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The Petroleum Geology of Western Turkmenistan: The Gograndag-Okarem Province

By
Max A. Torres
Max A. Torres
Repsol YPF, Houston, Texas, U.S.A.
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Published:
January 01, 2007

Abstract

The onshore Gograndag-Okarem province is located in the eastern flank of the Caspian Basin in western Turkmenistan. The South Caspian Basin intracontinental depression registered complex accretion and rifting phases from the late Paleozoic to the late Neogene, when collisional orogenies occurred in the surrounding thrust belts of the Alborz and Kopet Dagh Mountains. Combined flexure loading and thermal cooling resulted in high subsidence rates, evidenced by thick high-frequency third-order sequences. A large Pliocene westward-prograding deltaic system from the paleo-Amu Darya river deposited a clastic section of nearly 6000 m (19,686 ft) in thickness known as the Red Color group. This large, deltaic wedge was initially deposited possibly during a global sea level fall (5.5 Ma?) and progressed from backstepping to progradational arrangements during the Pliocene and Quaternary. This unit is thought to be roughly equivalent to the Productive Series in Azerbaijan. Late Pliocene detachment tectonics, as a result of dextral transcurrent motions in the Kopet Dagh thrust belt (Himalayan orogeny), resulted in a series of parallel, northeast–southwest fold trends, where hydrocarbons were trapped by four-way dip anticlines. Commercial accumulations were found only in the first and second of the five known anticline trends with modest discoveries in the third trend. Multistacked overpressured reservoirs in the Lower and Upper Red Color formations are interpreted as distributary channels, distributary mouth bars, and flood sandstones deposited in a fluvial-dominated low-energy deltaic setting. Climatically controlled third-order sequences of 100– 150m (330–492ft) in thickness were identified in well log sandseismicdata. Well-developed lowstand systems tracts (fluvial-distributary channels) are the main producing intervals and are capped by a transgressive systems tract or a dark shale unit (maximum flooding surface) (outer shelf, prodelta). Although present, high-stand systems tract sandstones (delta front) have less productive potential. Inter-granular effective porosity ranges from 16 to 27%, permeabilities range from 50 to 1000 md, and overpressures range from 10.5 to 16.5 ppg. Maturity studies indicate immature indigenous source rocks, and the present depth of the oil-window top is approximately at 4000 m (13,124 ft) in the producing areas. The postulated source rock is interpreted as the Maikop Series (Oligocene–lower Miocene), according to studies in Azerbaijan. Mud volcanoes, thrust and accommodation faulting, and vertical migration are thought to be suitable effective migration pathways. A multistacked gas and oil column and varying hydrocarbon properties reveal a complex multiphase migration history. The Gograndag-Okarem province petroleum system is designated as Maikop/Red Color group(.). Wells produce an average of 300 BOPD from a single reservoir, with gas-oil ratios that range from 600 to 5500 bbl/ft3 of gas in undersaturated and saturated systems, respectively. Oil is sweet, with 15–348 API, and paraffinic (13–20%). Postulated exploration scenarios include Red Color group deeper pools and Miocene unconformity traps. Further potential in the third structural trend is thought to be limited because of westward-diminishing reservoir quality, migration shadows, and late trap charging.

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Contents

AAPG Studies in Geology

Oil and Gas of the Greater Caspian Area

Pinar O. Yilmaz
Pinar O. Yilmaz
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Gary H. Isaksen
Gary H. Isaksen
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American Association of Petroleum Geologists
Volume
55
ISBN electronic:
9781629810348
Publication date:
January 01, 2007

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