Lithofacies types and reservoir characteristics of lacustrine carbonate rocks in the third member of Qianjiang Formation, Qianjiang Sag

doi:10.3969/j.issn.1672-7703.2025.02.004

Abstract

Abstract: In order to identify pore development characteristics and controlling factors for lacustrine carbonate reservoirs in Qianjiang
Formation, Qianjiang Sag, Jianghan Basin, the lithofacies and reservoir physical properties have systematically been analyzed of carbonated rocks in the third member of Qianjiang Formation by means of XRD, thin section, porosity, and high-pressure mercury injection data in typical wells. The study results show that: (1) A total of eight rock types have been identified, i.e., granular carbonate rock, micritic carbonate rock, granular mixed rock, fine-grained mixed rock, felsic-rich clastic rock, clayey shale, sulphate rock, and salt rock. (2) Various rock types are superimposed with each other, forming four major types of lithofacies combinations, namely felsic-rich clastic rock and shale lithofacies combination, granular mixed rock and fine-grained mixed rock intercalated with shale lithofacies combination, granular carbonate rock and micritic carbonate rock intercalated with shale lithofacies combination, and salt rock intercalated with shale lithofacies combination from north to south. (3) The total porosity of various rock types is similar, with an average range of 5.5%–7.3%, but pore sizes vary significantly. Granular carbonate rock and felsic-rich clastic rock have relatively large pore sizes, with average pore volume of micron-sized pores accounting for more than 10% and average throat radius of higher than 140 nm indicated by high-pressure mercury injection data; While the micritic carbonate rock and fine-grained mixed rock have relatively small pore throats, with pore volume of micron-sized pores accounting for less than 5% and average throat radius of lower than 10 nm. It is pointed out that granular carbonate rock and felsic-rich clastic rock have good reservoir physical properties and large pore size, which are conducive to hydrocarbon accumulation, flow, and production, showing predominant lithofacies types in lacustrine carbonate reservoirs and the most favorable exploration targets in the study area.

Key words: lacustrine carbonate rock, lithofacies, reservoir space, Qianjiang Formation, Jianghan Basin

CLC Number:

TE122.1

Wu Shiqiang, Guo Libin, Xu Shang, Man Huihui, Luo Shuxing, Li Xiaoling, Zhao Wen, Kong Jinping. Lithofacies types and reservoir characteristics of lacustrine carbonate rocks in the third member of Qianjiang Formation, Qianjiang Sag[J]. China Petroleum Exploration, 2025, 30(2): 42-53.

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