Region I Apsheron Peninsula

Oil- and gas-bearing zones in the Apsheron Peninsula are mainly of Middle Pliocene (Productive Series), Upper Pliocene (Apsheronian Stage), and Miocene (Diatom Suite, Chokrak Formation) ages. The main oil- and gas-bearing and productive interval here is the Productive Series, which is subdivided into two divisions. The Upper Productive Series (i.e., the upper division) includes the following suites (from top to bottom): Surakhany, Sabunchi, Balakhany, and "Pereryv" (the first break in deposition). The Lower Productive Series (i.e., the lower division) includes the following suites (from top to bottom): Nadkirmaku Glinistaya (Shaly)—NKG; Nadkirmaku Peschanaya (Sandy) —NKP; Kirmaku—KS; Podkirmaku—PK; and Kala—KaS. Oil and gas fields of the Apsheron Peninsula and Apsheron Archipelago are multi-bedded (up to 40 oil-bearing units). Most of the oil reserves occur in fields of the central part of the peninsula: Balakhany-Sabunchi-Ramany, Surakhany, Karachukhur, Zykh and Gum Deniz (Table 5-1). Toward the east and southeast (Buzovny-Mashtagi, Kala, Zyrya, and other oil fields) and toward the northwest and west (Binagady, Chakhnaglyar, Sulutepe, and other oil fields) of the central part of the peninsula, oil saturation increases in the Lower Productive

Figure 5-1. Oil and gas regional distribution, and fields and prospects of Azerbaijan and the South Caspian Basin (Modified after the Excursion Guide-Book for Azerbaijan SSR, Vol. I, 1984). 1—Boundaries between oil- and gas-bearing regions, 2—boundaries between oil- and gas-bearing areas, 3—oil fields, 4—gas and gas-condensate fields; Oil- and gas-bearing areas: 5—high oil and gas content, 6—moderate oil and gas content, 7—potential structure, 8—structure with low potential. Oil- and gas-bearing regions and areas (areas are shown in circlets): I—Apsheron-Gobustan region (areas: 1—Apsheron, 2—Shemakha-Gobustan); II—Pre-Caspian-Kuba region; III—Kura region (areas: 3—Lower Kura, 4—Kyurdamir, 5—Gyandzha, 6—Adzhinour, 7—Kura-Iori interfluve, 8—Alazan-Agrichai, 9—Dzhalilabad, 10—Baku Archipelago); IV—Araks area. Fields: 1—Balakhany-Sabunchi-Ramany, 2—Surakhany, 3—Karachukhur-Zykh, 4—Gum Deniz, 5—Gousany, 6—Kala, 7—Buzovny-Mashtagi, 8—Darvin Bank, 9—Pirallaghi Adasi, 10—Gyurgyan Deniz, 11—Chalov Adasi, 12—Azi Aslanov, 13—Palchygh Pilpilasi-Neft Dashlary, 14—Dzhanub, 15—Bakhar, 16—Binagady-Chakhnaglyar, 17— Sulutepe, 18—Yasamaly Valley, 19—Bibieibat, 20—Puta-Lokbatan, 21—Kyorgyoz-Kyzyltepe, 22—Karadag, 23—Shongar, 24—Umbaki, 25—Duvanny, 26—Dashgil, 27— Chondagar-Zorat, 28—Siazan-Nardaran, 29—Saadan, 30—Amirkhanly, 31—Eastern Zagly, 32—Zagly-Tengialty, 33—Kyurovdag, 34—Karabagly, 35—Khillin, 36—Neftechala, 37—Kyursangya, 38—Mishovdag, 39—Kalmas, 40—Pirsagat, 41—Malyi Kharami, 42—Kalamadyn, 43—Muradkhanly, 44—Kazanbulag, 45—Adzhidere, 46—Naftalan, 47—Mirbashir, 48—Sangachal, 49—Duvanny Deniz, 50—Khara Zyrya, 51—Bulla Deniz, 52—Garasu.

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Series and decreases in the Upper Productive Series. Oil accumulations in the Diatom Suite are present in the west and southwest of the peninsula (Binagady, Lokbatan, Kergyoz, and other fields).

Different traps are present in the Productive Series of the Apsheron Peninsula: structural (anticlinal and faulted), stratigraphic, and combination traps. Terrigenous (siliciclastic) reservoir rocks consist of sand, sandstone, and siltstone separated by shale interbeds. Reservoir rocks are highly porous and permeable.

The Baku Trough is a synclinal structure located between the Karachukhur-Zykh anticline to the east and Bibieibat uplift to the west. Rocks in the trough consist mainly of shale and sand alternating with limestone beds. The latter compose the upper part of the section forming a bench around the trough composed of Late Pliocene and Post-Pliocene deposits.

Kirmaku Oil Field is located in the central part of the Apsheron Peninsula, 15 km north of Baku, and between two large oil-bearing regions: the Balakhany-Sabunchi-Ramany group of oil fields to the southeast and the Binagady-Chakhnaglyar-Sulutepe group of oil fields to the southwest.

Three topographic features are distinguished in the area of Kirmaku Field: the Kirmaku Ridge, Binagady Height, and Bogboga Mud Volcano. The highest point is Kirmaku Mountain (104.7 m) located in the southern part of the Kirmaku Ridge. The surface of the mountain is covered with many tar pits and shallow wells, which produced oil in the past.

Structurally, Kirmaku Field has an asymmetric, box-like shape (Figures 5-2 and 5-3). Dips are 40-50° on the eastern flank, and 6070° on the western flank; dips decrease to 25° toward the crest, and on the periphery of the structure they decrease to 10°. The axis of structure extends about 3 km, and the width of the structure is about 400 m. The core consists of Paleogene and Neogene rocks.

The Kirmaku structure is made up of the Neogene rocks (Productive Series of Middle Pliocene and Pontian Stage of Lower Pliocene). The crest consists of Pontian shale surrounded by the Podkirmaku Suite of the Lower Productive Series. The structure consists mainly of the Kirmaku Suite deposits characterized by a frequent alternation of shale, silt and sand. Recent and old Caspian Sea deposits rest unconformably on older Neogene rocks exposed by erosion.

Figure 5-2. Geologic map of Kirmaku Oil Field (Modified after Alibekov et al, 1964). 1—Lower Balakhany Suite, 2—"Pereryv" Suite, 3—NKG Suite, 4—NKP Suite, 5—KS Suite, 6—PK Suite, 7—Pontian Stage.

Many geologists have studied the field structure. As a rule, however, they used rock samples only from outcrops. Additional detailed study, including exploratory drilling, was needed for field development. In the 1950s, 62 exploratory wells were drilled in three phases within the field area (Figures 5-2 and 5-3). Most of the wells were cored, and a total of 1,039 core samples were recovered and analyzed.

The major productive interval, the Kirmaku Suite (KS), is represented by alternating shale, very fine- to fine-grained, argillaceous sand, and silt of brown and gray color. Total thickness of the suite ranges from 250 to 260 m. The KS interval is the most consistent in thickness and lithology over the whole section of the Productive Series. Quantitatively, sand and silt content prevail over that of shale. The KS section consists of 74% sand, sandstone and silt, and of 26% shale and sandy-silty shale. Thickness of sand and shale beds varies between

Figure 5-3. Structural map and cross-section of Kirmaku Oil Field (Modified after Alibekov et al., 1964). (a) Structural map on the top of Pontian Stage: 1—well, 2—contour line on top of Pontian, 3—outcrops of Pontian rocks; (b) cross-section.

1-2 mm to 10-20 cm. Among sandy-shaly alternations one can observe thicker interbeds of sand and shale up to 3-4 m. The number and thickness of sandy-silty beds are higher in the lower portion of the section. Average porosity of reservoir rocks is 26%, and the carbonate cement content is 8-16%.

The underlying Podkirmaku Suite (PK) is the second oil-bearing formation penetrated by boreholes both in the crestal area of the structure and on its flanks. The PK Suite is the thickest (about 40 m) in the southern plunged portion of the structure. Toward the crest, thickness decreases significantly. The PK section is made up of medium- to coarse-grained quartz sand with large quartz grains and unevenly shaped pebbles. Sand is gray and light-gray in color, whereas pebbles are black. The upper part of the PK section contains medium-and fine-grained sand with some thin shale interbeds. In the lower and middle parts, grain size increases and shale interbeds disappear. Within the PK section, particularly in the lower part, one can observe inter-beds of very dense and hard calcareous sandstone. Thickness of this sandstone ranges from 10-20 cm to 50 cm. Average porosity of the reservoir rocks is 26-28%; carbonate cement content is 12-15%.

Kirmaku Oil Field has long been known as the place of oldest production of oil and asphalt. The precise date of earliest Kirmaku Oil Field production is unknown, but accounts date back as early as 1834.

Initially, oil was produced from shallow pits in outcrops using bailers. Later, shallow wells with timber-lined walls were dug. These wells were situated, mainly, on the eastern and southern slopes of Kirmaku Mountain, and to a considerably lower extent, on the western slope. Depending on the location within the area and on the depth of productive formation, well depth varied greatly. Average depth was 50-60 m; however, some were up to 190 m deep. Some wells were very shallow: no more than 10-20 m deep.

In the past, Kirmaku Field oil and gas wells were produced at maximum rates with rapid reservoir depletion. In some cases, flow per well reached 11-13 tpd (80-90 bpd). Production rate, however, could be sustained only for 1-2 months, and then declined to 1.0-1.5 tpd. Such practice, at that time, was believed to be normal, and most wells typically produced for several months and sometimes even for years. As production rate declined, wells were deepened to the next productive bed.

Peak monthly oil production reached 4,500-5,000 tons before 1914 and World War I. The total number of wells (in and out of operation) reached 1,500. About 50 of them (the most productive) were operated until 1926. Digging of new wells was stopped in 1913, and was prohibited from then on. Maximum potential production rate was 3-5 m / day and was based on well tests. The longest oil column encountered during well testing was 60-70 m at a depth interval of 100-120 m. In other wells, the length of oil column was smaller and, in some cases, wells were dry. As a rule, the wells produced no water. Water first appeared in 1914-1917 at the northern part of the eastern flank.

Oil was characterized by the following properties: density = 0.9580.988 g/cm3, Engler viscosity at 45°C = 10-16. A lighter oil with density of 0.903 g/cm and Engler viscosity of 6.84 was produced in Well 41 from a depth of 90-101 m.

At present, Kirmaku Oil Field is virtually depleted of moveable oil and should be considered as a deposit of bituminous sands.

Field development by routine well drilling probably will be quite ineffective. The use of one of the enhanced oil recovery methods (e.g., heat stimulation or injection of solvents) probably will not be effective, because the oil-saturated rocks are penetrated by many wells which will be very hard and expensive to seal.

Field development by mining appears to be a reasonable one. However, considering that the area has been produced for a long period of time, the advantage of this method should be verified by digging at least one experimental, sloped tunnel (with a drilling chamber) at the base of productive formation, for drilling updip boreholes.

Pilot horizontal wells (164, 72, and 187-m long) were drilled at the base of the southern slope of Kirmaku Mountain in 1956. The wells were drilled using water as a drilling fluid, and completed without casing. This project demonstrated a real possibility of producing oil from such wells. At the maximum penetration into productive formation (2.0 m), one of the flowing wells has been producing at approximately 5 m /day of total liquids including 40-60 kg of oil per day. Initial production was 10-11 m /day of total liquids and 80-110 kg of oil per day.

Using geological, analytical, and field data, one can conclude that drilling horizontal wells from the ground level is the most reasonable technique for secondary development of bituminous sands of Kirmaku

Oil Field. The advantage of this technique is due to: (1) absence of thick overburden, (2) absence of large volumes of liquids, (3) possibility for development of bituminous sands, and (4) presence of highly-developed infrastructure.

Bibieibat Oil Field occurs on a brachianticlinal uplift striking NNW-SSE. The first oil well was drilled here in 1848. The oil field was developed in the early 1870s. The entire Productive Series section is oil bearing.

Pliocene-Quaternary deposits are present in this area. The deposits form an asymmetric fold with steep western (up to 50°) and gentle eastern (15-27°) flanks. The anticline is broken by numerous transverse faults and its crest was penetrated by a mud volcano (Figure 5-4).

Deposits of Apsheronian Stage (Late Pliocene) and Pleistocene occur in the uplifts adjacent to the Baku Trough to the north, northwest and west. These deposits extend as a wide ridge in a north-south direction and infill the syncline separating Bibieibat and Shubany uplifts. Farther away, these deposits crop out along the eastern slope of Yasamaly Valley and plunge toward the Caspian Sea.

Yasamaly Valley is a monoclinal valley where beds on the right and left margins dip in the same direction. The rocks are of Late and Middle Pliocene age, and constitute the eastern flank of the Atashkyah-Shabandag diapiric fold to the west of the valley.

The road from Volchy Vorota (Wolf Gate) to the Eibat railway station crosses deposits of Apsheronian Stage (Late Pliocene). Overlying Akchagylian deposits are "disguised" under recent valley sediments. Farther, one can observe outcrops of the Upper Productive Series, consisting of alternating shale, sand and sandstone. The Yasamaly Valley Productive Series deposits in the eastern flank contain oil fields discovered in 1938 and wedge out toward the fold crest due to its diapiric structure.

Atashkyah structure is confined to the ridge of the same name. The structure is eroded, strikes north-south, and Oligocene-Miocene and Lower Pliocene deposits crop out in the core; they are bordered by the Middle Pliocene deposits. The western flank of structure dips steeply (45-65°), whereas the eastern flank may be vertical or even overturned. The brachyanticline is complicated by two major longitudinal faults of overthrust character. Oil occurs in the Productive Series.

Shabandag Oil Field is also located in Yasamaly Valley. The field was discovered in 1945. It is confined to an ENE flank of Shabandag

Figure 5-4. Structural map (a) and cross-section (b) of Bibieibat Oil Field. Stratigraphy: N2prd—Productive Series, N2ak—Akchagylian Stage, N2ap— Apsheronian Stage.

brachyanticline, filled with Middle and Upper Pliocene deposits. The core of uplift, which is dislocated, has diapiric structure. The SW flank is steep (50-70°), but dips more gently away from the axis of structure (Figure 5-5). Oil occurs in the Lower Productive Series. On the eastern flank of the Shabandag uplift, Diatom Suite deposits are also oil bearing.

The offshore portion of Dzheirankechmes Depression of the Central Gobustan is located southwest of the Baku Trough. It is filled with

Figure 5-5. Geologic cross-section of Shabandag Oil Field. Stratigraphy: K—Cretaceous, P3—Oligocene, N,1—Lower Miocene, N21—Lower Pliocene, N22—Middle Pliocene, N23—Upper Pliocene.

sediments of the Productive Series of Akchagylian and Apsheronian age. A number of narrow and wide anticlinal trends occur within this depression. Anticlines are faulted and wide zones of tectonic breccia are associated with fault zones, with mud volcanoes occurring at their centers. One of them is Lokbatan Mud Volcano, which is situated 15 km southwest of Baku.

Lokbatan Oil Field is located in the area of Lokbatan mud volcano. This field was discovered in 1932, when Well 62 blew out from Unit II of the Upper Productive Series (flow exceeded 1 Mtd or 7.3 Mbd). An oil gusher (up to 20 Mcmd or 706 Mcfd) blew out from Unit 4a in 1933, in Well 45 drilled in mud volcanic breccia 1,500 m east of the volcanic vent. The entire section of the Productive Series is oil bearing. There are 16 oil- and gas-saturated intervals.

The field is an asymmetric brachianticline trending latitudinally. The eastern flank is steep (about 55°), whereas the northern one is gentle (30-40°). The Productive Series rocks crop out at the crest of anticline, and are more argillaceous in comparison with those of the Bibieibat and Shubany fields. The argillaceous Oligocene-Miocene section is penetrated at the northern flank in Well 616. The anticline is complicated by a longitudinal fault (amplitude = 500 m), to which the Lokbatan mud volcano is confined (Figure 2-3); the southern flank is elevated. The fault becomes a thrust fault to the east (Figure 5-6).

Figure 5-6. Structural map (a) and cross-section (b) of Lokbatan Oil Field.

Shemakha-Gobustan Area. In this area oil and gas occurs only in Cretaceous, Paleogene, Miocene, and Pliocene deposits. Here, Umbaki Oil Field is being produced; oil pools are confined to Maikop Suite and Chokrak Formation. Also, Duvanny Gas Field is under production.

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