Eocene age deposits outcrop within the Kazakh Trough and further to north at Djeiranchel. These deposits appear to have been incorporated into the base of the thick Maykop Suite.
Lower Eocene
Lower Eocene sediments of the Kura-Gabirry region are represented by clayey lithofacies and consist of brown, brownish-gray, carbonaceous, tight clays with clayey marl and sandstone layers (Figure 11). According to the well log data from the western part of Kura-Gabirry Interfluve and the Kazakh Trough, tuffogenic rocks are observed together with the increase of their thickness. These rocks have been dated as Lower Eocene based upon microfauna analyses of globorotarica and pseudohastigerina; Globorotalia subbotina, gl. marginodentata, gl. aragogenesis and other forms are also present.
Figure 11. Lithofacies and isopach map of Lower Eocene in the Kura-Gabirry Interfluve
Based upon the well log data in Figure 10, electrical resistivity of Lower Eocene rocks at Tarsdallar is usually relatively week, measuring 1-1.5 ohm/m. The SP response is also relatively weak. However, in the Sajdag, Tauz-Kazakh and Girikhkesaman areas, there is an observable increase of SP values (with specific resistivity up to 10-12 ohm/m), probably due to the presence of alternating sandy marl, i.e. rocks with enhanced permeability.
The total thicknes of Lower Eocene ranges between 64-636 m. Mamadtepe Well No. 1 encountered Lower Eocene sediments of 636 m thickness in the 1914-2550 m interval. These sediments consist of gray carbonaceous clays, yellow sandstone and thick units of whiteish-gray marl with interbedded clay layers and occassional tuffs and clayey limestone. The Lower Eocene age of these particular units has been determined based upon typical foraminifera such as Globorotalia marginodentata, Globorotalia hispidicidaris, Globigerina nana, Pseudohastigerina eocaenica.
According to electric log data, the specific resistivity is well differentiated and in some intervals (i.e. 2460-2447 m, 2438 m, 2435 m and 2150-2130 m) measures 6-8 ohm/m . There is a strong SP curve that indicates relatively high rock permeability. As a whole, the SP curve is not differentiated.
Well No. 18 of the Tauz-Kazakh area encountered Lower Eocene deposits which are 400 m thick at the 820-1220 m interval. These deposits are represented by alternating greenish-gray clays and sandstone beds. Globorotalia ex.gr.aragonensis, Acarinina pentacamerata, and Ac.interposita are the general representatives of microfauna in this interval. The resistivity log rarely measures 3 ohm/m and the SP curve is also very weak.
Well No. 4 in the Sajdag area reached the top of Lower Eocene at a depth of 3375 m (Figure 10). Argillaceous marl and tight (nonporous) carbonate clays are deposited in the 3940-3885 m interval. Above 3765 m, is a thick bed of tight gray siltstones and clays, and higher in the coumn, near the top of Lower Eocene, are alternating clays and thick beds of marl. The clays and marl have been deposited in the 3810-3765 m and 3560-3490 m intervals. Various carbonate deposits are characterized by multiple forms of Glorobotalia marginodentata, Globigerina nana, and Gl. Comressaeforms.
According to electric log data, Lower Eocene strata, with relatively high resistivity of about 8-11 ohm/m (normal resistivity is roughly 4 ohm/m ) are observed in 3940-3860 m interval. The SP log is almost indistingushable. The 3810-3770 m interval is also characterized by the abrupt increase of the resistivity values up to 10-11 ohm/m (normal resistivity values do not exceed 3.8-4 ohm/m). The upper part of this interval is characterized by low resistivity values (less than 2 ohm/m). Only in the upper parts of the Lower Eocene horizons, at the 3385-3375 interval are two 5-7 m thick beds with resistivity values of 7ohm/m.
Approximately 26 m of Lower Eocene deposits were encountered at Molldag by Well No.1 in the 3806-3780 m interval. These deposits are represented by greenish-gray and gray clays and argillaceous marl containing sandstone layers. Globorotalia subbotinal, Gl. Marginodentata, and Globigerina quardriloculinoides represent the micro- fauna of this interval. Resistivity values of up to 4 ohm/m have been observed in this interval. The SP curve is indistingushable.
Deposits of upper Lower Eocene at Tarsdallar have been penetrated by Well Nos. 1, 5, 6, 9, 11, 16, 17, 20, 24, 26, 27 and 34 (Figure 11). The entire thickness of these sediments (approximately 60 m) was penetrated in only in 7 of the wells drilled at Tarsdallar (i.e. Well Nos. 5, 6, 9, 11, 20, 26 and 27). Lower Eocene deposits there are represented by brown, chocolate-brown, gray, and greenish-gray carbonaceous clays.
The upper part of Lower Eocene horizons are represented by marl. Sandstone layers are rarely observed there. In the core sample from the 2722-2712 m interval, and in the drilling mud samples from 2754 m, 2750 m, and 2745 m, were found a rich association of foraminifera (Globorotalia aragonensis, Gt. Marginodentata, Globorotalia subbotinal, Globigerina comressoeformis). Based upon these fauna, the age of deformation (folding) of these rocks also appears to be Lower Eocene.
Well No. 6, located less than 2 km from Well No. 5, encountered deposits of Lower Eocene (111 m thick) at the 2882-2993 m interval. These deposits are represented by greenish-gray, light and dark brown carbonaceous clays with sandstone layers. In core samples from the 2910-2900 m and 2940-2939 intervals, Globorotalia subbotinal, Gt. Marginodentata, and Acarinina triplex foraminifers were discovered. According to electric log data, the section is characterized by weak (i.e. 1-2 ohm/m) resistivity values. Other wells at Tarsdallar (i.e. Well Nos. 9, 11, 16, 20, 26 and 27) have the identical Lower Eocene lithofacies characteristics and thicknesses in 77-148 m range.
Middle Eocene
The deposits of Middle Eocene are the basic oil- and gas-bearing deposits of the Kura- Gabirry Interfluve. Areas within the interior of the Kura-Gabirry Interfluve are basically represented by volcanic-sedimentary facies that generally include alternating tuff, tuffite, sedimentary clay, argillite, and marl (Figures 12 and 13). Tuff, tuff-sandstone and tuff-marl with associated marl and argillite units appear to represent the general lithology of Middle Eocene in the Mamadtepe area. Their thickness is appproximately 104 m. Well No. 1 penetrated Middle Eocene in the 1810-1914 m interval. Globigerina pseudoeocaena and Globigerina frontosa are the microfaunal representatives for this interval.
Figure 12. Lithofacies and isopach map of Middle Eocene in the Kura-Gabirry Interfluve
Figure 13. Structue contour map of Middle Eocene in the Kura-Gabirry Interfluve
These deposits have been encountered at Tauz-Kazakh, Kazakh- Mamadtepe and Mamadtepe in Well Nos. 1 and 2 at Damirtepe-Udabno (Figure 14); Well Nos. 3, 4 and 5 at Sajdag and Well No. 1 at Molladag (Figure 15); Well No. 1 at Keyruk-Keylan and Well No. 1 at West Gyurzundag (Figure 16); Well Nos. 3, 4 and 7 at Gyurzundag and Well Nos. 2 and 3 at Beyuk Palantekan (Figure 17); and Well Nos. 1, 4, 5, 6, 8, 9, 11, 12, 16, 17, 20, 22, 24, 26, 27 and 34 at Tarsdallar. The thickness of Middle Eocene deposits varies from 44 m in Well No. 26 at Tarsdallar to 296 m in Well No. 2 at Damirtepe-Udabno.
Figure 14. Electric log of middle-upper Eocene section at Damirtepe-Udabno
Figure 15. Electric log of middle-upper Eocene at Damirtepe-Udabno-Sajdag-Molldag
Figure 16. Electric log of middle-upper Eocene at Keyruk-Keylan-Gyurzundag
Figure 17. Electric log of middle-upper Eocene section at Gyurzundag-Beyuk Palantekan
The microfauna of Middle Eocene is much less abundant than in Lower Eocene. In addition to dramatic decreases of microfauna species, the appearance of new foraminifera species (i.e. Acarinina bullbrooki, Globigerina frontosa, Gl. Pseudoeocaena) occurs in the Middle Eocene. Globigerina turkmenica and Gl.azerbaijanica characterize younger Middle Eocene strata.
The Middle Eocene section at Tauz-Kazakh and Kazakh-Mamadtepe (Well No. 1, thickness of 90 m in the 1450-1360 m interval) is represented by volcanic and volcanic-sedimentary facies that are associated with andesite, basalt, tuff-breccia, lava-breccia, and to a lesser extent by tuff and tuffite (Figure 12). Seams of sandstone, clay and marl have been also observed in these areas. Volcanic (lava) formations occur only in the southern part of the Kura valley, where the former center of volcanic activity appears to have been located. Abundant Acarinina bullbrooki and Globigerina eocaenica indicate the Middle Eocene age of these rocks.
In Well No. 18 at Tauz-Kazakh, the resistivity logs measure between 2 and 5 ohm/m. Resistivity and SP curves show frequent alternating between permeable and non-permeable rocks. Resistivity measured in Well No. 1 at Kazakh-Mamadtepe, is 100-150 ohm/m. The SP curve is well differentiated with enhanced permeability in the 1370-1357 m and 1430-1395 m intervals.
In the Damirtepe-Udabno Field, located in the northwestern part of the Kura-Gabirry Interfluve, Middle Eocene sediments (296 m thick) were discovered in Well No. 2 in the 3732-4041 m interval (Figure 14). These deposits are represented by gray tuff-gravels, tuff sandstone and whitish tuffs with layers of tight, dark gray carbonate clays and marls. The microfauna is represented by Acarinina sp. and Globigerina sp. Based upon resistivity logs, the Middle Eocene interval is characterized by rapidly increasing resistivity (i.e. up to 35-75 ohm/m). The SP log indicates relatively good permeability in the 3810-3970 m interval.
In the Sajdag Field, the maximum thickness (172 m) Middle Eocene sediments of were discovered in Well No. 4 in the 3206-3375 m interval. These deposits are represented by light-gray and greenish-gray porphyrite, gray siltstone with low carbonate content, tuff sandstone, tuff marl, tuffs and limestone. Single Acarinina ex. gr. bullbroori, Globigerina frontosa Middle Eocene foraminiferas were found in the rock samples.
Based upon resistivity logs (Figures 14-17), Middle Eocene intervals are characterized by rapidly increasing resistivity (i.e. up to 50-70 ohm/m). There are some resistivity peaks in the 3320-3326 m interval with corresponding SP values of up to 145 ohm/m, which characterizes relatively high permeability. In the upper part of the Middle Eocene section, the specific resistivity is 14-35 ohm/m, background resistivity is 10 ohm/m and the SP curve is well differentiated. These data suggest rocks of relatively high permeability.
The Middle Eocene interval of 3659-3780 m at Molladag Well No. 1 (121 m thick) is represented by tuff marl, tuff, tuff sandstone, sandstone, argillites, clayey marl and marl. Microfauna were found in the clayey marls, including: Acarinina rotundimarginodentata, Globigerina frontosa, Globorotalia off spinulosa and others. Based upon electric log data, the specific resistivity reaches 75 ohm/m while the background resistivity is 25 ohm/m. Although the SP curve is relatively weak, the resistivity curve is well differentiated.
The Keyruk-Keilan Well No. 1 penetrated Middle Eocene sediments (85 m thick) in the 3405-3490 m interval, which are represented by alternating greenish-gray marl, tuff marl, sandstone, tuffs, occassional argillites and limey clays. The marl in the 3428-3420 m interval is an organogenic clayey carbonate mass with numerous foraminifera, some of which were identified as Globigerina frontosa, Gl. boweri, Globigerina compacta, Acarinina ex.gr.triplex and Acarinina kievensis. The specific stratum resistivity approaches 10-18 ohm/m based upon electric log information, while the SP curve is relatively flat. In the 3460-3490 m interval, resistivity values are up to 50 ohm/m. The SP curve is well differentiated.
At the West Gyurzundag Well No. 1, Middle Eocene sediments are 233 m thick in the 4217-4450 m interval (Figure 16). This suite consists of marl and tuff marl, among which there are some sandstone, clay, tuff and tuff sandstone layers. The marl is clayey and extremely pyritized. The sandstone in the lower part of the section in the 4426-4420 m interval contains oil and it is also relatively coarse-grained. The clays are layered and contain siltstone and limestone. Tuffs are rarely observed in the upper part of the Middle Eocene.
Middle Eocene deposits have been dated based upon the presence of Globigerina tribabata, Acarinina rievensis and Ac.ex.gr.triplex. According to resistivity log data, the high resistivity suite represents the section where resistivity values reach 60-65 ohm/m. In the top of the suite (4220-4200 m) resistivity values vary between 10 and 14 ohm/m and the SP curve is well-differentiated, suggesting good rock permeability.
In Gyurzundag, the Middle Eocene was penetrated by Well Nos.1, 3, 4 and 7. The maximum thickness is 133 m. From the viewpoint of lithology and microfauna, the sections are identical to the section in Well No. 1 in West Gyurzundag. The specific resistivity is 50 ohm/m in the lower part of the section.
Middle Eocene deposits at the Beyuk Palantekan area have been penetrated by Well Nos. 2 and 3 in the 5131-5301 m interval (total Middle Eocene thickness in Well No. 2 is 170 m) and the 4750-4969 m interval (total Middle Eocene thickness in Well No. 3 is 220 m). These deposits are represented by tuffogenic and sedimentary rocks, marked by sandstones, argillite, tuff-argillite, siltstone, clays, calcareous clays, tuff-sandstones and tuff-siltstone. Specific resistivity of rocks is 50-60 ohm/m. The resistivity curve is weakly differentiated. The base of the Middle Eocene was not penetrated.
The Middle Eocene deposits investigated at Tarsdallar are based upon data reteived from 16 wells (i.e. Well Nos. 1, 4, 5, 6, 8, 9, 11, 12, 16, 17, 18, 22, 24, 26, 27 and 34). It was possible to determine the reduction of the thickness of the Middle Eocene deposits in Well Nos. 5 and 27. These deposits are mainly marl, sandstone, tuff-sandstones, and occassionally tuffs that contain seams of calcareous clays and shales. Samples collected at 2683 m, 2686 m and 2691 m contain Acarinina bullbrooki, Globigerina pseudoecaena and Globoratalia rensi.
Well No. 4 encountered Middle Eocene deposits (71m thick) in the 3040-3111 m interval. These deposits consist of greenish-gray marl, tuff-sandstone and tuff-marl with seams of greenish-gray tuffs and clays. Foraminifera in the 3085-3075 m interval include rare Globogerina frontosa, Gl.pseudococaena and others. In the section constructed from Well Nos. 11 and 17, the thickness of Middle Eocenee sediments appears to be 54 m and 64 m in the interval of 2471-2525 m and 2131-2192 m, respectively. These sediments consist of gray, greenish-gray marl, tuff-marl and tuff-sandstones with seams of clays and sandstones. Samples of the core taken at 2485-2495 m in Well No. 11 contain representatives of planktonic foraminifera including: Acarinina rotundimarginata, Globigerina frontosa, Globigerina azerbaijanica and Gl.incretacca. The specific resistivity of the rocks is roughly 18-23 ohm/m.
In Well No. 16, Middle Eocene deposits were penetrated and their thickness is approximately 64 m within the 2616-2680 m interval. This section is lithologically defined by interbedded sandstones, marl, tuff-sandstones and clays. There are individual seams of chalk up to 1 m thick. Foraminifera in the core from the 2630-2622 m interval include: Globoratalia spinulosa, Acarina rotundinargina and Pseudonastigerina micra. Resistivity values are 18-23 ohm/m.
In Well No. 24, a less than complete profile (110 m thick) of Middle Eocene deposits were encountered in the 4240-4350 m interval. Lithologically, the Middle Eocene is defined by interbedded greenish-gray marl, tuff-marl, gray argillaceous tuff-sandstones, dark-gray sandstones and occassional rare gray calcic argillites. The marl (4342-4398 m) is argillaceous, brown, dense, with an even fracture pattern. In the 4300-4398 m interval the tuff-marl is argillaceous, grayish-green, dense, with an even fracture pattern. The tuffs are crystalline and vitriolic (glassy), greenish-gray and generally have low resistivity.
Microfauna in the Middle Eocenee of this well is characterized as rich with foraminifera including: Acarinina bullbrooki, Globigerina frontosa, Gl. turkmenica, Globorotalia spinulosa and others. Electric logging indicates specific resistivity up to maximum values of 60-70 ohm/m. In the 4320-4278 m interval, the bottom and top of the beds are characterized by resistivities of 15-20 ohm/m, and 35 ohm/m at a depth of 4270-4228 m.
The maximum thickness of Middle Eocene deposits (289 m) at Tarsdalar was penetrated in Well No. 34 (located southwest of Well No. 24) in the 3384-3673 m interval. Based upon electric logging, this unit is represented by a thick monotonous sequence of high resistivities that increase toward the base of the strata. Lithologically, the section is no different from the sections in neighboring Well No. 24. Toward the southwest, near the folded Yenikend structure, there is a sharp reduction of the thickness of Middle Eocene deposits (25-26 m thick), in addition to a pronounced facies change which has been observed in Well No. 20.
Upper Eocene
Based upon well data, deposits of Upper Eocene are widely distributed in the Kura-Gabirry Interfluve (Figure 18). The wells which have been most investigated are: 1) the wells at Tauz-Kazah, 2) Well No. 1 at Kazakh-Mamadtepe and Well Nos. 3 and 4 at Sajdag (Figure 15),
3) Well Nos. 1, 3, 4 and 7 at Keyruk-KeylanGyurzundag, Well No. 1 at West Gyurzundag and Well Nos. 2 and 3 at Beyuk Palantekan (Figure 16), and 4) in numerous wells at Tarsdallar (e.g.. 1, 4, 5, 6, 8, 9, 11, 12, 13, 16, 17, 18, 20, 22, 24, 26, 27 and 34).
Figure 18. Lithofacies and isopach map of upper Eocene in the Kura-Gabirry region
The lower section of Upper Eocene (61 m to 370 m thick) is represented by a sandy-marl-argillaceous facies, which grades upward to clays and argillites with thin seams of sandstone, and occassionally tuff-sandstone and tuff-siltstone. In the section at Girakhkesaman and Kaflandere are units of coarse-grain detrital rocks and gravels. The boundary between Middle and Upper Eocene is a sharp break based upon the reduction of specific resistivity and the appearance Upper Eocene foraminifera including: Globigerinatheka tropicalis, Gl.corpulenta and Glouachitaensis.
In the section from Well No. 18 at Tauz-Kazah (620 m-430 m interval) and Well No. 1 at Kazah-Mamadtepe (1360 m-1010 m interval), Upper Eocene deposits reach a thickness of 190 m and 350 m, respectively, and are represeted by greenish-gray and gray carbonate clays with rare seams of sandstone and argillaceous marl in the base of the section. Microfauna includes: Globigerina ouachitaensis, Gl.irregularis, Globigerinatheka tropicalis, Gl.index and Bolivina antegressa. The resistivities are 1.5-2 ohm/m and the SP is poorly differentiated.
In the Mamadtepe area, Upper Eocene deposits (284 m thick) are found in 1526-1810 m interval in Well No. 1. These formations are characterised by gray, dark-gray marl, greenish-gray, carbonate clays with rare seams of sandstone. The observed microfauna include: Gl.corpulenta and Gl.galavisi. Background resistivity is 1.0 ohm/m and the SP curve is a straight line. A sequence of clay and sandstone is characterized by specific resistivity of 2-3 ohm/m in the 1618-1652 m interval. Testing in this interval indicated the presence of oil droplets in formation water (production was 6 m3 in a 24 hour period).
In the northwestern corner of the Kura-Gabirry Interfluve at Damirtepe-Udabno, Upper Eocene deposits (367 m thick) were encountered in the 3378-3745 m interval of Well No. 2. These deposits are represented by light-gray, blue-gray, carbonate-silty clays, with seams of marl and sandstone. In the lower part of the section are seams of tuffs, tuff-sands and gravels. Characteristic foraminifera include: Globigerinatheka tropicalis, Globigerinatheka index and Globigerina corpulenta.
Resistivities increase with increasing occurrence of carbonate rocks in the section. The specific resistivity measurements near the base of the section (3670-3730 m interval) are 7-10 ohm/m. In the 3632-3670 m interval, the specific resistivity is 1.8-2.0 ohm/m. The SP curve is poorly differentiated. In the upper part of the section at the 3670-3544 m interval are found frequent sequences of 1-3 m thick strata with increased specific resistivity of up to 3-4 ohm/m, and seldom up to 5-6 ohm/m. The SP curve is also not well differentiated. The 3478 m-3544 m interval contains clays with specific resistivity within the limits of background, i.e. 1.6-1 ohm/m. Higher in the section is a distinct 100 m thick sequence of clays, marls and sandstones and the 3378 m-3478 m interval contains a typical “ridge-like” appearance of the resistivity curve.
Upper Eocene deposits at Molladag (480 m thick), have been penetrated in the 3179-3659 m interval in parametric Well No. 1 (Figure 15). These deposits are represented by a sequence of greenish-gray clays, sandstones, marls, chalk, tuffs and siltstone. Various shale partings contain microfauna of Upper Eocene age, such as Globigerina corpulenta, Gl.galavisi and Gl.oocinalis. Electric logging indicates the section is a sequence of strata and thick benches of high specific resistivity of up to 10 ohm/m in base of the bench and up to 1.8-1.2 ohm/m) in the upper section. The 3463 m-3490 m, 3235 m-3275 m and 3288 m-3308 m intervals are characterized by increased specific resistivity of up to 10-12 ohm/m, and appear to correlate with the increasing density of marls and chalk.
In the Sajdag area, the Upper Eocene deposits have been penetrated in Well Nos. 3, 4 (Figure 15) and 5, which correspond to the intervals at 3280 m-3040 m (220 m thick), 3052 m-3203 m (154 m thick), and 3416 m-3250 m (166 m thick), respectively. These deposits are represented by gray sandstones, carbonate clays with rare seams of marl and argillite. The microfauna present include small quantities of Globigerunatheka tropicals and GI.ooficinalis. The electric logs indicate specific resistivity of rocks in the section varies from 5-6 ohm/m near the base, up to 2-3 ohm/m near the top. The 3050 m-3129 m interrval is characterized by reduced specific resistivity measuremnts of 1.0-1.2 ohm/m. The SP log is almost a straight line.
In the Keyruk-Keylan area, Upper Eocene deposits have been encountered in the 3109-3405 m interval (296 m thick) in Well No. 1 (Figure 16). Upper Eocene in the 3370 m-3405 m interval is marked by gray, greenish-gray, dense marl, tuff-marl, sandstone and tuff. Between 3370 m and 3350 m, there is pronounced ridge of increased specific resistivity of up to 10-12 ohm/m, with a positive SP curve; these readings occur above the so-called “above marl bench” (UMB), formed by marl and sandstone. Higher in the section, at 3300 m, are gray calcareous clays, with an occassional seam of dense sandstone and rare marl, all of which have poor resistivity responses. Background resistivities are 2-3 ohm/m and the spikes are no more than 5 ohm/m. The SP curve is represented by a straight line. Foraminifera include: Globigerinatheka tropicals, Gt.index, Globigerina corpulenta and Gl.galavisi.
The Upper Eocene at Gyurzundag and West Gyurzundag are divided into sandy marl and sandy-clays (bench), based upon their lithological and resistivity characteristics (Figures 16 and 17). The 15-35 m thick lower sandstone-marl bench (analog of the “above-marl bench” observed in the Gandja-Terter zone) corresponds to the lower horizon of Upper Eocene. It is represented by marl or tuffs with seams of sandstones and clays.
The “above-marl bench” has been discovered at Gyurzundag in Well No. 1 (4440 m-4472 m, 32 m thick), and Well No. 7 (4268 m-4303 m, 35 m thick) and at West Gyurzundag in Well No. 1 (4154 m-4192 m, 38 m thick). The marl is dark brown, in some places greenish-gray and fractured. On resistivity logs, the location of this “bench” is pronouned by increased readings of up to 10-12 ohm/m, and a non-differentiated SP curve.
Testing of Well No. 7 drilled into the “bench” yielded oil production. The upper sandstone “bench” reflects the lithological appearance of Upper Eocene and is marked by dark-gray and gray clays with seams of sandstone and some siltstone and shale. On resistivity log the “bench” is marked by a specific resistivity curve up to 2-5 ohm/m and an almost straight SP line. The total thickness of Upper Eocene in investigated section varies from 228 m to 283 m. Abundant foraminfera (Globigerinatheka tropicalis, GI.corpulenta, GI.officinalis and Gl.irregularis) exisit in these Upper Eocene deposits.
Upper Eocene deposits on Beyuk Palantekan (Figure 17) have been discovered by Well No. 2 (247 m thick within the 4884 m-5131 m interval) and Well No. 3 (249 m thick within the 4500 m-4749 m interval). The sections of these wells are represented by a sequence of limey clay, sandstone and rarely by marl, with numerous Globigerina tropicalis and Gl.ouachitaensis. The “above-marl bench” corresponds to resistivity logging within the 5093 m-5127 m (34 m thick) and 4702 m-4738 m (36 m thick) intervals. The “above marl bench” suite has been determined by electic logging in the 5093 m-5127 m (34 m thick) and 4702 m-4738 m (36 m thick) intervals.
Deposits of Upper Eocene have been investigated in almost all wells drilled at Tarsdallar (Well Nos. 1, 4, 5, 6, 8, 9, 11, 12, 13, 16, 17, 18, 20, 24, 26, 27 and 34). The total Upper Eocene thickness varies from 23 m (Well No. 9) to 370 m (Well No. 24). These deposits are represented by dark gray and greenish-gray clay, carbonaceous and lightly sandy clay with sandstone layers, siltstone and argillaceous marl. Tuffogenic rock layers have been observed in the sections of some of the wells.
The maximum thickness of Upper Eocene deposits penetrated by Well No. 13 is 246 m. These deposits are 370 m thick in Well No. 24, southeast of the Tarsdallar uplift. The minimum thicknesses occur over the Tarsdallar Uplift (i.e. Well Nos. 8, 9, 26 and 27). Based upon electric logs, the Upper Eocene section is characterized by poor resistivity, e.g. 1-2 ohm/m, with a slight increase in resistivity (2-3 ohm/m) occurring in the lowest part of the section in Well Nos. 5, 6, 12 and 18. Strata with increased specific resistivity of up to 6-7 ohm/m are observed in Well Nos. 4, 8, 9 and 27.
Maykop Suite
The Maykop Suite is not widely distributed within the Kura-Gabirry region (Figure 19). Maykop sediments outcrop from north to south as narrow abrupt layers within the limits of Arkhashensu, Aramdara, Alachig, Yaylachig, Armudli, and Chobandag fold structures. Maykop rocks also outcrop along mapped faults (Figure 20). The sediments of the Maykop Suite are represented, on the south side of Chobandag Ridge, by thinly layered gray (and brown in the weathered surface) foliated, non-carbonaceous clays such as jarosite and gypsum. There are abundant marlaceous and sideritic concretions among the clays in the upper part of the section. Sideritic concretions are highly developed in Maykop deposits of the Alachyg area. On the north side of the Alachyg fold structure, the Maykop Suite is entirely buried by Middle Sarmatian sediments. Maykop deposits of the Alachyg area do not differ from those at Chobandag.
Figure 19. Lithofacies and isopach map of Maykop in the Kura-Gabirry Interfluve
Figure 20. Structure contour map of Lower Maykop deposits in the Kura-Gabirry Interfluve
Maykop deposits have been penetrated by almost all deep exploratory wells drilled in the Kura-Gabirry Interfluve, and also by numerous prospecting wells located in Tauz- Kazakh, Khatunli, Kaflandere, Girakhkesaman, Kirzan-Khuluf and Mamadtepe. The deposits are basically clay lithofacies with a gradual increase in fold intensity toward the north.
The thickness of Maykop deposits varies widely between 0 to 2875 m. These deposits are represented by dark gray (with greenish tint) and pastel-colored carbonaceous clays with rare 0.5-1 m thick layers (poor resistivity) of tuffogenic sandstone, grayish-brown tight marl, volcanic ash and conglomerate. The clays contain plant remains and fish scales.
Alternating beds of sandstone and clay could be observed in the lower part of the exposed section of Maykop deposits in the Girakhkesaman area. The thickness of some sandy layers is roughly 1-4 m, while the cumulative thickness of sandy strata is 30-40 m. As is observed from the Maykop sections in various wells, their thickness in the Khatunli area decreases from northeast (760 m thick) to southwest (up to several tens of m thick). The decrease of Maykop thickness is probably the result of erosion during post-depositional transgressions.
Fine- to medium-grain gray sand and sandstone layers are present in the clayey strata of the Lower Maykop in the southeastern part of the Kura-Gabirry Interfluve, particularly at Kirzan-Khuluf. In most cases, the sandstone layers are characterized by tight, well-granulated grains, some of which are clayey-feldspathic, along with tighly-cemented fine-grain sandstone with low resistivity. The thickness of sandy substrata does not exceed 1-3 m. Only in rare cases is the thickness 5-6 m. In the alternating beds of sand and clay observed in the Maykop section, sand is the dominant material. The 10-125 m thick upper suite was penetrated by Well Nos. 5, 9 and 10. Well No. 8 reached the 125 m thick lower suite of Maykop sediments, which consists mainly of detrital rock fragments.
Based upon electric logs, Maykop deposits are characterized by low resistivity and undifferentiated SP curves of 1-2 ohm/m (Figures 21, 22 and 23). An increase of measured specific resistivity up to 4-8 ohm/m has been seldom observed, but does occur within a few marl and sandstone layers. Specific resistivity increases in the sandy beds are characterized by relatively higher permeability.
Maykop sediments that were encountered in deep wells have rather monotonous well log and lithological characteristics, such as clays with sand and marly layers that form alternating beds of sandy-argillaceous deposits. The thickness of the Maykop Suite varies from 579 m in Well No. 17 at Tarsdallar, up to 2875 m in Well No. 1 at Sajdag. Also noteworthy is the gradual replacement of sandy beds by clays at the base, with increasing clays occurring near the top of the Maykop.
Figure 21. Electric log of Maykop section at Tarsdallar
Figure 22. Electric log of Maykop at Beyuk Palantekan-Keyruk Keylan
Figure 23. Electric log of Maykop section at Mamadtepe-Molldag
Sandy layers are basically concentrated in the Middle Oligocene interval of the Maykop Suite. The Maykop section in the Chatma Anticlinorium is dominated by argillaceous facies. These clay strata do not contain microfauna but plant and fish remains abound. The clay layers are deposited on the beds of Sakaraul Stage, in the uppermost part of the Maykop section, and are considered as an analog of the Kozakhursk Stage. Thus, due to the monotony of the section and the presence of faulting, anomalously high resistivity measurements have been observed at or near faults, and, supposedly it is not practical to determine the true thickness of the Maykop section based upon electric log data. Therefore, the net pay isopach map that has been drawn for the Maykop shows only observable thicknesses for Maykop sediments from wells.
Tarkhanian Horizon
Similar to the Maykop Horizon, deposits of the Tarkhanian Horizon have a limited distribution in the Kura-Gabirry region (Figure 24). The Tarkhanian Horizon outcrops out only in the core of the Alachig, Armund and Chobandag structures of the Chatma Anticlinorium. Stratigraphically, this horizon is not separately distingushed, but rather is considered together with the Chokrakian Horizon within the Kura-Gabirry region.
Figure 24. Lithofacies and isopach map of the Tarkhanian Suite in the Kura-Gabirry Interfluve
Of note are the gray platey carbonate clays with seams of light-gray marl, which contain large quantities of coral in the Tarkhanian Horizon of the Chobandag region. These strata totally blanket the underlying Maykop Suite. In Alachig, Armudli and the extreme southeastern Chobandag, Tarkhanian deposits entirely cover the Chokrakian Horizon and include Spirialis sp. as a characteristic fauna. Spirialis sp. are particularly abundant at the base of the Chokrakian Horizon. The transition from the Tarkhanian Horizon to the Chokrakian Hoizon is associated with the disappearance of corals and the occurance of Spirialis sp. The argillaceous lithofacies of Tarkhaniandeposits gradually changes to sandstone with a simultaneuos increase in thickness toward the west.
Resistivity logs of upper Tarkhanian deposits are represented as a weakly differentiated curve within the limits of background readings, but do exhibit some increased resistivity. Resistivity curves exhibit a smooth decrease in the background readings from the top of the Tarkhanian Horizon to near the base (Figure 25). The SP log is straight and corresponds to the argillaceous content of Tarkhanian deposits. The Takhanian Horizon thickeness varies from 10 m to 47 m.
Figure 25. Electric log of Tarkhanian-Chokrakian suites in the Kura-Gabirry Interfluve
Within the Djeiranchel Synclinorium of the Kura-Gabirry Interfluve, drilling data suggets an absence of the Tarkhanian and Chokrakian horizons, compared to areas close to the mountains. There, Chokrakian layers of basal conglomerates occur mainly across erosion surfaces of upper Maykop deposits. This would suggest that during Tarkhanian-Chokrakian time there was an increase in the rate of subsidence of the basin with respect to the surrounding the mountains of the Kura-Gabirry Interfluve, and as a result, a change in the lithofacies had occurred. In the central part of the basin, particularly in the Chatma Anticlinorium, there is a definitive correspondence between the occurrence of Tarkhanian-Chokrakian layers and the underlying upper Maykop deposits, based upon the resistivity signature of these layers (Figure 25).
Chokrakian Horizon
The outcropped deposits of the Chokrakian Horizon are located at the same places as those of the Tarkhanian Horizon (Figure 26). Within the limits of Kura-Gabirry Interfluve, the Chokrakian Horizon deposits are represented by two distinct lithofacies. The first lithofacies is argillaceous marl that developed to the southeast from Alachig and it represented by gray or green clays containing marl and the spirilis fauna. The second lithofacies is an argillaceous sandstone which has developed to the northeast of Alahig, and is represented by yellow-gray and green, highly sandy clays, argillaceous sandstones and gray coarse-grain sandstones containing: Cardium multicostatum Bross Venus sp., Syndesmya alba Wood.,Spirialis sp. and Leda sp.
Figure 26. Lithofacies and isopach map of the Chokrakian Suite in the Kura-Gabirry Interfluve
The Chokrakian Horizon is a completely different lithofacies which is not typical in the Kura-Gabirry Interfluve and which outcrops at the Chobandag fold structure. There, Chokrakian deposits outcrop along the north limb of the Chobandag fold structure, creating a separate ridge-shaped topographic high. The Chokrakian deposits are represented by light, brecciform, calcareous dolomite containing abundant corals and mollusks. From among the fauna were defined the following forms: Trochus Chokrakianensis Koles., Arka cf.Turonica duj. and Modiolus marginatus (Eichw), all of which date the Chokrakian age of the enclosing sediments.
The abundant accumulation of corals implies the existence of a local Chokrakian basin that tended to favor the development and distribution of particular coral species. Based upon electric log data (Figure 25), the Chokrakian Horizon is defined as a jagged resistivity curve with specific resistivity of 2-3 ohm/m. The logs appear as separate kicks indicating frequently repeating, thin marl seams, dolomite and sandstone, with specific a resistivity 10-20 ohm/m. A smooth SP log indicates the relative impermeability of the rocks that constitute the Chokrakian section.
The well sections at Tarsdallar indicate a slightly different set of indicators, particularly increasing content of rudaceous material (i.e. much coarser than sand; peebly, cobbly gravel-type deposits). The formation of an argillaceous-marl facies occurs toward the southeast of Tarsdallar, but toward the northeast is a sandy-argillaceous facies.
Deposits of Upper Chokrakian in the Kura-Gabirry Interfluve are characterized by the following complex of microfauna: Quinqueloculina akneriana Orb., Q.cireularis (Borvemann), Q.reussi Bogd., Q.Consobrina (Orb)., Q.akneriana longa Gerke, Q.akneriana rotunda (Gerke), Porosononion martkobi (Bogd.), Florius boueanus (Orb.), Nonion punctatus (Orb.), N.bogdanowiczi Volosh., Entosolenia cubanica Bogd., E.mironovi Bogd., Elphidium jozephinnum (Orb.), TsChokrakianella caucasica (Bogd.), Sigmoilina tsChokrakianensis (Gerke), Pseudopolymorphina uniserialis Surin. and Articulina tscokrakensis Bogd.
The base of the Chokrakian Horizon has been investigated by electric logging and deep drilling. These data have been much better correlated for the Chokrakian rocks, as opposed to either the Tarkhanian Horizon or Maykop Suite. In the Chokrakian section, the amount of marl and sandstone seams increase from the base toward the top. Chokrakian layers that have been encountered in wells at Tarsdallar show that resistivity logs are characterized by a relatively enhanced SP curve and increased specific resistivity of all the strata of up to 5-6 ohm/m, with a background measurement of 2.0 ohm/m. The resistivity log has “ridge-type” appearance, suggesting the presence of sharp-edged 1-1.5 m thick strata that correspond to sandstone, dolomites and marl documented by drilling (Figure 25).
Based upon the resistivity log, the Chokrakian section can be subdivided into 2 parts, i.e. a lower, more argillaceous unit and an upper unit that exhibits an increase in the amount of sandstone and marl seams, and a corresponding increase of resistivity from 1.0 to 2.0 ohm/m. The resistivities of individual strata also increase from 2.0 to 6-8 ohm/m. The total thickness of Chokrakian layers increase from south to north (i.e. from 17 m-154 m to 26 m-309 m) and increase from west to east (i.e. from 235 m (Well No. 16) to 334 m as observed in Well No. 34). The increase of thickness has occurred in the direction from Well No. 1 at Keyryuk-Keylan (93 m thick) to Beyuk Palantekan (394 m thick). At Gyurzundag, the thickness of Chokrakian layers approaches 263 m. Based upon data from wells at Akhtepe, Gyurzundag and the Beyuk Palantekan areas (as distinguished from the Tarsdallar region), the amount of disaggregated material in the Chokrakian section is distributed more equally and the resistivity of the strata does not increase.
At the Molladag and Damirtepe-Udabno areas, the Chokrakian section becomes more argillaceous. Resistivity and SP curves are relatively weak. The thickness in Well No. 1 at Molladag is 174 m, and in Well Nos. 2 and 3 at Damirtepe-Udabno, the thickness is 191 m-213 m (Figure 25). The reduction of thickness and lithofacies variability of Chokrakian deposits can be observed south of these areas. For example, in the region around Poyla Station, the thickness of Chokrakian deposits is 40 m and is represented by mainly by clays and dolomitized marl, which contain Spirialis sp. and Leda subfragilis Chem.
Further north in the Mamadtepe region, Chokrakian deposits have been encountered by structural-prospecting wells, and are represented mainly by grayish-green sandy clays, usually massive, with numerous seams of greenish-gray sands, gray, light-gray and dense fine- to medium-grain sandstones and gray hard fractured marl. Fish scales can be readily observed while plant remains are rare. Spirialis sp., Syndesmya cf alba Wood and Leda subfragilis Chem are contained within the clays. The thickness of the Chokrakian Horizon in the Mamadtepe region is 35 m-40 m.
Karaganian Horizon
Cross sections based upon structural and deep prospect wells drilled in the Kura-Gabirry Interfluve have provided information on the occurrence and thickness of the Karaganian Horizon, and established it as an independent stratigraphic unit (Figure 27). During drilling, these deposits were intially lumped together with those of the Konkian Horizon as a subdivision of the Miocene complex.
Figure 27. Lithofacies and isopach map of the Karaganian Suite in the Kura-Gabirry Interfluve
Deposits of the Karaganian and Konkian horizons outcrop in the northern part of the Kura-Gabirry Interfluve, in the Alachig, Armudli, Molladag and Chobandag region. To the east the deposits are more or less continuous to the south of Eldaroyugi. These horizons have been encountered in almost all deep prospecting wells drilled in the “Akstafa Block”, in addition to Beyuk Palantekan and Eldaroyugi. In the western Kura-Gabirry Interfluve, Karaganian and Konkian layers are defined, mainly as sandstone facies and according to the observed fauna, the horizons are easily split into distinct stratigraphic units.
According to data from the Arkhashensu region, Karaganian deposits are represented by sandstones, argillaceous sands and sandy clays with a characteristic association of fauna including: Spaniodontella pulchella Baily, Sp.Tapesoides Andrus., Sp. Oristodon Andrus., Sp.Andrussovi Toula and Melanopsis sp. The thickness of the horizon is 225 m. The foraminifera complex encountered in deposits from wells in the Karaganian Horizon is relatively sparse but includes: Elphidium kudakoense Bogd., Nonion punctatus (Orb.), Ammonia beccarii (Linne) and Quinqueloculina sseminulum (Linne).
Electric logs are characterized by a strongly indented resistivity curve with specific resistivity of 2-3 ohm/m and precise “dagger-shaped peaks”, corresponding to 1-3 m thick marl strata, dolomite and sandstone with visible specific resistivity in the 10-20 ohm/m range, while the SP log is slightly dissected (Figure 28). The deposits of Karaganian age within the limits of the study area have not undergone significant facies changes. Compared with Arkhashen or Spaniodontel layers of Eastern Georgia, the Karaganian strata are a separate subdivision of Eastern Paratetis.
Figure 28. Electric log of Karaganian-Konkian section in the Kura-Gabirry Interfluve
At Tarsdallar, wells drilled into the thickest part of the Karaganian deposits (Well Nos. 5, 6, 17, 22 and 26) indicate the horizon is represented by a sequence of “benches”, characterized by relatively higher specific resistivity of up to 10-12 ohm/m, and as much as 40 ohm/m, with a background of 2-3 ohm/m. In the Chatma Anticlinoria (i.e. Beyuk Palantekan, Akhtepe, Molladag, Damirtepe-Udabno, Sajdag, Armudli, Keyryuk-Keylan and Gyurzundag areas) the resistivity curves show a “ridge-like” form, but the resistivity of specific strata are only in the 4-5 ohm/m range (Figure 28). The SP curve within the Karaganian Horizon is differentiated. As a rule, increased resistivity corresponds the occurrence of seams of tightly-cemented sandstone, dolomite and occassional marl. The maximum thickness of Karaganian Horizon encountered in Well No. 34 at Tardallar and Well No. 2 at Armudli is in the 340 m-763 m range.
Konkian Horizon
During Konkian time, sandy-argillaceous facies were deposited within the Djeiranchel Synclinoria and argillaceous marl facies were dominant in the Chatma Anticlinorium (Figure 29). The thickness of the Konkian Horizon determined in wells varies from 56 m in Well No. 1 at Molladag, up to 190m in Well No. 2 at Sazhdag. The maximum drilled thickness is 222 m in Well No. 1 in West Gyurzundag and 218 m in Well No. 1 in Damirtepe-Udabno.
Figure 29. Lithofacies and isopach map of the Konkian Suite in the Kura-Gabirry Interfluve
Deposits of Konkian age are reliably dated by existence of the following representatives of foraminifera: Elphidium kudakoenses Bogd., E.macellum (Ficht.et Moll.), E.sp.n., Entosolenia cubanica Bogd., E.ex gr.marginata (Walk.et Boys), Nonion punctatus (Orb.), N.miocenicus sp.nov., Porosononion martkobi (Bogd.), Miliolina sp.nov. and Quinqueloculina consobrina (Orb.).
The electric log characteristics of these deposits are within the limits observed in the region while the displaying a general tendency of reduced resistivity (Figure 28). The boundary between the Konkian and Karaganian horizons in the eastern study area is characterzed by specific resistivity that does not exceed 5 ohm/m, with a background close to 1.0 ohm/m. While the resistivity curve has “ridge-type” appearance, separate sharp peaks indicate the existence of distinct seams of marl and dolomite. The SP curve is weakly differentiated. In the west and northwest study area, the specific resistivity of Konkian age rocks does not exceed 3 ohm/m, with a background of 1.0 ohm/m. The undifferentiated SP curve generally corresponds to the described section, and is better defined in marl and dolomite strata.
Sarmatian Stage
Sarmatian deposits are widely distributed over most ot the Kura-Gabirry Interfluve, including in the Kura region and in the eastern interfluve. These deposits have been mapped as narrow northwest-southeast-oriented zones that extend into Georgia. On the Eldaroyugi, Molladag and Chobandag anticlines, Sarmatian deposits cover the entire folds. Sarmatian outcrops are observed in the flanks of anticlines (i.e. Beyuk Palantekan, Gurzundag, Keyruk-Keylan, Karatepe and Mamadtepe), while the surface rocks on anticlines located further to the south are of Apsheronian-Akchagylian age.
Sarmatian deposits occur beneath Pliocene cover, and from north to south throughout the study area there is a decrease of the total thickness of Sarmatian sediments as they were subjected to erosion, forming unconformable surfaces beneath Upper Pliocene deposits. This is confirmed by data from wells drilled on the east side of the Kura River and in the surrounding mountains. There, Akchagylian Stage deposits lie directly on sediments of the Maykop Suite, and to the south the Akchagylian overlie Upper Cretaceous rocks, particularly in the Dallar and Dallar-Tovuz areas. On the basis of lithological, macro- and micropaleontological analyses and resistivity logs, the Sarmatian deposits have been divided into three units as described below.
Lower Sarmatian
Lower Sarmatian deposits protrude as a narrow zone across the Akhtatepe, Chobandag, Molladag, Sazhdag, Alachyg, Yaylachyg, Udabno and Mamadtepe areas (Figure 30). On the southern slope of Akhtatepe, these deposits outcrop along the line of the Erikdar Overthrust and have been overthrust onto Akchagylian and Apsheronian deposits. Lower Sarmatian rocks there are represented by a sequence of thinly-laminated gray and grayish-brown clays with seams of gray, dense jointed marl. The local outcrop thickness of Lower Sarmatian there is 10-12 m.
Figure 30. Lithofacies and isopach map of the lower Sarmatian in the Kura-Gabirry Interfluve
In the Chobandag area, Lower Sarmatian deposits are defined in the lower part by clays, and in the upper part by sandstone. Typical for the upper sandy suite is the 30 m thick bed of coarse-grain sandstone, which contains: Ervilia podolica Eichw., Mactra eichwaldi Lask., Cardium gracile Pusch and other forms. The outcrop thickness of the Lower Sarmatian on the Chobandag Ridge reaches 200 m-250 m. However, a different section is observed to the south of Baydy. There, the upper part of the Lower Sarmatian consists of abundant seams of sandstone. Within the clays, Syndesmya reflexa Eichw have been observed.
Lower Sarmatian strata have been encountered in structural-prospecting wells at Mamadtepe, Tarsdallar, Armudly, Sazhdag, Molladag, Akhtepe and Beyuk Palantekan, and in prospecting-exploration wells drilled within the "Akstafa Block" (Figure 31). According to data from structural-prospecting drilling at the Mamadtepe and Kushkuna anticlines, Lower Sarmatian is represented by uniform gray, dense, stratified clays with thin seams of light yellow clays, fine-grain sands, greenish-gray clays, marl and sandstone. There, Lower and Middle Sarmatian deposits do not differ one from another lithologically, as both are defined by the argillaceous facies and are only divided according to the fauna they contain. Fauna contained in the 170 m thick Lower Sarmatian include: Syndesmya reflexa Eichw, Cardium vindobonesis Lask., C.ruthenicum Lask., Mactra eichwaldi :ask., Ervilia dissita Eichw and others.
Figure 31. Electric log of lower Sarmatian section in the Chatma Anticlinorium
On the Akhtepe and Beyuk Palantekan anticlines, the Lower Sarmatian encountered in structural wells that are located at the foot of the southern slope of the ridge, are lithologically divided into two parts. The lower part is a 200 m thick argillaceous suite defined by dark-gray and brownish-gray clays with abundant thin seams of dense yellowish, gray and dark-gray marl and rare thin seams of fine-grain sandstone. The upper part is a sandy suite that is represented by a sequence of gray medium- and coarse-grain sandstones and conglomerates with “benches” of banded gray and brownish-gray clays. Among these 70 m thick deposits, the following forms have been found: Solen subfragilis M.Hoern., Mactra cf. andrussovi Koles., Mactra eichwaldi Lask., Miliolina reussi Bodg., var. Bullodis Bodg., Nonionaff.martcobi Bodg., and others.
The Lower Sarmatian section has been penetrated by structural-prospecting wells, drilled in the Beyuk Palantekan area. In the Molladag region, Lower Sarmatian deposits have been observed in the Molladag Anticline, and are defined as a sequence of gray, dark-gray, greenish-gray clays with rare seams of marl and gray fine-grain thin sandstone. The Lower Sarmatian thickness there is 350-400 m. Analogous facies of Lower Sarmatian deposits are represented in the Sazhdag region as well, where the outcrop thickness is 250-300m and the thickness encountered in wells is 298 m (Figure 31).
In the Damirtepe-Udabno area, data from deep prospecting wells indicates that the Lower Sarmatian thickness fluctuates from 118 m in Well No. 3, up to 294 m in Well No. 1. In the Armudly area, Lower Sarmatian layers, penetrated by structural-prospecting wells, consist of gray dense sandy clays and dense, tightly-cemented fine- to medium-grain sandstone. The thickness of the sandstone is less than 1.0-1.5 m. There are a few 1 m thick seams of marl in the section. Also, in Well No. 2 at Sazhdag, the Lower Sarmatian interval ranges from 0-150 to 298 m in thickness.
The Lower Sarmatian is referred to as “VII petrographical horizon”, which is characterized by the absence of pyrite and a relatively small content of transparent platey minerals (2.93%). Among the latter, muscovite, chlorite and biotite (2%) are most abundant. The heavy mineral fraction consists of brown ironstone, magnetite and ilmenite. According to available rare samples of well core material, the lower Sarmatian section is represented by a lower argillaceous and an upper sandy layer, and includes the following complex of foraminifera: Milionella reussi (Bodg.), M.Sarmatianica (Karr.) Quinueloculina consobrina (Orb.), Q.complanata (Ger.et Issayeva), Porosononion subgranosus (Egg.), P.martkobi (Bodg), Nonion punctatus (Orb). N.franosus (Orb), N.ex gr. marginata (Walk et Boys), N.miocenicus sp.nov, Florius bogdanowiczi (Orb), Digilena Sarmatianica bogd.et Volosh, Entosolenia cubanica (Bogd.), E. ex gr. Marginata (Walk et Boys.), Elphidium aculetaum (Orb), E.macellum (Ficht.et Moll.), Articulina problema Bogd., Ammonia beccarii (Linne), Globigerina sp.nov and Globigerina sp.nov.
The electric logs suggest that the argillaceous suite is characterized by a weakly indented resistivity that smooths considerably at the boundary with the overlying sandy suite curve (Figure 31). There is an increasing total background resistivity and a considerably differentiated SP curve. The resistivity of the sandy strata does not exceed 2.0 ohm/m.
Middle Sarmatian
Middle Sarmatian deposits have a wider distributon in the study area than the Lower Sarmatian, and characterized by a relatively sharp variation of their facies. Middle Sarmatian outcrops extend as a relatively wide zone, beginning from the Alachyg Mountain, continuing eastward along the southern slopes of the Chobandag, Akhtatapa and Eldaroyugi ridges. The Middle Sarmatian deposits outcrop toward the south from this zone, i.e., in the Mamadtepe, Sazhdag, Molladag, Beyuk Palantekan and Keyruk-Keylan areas. In addition to the natural outcrops, Middle medium Sarmatian deposits have been drilled in Mamadtepe, Molladag, Damirtepe-Udabno, Sazhdag, Beyuk Palantekan, Akhtepe, Keyruk-keylan, Gyurzundag and Tarsdallar (Figure 32).
Figure 32. Lithofacies and isopach map of middle Sarmatian in the Kura-Gabirry Interfluve
On the basis of paleontology, facies analyses and electric log surveys in drilled wells, the Middle Sarmatian can be divided into upper subhorizon referred to as the “Cryptomactra” and a lower subhorizon which contains typical Middle Sarmatian fauna of the “southern Russian type”. These two subhorizons are described below.
Cryptomactra Subhorizon
Based upon resistivity logs, the lower border of the Cryptomactra subhorizon is indicated by an increase of the specific resistivity of up to 1.5-2.0 ohm/m. This curve is accompanied by a weakly indented SP curve which corresponds to a relatively more argillaceous part of the section, up to 1.5-2.0 ohm/m, indicating the presence of thin sandy strata in the section. The upper part of the Middle Sarmatian section is characterized by increased sand content. Therefore, the resistivity log diagrams are dissected curves with specific resistivity of 5-10 ohm/m, which corresponds to sandy “benches”, the thickness of which varies from 3-5 m to 30 m, and the background values of the specific resistivitys vary from 1.5 to 2.0 ohm/m.
The deposits of Cryptomactra layers and the layers with a typical Middle Sarmatian fauna association include an identical foraminifera complex: Porosonino martcobi (Bogd.), P.subfranusis (Egg.), P.granusus, (Orb.), Nonion punctatus (Orb.), Dogielina Sarmatianica (Bodg.et Volosh.), Elphidium maccellum (Ficht.et Moll.), Quinqueloculina voloshinovae (Bogd.) and Q.comsobrina (Orb.), corresponding to the bessarabian substage of the Eastern Paratetis.
The Cryptomactra subhorizon is everywhere conformable on Lower Sarmatian deposits. In cores extracted from the structural wells in Beyuk Palantekan, the Cryptomactra layers are represented by gray, dark gray laminated clays with numerous seams (from 1 cm to 1.5 m) of dense fine-grain sandstone and marl; the thickness is 580 m. Cryptomactra layers are also represented in the Eldaroyugi section. West of Eldaroyugi, Cryptomactra deposits are gradually replaced by sandstones and their thickness increases. Thus, in the Akhtapa region, the lower part of the horizon is represented by gray fine- to medium- grain sandstone with clay seams. The upper part of the section is principally represented by argillaceous facies and is also characterized by Cryptomactra pesanseris Andrus. The total thickness of the horizon, recorded in Well Nos. 1, 2 and at Akhtapa, is 400-500 m.
In the Chobandag and Molladag areas, the Cryptomactra subhorizon is defined by a sequence of 10-15 m thick, dense, fine-grain sandstones. The thickness fluctuates between 270 and 300 m. The thickness of Cryptomactra in deep wells is 462 m. The Cryptomactra layers in the Keyruk-Keylan are pronounced in sections constructed from structural-prospecting well data and deep exploration drilling data. These layers are represented by a monotonous gray, dense, slightly carbonate sandy stratified clay with included seams of dark gray clays, fine-grain sands and occassionally by tightly dolomitized marl (1 m thick). Thin layers of white and yellowish-white volcanic ash are included in the clays, as well as inclusions of vegetative remnants and fauna such as cryptomactra pesanseris Andrus, Spirialis sp., Modiola Sarmatianica Gat. and Hodrobia sustriatula Koles. The clays of the Cryptomactra layers have specific electrical resistivities of 2.5-3 ohm/m. Middle Sarmatian thickness is 170-200m.
At Mamadtepe, Middle Sarmatian is observed in the axis of an anticlinal fold and is represented by clays that are lithologically similar with the argillaceous strata of the Lower Sarmatian of this region. This argillaceous strata is covered by a “bench” of light-gray, medium- to coarse-grained sand and sandstone; occassionally grading into conglomerate or seams of marl and coquina. The argillaceous strata contains: Cardium plicatofittoni Sinz., C.incuratum Koles., C.danovi Koles., Mactra urupica Dan., Modiolla incrassata d'Orb., M. naviculaoides Koles., Tapes naviculatus and others. The lower argillaceous “bench” probably corresponds to the Cryptomactra layers, and the upper sandy “bench” is associated with the layers with the typical Sarmatian fauna. The thickness of the Middle Sarmatian in this area is 140 m.
At the Eldaroyugi Uplift, the southern slope is principally Middle Sarmatian sediments. There, the Cryptomactra layers consist of gray, bluish-gray, greenish-gray and brownish-gray, dense clays with numerous seams of brown marl and medium-grain sandstone with thicknesses of up to 0.5 m. Based upon outcrops in the Eldaroyugi region, the thickness of Cryptomactra layers reaches 280 m. The fossils whch have been identified in these rocks include: Cryptomactra pesanseris Andrus, Modiola cf. Saratica Gat., Cardium sp. and Tapes naviculatus Andrus.
At Arkhashensu, Cryptomactra deposits are described as gray, medium- to coarse-grain sandstones with pebble inclusions. Further to the west, in the Karayaz Steppe, they are replaced by multi-colored continental-type deposits, suggesting a basic facies change between the Middle Sarmatian basin and the upper Middle Sarmatian. Various parts of the Middle Sarmatian basin were characterized by distinctive environments of deposition. For example, Middle Sarmatian Cryptomactra sediments were deposited in the eastern Kura-Gabirry Interfluve at Akhtakhtepe, Palantekan and Eldatoyugi.
In areas west and northwest of Molladag, Middle Sarmatian is divided into two parts: The upper part of the Middle Sarmatian at Molladag is represented by a sequence of gray, fine-grain carbonate (20-25%) sandstone and gray clays. Near the upper boundary of the Cryptomactra horizon, there is one stratum of conglomerate with a thickness of 10 m. The entire section is characterized by the association of certain fauna, including: Cardium cf.futtoni d'Orb., Mactra sp.;Tapes vitalianus d'Orb.,T.gregarius Partsch.; Modiola Sarmatianica Gat., Donax dentiger Eichw.; Mactra fabreana d'Orb., M. naviculata Baily.; Solen sp.; Buccinium sp.; Trochus sp. and others.
The mineralogical content of the Cryptomactra deposits are characterized by a significant decrease in hornblende and epidote and an increase in magnetite, ilmenite and a group of heavy minerals, which correspond to horizons V and VI in the Chobandag section. The horizon thickness at Molladag is 450-500 m, and was measured as 462 m in Well No. 1. In the Chobandag and Chatma regions, deposits which are analogous to Cryptomactra sediments are defined by a sequence of thick, gray micro- to medium-grain sandstones, gray and green clays. The thickness of these deposits is 400-450 m.
Upper Sarmatian
Upper Sarmatian deposits within the study area have the largest distribution of all Sarmatian deposits, and are conformable upon Middle Sarmatian. These rocks form a continuous outcrop zone in the northern Kura-Gabirry Interfluve, from the northern slope of the Alachygna Mountain in the west, to the Eldar Steppe in the east. Outcrops of Upper Sarmatian are observed in Gyurzundag, Keyruk-Keylan and Beyuk Palantekan regions (Figures 33 and 34).
Figure 33. Structure contour map of upper Sarmatian (basal) in the Kura-Gabirry Interfluve
Figure 34. Structure contour map of upper Sarmatian (top) in the Kura-Gabirry Interfluve
Upper Sarmatian facies vary sharply by area (Figure 35). These deposits are a complex of coastal shallow-water, lagoonal, and freshwater lake and delta river environments. Environments of deposition of these sediments are characterized by their instability with respect to lithological content. The Upper Sarmatian described from outcrop are divided into three horizons, each being of an independent stratigraphic significance. These horizons, from oldest to youngest are: Rostov Horizon, Kherson Horizon and Eldar Horizon.
The Rostov, Kherson and Eldar horizons correspond to the Karpin, Kotov and Eldar horizons, respectively. The Karpin, Kotov and Eldar horizons are located in the vicinity of the Black Sea. The Rostov Horizon refers to the lower part of the Upper Sarmatian and outcrops on the southern slope of the western part of the Eldartoyugi Uplift. The outcrop is described as thick grayish-brown, layered chalk and gray clays with rare sandstone seams. In some places the thickness of the sandstone seams increases up to 10-16 m.
Figure 35. Lithofacies and isopach map of upper Sarmatian in the Kura-Gabirry Interfluve
The argillaceous facies contains remnants of mollusk fauna, including: Mactra luxata Zhiz., M.timida Zhiz., M.naviculata Baily., Solen subfragilis R.Hoern. and Hydrobia kolesnicovi Sult. The thickness of the Rostov Horizon at the Eldaroyugi Uplift is 350 m. According to results of structural drilling and electric logs in the eastern part of the Kura- Gabirry Interfluve, particularly along the Eldaroyugi and Beyuk Palantekan uplifts, the 445 m thick Upper Sarmatian is divided into the Ior (lower) and Eldar suites.
The Iori Suite, corresponds to the Rostov Horizon and is represented by banded gray, brown and greenish-gray, dense clays with “benches” of chalk and sandstone (up to 25 m thick), which in some places are impregnated with oil. Near the village of Kasaman, these sandstones are fractured and contain gryphons, from which oil, water and hydrocarbon gas has emanated. These deposits contain: Macra caspia Eichw., M. bulgarica Toula., M.nalivkini Koles. planorbis sp., Melonopsis sp. and others.
At Mamadtepe and Keyruk-Keylan, Upper Sarmatian has been eroded and Upper Pliocene rocks overlie Middle Sarmatian deposits. At Chobandag, Upper Sarmatian deposits are represented by a sequence of brown and gray clays with fine- and medium-grain sandstone. The thickness of the horizon there is 300-350 m. Outcrops of the lower horizon are exposed southeast of Gyrzundag Mountain, however, they were also penetrated by Well Nos. 3, 4, 5, 6, 7 and 12. The deposits described are represented by gray, brown-gray clays containing Mactra timida Zhiz., M. naviculata Baily., Mactra sp. and others. West of Gyurzundag Mountain, Upper Sarmatian facies are gradually replaced by multi-colored sandy-argillaceous rocks that contain no marine fossils. At Molladag, the entire Upper Sarmatian section is represented by multi-colored sandy-argillaceous deposits up to 110 m thick. The total thickness Upper Sarmatian deposits penetrated in wells at Molladag was 140 m.
Herson Horizon
The Herson Horizon corresponds to the Middle part of Upper Sarmatian and is represented on the northern slope of the Eldaroyugi Uplift by a sequence of thick, dense, coarse- to fine-grain grayish-brown sandstone, and brownish-gray (or reddish-brown) clay. Often in this “bench” there is argillaceous coquina and sandstone, and in some places they are associated with thin seams of chalk. Individual strata of sandstone are 20-30 m thick, and extend to the west into Georgia. In addition, typical fauna fossils in these sediments includes: Mactra bulgarica Toula., M.caspia Eichw., M.crassiolis Sinz. and Solen subfragilis R.Hoern.
In 1955, landslides along the southwest part of the Eldaroyugi Uplift exposed fossil remnants of both marine and terrestial animals including: hipparion (three-toed horse), antelope (Sp.), trogocerus, giraffe akhtiyaria, rhinoceros-acerathere, seal, Eldar hyena, mastodon and Eldar pig. The bones of these vertebrates are not in anatomical order, which suggests that the Eldaroyugi area was formally a coastal zone of the Herson Basin, where the extinct vertebrate bones may have been transported from surrounding areas.
The numerous shows and production of oil in the Kura-Gabirry Interfluve appear to correlate with sandy strata of the Herson Horizon. North of the Akhtatepe Uplift (along the continuation of the north slope of Eldaoryugi Uplift) the Herson Horizon contains oil as well as lignite and bituminous coal. The sandy strata thickness ranges from 0.5 to 1.5 m. To the west near Baydu, the sandy strata of the Herson Horizon thins to just 70 cm, however, the total thickness of the Herson Horizon is 620 m.
South of Akhtatepe, at Keyruk-Keyla, layers of Upper Sarmatian were encountered during drilling of structural wells. There, as mentioned above, strata associated with the Herson Horizon consistute an argillaceous suite. Based upon well cores, these deposits are represented by gray and greenish-gray, dense sand with thin seams of pure fine-grain dense sands, sandstones and some clays.
In Upper Sarmatian deposits which have not been subdivided into horizons, the following fauna have been observed: Mactra cf. Nalivkini Koles., M. cf. luxata Zhiz.M. cf. timida Zhiz. M. crassicollis Sinz., M.caspia Eichw., Solen subfragilis R.Hoern and others. The thickness of these Upper Sarmatian deposits penetrated by wells is 94 m. At Gyurzundag, Upper Sarmatian rocks outcrop in the eastern part of the fold and along the southern slope of the ridge. There, two suites have been distinguished. The lower sandy suite or Rostov Horizon, is represented by thick “benches” of fine- to medium-grain grayish sandstones and sands that contain argillaceous seams. These deposits contain: Mactra caspia Eichw., M.nalivkini Koles.and M.crassiolis Sinz. The upper argillaceous suite or Herson Horizon is defined by greenish-gray and brownish-gray clays containing vegetative remnants and iron oxide stains and inclusions of gypsum. Well data indicate that the total thickness of the Henson Horizon is 350-420 m.
Eldar Suite
The Eldar Suite, the uppermost unit in the Upper Sarmatian section, is widely distributed within the Kura-Gabirry region and lies conformably on the Kherson Horizon. The Eldar Suite outcrops along the northern flanks of the Eldaroyugi, Alichig, Chobandag and Keyryuk-Keylan uplifts and northwest of the the Molladag uplift. This suite is represented by sequence of brown and brownish-green clays with thin seams of gypsum and jarosite. The suite includes freshwater mollusks such as Unio, Planorbis, and Helix, in addition to vertebrate bone fragments.
Along the western Eldaroyugi Uplift, the clays of the Eldar Suite contain remanants of terrestial vertebrate fossils including: turtle thoraxes (genus Thestuola), antelope, ostrich and hipparion. Discovery of ostrich fossils suggests that during the deposition of the Eldar Suite, the surrounding Upper Sarmatian basin was a desert. In the deep wells the observed thickness of Upper Sarmatian deposits ranges between 450-900 m.
On the north slope of the Akhtakhtatepe Uplift, Upper Sarmatian terrestrial deposits include very thick sandstone, which resembles the sandstone of the Shirak rock mass of Georgia. The thickness of thes Upper Sarmatian deposits is 340 m. To the west of Molladag, Eldar Suite deposits become more coarse-grain and contain litle or no fossil remanants. Within the limits of the interfluve, the Upper Sarmatian has a poor fossil record for certain foraminifera complexes, including: Porosononion granosus (Orb.), Nonion punctatus (Orb.), Elphidium maellum (Ficht.et Moll.) and Ammonias beccarii (Linne).
At Sajdag, Armudli and Damirtapa-Udabno, electric logs indicate that these deposits have strongly dissected resistivity and SP curves (Figure 36). The lower part of the section, consisting of sandy “benches” is defined by specific resistivity of up to 25 ohm/m, while the SP curve is differentiated. The middle part of the section is characterized by specific resistivity of up to 3-5 ohm/m and a differentiated SP curve. The upper section is represented by argillaceous units and strata in which resistivity does not exceed 3-5 ohm/m and with a non-differentiated SP curve.
Figure 36. Electric log of upper Sarmatian section in the Chatma Anticlinorium
Shirak Suite
The Shirak Suite is a complex stratigraphic sequence of rocks that involves the top of the Miocene and the Lower and Middle Pliocene. The Shirak Suite is nearly absent within the Kura-Gabirry Interfluve. Outcrops of the Shirak Suite occur only within the northeastern Eldaroyugi Uplift, where the suite is nonconformable (by 4-5 degrees) on top of the Upper Sarmatian. The rocks are represented by non-equidimensional, weakly-cemented gray sandstone and variegated clays, in which there have been accumulations of freshwater mollusks (i.e. Unio and Planorbis), and some vertebrate remains.
Occurrence of Dinatherium in the upper part of the Shirak Suite correlates with the Pontian Stage. Drilling has penetrated the limits of the Eldar-Oyugin fold in Wells Nos. 1, 3 and 4, and resistivity logging indicates strongly a differentiated SP curve and relatively high specific resistivity of up to 20-25 ohm/m within the general background of 4-5 ohm/m. Based upon selected core samples, the section is lithologically represented by coarse-grain sandstone, gravels and poorly-sorted, variegated clays. The thickness of Chirak Suite encountered in wells is 680-550 m.
The Shirak Suite is widely distributed in Georgia, particularly in the East Kachetii (Mirzaani), where it contains commercial quantities of oil. There, the thickness of these deposits reaches 2000-2500 m. The entire section is divided into two parts: a lower argillaceous unit with seams of gray marl and sandy conglomerate. South of Eldaroyugi Uplift, the Shirak Suite deposits are not defined.
The absence of the Shirak Suite in the Kura-Gabirry Interfluve has been explained by some investigators as the result of pre-Akchagilian (Upper Pliocene) erosion. However, this explanation may not be entirely correct. For example, it is difficult to imagine that the Chirak Suite is 2000-2500 m thick in nearby Georgia (west of the Iori River) and absent in the neighboring Kura-Gabirry Interfluve. Secondly, the correlation of the zero isopach line for the Shirak Suite and Sarmatian deposits suggests that large-scale erosion on the top of the Upper Sarmatian had not occurred.
There may be an alternative explanation for the absence of the Shirak Suite in the interfluve. The angular unconformity between the Akchagilian Stage and the underlying rocks in the Kura-Gabirry Interfluve may have been caused by non-deposition and extensive mountain building in the Eastern Caucasus. This regional uplift occurred throughout most of Meotian (Upper Miocene) and Lower and Middle Pliocene. The upper surface of the Eldar Suite appears to have been cut by a transgressive non-conformity or paraconformity of 5-6 degrees. This has been confirmed by data from numerous structural and prospecting wells, and suggests that at the end of the upper Sarmatian, the entire Kura-Gabirry Interfluve was rising. Thus, the regime of continental deposits in the Kura-Gabirry Interfluve was probably not eroded during the Lower and Middle Pliocene, and the eastern Kura-Gabirry Interfluve constituted the southern boundary of the Shirak Suite basin.
Upper Pliocene
Upper Pliocene sediments in the Kura-Gabirry Interfluve were deposited as a transgressive series over an angular unconformity cutting across Sarmatian through Upper Cretaceous rocks. Upper Pliocene deposits are very widely distributed, filling all the synclinal basins in the northern interfluve. In the southern interfluve, Upper Pliocene deposits have been folded as part of the anticlines of the region. The cross section of Upper Pliocene is well-defined by the Akchagilian and, particulary, the Apsheronian stages.
Agchagilian Stage
Akchagilian deposits in the Kura-Gabirry Interfluve and in neighboring Georgia are very widely distributed (Figure 37). Classical cross sections exist in anticlinal structures of the Little and Beyuk Palantekan, Gyurzundag, Molladag, Mamadtepe, Kushkuna (1 and 2) and Keyruk-Keylan fields. Layers of Akchagilian to the north of the Gabirry River were transgressively deposited over the Shirak Suite, and south of the Gabirry River they were deposited on older sediments.
Figure 37. Lithofacies and isopach map of the Akchagilian Suite in the Kura-Gabirry Interfluve
The Akchagilian deposits are represented by a sequence of sandy coquina, sandstone, thinly-layered sands, massive gray-brown, greenish-blue clays containing chalks, conglomerate and volcanic ash. On the basis of detailed lithological and paleontological analyses, investigators have divided the Akchagilian Stage into lower, middle and upper layers.
The lower part of the Akchagilian is floored by volcanic ash, upon which was deposited a sequence of light-gray and brown argillaceous coquinas with seams of relatively dense sandstone. Paleontologically, this interval is characterized by an association of: Potamides caspius Andrus., Mactra subcaspia Andrus., M.karabugasica Andrus. and Cadium dombra Andrus. The regional cross section of the horizon suggests that the Akchgil is one of the “layers from Potamides”. The thickness of the lowrer part of the Akchagilian Stage is 150-200m.
The section of the Middle Akchagilian Stage contains a complex of fauna distinct from the lower Akchagilian and includes: Cardium radiiferum Andrus. and C.nicitini Andrus, and some fine forms of family Mactridae. The facies do not differ much from the lower Akchagilian, except for the presence of distinctive seams of thin dark-blue clays, which contain the above mentioned fossils.
At the top of middle layer are freshwater deposits containing Planorbis and Helix; the uppermost layer is a distincitive coquina conglomerate. The appearance of freshwater fauna indicates strong desalination of this basin and the sharp transition of deepwater facies to conglomerates suggests that the basin is shallowing. The sharp change of environments of deposition indicates that deepwater fauna of Middle layer have died out. The thickness of the Middle horizon is 250 m, and the boundary between the Middle and upper Akchagilian has been lost within the strata of coquina conglomerate.
The upper Akchagilian is represented mainly by argillaceous sediments with occasional sandy units. The upper layer contains much fewer fauna, however, mactrs. M.pisum Andrus. are more abundant than in either the middle or lower layers. There are also occasional Potamides caspius Andrus. The thickness of the upper layer is 120 m.
In the western part of the interfluve at the Mamadtepe Uplift, the Akchagilian Stage is represented by a sequence of green, blueish-green, yellow and gray clays, with seams of gray, ginger-brown and fine- to medium-grain sands and sandstone. There are also thin seams of black clays with abundant plant remanants, volcanic ash, and disaggragated pebbles. The amount of sandiness increases from the flank to the crest of the anticline. According to resistivity log data there is a “bench” of conglomerate at the base of the Akchagilian. The total thickness of Akchagilian deposits in the Mamadtepe is 200 m.
Further south at Kushkuna-1, the Akchagilian section is represented mainly by sequences of gray, grayish-green and green sandy clays with rare seams of black clays, gray sands and volcanic ash. At the base of the Akchagilian Stage is a 5 m thick basal conglomerate. On the east bank of the Kura River, the Akchagilian lies directly on Maykop Suite and older deposits, and is almost incontact with carbonate rocks of the Upper Cretaceous.
In the neighboring area of Dalimamedli, Well Nos. 3 and 4 have penetrated both Akchagilian and Upper Cretaceous effusive rocks. The thickness of Akchagilian deposits is approximately 70-120 m. In addition, the transition from marine to continental deposits has occurred in the area, i.e. the gradual substitution of clays by sandy material and then by conglomerates can be observed. Also, based upon seismic data, the Akchagilian layers were not involved in local folding.
Near the village of Akstafa, Akchagilian Stage marine sediments transition to continental deposits. There, at the base of the Akchagilian Stage are found: Mactra karabugasica Andrus., M.subcaspia Andrus., Classiola inbermedia Andrus and Mactra venjukovi Andrus. Near the Kura River, Akchagilian deposits include fauna which best characterizes the Middle Akchagilian layer, such as: Cardium dombra Andrus., C.aff.nikittini Andrus., Macra ossoskovi Andrus. and M.inoatrancevi.
On the Gedakdesh Ridge of the Gyurzundag Anticline and southward in the Keyruk-Keylan region, Akchagilian deposits are represented by gray, greenish-gray and less often by grayish -brown clays with seams of gray, fine- to medium-grain friable sandstone. There, at the base of Akchagilian exists a conglomerate lyer of 30 m thickness. According to data from prospecting wells at Keyruk-Keylan, the thickness of Akchgil deposits is 364 m, and to the north in the Beyuk Palantekan, the thickness increases to 486 m in Well No. 1. Locally, the total thickness of the Akchagilian Stage is 520 m.
In the eastern Kura-Gabirry Interfluve, particularly at the Small Palantekan Uplift, the Akchagilian Stage outcrops at the fold crest. There, the sediments are represented by variegated clays with an outcrop thickness of 260 m, with associated sandstone and coquina chalk with a thickness of 250 m. Based upon data from Well No. 2, the total thickness of the Akchgil is locally 787 m.
The mineralogical content of Akchagilian deposits in the eastern interfluve is characterized by the following description: 1) the light fraction is quartz (0-18%), feldspars (0-35%), volcanic glass (0-97%), and the remainder is rock fragments and some clay group minerals, 2) the heavy mineral fraction is essentially amphibole (0.5-73.6%) and pyroxene (0-38%). The remaining heavy fraction is represented by magnetite and ilmenite (2-50%), hematite (0-67.7%) and pyrite (0-5%). The transparent minerals include garnet, zircon, tourmaline, rutile, epidote, zoisite (0-16%), barite (0-8%), and muscovite and chlorite (0-44.3%). The most common correlateable materials for the Akchagilian Stage rocks are the amphiboles, pyroxenes, muscovite and chlorite.
Apsheronian Stage
The Apsheronian Stage deposits in the Kura-Gabirry Interfluve are continental in character. Marine and freshwater sediments of Apsheronian age are deposited only in the southeastern interfluve, at the Kichik and Beyuk Palantekan anticlines, and in the eastern part of the Gyurzundag and Keyruk-Keylan folds. The contact between Akchagilian and Apsheronian stages in the eastern part of interfluve is well defined.
In the Beyuk Palantekan region, the Apsheronian layers have been deposited over an angular unconformity (3-4 degrees) that cuts the top of the Akchagilian sediments. There, at the contact between these units is a 1 m thick “bench” of basal conglomerate. The Apsheronian deposits in the northern fold of the Gedakshen Ridge, particularly between the Akhtapa and Gyurzundag ridges, is underlain by conglomerates. The Apsheronian facies in this area vary sharply in the cross section. In the bottom unit of the stage are clays containing freshwater coastal fauna such as: Micromelamia subcaspia Andrus., Dreissensia rostriformis Desh.and Neritina pallasi Lindh.
The upper part of Apsheronian Stage is characterized by continental facies, in which half-marine fossils are absent, but instead contain only freshwater Helix, Planorbisand Unio. Among the brown, red-brown and greenish-gray clays, there are often seams of dense coarse-grain reddish-pink sandstone (with a thickness of up to 5 m) and conglomerate. In the Kura-Gabirry region, the Apsheronian Stage is divided into two parts: the lower marine unit, the base of which is well-defined by yellow clays with Apsheronian fauna (70 m thick), and an upper unit with large areal distribution, continental in appearance and including seams of volcanic ash. The thickness of the continental sediments is 170 m.
The lower unit of Apsheronian Stage is gradually replaced toward the northwest by the upper continental unit and, but to the east and south (Palantekan and Keyruk-Keylan anticlines) the thickness of the lower unit increases. Based upon data from local prospecting wells, the total thickness of the Apsheronian Stage is 499-500 m.
At the Palantekan Uplift, the Apsheronian Stage is divided into three horizons, lower, Middle and upper. In this subdivision, however, only the lithological content of the Apsheronian stage is taken into account. The bottom of the stage is represented by a sequence of clays and sandstone, with clays being dominant. The thickness is 200 m. The medium horizon is defined by the same sediments as in the lower horizon, except the sandy seams are dominant, and are capped by a conglomerate. The thickness of the middle horizon is 200 m. The upper horizon is represented by a sequence of clays, sandstone, sands, conglomerate and seams of volcanic ash. The thickness is 150 m.
The total thickness of the Apsheronian Stage has been approximated at 550 m, however, according to the drilling data the true thickness approaches 858 m. In the western interfluve at Mamadtepe, the Apsheronian deposits are represented as continental facies, including distinct yellow-brown, very sandy clays, with inclusions of gypsum, seams of sand, sandstone and shale. The sands ultimately transition into shale or sandy clays. The maximum thickness is 290 m.
On the east bank of the Kura River, near Akstafa, the thickness of the continental unit decreases to 200 m. The continental Apsheronian deposits are also widely distributed at Molladag and Ortagash. There, the entire section of Apsheronian Stage consists of a sequence of yellow and red-brown loams with seams of fine- and medium-grain sands, sandstone and shale. Included in the clays there are Helix and Planorbis, the presence of which indicates continental conditions of deposition.
Thus, in the first half of the Apsheronian Stage, within the interfluve, were two radically different facies: one facies was situated east of Gyurzundag, where offshore deposits were being deposited, while the other facies existed to the west, where continental-freshwater deposits were being deposited. Continental conditions in the second half of the Apsheronian Stage blanketed the central and eastern parts of the interfluve. Consequently, continental-freshwater deposits, defined by brown, yellowish-brown loams and shales were deposited everywhere in the Kura-Gabirry Interfluve.
Quaternary Deposits
Quaternary deposits occupy a large area of the Kura-Gabirry Interfluve. They cap the cross sections of all synclinal deposits, and are represented in the landscape of the study area by intermontane valleys, as valley fill of the Kura and Gabirry rivers. Occassionally there are Quaternary deposits on the ridge tops (i.e. at Akhtatepe, Gyurzundag and Beyuk Palantekan ridges). Based upon their elevation and facies variability, Quaternary deposits have been divided into two parts: 1) ancient river and lake deposits and 2) younger river alluvium.
The ancient river deposits are represented by conglomerates and shales with various size rock fragments, which form the ancient terraces of the Gabirry River along the northern slope of the Akhtatepe and Eldaroyugi uplifts. The ancient lake deposits are established north of the Akhtatepe Uplift, and on the north slope of the western Eldaroyugi Uplift, where they occupy a large area at 400 m elevation above the Gabirri River. These deposits are represented by clays with poor resistivity and loams containing Helix and Planorbis. The thickness of these deposits is 8 m.
Younger river sediments extend along the banks of both of the Kura and Gabirri rivers, forming small step-like terraces from 3 to 20 m in height, and are characterized by a “bench” of shales and coarse-grain sands with lens-shaped seams of sandy clays. The remaining surface of the interfluve is occupied by thin Holocene (Recent) deposits covered with sparse vegetation.
OIL-GAS-WATER CONTENT
Production and shows of oil have been discovered during drilling in sediments of the Kura-Gabirry Interfluve. The litho-stratigraphic complexes of this region in which oil and gas have been found include:
· Upper Cretaceous-Lower Paleocene carbonate deposits
· Lower Eocene sandy-silt sediments
· Middle Eocene tuffogenic-pyroclastic, tuffogenic-terrigenous and terrigenous-carbonates
· Upper Eocene sandy-silt sediments
· Maykop Suite (Oliocene- Lower Miocene) sandy-silty sediments
· Chokrakian-Karaganian-Konkian (Miocene) terrigenous-carbonate sediments
· Sarmatian (Miocene) sandy-silty sediments
A significant quantity of oil and gas shows have occurred both on the surface (seeps) and during testing of wells (shows) drilled in the “Akstafa Block” of the Kura-Gabirry Interfluve (Tables 1 and 2). A description of these oil and gas shows and surface seeps is presented below.
Oil and Gas Seeps
The main oil seeps of the Kura-Gabirry Interfluve, are located in the northern Chatma tectonic zone, where they form a broad northwest-southeast oriented trend. They occur in the southeast part of the region, mainly from Sarmatian Stage (Miocene) deposits, and from the Maykop Suite. Surface seeps of oil and gas in Kura-Gabirry Interfluve are divided into five groups, according to their location:
1. The Alandarin group includes the oil seeps from Upper Sarmatian sandstones in the Alandarin ravine and on the northeast slope of Ailadjik Ridge. The thickness of the sandstones exceeds 100 m. Mineral-charged waters also flow from two locations, along with small streams of thick oxidized oil.
2. The Alachig group of oil seeps is situated along the axes of the Alachig fold in association with numerous mud cones, salses and gryphons. In addition to liquid oil which has crusted upon outcrops along the ridge, gryphons flow gas and water with oil particles. The eruption of the mud volcano products contain oil shows within fractures in Maykop, Chokrakian and Karaganian-Konkian age rocks. Within the eastern pereclinal folds at Polpoytap, there are outcrops of oil-saturated Middle Sarmatian sandstone, associated with a zone of faulting in which the fault plane is also saturated with oil.
3. The Katar group of oil seeps is associated with rocks of the Upper Sarmatian along the south slope of the Katar Ridge, which is part of the north limb of the Alachig Anticline. There are three sandstone strata with an average thickness of 42 m that have been described as being irregulary saturated by oil. In the western part of the ridge, weakly- cemented sandstones are saturated with oil, and in the eastern part of the ridge there is a minor oil and gas seep along with formation water from the sandy strata.
4. The Tyulkitapin group of oil and gas seeps are associated with mud volcano knols, which are situated along an east-west-trending fault that parallels an anticlinal axis. Bitter salt water containing oil particles and combustible gas are seeping from the knols. The largest knol on the ridge and has a diameter of 2.5-3.0 m, and produces a seep of black resinous-asphalt, oil, gas, and calcium-chloride water charged with hydrogen sulfide. Oil and gas seeps and shows are generally associated with outcrops of Upper Sarmatian sandy strata that occur in deep ravines. In total there are 17 oil saturated strata with the thicknesses from 0.2 to 30 m. Based upon 1872 data from the Mining Department, dug wells in this area produced 4 tons of oil/day.
5. The Eldaroyugi group of oil seeps is located on the north limb of the Eldaroyugi Anticline, where three sandy Upper Sarmatian oil-saturated strata outcrop; their total thickness is 50 m. All natural oil and gas seeps are associated with Upper Sarmatian sandy “benches”.
Oil shows which have occurred in structural-prospecting, parametric, prospecting and exploration wells are described below. For the most part, these include the Maykop Suite within the Kura-Gabirry Interfluve, which has been drilled and developed in all areas where structural, prospecting and exploration drilling has occurred.
The Girahkesan area, structural Well Nos. 8, 14, 16, 26 and 40 encountered samples of a thin sequence of coarse-grain sandstone and clays with the smell of gas. In Well No. 49, a blowout of gas occurred at the 644 m interval, subsequently burning the borehole.
At Khatunli, oil and gas shows have been observed in structural Well No. 8, at the 920-966 m interval, within clays containing seams of fine-grain sand which smell of oil. According to the hydrocarbon analysis, the content of diffused bitum in the clays varies up to 0.025%. The bitumen consists of light oil and some resin.
At Mamadtepe, during drilling of parametric Well No. 1 in the Maykop Suite, there were no noticable oil and gas shows in the 665-1526 m interval.
At Damirtapa-Udabno, Maykop Suite rocks were penetrated by parametric Well No. 1 and prospecting Well Nos. 2 and 3. During the drilling of the Well No. 1, in the 1950-3886 m interval, and Well No. 2, in the 1603-3388 m interval, there were no noticable oil or gas shows. At Well No. 3, in the 1780-3600 m interval, an absorbed fluid density of 1.80-1.94 g/cm3 occurred at depths of 1962, 2085, 2115 and 3348 m. Down hole testing was not conducted.
At Sagdag, Maykop deposits were penetrated in structural Well No. 4, parametric Well No. 1 and prospecting Well Nos. 3, 4 and 5. Parametric Well No. 1 was drilled near the fold axis in the northeastern limb of the Sagdag fold. In the 1138-4000 m interval, oil saturation was noted in an argillaceous, non-carbonate, thin bedded, fine-grain sandstone. Similarly, at the 2465-2467m interval, a seam of fractured dolomite had a smell of oil. Near the well bottom at the 3730-3755 m and 3800-3810 m intervals, oil and gas shows occur in seams of sandstone and dolomite.
During testing of the 1554-1560 m, 1567-1587 m intervals, an absorbed solution density of 2.22 g/cm3 was produced. During the drilling of the 1752-1754 m interval, there was a show of gas. During testing at 3242 m, the absorbed fluid density was 2.08 g/cm3. Additional gas shows were discovered at 3490 m, 3514 m and 3842 m during well testing; density of the absorbed fluid density was 2.20 g/cm3. During drilling of Well Nos. 3, 4 and 5, no shows were found.
At Armudli, in the structural Well No. 26, drilled in the fold limb, encountered a gas show in the Maykop Suite. Similarly, at the Adgibulag Anticline in Well No. 16 (249 m), an absorbed solution density of 1.70 g/cm3 was encountered. In parametric Well No. 2 at Armudli, during drilling in the Maykop Suite (848-2662 m interval), testing produced an absorbed fluid density of 1.98 g/cm3 at a depth of 1680 m. During testing at 3815 m (within the limits of the Maykop section, i.e. 3289-5023 m) an absorbed fluid density of 2.16 g/cm3 was produced from 3750 m, and after 30 minutes, the density was reduced to 2.06 g/cm3. Identical gas shows repeated during deepening of the well at the depths 4125 m and 4200 m.
At Khatunli, shows of oil and gas, associated with the Maykop Suite were only indicated in structural Well No. 8, from the 920-966 m interval that contained gray, fine-grain sand with a weak smell of oil.
At Kurzan-Khuluf, in Well Nos. 8 (1090-1091 m) and 9 (971 m), the smell of oil occurred in brownish-gray, medium-grain, weakly-cemented Maykop sandstone. Hydrocarbon analyses of the Maykop clay samples from Well Nos. 5 and 7, indicated the presence of approximately 0.07 to 0.3 percent light oil and oily resinous bitumins.
At Keyruk-Keylan, well drilling in the Maykop section produced shows and was conducted without any difficulties. However, at Tarsdallar, well drilling in Maykop sediments was accompanied by downhole formation collapse, pieces of which were carried up using heavy drilling muds that masked oil and gas shows. Oil and gas shows observed within the Maykop Suite occurred in the following areas and respective wells:
Tarsdallar Area
Well No. 1, during testing at 2170 m, 2187 m, 2200 m and 2669 m, a fluid was produced with absorbed fluid densities of 2.00-2,05 g/cm3, and 1.18-1.30 g/cm3, including debris retrieved from the collapsed wellbore.
Well No. 3, during drilling at 2061 m, a fluid was retrieved with an absorbed fluid density of 2.05-2.13 g/cm3. At 2100 m, the absorbed fluid density was 2.14 g/cm3.
Well No. 4, encountered Maykop Suite sediments within the 1995-3012 m interval. In the 2971-2979 m and 3007-3014 m intervals, the cuttings represent non-carbonate clays with fine-grained sandstone and a strong smell of oil and gas.
Well No. 6, during the drilling in Maykop sediments at 2513 m and 2656 m depth, a fluid was produced with the absorbed fluid density of 1.94-2.10 g/cm3, the the density gradually reduced to 1.84-1.60 g/cm3.
Well No. 8, during development of the 2200-2212 m interval, the absorbed fluid density was 1.94 to 1.40 g/cm3, and was 1.94 g/cm3 at 2470 m and 2577 m depths.
Well No. 11, gas shows were observed during drilling in Maykop rocks at 1975 m and 2052 m, and during testing at 1689 m depth. The absorbed fluid density was 2.02-2.04 g/cm3. Oil and gas shows were present at 2188 m, 2240 m and 2245 m depth.
Well No. 14, in the Maykop deposits, 6 m thick sandy strata are present at the 1976-2034 m interval. Continued drilling after the sandy strata had been penetrated resulted in intensive gas shows. While testing at 2049 m, 2079 m, 2097 m and 2113 m, the drilling fluid had considereable absorbed gas, and the density gradually decreased from 1.80-1.90 g/cm3 to 1.10-1.30 g/cm3. The gas shows continued upon further drilling. During development at the 1940-2113 m interval, the absorbed fluid density was 1.60-1.80 g/cm3. Additional gas shows occurred during drillling at the 2112-2415 m interval.
Well No. 18, during drilling and testing at 1855 m, 1882 m, 1908 m and 1930 m the absorbed fluid density was 1.96-2.10 g/cm3, decreasing to 1.20-1.30 g/cm3.
Well No. 20, during drilling at 1824 m, for 30 minutes, the fluid contained absorbed gas. Testing at 2255 m produced an absorbed fluid density that decreased from 2.00 g/cm3 to 1.45 g/cm3. Testing at 2400 m produced absorbed oil and gas; the density was gradually reduced from 2.05 g/cm3 to 1.95 g/cm3 within 1.5 hours.
Well No. 22, during enlargement of the borehole at 1173 m depth (top of the Maykop Suite) the drilling fluid density of 1.50 g/cm3 included absorbed gas with a fluid density of 1.38 g/cm3. During testing at 1411 m, within the 1238-1411 m development interval, the produced fluid was absorbed gas and water with an absorbed fluid density that decreased from 1.56 g/cm3 to 1.30 g/cm3.
Well No. 26, during drilling at 2969 m and 2981 m depth, the absorbed fluid density was gradually reduced from 1.96 g/cm3 to 1.75 g/cm3.
Well test data for Tarsdallar are presented in Table 2.
Gyurzundag Area
Parametric Well No. 1, during drilling in the Maykop Suite in the 2338-2660 m interval, had a drilling fluid density decrease from 2.04 g/cm3 to 1.96-1.92 g/cm3. During testing at 3207 m, during the lowering of the stratotester, within 45 minutes the fluid was absorbed by gas with the fluid density decreasing from 2.08 g/cm3 to 1.65 g/cm3. During testing at 3252 m, the drilling fluid had a density of 2.0-2.20 g/cm3 and was constantly absorbed by oil and gas. After pumping ceased, increased inflow of fluid mixed with oil film was observed. While testing at 3449 m, drilling fluid was absorbed by gas with oil film, and within 1.5 hours the density of the fluid decreased from 2.12 g/cm3 to 1.56 g/cm3.
During drilling and testing at 3490 m, 3543 m, 3834 m and 3910 m depths, the drilling fluid discharge was absorbed by gas and oil film and the density of the fluid was reduced from 2.12 g/cm3 to 1.56 g/cm3. During drilling at the 4007-4010 m interval, drilling fluid density decreased from 2.12 g/cm3 to 1.85 g/cm3. However, during testing at 4017 m, 4023 m and 4086 m, the drilling fluid (density 2.00-2.02 g/cm3) was re-absorbed by gas and oil film.
Akstafa Block
During drilling within Upper Cretaceous deposits of the Akstafa Block, shows of oil, gas, water and absorption of drilling fluid were observed and are briefly described below.
Well No. 4 at Sajdag, during drilling within the 4185-4276 m interval, the drilling fluid (density 1.14-1.16 g/cm3) was discharged as gas.During testing in the 4033-4058 m interval, water was produced at a rate of 35.6 m3/day.
Well No. 1 at Mamadtepe, during drilling, absorption of the drilling fluid (density 1.30-1.32 g/cm3) occurred. Circulation was restored due to the decreae in density to 1.18 g/cm3. During testing within the 2565-2655 m, 2590-2719 m and 3137-3356 m intervals formation water flowed at a rate of 58, 56 and 67 m3/s, respectively, without any shows of oil or gas.
In Well No. 5 at Tarsdallar, Upper Cretaceous carbonate rocks were tested in the 3060-3114 m interval. There was no flow. Well No. 9 at Tarsdallar, during drilling at 3832 m, 3850 m and 3987 m depths, had a fluid density of 1.20-1.25 g/cm3 which was re-absorbed by gas and oil films. Testing defined the existence of formation water flowing at a rate of 40-50 m3/day in the 3875-4024 m interval. During drilling of the 3957-3990 m interval, montmorilonittesands saturated by light oil were discharged in the drilling fluid. Logging in this interval of the section is characterizing by a non-differentiated resistivity curve and non-dissected SP curve.
During testing in Lower Eocene deposits the following oil, gas and water shows were recorded: Well No. 1 at Mamadtepe, Lower Eocene testing was carried at 1800-1955 m, 2138-2207-2305 m, 2204-2339 m and 2401-2538 m depths. Formation water flowed at a rate of 2-3 m3/day. The upper part of the 1800-1915 m testing interval may be within Middle Eocene rocks.
Wells have been drilled at the Damirtapa-Udabno and Molladag areas in the Lower Eocene section without any shows or complications. In Well No. 5 at Tarsdallar, drilling fluid (density 1.70-1.80 g/cm3) at the 2735-2743 m interval was re-absorbed by gas with oil films after 15 minutes. The Lower Eocene was also tested in Well No. 26. During the test of the 3470-3526 m interval, inflow of formation water was 3-4 m3/day. The main volume of shows and inflows of hydrocarbons were produced from Middle Eocene intervals.
At Mamadtepe in Well No.1, the interval of 1796-1870 m was perforated during the inflow of formation water with a rate of 48 m3/day. The water-hydrocarbon-sodium, has a specific gravity of 1.0042 g/cm3 and temperature of 200 C.
At Damirtapa-Udabno, in Well No. 1 at the depth of 4083 m, drilling in the Middle Eocene rocks was accompanied by absorption of drilling fluid with a density of 1.82 g/cm3. Testing after the sand perforation of the 4095-4011 m interval resulted in 4-5 m3/day of oil produced with gas from 8mm carbine (Rexp – 80 atm, Rbuf – 170 atm). In the Well No. 2 in the Middle Eocene, five intervals were tested after perforation of the producing section: 3970-3953 m, 3950-3970 m, 3830-3820 m, 3824-3888 m and 3814-3761 m. These intervals produced mainly water with poor showings of gas.
At Molladag, within the Middle Eocene, two intervals were tested: 1) 3632-3700 m, partially within Upper Eocene rocks and 2) 3780-3719 m. In both cases the inflow of formation water was 7 m3/day. The formation pressures average 403-426 g/cm3.
During drilling of Well No. 1 at Western Gyurzundag, absorption was observed during testing at the 4281 m and 4240-4260 m interval with fluid density of 1.40-1.42 g/cm3 and viscosity of 35-50 sec. During Middle Eocene testing within the 4213-4443 m interval, the rate of formation water inflow was 1 m3/day and oil film was present.
In the Well No. 1 at Keyryuk-Keylan, drilling at the 3441 m, 3442 m and 3450 m depths, absorption of drilling fluid with a density of 1.46-1.55 g/cm3 was observed and drilling was continued after the reducing the fluid density to 1.44-1.40 g/cm3. During testing in the 3445-3417 m interval, water flowed at a rate of 10-15 m3/day.
In the wells at Gyurzundag, the following shows and inflows have been recorded:
In Well No. 1 during testing in the 4538 m interval the fluid density of 1.60 g/cm3 was absorbed; in Well No. 3 at the 4368 m depth, the fluid density of 1.62 g/cm3 was absorbed; during testing within the 4327-4361 m interval, oil inflow occurred at a rate of 25-100 m3/day; in Well No. 4, during drilling at the 4510 m depth, fluid density of 1.40-1.42 g/cm3 and viscosity of 45-50 sec was re-absorbed by gas and oil films; in Well No. 7, in the 4458-4350 m interval, testing produced 10.2 m3/day of oil.
In the Beyuk Palantekan area, during drilling of Well No. 3, at the 4825 m, 4937 m, 4940 m, 4948 m, 4949 m, 4951 m, 4960 m, 4966 m and 4967 m depths, absorption of the drilling fluid (density of 1.48-1.58 g/cm3) had occurred. However, during drilling of the 4727-4740 m interval, intense oil shows occurred in the 4740-4840 m interval and fluid that discharged was re-absorbed by gas and oil films (fluid density was 1.52-1.58 g/cm3).
During testing of the 4950-4731 m and 4731-4700 m intervals, water inflowed at a rate of 1.4-2.0 m3/sec. Only during testing for inflows from the 5146-5250 m intervals did the water inflow at a rate of 10-17 m3/day. In the 5112-5294 m interval, water inflowed at rate of 1 m3/day and was re-absorbed by gas.
At Sajdag, in Well No. 3, testing of Middle Eocene rocks has been conducted in three promising intervals: 1) 3147-3214 m- inflow of formation water with gas emanation at a rate of 30 m3/day, 2) 3213-3268 m-water inflow at a rateof 72 m3/sec, 3) 3268-3341 m-formation water with the gas emanation at a rate of 200 m3/day. Drilling in Well No. 4 in the 3270 m and 3420 m intervals recorded absorption of fluid (density 1.98-1.96 g/cm3) and viscosity of 90-100sec.
Further drilling was continued by reducing fluid density to 1.52-1.48 g/cm3. Additional testing was conducted in: 1) the 3320-3303 m interval, water inflowed at a rate of 140 m3/day with gas emanations and 2) the 3306-3420 m interval, water inflowed at a rate of 90 m3/day with gas emanations. In Well No. 5, testing at the 3533 m depth used a fluid density of 1.35-1.45 g/cm3, which was re-absorbed by gas and oil films.
At Tarsdallar, drilling in Middle Eocene was accompanied by absorption of drilling fluid and oil-gas shows: 1) in Well No. 1 at the 2892 m depth, absorption of fluid with a density of 2.0-2.05 g/cm3 and viscosity of 130-150 sec was observed, and 2) in Well No. 6 at the 2792 m, 2995 m and 3000 m depths, discharged fluid with a density of 1.85 g/cm3 was re-absorbed by gas, 3) in Well No. 8 at the 2891 m depth, the partly absorbed fluid had a density of 1.75 g/cm3 and viscosity of 45-50 sec., 4) in Well No. 16 at the 2682 m depth, absorption of fluid with a density of 1.40-1.47 g/cm3 was recorded, 5) in Well No. 18, during testing at the 2435 m and 2550 m depths, absorption of fluid with a density of 2.06-2.08 g/cm3 was observed, and 6) in Well No. 24 during testing at the 4256 m, 4130 m and 4230 m depths, discharged fluid with a density of 1.98-2.0 g/cm3 was re-absorbed by gas and oil.
Additional testing in Middle Eocene intervals (Table 2) was carried out at Tarsdallar:
1) in Well No. 1 in the 2865-2882 m interval, 250 m3/day was produced (for three days 430t/day were produced, r exp – 5,0 Mpa, Rbuf – 10,0 Mpa and Rpl – 43 Mpa); 2) in Well No. 4 in the 3052-3111 m interval the initial production 160 m3/day, during the Rbuf – 62 Mpa and Rexp – 31 Mpa; 3) in Well No. 6 during testing after perforation of the 2859-? Interval, water inflowed at a rate of 7-8 m3/day with oil film; 4) in Well No. 8, during testing of the 2891-2925 m interval, after 4, 7 and 10 mm carbine, oil flowed produced with gas at a rate of 25-30 m3/day during the Rbuf – 0-12 Mpa and R exp – 0-35 Mpa was produced; 5) in Well No. 9 during testing of: the 2985-2998 m interval, oil inflow of 20 m3/day was produced and, from a second 2998-3018 m interval, formation water inflowed at a rate of 0.4 m3/day; 6) in Well No. 11, two intervals were tested: the first test at 2483-2528 m interval flowed water at a rate of 90-95 m3/day and the second test, at the 2436-2495 m interval flowed water at a rate of 35 m3/day; 7) in Well No. 16, testing of the 2708-2611 m and 2667-2609 m intervals inflowed formation water at a rate of 6 m3/day; 8) in Well No. 17, the 2137-2185 m interval was tested by a 14 mm diameter hole through which formation water with oil film flowed at a rate of 80-90 m3/day, and from the 2137-2242 m interval, the well produced 60 m3/day of liquid, 4 m3/day of which was oil; 9) in Well No. 24, both attempts to test Middle Eocene were unsuccessful due to th existence of a cavern (caving); 10) in Well No. 27, testing was carried out in three intervals: 2957-2979 m- paker deformation, 2958-3023 m-15 m3/day of fluid with oil film and gas emanation, and 2958-3023 m-15 m3/day of fluid with oil film and gas emanation; 11) in Well No. 34, three intervals were tested during the drilling- intervals 3375-3463 m and 3374-3532 m were futile, and interval 3539-3616 m flowed fluid with the oil film at a rate of 1.9 m3/day. After column lowering in the 3444-3370 m interval (PK – 103 mm, TSH – 65 mm), fluid re-absorbed by gas was produced.
During drilling in Upper Eocene, the following shows and absorptions were noted across the region: 1) Sajdag area, in Well No. 4 at the 3085 m, 3135 m and 3148 m depths-absorption of the drilling fluid with a density of 1.92 g/cm3 and viscosity of 100-150 sec; 2) Molladag area in Well No. 1 at the 3472 m, 3570 m and 3578 m depths- fluid with a density of 1.36-1.40 g/cm3 and viscosity of 40-50 sec was absorbed. During washing, gas and oil film was observed; 3) Gyurzundag area, in Well No. 1 at the 4086 m, 4280 m and 4340 m depths- fluid with a density of 2.04-2.10 g/cm3 was absorbed; in Well No. 3 at the 4112 m depth-absorption of fluid with a density of 2.15 g/cm3 was observed; in Well No. 4, absorption of washing fluid with a density of 1.62-1.66 g/cm3 took place, but during washing of the 4250 m, 4426 m, 4452 m, 4467 m and 4483 m depths-the drilling fluid was re-absorbed by gas and oil films; in Well No. 7 at the 4080 m depth-absorption of the drilling fluid with a density of 2.05-1.96 g/cm3 were recorded.
At Beyuk Palantekan in Well No. 3, during drilling at the 4450 m and 4560 m depths (drilling fluid density of 2.22-2.24 g/cm3), intensive gas and water shows were observed.
At Tarsdallar in Well No. 1, during drilling of the 2784-2800 m interval, drilling fluid (density 2.0-2.05 g/cm3) was absorbed. During testing in Well No. 8 at 2850 m depth, partial absorption of the drilling fluid (density 2.0-2.05 g/cm3) and viscosity 50-80 sec, was observed. In Well No. 13, at 3707 m depth, drilling fluid (density 2.18-2.20 g/cm3) discharged re-absorbed by gas and oil film. In Well No. 16, during testing at 2608 m depth, drilling fluid with a density of 1.45-1.46 g/cm3 discharged re-absorbed by gas. In Well No. 17, at the 4015 m depth, drilling fluid (density 1.98-2.02 g/cm3) was re-absorbed by gas. In Well No. 34 at the 3110 m depth, absorption of the washing fluid (density 2.02-2.12 g/cm3) was noted, but during washing at the 3320-3340 m interval, a gas show was observed.
At Molladag, four intervals were tested using a stratumtester: 1) 3480-3512 m interval- formation water inflowed at a rate of 35 m3/day (Rpl – 510 atm), 2) 3486-3550 m interval- formation water inflowed at a rate of 30 m3/day (Rpl – 460 atm), 3) 3486-3580 m interval- formation water inflowed at a rate of 18 m3/day and 4) 3583-3633 m interval -formation water inflowed at a rate of 20 m3/day.
At Mamadtepe in Well No. 1, the Upper Eocene interval of 1796-1870 m was examined and formation water inflowed at a rate of 254 atm. The water-hydrocarbonated-sodium charged, had a specific gravity of 1.0042 g/cm32 at 20°C.
At Damirtapa-Udabno, examination of an Upper Eocene interval was conducted only in Well No. 2. Four interval tests were performed: intervals 3654-3704 m, 3654-3647 m and 3645-3600 m had no inflow, but interval 3705-3745 m flowed 16-18 m3/day without signs of oil-gas-saturation.
At Gyurzundag in Well No. 3, the 4327-4361 m interval, which covers the “upper marl bench” (Upper Eocenee and top Middle Eocene) was tested. The produced oil from this interval reached 25-100 ton/day. In Well No. 7, during testing of the 4270-4300 m interval (“upper marl bench” of Upper Eocene), oil inflowed at a rate of from 5.9 up to 40 ton/day, along with 3.5 m3/day water (after perforation PKOT-73 mm and PKM-8-total 380 holes). At west Gyrzundag in Well No. 1, two intervals were tested: 1) 4179-4270 m depth- fluid inflow of 2-4 m3/day and 2) 4179-4318 m depth-inflow of 1 m3/day of fluid.
At Beyuk Palantekan, testing of Upper Eocene rocks was conducted in two wells: 1) in Well No. 2 at the 5115-5117 m interval, oil inflowed at a rate of 12 m3/day, but the production from the 5112-5294 m interval yielded 1.0 m3/day of oil with gas emanation, and 2) in Well No. 3, the 4727-4740 m interval was tested and water inflowed up to 8.7 m3/day with oil film. Testing within the 4730-4840 m interval yielded water inflow of roughly 4 m3/day.
At Tarsdallar, Upper Eocene deposits were tested in: 1) Well No. 16, during testing of the 2578-2608 m interval, water with oil film inflowed at a rate of 85-90 m3/day, 2) Well No. 22, during testing of the 1956-1968 m and 1956-1983 m intervals, formation water flowed at a rate of 22.0 and 10m3/day, with insignificant gas content with Rpl – 230-260 atm., 3) Well No. 27, the 2905-2929 interval was tested (PKR – 196 holes), and found to yield 0.5 m3/day of water with oil film, 4) Well No. 34, the 3665-3575 m interval was tested and inflow of absorpted fluid with oil film reached 8.4 m3/day, and during testing in the 3370-3544 m interval (perforation by PK-103 mm, TSHT-84mm and TSH-65mm) produced fluid with gas emanation.
GEOCHEMISTRY OF OILS AND ROCKS
Investigation of organic matter distributed in rocks of the Kura-Gabirry Interfluve indicates that the material consists preominanatly of fluorescent amorphinite Am (type II kerogen, volume <90%), which was probably extracted from algal remains that were biologically degraded during the sediment accumulation (i.e. algal amorphinite). Well-preserved alginite A (type I kerogen) forms in a marine environment, notwithstanding its small amount. The organic mass does not contain sufficient onshore-type vegetation according to the analyses of kerogen. There is an observed intensive transition to maserals from green fluorescence to greenish-yellow fluorescence, indicating thermal immaturity of the samples. These observations were confirmed by biomarker data interpretation (VR-0.40 to 0.50%).
Numerous inclusions of pyrite in the rock indicate conditions favorable for preservation of organic sediment material. High fluorescence of the samples, the equivalent of which is the reflection capability data of vitrinite, indicates that the samples are thermally immature while having the capacity to generating oil (i.e. total organic carbon content TOC=1.90%, genetic rock potential (S1+S2)= 4.2 mgr. HC/gr. of rock). Only one of the available samples (i.e. Beyuk Palantekan, Well No. 23, 4700-4710 m interval, showed less intensive fluorescence. This is an indication of a minor increase in thermal maturity (TOC=2.10%; (S1+S2)= 9.30 mgr. HC/gr. of rock), i.e. the rock is at the transition to an oil-generating phase.
Upper Cretaceous samples from Tarsdallar have relatively low organic content (TOC=0.02%) and their oil generating potential is also very low. It is quite probable that the environment of deposition at Tarsdallar was somewhat acidic, and as result, the favorable conditions for preservation of organic mass were limited. Oil samples from various other fields within the Kura-Gabirry Interfluve were also analyzed. The results of oil sample analyses were compared in order to identify: 1) oil source rock intervals in which the analyzed oil was generated, 2) maturity level, and 3) source rock environment of deposition. Comparison of analyses indicated that there are Middle Eocene and Lower Upper Eocene oils with high maturity levels and very similar physiochemical characteristics. Most probably, these oils had one common source.
Based on the comparison of oil and rock analyses, the Lower Eocene clays may be the most probable hydrocarbon source of the oils. This situation may be true, particularly because the composition of the oils differ with their comparatively more developed lithogenesis (MK2 and MK3 stages of mesokatogenesis), thermal maturity, thickness, and organic substance and bitumen content. Therefore, these rocks have relatively much more developed oil generating potential.
Upper Eocene clays and Maykop clayey shales appear to have relatively high oil generating potential, due in part to their great thickness, abundantly distributed organic substances and favorable geochemical evolution. Given these circumstances, the Upper Eocene and Maykop rocks are potentially at the oil generation stage, provided that they will subside to favorable depth for transition from initial organic substance to oil hydrocarbons. The Upper Eocene deposits are partially influenced by mesokatogenesis (MK1 stage of mesokatogenesis).
The results of regional maturation studies in the Kura-Gabirry Interfluve (including increased sediment thickness toward the north, reletively high total organic carbon content (%TOC), reflection capabilities of vitirinite (Ro) and geothermal gradients) clearly suggest that the best location for mature oil source rocks is in the northern part of the area along the axis of the Iori Basin.
SUMMARY AND PROPOSED FUTURE WORK
The “Akstafa Block” covers a significant part of the Kura-Gabirry Interfluve, i.e. from the Mingechevir Reservoir in the east to the Georgian boundary in the west. The study area discussed in this report is about 1950 km2. Geological investigation of the interfluve region was begun more than 100 years ago when the abundance of surface oil seeps attracted the attention of geologists. A detailed and planned investigation of the area was started, which surged in activity, especially during the post-World War II years, when plane-table mapping was conducted at the 1:25,000 scale. Almost the all structures were involved in structural prospect drilling from depths of 500 m to 1800 m.
Geophysical methods of investigation have been used in the region since 1949, particularly gravity and magnetic surveys, as well as electric logging. Seismic reflection surveys were started in 1964, followed by seismic refraction. These investigations focused on deep Mesozoic and Paleogene deposits and provided the basis for further exploration of local structures prior to exploratory drilling for oil and gas.
By 1971, the Kura-Gabirry Interfluve had a total of 52 parametric, prospecting and exploration wells drilled, with an accumulated total of 180,000 m drilled. Drilling of deep wells was carried out in 13 areas, the most important was the structure at Tarsdallar, which was covered by 27 wells (Figures 38 and 39). Other structures were investigated by drilling single wells.
As a result of the long-term geological and geophysical investigations, the Kura-Gabirry Interfluve has been characterized as a complex structural region. In the drilled interval of sedimentary cover, two abrupt structural boundaries, between Mesozoic and Paleogene, and between Miocene and Quaternary have been observed. The upper structural level (Miocene-Quaternary) is more complicated and is characterized by tilted strata, the existence of regional thrusts and regional angular unconformities. The lower structural level (Mesozoic-Paleogene) is characteristically gently folded, with fold orientations roughly east-west. Some of the buried thrusts in these units are up to 12-18 km in length.
Figure 38. Seismo-geological profile of the Tarsdallar structural high (NW-SE)
Regional investigations have collectively suggested that the most favorable conditions for the formation and accumulation of oil occurred in the Mesozoic-Eocene interval. The thickness of these sediments increases toward the west, and well drilling in these rocks is everywhere accompanied by intense shows and absorbtion of drilling fluid. The most abundant shows, discovered during drilling at Tarsdallar, are in Upper-Middle Eocene sandy and tuffogenic-volcanogenic reservoirs. The first Well No. 1 drilled at Tarsdallar was a blowout with an initial production rate of up to 250 tons/day of oil. Commerical was also produced in three of the first ten wells drilled, i.e. Well Nos. 4, 8 and 9. Production to data has been calculated at 118,000 tons, with an estimated inplace reserve of 1,264,000 tons.
Figure 39. Seismo-geological profile of the Tarsdallar structural high (W-E)
The largest producing reservoirs appear to be located in the northern and northwestern areas of the Kura-Gabirry Interfluve. For example, Damirtapa-Udabno (Figure 40), Gyurzundag (Figures 41, 42 and 43), and Beyuk Palantekan (Figures 44 and 45 and 46) have commercial production rates of up to 100 tons/day based upon drilling and testing of wells in Eocene deposits (e.g. Well No. 3 at Gyurzundag). The potential oil reserves on the region are estimated to be about 100-300 million of tons.
Figure 40. Seismo-geological profile of the Damirtepe-Udabno region
Figure 41. Seismo-geological profile of the Gyurzundag-Akhtepe structural high
Figure 42. Seismo-geological profile of Keyruk-Keylan—Gyurzundag—Beyuk Palantekan
Figure 43. Seismo-geological profile of the West Gyurzundag—Gyurzundag structural high
Overall favorable geological conditions have existed for oil and gas formation in the Kura-Gabirry Interfluve. Moreover, data calculations of oil and gas content appear to support the prospectivity of new fields. Nevertheless, new exploration was slowed or halted in connection with recent economic conditions in the oil industry. Analyses of geological and geophysical data from the “Akstafa Block” suggests that: the most abundant oil and gas interval in the sedimentary complex thus far investigated (i.e. by drilling that has reached 5000 m depths), are the terrigenous-carbonate and fractured-tuffogenic reservoirs of Eocene age, and the sandy reservoirs of the Maykop Suite and the Sarmatian Stage.
Figure 44. Seismo-geological profile of the Djeiranchel-Beyuk Palantekan region
Figure 45. Seismo-geological profile of the Akhtepe-Palantekan-Tarsdallar structural high
Figure 46. Seismo-geological profile of the Tarsdallar-Beyuk Palantekan region
Exploration efforts have revealed commercial potential in the beds that are dipping toward the northeast and are deeply buried beneath the Damirtepe-Udabno thrust. Figures 6 and 40). The plane of this thrust fault appears to serve as a mechanism for sealing commercial oil and gas potential in the underlying rocks. Other important factors regarding the accumulation of commercial oil and gas beneath the thrust are the consistant bed thicknesses (volume) and the degradation of reservoir conditions in the Middle Eocene section (migration), particularly in the section containing impermeable argillaceous rocks (i.e. Well Nos. 5, 6 and 26 at Tarsdallar).
Certain other regional structures have attracted the attention of geologists regarding the large oil and gas reservoir potential, particularly the structures situated within the eastern Chatma Anticlinorium (Figure 47). There exist much improved reservoir facies characteristics in the Eocene section, e.g. the middle and top of the “upper marl bench”, as well as the Middle Sarmatian units, and others previously described. There is currently commercial oil production in wells at Gyurzundag (Figures 41, 42 and 43) and the Beyuk Palantekan area (Figures 42, 44 and 45), suggesting that additional exploration work in these areas could be fruitful.
Figure 47. Seismo-geological profile of the Lessor Caucasus-Chatma Anticlinorium regional line
The neighboring Akstafa, North Kesaman and Palantekan structures should probably be considered for drilling evaluation. Eocene deposits appear to be prospective in the northwestern part of the Kura-Gabirry Interfluve. In Georgia, the Samgory and Ninozminda fields are being developed in a region where Midlde Eocene section appears to be significantly thickened. Locally, on the Azeri side of the border, the relatively large Jandar, Soyugbulag and Alimardanli folds were discovered during seismic investigation. The prospective nature of these structures may be associated with large volume anticlinal traps.
The central part of the Chatma Anticlinorium, in the Azeri-Georgia border region from Sajdag to Akhtepe (Figure 47), has not been excluded from the number of prospective areas, however, the regional topographic relief constrains the amount of exploration that can be accomplished in this territory.
In the region of Gyurzundag (Figures 41, 42 and 43), West Gyurzundag (Figure 43) Akhtepe (Figure 41) and Beyuk Palantekan (Figures 42, 44, 45 and 46), further exploration is needed to select the best drilling targets. This will require acquisition of two or three seismic lines, data interpretation and some subsequent geologic mapping. The plunging section of the nearby Tarsdallar structure may serve as a guide to these exploration efforts.
In the above mentioned and possibly other prospective areas, it is proposed that preliminary seismic data acquisition be conducted for the purpose of selecting smaller target areas for both 3D seismic survey(s) and exploratory drilling.