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Abstract

AAPG Bulletin, V. 102, No. 12 (December 2018), P. 2447-2480.

Copyright ©2018. The American Association of Petroleum Geologists. All rights reserved.

DOI: 10.1306/0424181617217089

Ahdeb oil field, Mesopotamian Basin, Iraq: Reservoir architecture and oil charge history

Hucheng Deng,1 Meiyan Fu,2 Tingting Huang,3 Jon G. Gluyas,4 Mingsheng Tong,5 Xingjian Wang,6 Wen Zhou,7 and Fei Liu8

1College of Energy Resources, Chengdu University of Technology, 1 Erxianqiao Dongsan Road, Chengdu, Sichuan 610059, China; State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, China; [email protected]
2College of Energy Resources, Chengdu University of Technology, 1 Erxianqiao Dongsan Road, Chengdu, Sichuan 610059, China; Department of Earth Science, Durham University, Durham DH1 3LE, United Kingdom; [email protected]
3Geological Exploration and Development Research Institute of Chuanqing Drilling Engineering Co., Ltd., China National Petroleum Corporation, 83 North of Jianshe Road, Chengdu, Sichuan 610051, China; [email protected]
4Department of Earth Sciences, Durham University, South Road, Durham DH1 3LE, United Kingdom; [email protected]
5Geological Exploration and Development Research Institute of Chuanqing Drilling Engineering Co., Ltd., China National Petroleum Corporation, 83 North of Jianshe Road, Chengdu, Sichuan 610051, China; [email protected]
6State Key Laboratory of Oil and Gas Reservoir Geology and Exploration, 1 Erxianqiao Dongsan Road, Chengdu, Sichuan 610059, China; [email protected]
7College of Energy, Chengdu University of Technology, 1 Erxianqiao Dongsan Road, Chengdu, Sichuan 610059, China; State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, China; [email protected] cdut.edu.cn
8Zhenhua Oil Research Centre, 10 Jian She Road, Chengdu, Sichuan 610051, China; [email protected]

ABSTRACT

The Ahdeb oil field is located in the Mesopotamian Basin of central Iraq within a northwest–southeast-trending anticline. Seven oil-bearing layers exist in the eastern area in the field, but there is only one oil-bearing layer in the western area. This study reveals that the reservoir filling process resulted from the difference in the elements in the petroleum system, the oil generation and migration process, and the formation of the structural trap. Most oils in the field, with pristane/phytane < 1 and a high relative abundance of hopanes exceeding C30, were generated from the Upper Jurassic–Lower Cretaceous Chia Gara Formation, whereas some oils were generated from the Lower Cretaceous Ratawi and Zubair Formations. The mid-Upper Cretaceous reservoirs in the field are composed of lime grainstones, packstones, and wackestones.

The main oil accumulation occurred during the Maastrichtian, coinciding with peak oil generation from the Chia Gara Formation with a 50% transformation ratio from organic matter to oil. The reservoirs of the eastern structural trap in the field were filled with large amounts of medium to heavy oils. After the formation of two structural traps in the western area in the mid-Miocene, oils pre-existing in the second layer of the Khasib Formation in the east began migrating toward the structural traps in the west during the late Miocene, as verified by relatively higher 1-/4-methylcarbazole and 1,8-/2,7-dimethycarbazole ratios of oils in the west than that in the east and residual solid bitumen in the east. The strike-slip fault might also have restricted oil or gas migration during the Miocene, limiting oil accumulation in the west.

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