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Abstract

AAPG Bulletin, V. 105, No. 12 (December 2021), P. 2349-2380.

Copyright ©2021. The American Association of Petroleum Geologists. All rights reserved.

DOI: 10.1306/07022119211

Petroleum system for the continuous oil play in the lacustrine Lower Triassic, Junggar Basin, China

Keyu Tao,1 Jian Cao,2 Wenxuan Hu,3 Dongming Zhi,4 Dewen Lei,5 Yong Tang,6 Jianhua Qu,7 Xun Kang,8 and Leslie B. Magoon9

1State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering, Nanjing University, Nanjing, Jiangsu, China; [email protected]
2State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering, Nanjing University, Nanjing, Jiangsu, China; [email protected]
3State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering, Nanjing University, Nanjing, Jiangsu, China; [email protected]
4Research Institute of Petroleum Exploration and Development, PetroChina Xinjiang Oilfield Company, Karamay, Xinjiang, China; [email protected]
5Research Institute of Petroleum Exploration and Development, PetroChina Xinjiang Oilfield Company, Karamay, Xinjiang, China; [email protected]
6Research Institute of Petroleum Exploration and Development, PetroChina Xinjiang Oilfield Company, Karamay, Xinjiang, China; [email protected]
7Research Institute of Petroleum Exploration and Development, PetroChina Xinjiang Oilfield Company, Karamay, Xinjiang, China; [email protected]
8State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering, Nanjing University, Nanjing, Jiangsu, China; [email protected]
9Department of Geological and Environmental Sciences, Stanford University, Stanford, California; [email protected]

ABSTRACT

Continuous petroleum accumulations are becoming important in petroleum exploration. This paper reports a new giant oil play within a lacustrine stratum, the Lower Triassic Baikouquan Formation of the northwestern Junggar Basin, northwestern China. This giant oil play is typical of a continuous petroleum accumulation, with low reservoir porosity and permeability (averages of 7.52% and 0.97 md, respectively), continuous hydrocarbon distribution over a large area (∼1000 km2), stratigraphic traps, and anomalously high formation pressure (pressure coefficient >1.1). Detailed molecular as well as isotope geochemistry of hydrocarbons reveal that crude oil and natural gas in the Baikouquan oil play were derived predominantly from the alkaline lacustrine source rock of the lower Permian Fengcheng Formation. Dolomitic source rock is the main contributor to the crude oil and was deposited under anoxic, saline to hypersaline conditions. The analysis of spatial difference of oil maturity in combination with stratigraphic burial-thermal evolution indicates multiple charging events and vertical migration as the dominant process for oil charging in the Baikouquan play. As such, this giant Baikouquan oil play is interpreted to differ from classic continuous petroleum accumulation because of long-distance (1500–2500 m) vertical hydrocarbon migration from deeper Permian sources and is thus referred to as a somewhat atypical continuous oil play in this study. A strike-slip fault network provides migration pathways for the vertical oil charging, and a fan–delta-front conglomerate facies provides high-quality reservoir rocks. The discovery of the Baikouquan oil play exemplifies the successful exploration of a large-area continuous oil accumulation at a long distance (kilometers) from the pod of active source rock, and highlights new exploration opportunities worldwide within continuous oil accumulations, where the slope and central zones of a sag might represent viable petroleum reservoir rock despite their distance from a mature source rock.

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