INTERNA TlONAL FEATURE

OFFSHORE OIL AND GAS FIELDS IN AZERBAIJAN:

HISTORY AND DESCRIPTION, PART I* by Prof. Leonid A. Buryakovsky

Independent Petroleum Geologist Houston, Texas

Abstract The geological structure, andoil and gas content of the

Caspian Sea in the limits of the Azerbaijan Republic borders are described, including a Caspian Sea overview, geotectonic features, oil and gas zonation, history of oil and gas fields discovery, geological; structure of fields, and reservoir development.

Introduction One of the characteristics of modern development of

the world oil and gas industry is the increasing role of marine oil and gas production. At present one hundred countries survey the sea and ocean shelf, and almost forty countries are already producing oil and gas from offshore fields. More than 400 offshore oil and gas fiekls are in development. Development of continental shelf oil and gas resources is one of the most important directions in developing our remaining petroleum resources.

The States (Republics) of the CIS have enormous offshore oil and gas potential. The continental shelves of the Caspian, Azov, Black, Barents, Kara, Pechora, Okhotsk, and other seas are the most prornieing areas for discovery, exploration and development of oil and gas fields. Among them, the Caspian Sea is one of the most interesting oil- and gas-bearing regions. A knowledge of geological structure and oil and gas content of the Caspian Sea is of more than local interest. This knowledge may be useful to American petroleum geologists because of many geological (structural) similarities of the Caspian Sea and the Gulf of Mexico.

Caspian Sea overview The Caspian Sea is a highly promising oil- and gas-

bearing region because oil and gas provinces situated on the land of Azerbaijan, Russia, Kazakhstan, Turkmenistan and Iran extend into the Caspian Sea area (Fig. 1). The Caspian Sea is the world's largest salt lake. Its length from north to south is 1174 km, average width 326 km, and total area is 375,OOO km2. The water depth in the central part of the sea reaches up to 788 m and that in the southern part, up to 1025 m. It has no outlet, and although the surface level fluctuates, it averages about 25 m below sea level according to the recent measurements. The total area of the Soviet portion of the Caspian Sea is 322,000 km2, including the shelf zone. A general overview of the hydrocarbon potential of the Caspian Sea area shows that a region without hydrocarbon prospectivity can hardly be found in this vast

'To be continued in the September 93 Bulletin.

area. About 150 prospective structures have been dis- covered, however the total number may be up to 350. More than 45% of total Caspian Sea area has water depths less than 50 m, and about 10% has water depths from 50 to 100 m. About two-thirds of the sea is shallower than 200 m.

The basin is a part of the eastern portion of the Pre- Tethys Sea which began to develop in Early Paleogene during the Alpine-Himalayan orogenic movements. The Caspian Sea area includes three major geotectonic ele- ments: Pre-Caspian region of the Russian Platform in the north, Scythian-Turonian Epi-Hercynian Platform in the

Mangyshlak \

Fig. 1. Caspian Sea area.

Bulletin Houston Geological Society. June 1993

middle portion of the sea, and Alpine Geosyncline zone in the south. Three distinct sub-basins (northern, middle and southern) are related to these maior structural elements.

The'southern basin has a high density of confirmed structures, whereas the middle and northern basins have not been well studied (Fig. 2). Hydrocarbon reserves have been discovered and developed in the areas with water depths up to 60 m, and five oil and gas fields have been discovered in water depths up to 200 m. Hydrocarbon potential from 33 oil and gas fields is estimated at 10 billion tons. Thirty-one of the fields are in the South Caspian Basin, 23 in Azerbaijan, and eight in Turkmenistan. Two are in Kazakhstan to the north.

Fig. 2. Oil and gas distribution in Caspian Sea area: 1 - highly favorable areas; 2 - areas favorable for oil and gas; 3 - discovered local structures; 4 - oil and gas fields; 5 - southern limit of salt domes; 6 - boundary between Pre- paleozoic Russian Platform and Epihercynidic Scythian- Turanian Platform: 7 - southern limit of Epihercynidic Plat- form; 8 - Alpine mountain systems.

At present, exploration is conducted in the offshore areas of Azerbaijan, Turkmenistan, Kazakhstan, and Russian parts of the Caspian Sea. The main goal of deep exploratory drilling in the Azerbaijani and Turkmenian parts of the Caspian Sea (Apsheron and Baku archipelagoes, eastern part of Apsheron-Pre-Balkhan zone of uplifts and South Turkmenistan Shelf) is to discover new oil and gas fields and to delineate those already discovered in the Productive Unit section (Middle Pliocene). In the Kazakh and Russian parts of the sea the goal is to study the oil and gas content of Mesozoic deposits.

Geologists and geophysicists have identified more than four anticlinal structures within the western part of the South Caspian Basin, most of which are prospective for oil and gas. Banka Darvina, Artyom Island, Gyurgyany-more, Zhiloy Island, Banka Yuzhnaya, Gryazevaya Sopka, Neftyaniye Kamni, Guneshli, Azeri, Peschany-more, Bak- har, Sangachaly-more, Duvanny-more, Bulla Island, Bulla- more, and other oil and gas fields are in operation. The largest of these fields are Neftyaniye Kamni, Bakhar, Sangachaly-more, Duvanny-more, Bulla Island, and Bulla- more. Over 10 are being explored in detail.

Intensive offshore development in Azerbaijan began in 1949. Since then, 23 fields have produced 12 mln. tons of oil and condensate, and 11 billion m3 of gas, about half of their recoverable reserves. All fields are multipay with 3 to 30 producing horizons in Middle Pliocene sandstones and siltstones. More than 3000 wells have been drilled from over 1000 platforms.

In the Caspian Sea production wells are drilled out from individual platforms. Until recently, platforms were built for 40 m sea depths; at present platforms are being installed at depths of 110 m and more. Floating drilling rigs are used for exploration. Eight such rigs are now in operation, five of which are self-lifting and can operate in 70 m of water and drill wells to 6500m. Three semi-submersible drilling rigs are in operation on the Guneshli and Kaverochkin structures in 165 m of water. At present, prospect drilling in the Caspian Sea is carried out at depths of 200 m. The deepest well drilled is 6500 m.

The South Caspian Basin is characterized by deep water on the west and shallow water on the east. It is separated from the Middle Caspian Basin by the Caucasus- Kopet-Dagh Fault. A ridge of uplifts, the Apsheron-Pre- Balkhan zone, extending NW-SE between the Apsheron and Cheleken peninsulas, forms a narrow subsea topo- graphic high. All major fields in the area are related to this regional feature. There are three oil- and gas-bearing zones in the South Caspian Basin that belong to Azerbaijan: I - the Apsheron-Archipelago and Apsheron-Pre-Balkhan zone of uplifts, I1 - the South Apsheron offshore zone, and I11 - the Baku Archipelago zone. Two other zones in the South Caspian Basin are IV - Turkmenian Shelf and V - the deep- sea zone (Figs. 2 and 3).

Zone I: Apsheron Archipelago and Threshold The main oil- and gas-bearing series of the Apsheron

Archipelago and Apsheron-Pre-Balkhan zone of uplifts (the so-called Apsheron Threshold) is the Productive Unit (Middle Pliocene). It includes about 90% of the discovered hydrocarbon reserves of the Caspian Sea. Upper Miocene diatomaceous layers are exposed in the core of the most significant uplifts of the Apsheron Archipelago: Zhiloy Island

Bulletin Houston Geolog~csl Saciety. June 1993

Fig. 3. Zonation of the South Caspian Basin and disposition of oil and gas fields and local structures: Zones: I - Apsheron Archipelago and Threshold; I1 - South Apsheron offshore zone; 111 - Baku Archipelago; IV - Turkmenian Shelf; V - the deep-sea zone Oil and gas fields: 1 - Banka Apsheronskaya, 2 - Banka Darvina, 3 - Artyoma Island (North), 4 - Artyoma Island (South), 5 - Gyurgyany-more, 6 Banka Yuzhnaya, 7 - Kamni Grigorenko, 8 - Zhiloi Island, 9 - Azi Aslanova, 10 - Gryazevaya Sopka, 11 - Neftyaniye Kamni, 12 - Guneshli, 13 - Kaverochkin, 14 - Azeri, 15 - Promezhutochnaya, 16 - Livanova-West, 17 - Livanova-Center, 18 - Livanova-East, 19 - Barinova, 20 - Gubkina, 21 - LAM, 22 - Zhdanova, 23 - Prichelekenskoye, 24 - Zyrya, 25 - Peschany-more, 26 Bakhar, 27 - Bibiebat, 28 - Karadag, 29 - Sangachaly-more, 30 - Duvanny-more, 31 - Bulla Island, 32 - Bulla-more, 33 - Khamamdag-more, 34 - Garasu.

and Neftyaniye Kamni. The Banka Apsheronskaya, Artyom Island, Zhiloy Island, Gryazevaya Sopka, Neftyaniye Kamni, Guneshli (previously named after the 28th of April), and Azeri uplifts are complicated by mud volcanoes.

According to the presence and degree of oil and gas fields, the Apsheron threshold is divided into western and eastern parts (Fig. 3) which are delineated along the edge of the eastern limb of the Promezhutochnaya Fold. The northernmost structural element of this complicated tectonic zone is an anticlinal zone, which includes the following uplifts: the Kamni Dva Brata (Two Brothers' Rocks), Banka Apsheronskaya, Banka Andriyevskogo, Shapirovsky uplifts and the "40th Anniversary of Azerbaijan Uplift." Another structural belt parallel to the first stretches to the southwest and includes the Kamni Grigorenko, Zhiloy Island, Grayazevaya Sopka, Neftyaniye Kamni, Guneshli, Azeri and Promezhutochnaya uplifts.

Among these fields, the history of Neftyaniye Kamni reflects pioneering in the development of offshore oil and gas fields. Exploration in the area of Neftyaniye Kamni and ensuing development marked the beginning of operation from offshore man-made structures.

The Neftyaniye Kamni Oil Field Location and history. The field is situated in the

western part of the Apsheron Threshold (Fig. 3), which is a connecting link between the southeastern end of the Greater Caucasus and Pri-Balkhan zone of uplifts in western Turkmenistan. The Apsheron Threshold is the tectonic element that constitutes the northern part of the South Caspian Basin, it is one of the most explored and promising zones of the Caspian Sea.

The Neftyaniye Kamni Oil Field is the eastern most above-water projection of the submerged ridge of the Apsheron Threshold and is situated 55 km southeast of Artyom, 110 km east of Baku (Fig. 4).

Neftyaniye Kamni is located in open sea with depths of 15-25 m. The sea floor is composed of sandy-clayey rocks, among which compact sandstones occur. Detrital deposits consist of sand and shells. The character of the bottom relief depends directly on the structure and lithology of the bedrock. Outcrops of the Productive Unit, appearing above sea level, are spread over an area of more than 12 km2; the length of the strip is about 6-7 km, its width is 2-3 km. Some outcrops emerge above water level at 2-3 m, and others are

Bullelln Houston Geological Society. June 1993 14

Fig. 4. Location offshore of the Neftyaniye Kamni Oil Field.

seen only in rough waters. All of these projections extend from the northwest to the southeast bordering the anticlinal crest. The exposed sandy horizons continuously transmit oil and gas to the sea surface. This manifestation is so intense that in calm weather the water surface is covered by an oil film, and gas bubbles "boil" to the surface. Wind and rough sea carry oil onto the sandstone outcrops, the surface of which is covered by an oil film. Because of this oil staining of the rocks emerging above the water level, this area is called Neftyaniye Kamni - Oil Stones.

The earliest geologic description Neftyaniye Kamni as "a small archipelago of underwater stones and rocks" has been found in the publications of the well-known researcher of the Caucasus, academician G. V. Abikh, who in 1863 gave a detailed geomorphological description of the Neftyaniye Kamni area. He also pointed out hydrocarbon gas and oil shows.

Descriptions of tectonics and stratigraphy of the Neftyaniye Kamni area were presented by G . Sogren (1892) and N. A. Lebedev (1902). Some years later, the geological structure of the area was reconsidered by S. A. Kovalevsky (1926), S. M. Apresov (1933) and M. F. Mirchink (1939). In 1945-1949 the Azerbaijan Oil Expedition of the Academy of Sciences of the USSR, under the guidance of A. K. Aliyev, investigated the Neftyaniye Kamni area. As the result the preliminary geological map of the area was compiled and the exploration plan for the region was worked out.

Exploration was begun in the Neftyaniye Kamni area in August 1949. The first oil influx of 100 tons (- 550 bbl per day) was was obtained in November from the first well completed in the Productive Unit on a 5 mm choke, under a wellhead pressure of 70 atm. The rate of exploration drilling increased; it was ascertained that the whole sequence of the Productive Unit contains commercial oil and gas accumu- lations.

The first well was rigged up in a short period of time on the largest outcrop. Also, a small house with radio station, providing day-and-night connection with the land was built for the team on piles sunk into the sea bottom. The team was guided by toolpusher M. P. Kaverochkin. Drilling was carried out in very difficult conditions; but people worked dedicatedly, ignoring storms and penetrating winds.

The second well in the area of the Neftyaniye Kamni was constructed on a large block foundation of''MOSm type designed by A. A. Mezhlumov, S. A. Orudzhev and Yu. A. Safarov in 1949. A young toolpusher, K. A. Abasov, was charged with drilling this well.

Commercial quantities of oil necessitated the creation of a comprehensive material and technical support network that would allow the insistent assault of sea depths. With this goal in mind, seven old ships were moved to the inhospitable and dangerous Black Rocks (Oil Stones). The ships were placed in semicircle and sunk on a shoal. The artificial island thus formed was romantically called "The Island of Seven Ships". Mechanical workshops, a store- house and an office were placed on the ships' decks and the cabins were used as living quarters. It was decided to connect the outcrops with each other by trestles and to form an artificial island in the open sea. The following long- term practice of offshore field development in extensively difficult hydrometeorological conditions proved the cor- rectness of the trestle method for development in water depths of 10-40 m. On February 18, 1951, the first tanker filled with produced oil left the moorage of new town in the open sea.

Nowadays the initial of Soviet offshore oil field development is a complex of hydrotechnical structures spreading over 200 km. All conditions necessary for work and recreation have been created for the offshore oilmen. There one can see the dwelling settlement, Palace of Culture, shops, hospital, cinema, etc. Power supply for the field facilities and the town is provided by an autonomous power station built on the platform area. At present, five story hotel-like dwellings, a swimming pool, a compressor station, etc., have been built on "The Island of Seven Ships".

Geology. Since the beginning of exploration, more than 1000 exploratory, producing and injection wells have been drilled in the region of Neftyaniye Kamni, which allowed field delineation and development at first in the southwestern fold limb and then in the southeastern limb, as well as detailed study of the geology of the field.

The stratigraphy found in the anticlinal structure of Neftyaniye Kamni is defined from upper Pliocene Koun to

15 Bullet~n Houston Geoloqlcal Soc~ety June 1993

Apsheronian deposits. The beds of the Productive Unit and overlying Akchagylian and Apsheronian stage rocks (Upper Pliocene) crop out in the core of the fold.

Tectonically, the field coincides with a large brachyanti- cline.* The Neftyaniye Kamni Fold is an asymmetrical structure (Fig. 5); at the southwestern limb dip angles are 35-40'. The northeastern limb dips 45-50'. The fold is complicated by transverse and longitudinal faults which involve the entire Productive Unit. A large longitudinal thrust fault extends along the northeastern limb of the fold, causing the southwestern limb to overlap the northeastern limb. Mud volcanism in the area is connected with this fault. The fold is further complicated by a series of faults transverse to its axis. The majority of these faults are set against the main longitudinal disturbance and cross the entire Productive Unit. Fault plane dip range from 60-90" and stretch mainly in a southeastern direction. Maximum bed displacement occurs at the fold crest and decreasing and disappearing toward the limbs.

On the basis of oil saturation and conditions of oil occurrence, the Neftyaniye Kamni structure is divided into five large, separate tectonic blocks (Fig. 5): I) the north. western part of the fold; 11) the central part of the south- western wing of the fold; 111) the central part of the northeastern wing; IV) the southeastern pericline** of the southwestern wing; and V) the southeastern pericline of the northeastern wing.

The oil and gas producing zone of the Neftyaniye Kamni Field is the Productive Unit, which is in turn divided in to the following suites and horizons upwards. Kalin- skaya which is divided into horizons KaS,, KaS,, KaS,, and KaS,; Podkirmakinskaya, which is divided into horizons

*Brachyanticline: Russian term for a long, narrow anticline. "Pericline: Russian term for the t w o secondary limbs of an elongated, closed

structure.

PK,, PK,, and PK,; Kirmakinskaya, which is divided into horizons KS,, and KS,; Nadkirmakinskaya peschanaya (sandy) - NKP; Nadkirmakinskaya glinistaya (clayey) -NKG; "Pereryv" ("Break"); Balakhanskaya, which is divided into horizons X, IX, VIII, VII, VI, and V; Sabunchinskaya, which is divided into horizons IV, 111, and 11; and Surakhanskaya (I and I' horizons) (Fig. 6) Approximately 30 oil-and gas- saturated horizons have been identified in these horizons (Figs. 7 and 8).

Field development. From the very beginning of the development of the Neftyaniye Kamni Field, different water flooding options were used in order to maintain pressures in the productive formations. Water flooding provided high economic efficiency of oil production by maintaining high flow rates.

According to log and well test data, the second tectonic block (main block) contains three separate sandy-silty productive formations, divided by thick shale interbeds, in the Kalinskaya Suite sequence. Among them the KaS, and KaS, horizons are characterized by good oil saturation and production. The KaS, horizon has a large gas cap, and the KaS3 horizon is gas-bearing.

The main productive formation of the field is the Podkirmakinskaya Suite. The first wells completed in the oil-bearing sequence of this suite had very high yields. The entire thickness of the Podkirmakinskaya Suite is oil- saturated. The suite is divided into two main wroductive formations, PK, and PK,, which are separated from one another by 2-5 m shale layer. The average thickness of the PK, is 40 m; and of PK, is 45 m. At the pool roof the thickness of the shale layer between PK, and PK, decreases and sometimes disappears. Otherwise the thickness of the shale layer increases from the crest of structure toward the limbs. The pools of the Podkirmakinskaya Suite are characterized by water drive; gas caps are lacking.

Fig. 5. Structural map of the Neftyaniye Kamni Field: 1 - zone of the Diatom and Maikop (Oligocene-Lower Miocene) crumpled rocks; 2 - faults that disrupt continuity; 3 - area of oil distribution; 4 - wells.

Bulletin Houston Geological Society. June 1993 16

Azerbaijan

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Fig. 7. Geologic cross-section of the Neftyaniye Kamni Field: 1 - oil; 2 - gas; 3 - faults that disrupt continuity 4 -The Diatom and Maikop (Oligocene-Lower Miocene) crumpled rocks; 5 - the Koun (Middle Eocene) crumpled rocks.

Fig. 8. Diagram of distribution of oil accumulations in the Gryazevaya Sopka and Neftyaniye Kamni Fields: 1 - faults; 2-6 - contours of oil accumulations: 2 - X horizon of the Balakhanskaya Suite, 3 - "Pereryv" Suite, 4 - NKP suite, 5 - KS and PK suites, 6 - KaS suite; 7 - boundary of deposits.

Fig. 9a shows the distribution of producing and injection wells, and Fig. 96 shows the production history of the PK, horizon in the second tectonic block. Fig. 10a is a map of OWC migration due to waterflood from advance during PK, horizon exploitation, and Fig. 106 is a map of the water encroachment rate in the same horizon in terms of water cut.

Oil saturation of the Kirmakinskaya Suite is confined to its lowest part (79-80 m from the bottom). The oil saturated section of the Kirmakinskaya Suite is divided into two separate productive horizons, the KS, and KS,. The upper horizon KS, is less productive.

In the third, fourth and fifth tectonic blocks oil satu- ration occurs, besides the above-mentioned productive horizons, in the Nadkirmakinskaya sandy and "Pereryv" suites and to the upper part of the Productive Unit. The Nadkirmakinskaya sandy suite is distinguished by great oil content throughout the entire formation thickness. In the "Pereryv" Suite four to five productive beds are defined in the productive section, separated by shale interbeds of small thicknesses. These beds are saturated unevenly. Horizons X, VI, V, IV, 111, I and I' are oil bearing within the same bands as the "Pereryv" Suite. The IX, W I and W horizons have the largest oil-saturated areas. In spite of their

Bulletin Hornton Geologicdl Society. JUM 1963

Fig. 9. Distribution of producing and injection wells a (a) and production history (b) of PK, horizon, Neftyaniye Kamni Field.

1 - producing well; 2 - injection well; 3 - current OWC; 4- OWC; P,-aberagereservoir pressure. atm; Q, . daily water injection rate, mJ; N - number of producing wells; Q,,' - rhe same with natural depletion drive. t .

shallow depths (from 100 to 500 m), these horizons are characterized by large oil output.

Theoilin these productive formationsis saturated with hydrocarbon gases; in addition, purely gas only accumu- lations also occur here. The hydrocarbon gases of the Neftyaniye Kamni Field are largely 01 the methanic group. The casinghead gases contain admixed CO,. The compo- sitionof the gases by horizon is presented in Table 1. On an average, the thenatural gasesof the Neftyaniye KamniField contain 68.1 to 96.7% methane, 0.64 to 5.14ethane. 0.13 to 1.58% propane. 0.06 to 1.58% butane. and 0.13 to 2.54% higher hydrocarbons. The content of CO, by volume is 1 to 23% The specificgravily ofthegas with respect toairranges from 9.5814 to 0.8846. The gases are classified as dry, although several analyses show a content of keavy hydro. carbons up to 100 9/ni].

Gas saturation increases with an increase in c l a ~ content and with adecrease insandcontent of the reservoir rocks. A decrease in the thickness of the sandy beds is accompanied by a change in the grain size of the rocks; the content of the grain fraction less than 0.01 mm increases.

For example, the Podkirmakinskaya Suite contains an average of 65.70% sandy strata, and about 20% of these sands consist of fractions less than 0.01 mm. The initial gas.oil ratio (GOR) was 35.40 m3/m3. n i e Kirmakinskaya Suite is characterized by a high content of clayey beds and very thin (> 1 cm) sandy-clayey intercalations. The sandy layersconstitutenomore than4560%of theentire thickness of suite; moreover, grain size fractions of less than 0.01 mm constitute 25% of these layers. The initial GOR of the Kirmakinskaya Suite was almost twice that of the Podkir. makinskaya Suite, reaching 70.75 rn31rnl. At the beginning of field development, the pools of both formations were in the same energy state. The lithologic features of the

Podkirmakinskaya Suite (predominance of sandstones in the section, their excellent sorting, and a coarser grain size causinggoodpermeability)didnot contribute to theaccumu- lation of free gas; the gas, due toils great mobility, moved into the Kirmakinskaya Suite. which consists of thin sandy- clayey inlercalations with a large grain surface area.

A characteristic feature of the Kalinskaya Suite is a change of the oil pool of KaS, to a gas pool on the far southeast down-dip part of the fold (the fourth tectonic block). From the crest to the periphery of the structure. the dimensions of the grains decrease and the clay content of the reservoir increases. This is expressed clearly in the KaS, section, where as a result, a gas pool has developed with a small oil fringeextending along the periphery. The boundary of gas.saturated reservoir intersects the structural contour lines of the stratum from higher levels to lower. A similar change of an oil pool to a gas pool is observed in other

b

1 Fig. 10. Maps of annual OWC migration (a) and water cut (b),

1 Neftyaniye Kamni Field.

horizons of the periclinal area, but in these the gas is concentrated close to the crest and forms a gas caps.

The relationship between the oil and the gas changes during field development, depending on the different physical and geological conditions (energy state, mechanism of drainage, etc.). In a single phase state the reservoir oil is either completely saturated by gas or it is unsaturated. At the beginning of development of the oil pools of the Neftyaniye Kamni Field, the degree of gas saturation of the oil ranged from 0.6 to 3.0 MPa; the gas was dissolved in the oil and separated from it only in the well bore above the perforated interval. The high pressure existing when the gas-saturated oil reservoirs were opened permitted all the gas except the methane, CO,, and a portion of the ethane to be retained in solution in the oil. With the drop in pressure resulting from draining the pool, other hydrocarbons began

to appear in the gas phase. The gas is enriched by ethane, propane, butane, and higher-boiling hydrocarbons. As a consequence, the specific gravity of the gas increases and becomes a variable value depending on the length of time of the development and the rate of decrease in reservoir pressure.

In the crest area the presure drops more intensively and further, the oil here is less compressed; therefore, the content of methane increases from the crest toward the margin of the pool and in this same direction there is a decrease in the specific gravity of the gas. This is seen in the example of the Podkirmakinskaya reservoir (Table 2).

Long before opening the oil pool the crestal portions lost gas, largely methane, in larger quantities than did the flanks. As a result of the redistribution of oil and gas in a formation reservoir, the difference between the parts of the

43 Bulletin Houston Geolog~cal Soctety. June 1993

Content , % - volume

Methane Ethane Propane

Table 1: Composition of gas by horizon, Neftyaniye Kamnai Field. I' 1 ij

Table 2:

Perforated interval, m

Methane, %

68.1

68.7

77.7

77.4

85.8

80.7

88.8

94.3

Specific Gravity

0.8838

0.8763

0.7781

0.7742

0.6425

0.7573

0.6678

0.5972

Selected gas parameters from the Podkirminskaya reser- oir, Neftyaniye Kamni Field.

pool should disappear with time. However, losses of methane at the crest and its transfer along the stratum from the margin to the crest take place simultaneously, and this leads ultimately. to some decrease in the methane content and to an increase in the specific gravity of the gas in the crestal portions of the pool.

Along with successful development of the Neftyaniye Kamni Field, wells are being drilled adjacent to the field.

The Gryazevaya Sopka Oil Field

Location and history. The Gryazevaya Sopka (Mud Volcano) Oil Field is located in the Caspian Sea to the east of Baku and the southeast of Artyom Island (Fig. 3). The main base for exploration and development is on the Neftyaniye Kamni Field, 4 km to the southeast. The first well, #22, was spudded on August 10, 1952 o n the up-dip area of the southwest flank of the fold, but on December 11, 1952, this well and its platform was destroyed by a severe storm. The first production was obtained in well #20, which was located in the crestal area. In subsequent years many exploratory and producing wells were drilled, which en-

Butane Higher

Specific Gravity

Higher, g/cm3

47.4 12.6 30.3 53.3 25.3 39.4 46.4 70.4 40.0

countered oil pools in the lower division of the Productive Unit.

Geology. During the initial period of prospecting it was thought that the Gryazevaya Sopka was an extension of the large Neftyaniye Kamni Fold. Additional study during 1954- 1955 caused the structural maps to be revised and dis- tinguished the independent brachyanticlinal uplift of Gryazevaya Sopka. It is separated from the Neftyaniye Kamni structure by a small saddle (Fig. 8).

The geologic section of the Gryazevaya Sopka Field has been studied extensively by deep drilling. Sediments of Pliocene age (Productive Unit and Pontian State) have been encountered and studied. The Pontian sediments are repre- sented by deep-water facies which are gray and dark gray, unconsolidated, and contain thin limy clay beds. Sandy varieties are rare. Characteristic fossils pre,sent are Para- cypria loezyi Lal., Leptocythere praebacuana Liv., Loxo- concha alata Schn., Loxoconcha eichwaldi Liv., other ostracods, and pelecypods.

The sediments of the Productive Unit, where the oil pools occur, have been studied the most thoroughly. Sediments of both the upper and lower divisions have been encountered in this area. The base of the upper division occurs a t an average depth of 260 m, with a variation from zero where rocks of the lower division crop out on the sea floor to 500 m o n the perpheral parts of the fold. Along the crest of the fold, rocks of the Kirmakinskaya and Nadkir- makinskaya sandy (NKP) and Nadkirmakinskaya clayey (NKG) suites are observed.

The total thickness of the lower division of the Pro- ductive Unit is 900 m on the average and ranges from 700 to 1200 m. The productive sub-units, from oldest to youngest are described below.

The main productive formation is the Kalinskaya Suite, which rests directly on Pontian sediments and is composed largely of clayey-sandy rocks interbedded with sands, sandstones, and siltstones, with rare admixtures of gravel. The apparent thickness of the sandy-clayey members of the Kalinskaya Suite is about 300 m. The shales predominate over the sands and constitute 60% of the total thickness of the formation. In the area of the Gryazevaya Sopka Field, the Kalinskaya Suite is divided into four sandy horizons with thicknesses from 20 to 30 m, separated from one another by thick clayey partings (Fig. 11).

Bulletin Houston Geological Society. June 1993 44

we11 20 Well 505 Well 80 we11 425

Fig. 11. Correlation of electric logs on the top of Kalinskaya Suite at the Gryazevaya Sopka Field.

The sandy horizon is represented by gray and light gray medium-grained quartz sands and sandstones with some fine-grained clayey varieties. The clayey partings are gray and light gray sandy shales. The sandy rocks of the ~ a l i n s k a ~ a Suite are characterized by varying grain sizes. The averase contents of grain-size fractions are as follows:

fraction): quartz - 53.3%; feldspar - 17%; rock fragments -29.6%, and glauconite - 0.1%. The heavy fraction contains the following minerals: pyrite - 14%; magnetite-ilmenite .2%; nonmetallic (opaque) - 13%; micas and chlorite - 8%; and glauconite - 19%. The content of limonite, garnet, zircon, tourmaline, biotite, kyanite, staurolite, and sillimanite is about 1% each.

The Podkirmakinskaya Suite has an average apparent thickness of 100 m and is represented by a member of gray quartz sands and sandstones with some admixed clay particles. The shale beds in the Podkirmakinskaya Suite section are few to up to 30% of the total thickness of the suite. Two separate horizons are distinguished in the Podkirmakinskaya Suite: PK, and PK,, each of which is represented by sandy beds containing up to 3-4 layers. These horizons are separated by shaly beds of variable thickness. The sands are poorly sorted and were de- termined microscopically to be fine- and medium grained. The shales are poorly bedded and are often sandy. The percentages of grain size fractions in the reservoirs are as follows: M . 2 5 mm - 1%; 0.25 to 0.1 mm - 24.8%; 0.1 to 0.01 mm - 45.7%; <0.01 mm - 28.5%. The cementing carbonate content is about 10%. Average porosity is 20%, and per- meability is on the order of 100-120 millidarcies.

The Kirmakinskaya Suite is a uniform unit of alternating fine-grained sands and sandstones, shales, and clayey sands with an average apparent thickness of about 300 m. This alternation extends to smallLcale bedding, where the sandy bedsare from 1 to 7 m thick. Most sandy strataoccur in the middle and lower parts of the suite. The middle sandy member, with a thickness of 10-15 m, is distinguished by high resistivity on the electric log. The bottom member attains a thickness of 50 m. The light fraction of the sands contains 50% quartz, 42% feldspar, and 8% rock fragments. The heavy fraction consists of 72% pyrite, 11% mica and chlorite, 10% opaque nonmetallic minerals, and 5% glauco- nite.

The Nadkirmakinskaya sandy suite consists of medium and coarse-grained quartz sands with beds of sandstones, which are largely at the bottom. Shale beds are very rare and thin. The average apparent thickness is 35 m. The sands constitute about 7000of the total thicknessof the suite. The Nadkirmakinskaya clayey suite consists largely of shales with rare thin beds of sands and siltstones. The shaliness of the section increases from the bottom toward the top. The apparent thicknessof the Nadkirmakinskaya clayey suite is 125 m. The shales of Nadkirmakinskaya clayey suite are

>0.25 mm-- 6.9%; 0.25 t o 0.1 mm - 27.5%; 0.1 to 0.01 mm -37.2%; <0.01 mm - 284%. The averagecementing carbonate content is 14.2%, ranging from 4 to 39.490. the average porosity is 17% with a range from 8.3 to 33.4%. Permeability is not high, being from a few to 500 millidarcies. According to a petrographic analysis, the KaS reservoirs are characterized by the following composition (light

6

Fig. 12. Geologic cross-sections NW 2 9 5 8 0 3 7 0 SE

of the Gryazevaya Sopka Field:

a -transverse; b - longitudinal.

dark gray and brownish gray. The sands are fine-grained, than the southwestern flank. The angle of dip of the gray, and light gray; they constitute 20% of the total southwestern flank is 35-37", and of the northeastern is thickness of the suite. 40-45" (Fig. 12a). The angle of dip of the southeast closure is

The "Pereryv" Suite and the base of the Balakhanskaya about 16", and that of the northwest pericline is on the order Suite are the sediments of the upper division of the of 10-12" (Fig. 12b). The angles of dip increase with depth in Productive Unit and compose on the whole the marginal connection with an increase in thickness of individual and periclinal parts of the fold. Near the base of this series of formations on the flanks. The increase in angles of dip on sediments is distinguished a sandy marker called the "first both flanks of the structure is shown in Table 3. break". It is about 100 m thick. The "first break" is A large longitudinal fracture is oriented along the crest represented by medium- and coarse-grained sands and of the fold, and is a continuation of a regional longitudinal sandstones. fault that has been traced through the Neftyaniye Kamni

The sediments of the Balakhanskaya Suite are more or and Zhiloy Island structures. Marine seismic surveys con- less fully represented on the peripheral parts of the fold firm the existence of this fault. The vent of a mud volcano where their apparent thickness reaches 400m. On the other has been observed in the vicinity of wells #75 and #79. On parts of Gryazevaya Sopka structure, only the bottom part this basis the entire area has received thename "Gryazevaya of this suite is found and its thickness is no more than 150 m. Sopka" - "Mud volcano".

The Gryazevaya Sopka brachyanticlinal fold is located Field development. According to core and log data, on a regional tectonic line that extends from the Kamni the horizons of the lower division of the Productive Unit Grigorenko structure on the south-east through the Zhiloy (KaS, PK, and KS) are oil saturated; the higher horizons do Island, Azi Aslanov, Gryazevaya Sopka, Neftyaniye Kamni not contain oil (Figs. 8and 12). According to the electric log structures; it is a local uplift on this trend. The length of the the sandy oil-bearing horizons of the Kalinskaya Suite are fold is more than 6.5 km. The structural surface on the top of distinguished by peaks from 15 to 50 0hm.m and individual the Podkirmakinskaya Suite mapped according to drilling peaks reach 70 0hm.m. The SP curves are indecipherable, data is shown on Fig. 8. The crestal area takes the form of a although negative anomalies with amplitudes up to 10 mV narrow ridge, and within the 500 m structural contour the are observed opposite porous, permeable strata. The crest is 4 km long and 0.4 to 0.5 km wide. The crestal area is horizons of the Podkirmakinskaya Suite are distinguished located eccentrically with respect to the perimeter of the by an apparent resistivity from 20 to 60 0hm.m and by uplift and is close to the saddle that separates it from the negative SP anomalies. In the non-oil-bearing part of the Neftyaniye Kamni Uplift. From the southeast to the north- strata the horizons of the Podkirmakinskaya Suite are west, the crestal area constitutes about one-fourth of the marked by a resistivity of 3 to 8 Ohmem. In the Kirmakin- entire uplift. The northwest pericline makes a gentle turn to skaya Suite the bottom member has a resistivity up to the west, and the axis of the fold inscribes a curved line Ohmem and the middle up to 25 Ohm-m. The rest of the oriented on an azimuth of 100" to 135". The fold is somewhat sandy-clayey non-oil-bearing horizons have resistivity from asymmetric, as the northeastern flank of the fold is longer 1 to 5 Ohm-m.

Bulletin Houston Geological Soaety. June 1993

a

SW 122 zur+$ .v

The main oil producing formation in the field is the Kalinskaya Suite. Flowing oil was obtained in wells located in the crested area and on the southwestern flank of the fold. In two wells located at the crested area, a gas influx was obtained. Table 4 shows characteristics of the initial period of exploitation of the Kalinskaya Suite by the wells. Gas wells flowed 50,000 to 100,000 m3 per day.

Comparison of electrical logs and test results indicates uneven oil saturation depending on the location of the well on the structure. The oil saturation of the Kalinskaya Suite improves markedly toward the northwestern perimeter and on the southwestern flank. The specific gravity of the oils range from 0.9208 to 0.9438, with an average value of 0.9290. The oil has a high viscosity. The viscosity was determined at 20°C only for the lightest oils. The rest of the oils do not flow

Table 3: Dip angles of strata, Gryazevaya Sopka brachyanticlinal fold.

SW flank

35'

36'

36'

37 '

38 '

Suite

NKG

NKP

KS

PK

KaS

Table 4: Initial production rates, Gryazevaya Sopka Field.

NE flank

38'

42'

43 ' 45'

46 '

Daily Production rate, tons

32

at 20°C. Comparing the properties of the oil of the Kalinskaya Suite at the Gryazevaya Sopka Field with the oil of the same suite at the Neftyaniye Kamni Field, it is noted that the oil of the Gryazevaya Sopka Field is heavier, more tarry, and more viscous; its properties are close to the properties of oil of the Zhiloy Island Field.

During the exploration phase, formation waters were recovered from horizons of the Podkirmakinskaya and the Kalinskaya suites. They support the oil accumulations in all horizons; this accounts for the active water drive. The formation waters of the Gryazevaya Sopka Field are alkaline waters of sodium bicarbonate type, class S,A,A, with an absence or a very low content of sulphates (up to 0.0008g-eqv per 100 g of water). The average total salinity is 0.0524 to 0.0814 g-eqv. The total salinity is 22.2 g/l with a range from 20.0 to 27.6 g/I. Palmer characteristics; S, = 81.5% A, = 15.9%. A, = 2.6%. The NA/C1 ratio ranges from 1.03 to 1.5, and the Ca/Mg from 1 to 2. The average anion content (in g-eqv per 100 g of water): Na+K - 0.0308; Ca -0.0005; Mg - 0.0003. The content of naphthenic acids is 0.0007 g-eqv. The formation waters of the Gryazevaya Sopka Field are more saline than the waters of the Neftyaniye Kamni Field but belong to the same type of alkaline waters.

Wellhead pressure. MPa

0.5

Part II will be published in the September 1993 Bulletin.