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Abstract

DOI: 10.1306/04151614016

Hydrocarbon accumulation processes in the Dabei tight-gas reservoirs, Kuqa Subbasin, Tarim Basin, northwest China

Xiaowen Guo,1 Keyu Liu,2 Chengzao Jia,3 Yan Song,4 Mengjun Zhao,5 Qingong Zhuo,6 and Xuesong Lu7

1Key Laboratory of Tectonics and Petroleum Resources, China University of Geosciences, Ministry of Education, Wuhan 430074, China; present address: Department of Petroleum Geology, Faculty of Earth Resources, China University of Geosciences, no. 388 Lumo Road, Wuhan 430074, China; [email protected]
2Research Institute of Petroleum Exploration and Development, PetroChina, Beijing 100083, China; present address: School of Geosciences, China University of Petroleum (East China), no. 66, Changjiang West Road, Huangdao District, Qingdao, Shandong Province 266580, China; [email protected]
3Research Institute of Petroleum Exploration and Development, PetroChina, no. 80, Xueyuan Road, Haidian District, Beijing 100083, China; [email protected]
4China University of Petroleum, Changping, Beijing 102249, China; present address: Research Institute of Petroleum Exploration and Development, PetroChina, no. 80, Xueyuan Road, Haidian District, Beijing 100083, China; [email protected]
5Research Institute of Petroleum Exploration and Development, PetroChina, no. 80, Xueyuan Road, Haidian District, Beijing 100083, China; [email protected]
6Research Institute of Petroleum Exploration and Development, PetroChina, no. 80, Xueyuan Road, Haidian District, Beijing 100083, China; [email protected]
7Research Institute of Petroleum Exploration and Development, PetroChina, no. 80, Xueyuan Road, Haidian District, Beijing 100083, China; [email protected]

ABSTRACT

The Dabei Gas Field is a recently discovered giant tight-gas field in the Kuqa Subbasin, western China. The reservoir porosity and permeability mainly range from 1% to 8% and from 0.01 to 1 md, respectively. The hydrocarbon (both gas and light oil) accumulation processes in the tight-sandstone reservoirs were studied based on detailed reservoir characterization, thermal maturity of both gas and light oil, hydrocarbon charge history, regional tectonic compression, and thrusting. Two episodes of oil and one episode of natural-gas charge were delineated in the tight-sandstone reservoir, as evidenced by (1) similar sources but different maturities for the gas and light oil, (2) the presence of abundant bitumen in the tight-sandstone reservoir, (3) the presence of both hydrocarbon gas inclusions and oil inclusions with two distinct fluorescence colors, and (4) the presence of two groups of aqueous inclusions (coeval with the petroleum inclusions) with contrasting homogenization temperatures and salinities. The oil inclusions with the blue-white fluorescence color were determined to have been trapped at 5–4 Ma, whereas the gas charge may have occurred at circa 3–2 Ma, corresponding to a salinity change recorded in the aqueous inclusions. The hydrocarbon accumulation processes appeared to be controlled by the tectonic compression of the South Tianshan Mountains. Intense tectonic compression caused thrust fault reactivation, which provided pathways for hydrocarbon migration. Overpressure evolution of the reservoir indicates that an intense tectonic compression began at circa 5 Ma, which caused thrust activation and concomitant oil charge into the relatively porous part of the reservoir. Subsequent tectonic compression caused uplift and erosion associated with thrusting at the end of the Kuqa Formation deposition (ca. 3 Ma), with thrust faults and fractures acting as major migration pathways for the gas accumulation in the already-tight sandstone reservoir resulting from both compaction and tectonic compression.

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