Exploration breakthrough and resource potential of limy source rock gas in Da’an area in the western Chongqing, Sichuan Basin

doi:10.3969/j.issn.1672-7703.2024.02.003

Abstract

Abstract: A major breakthrough has been made in the exploration of limy source rock gas in the first member of Maokou Formation (Mao 1 member) in Well DB1H in Da’an area in the western Chongqing, Sichuan Basin, which has important reference and demonstration significance for the intra-source exploration of limy source rock unconventional gas in the Basin. The first horizontal well DB1H was drilled to evaluate the dark limy source rock gas reservoir in Mao 1 member in Sichuan Basin and a high gas rate of 55.6×10⁴ m³/d was tested after acidizing and fracturing. The discovery process of limy source rock gas in Mao 1 member in Da’an area has systematically been introduced, and the resource prospect in Sichuan Basin has been estimated. The analysis of geological characteristics of limy source rock gas in Mao 1 member in Da’an area in the western Chongqing shows that the main lithology is composed of medium-gentle slope facies deep gray-black organic-rich micritic bioclastic limestone, with stable distribution in the region, which is an important marine limy source rock in the Middle and Upper Yangtze region in South China. The hydrocarbon accumulation process of limy source rock gas in Mao 1 member showed an “intra-source integrated evolution” of organic-rich carbonate rock deposition, diagenesis, hydrocarbon generation, reservoir formation, hydrocarbon accumulation and preservation, which had characteristics of “source rock and reservoir integration, in-situ hydrocarbon enrichment, and contiguous gas distribution”. The micro-sized pores in source rock, and the dissolution pores and micro-fracture network system associated with faults served as the main reservoir space, forming two types of reservoirs, i.e., matrix porosity type (primary) and fracture-porosity type (transformed). The hydrocarbon accumulation pattern of “mainly source rock and reservoir integration and enrichment in local structural transition zone after short-distance migration” has been established and the sweet spot evaluation system has been constructed. The key factors for gas enrichment and high-yield production in the new type of limy source rock reservoir in Mao 1 member include the development of organic rich dark limy source rock, favorable paleo uplift, anticlinal tectonic settings at present, and fault-controlled karst and extensional micro-fractures. The estimated resources of limy source rock gas in Mao 1 member are 2×10¹² m³in Sichuan Basin, which is a new unconventional field for increasing reserves and production in the basin.

CLC Number:

TE122.1

Liang Xing, Zhang Lei, Jiang Liwei, Shan Chang’an, Pan Feng, Luo Yufeng, Meng Yang, Wang Gaocheng, Shu Honglin, Zhu Douxing, Li Boshuo, Wang Zhendong, Yao Qiuchang, Xu Zhengyu. Exploration breakthrough and resource potential of limy source rock gas in Da’an area in the western Chongqing, Sichuan Basin[J]. China Petroleum Exploration, 2024, 29(2): 30-45.

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