A major discovery in the second member of the Paleogene Kongdian Formation in Well Cangtan1 in Cangdong deep subsag area in Bohai Bay Basin and its exploration significance

doi:10.3969/j.issn.1672-7703.2024.02.002

Abstract

Abstract: Recently, the high-yield oil flow was obtained in the second member of the Paleogene Kongdian Formation (Kong 2 member) in a risk exploration well Cangtan 1 drilled by PetroChina, indicating a major breakthrough in the exploration of deep lithologic oil and gas reservoirs in Cangdong Sag in Bohai Bay Basin. Based on the understanding of Well Cangtan 1, favorable conditions for hydrocarbon accumulation in Cangdong deep subsag area are systematically analyzed to evaluate the exploration prospects and identify the favorable exploration orientation. The study results show that, during the deposition period of Kong 2 member, Cangdong deep subsag area was a subsidence center controlled by Cangdong Fault, providing accommodation for the development of semi deep-deep lake facies source rock. During the lake expansion period, source rock was widely deposited in the deep subsag area, with Type Ⅱ organic matter, high TOC, and mature-highly mature thermal evolution stage (average R_o of 1.3%). The deep subsag area was located at the edge of the lake basin, developing a complete provenance-channel-accumulation system between the basin and mountains, and forming multiple large-scale fan delta reservoirs in the lake basin, which provided favorable conditions for the formation of large-scale lithologic oil and gas reservoirs. The source rock was characterized by early oil generation and expulsion, and continuous oil charging, and the associated acidic fluids and hydrocarbon generation pressurization promoted the development of secondary pores such as intergranular and intragranular dissolution pores. The mature stage of source rock well matched with the development of reservoir, and conventional sandstone oil reservoir and shale oil reservoir were contiguously developed in the deep subsag area. The comprehensive analysis indicates that Kong 2 member in Cangdong deep subsag area has good exploration prospects, and multiple fan delta sand bodies developed in the basin margin have the advantage of near-source hydrocarbon accumulation, which shows a major replacement field for the large-scale reserve increase.

CLC Number:

TE111.1

Zhou Lihong, Chen Changwei, Sun Tong, Song Shunyao, Dong Xiaowei, Wu Xuesong, Yang Peng, Wang Shuai, Duan Runmei, Liu Huifang, Li Xiaojing, Guo Qiuxia. A major discovery in the second member of the Paleogene Kongdian Formation in Well Cangtan1 in Cangdong deep subsag area in Bohai Bay Basin and its exploration significance[J]. China Petroleum Exploration, 2024, 29(2): 16-29.

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