Geological characteristics of the second member of the Permian Wujiaping Formation in the Longmenba Section, eastern Chongqing

doi:10.3969/j.issn.1006-6535.2025.05.008

Abstract

Abstract: Currently, commercial development of shale gas has been achieved in the Second Member of the Permian Wujiaping Formation (referred to as Wu 2 Member) in the Hongxing Area within the Liangping-Kaijiang Trough in eastern Chongqing. However, research on shale gas accumulation conditions in the north-central part of the western Hubei Trough remains insufficient. Therefore, through detailed measurement and sample analysis of the Permian Wu 2 Member stratigraphic section in Longmenba, Fengjie County, eastern Chongqing, the characteristics of the Wu 2 Member shale reservoir were clarified and the shale gas exploration potential areas in western Hubei-eastern Chongqing were predicted. The results indicate that the thickness of organic-rich shale in the Wu 2 Member reaches 29.3 m and can be divided into five sub-layers. The organic-rich intervals are sub-layers 1, 3, 4 and 5, mainly composed of black argillaceous siliceous rocks interbedded with siliceous shale, with increasing calcareous content upward in the formation; sub-layers 1 and 3 are volcanic ash-dense intervals,with the first appearance of the conodont C.wangi near the top of bed 101 as the boundary between the Wujiapingian and Changxingian stages; the organic-rich intervals were deposited in a humid,semi-humid,semi-arid climate with anoxic bottom water and high productivity paleoenvironments. The average TOC is 6.34%, characterizing a carbon riched, silicon riched, low porosity, low permeability reservoir. Compared with the Hongxing Area and the Enshi Area, although the Wu 2 Member has a relatively shallow (mostly less than 2 000 m) burial depth, it has large thickness (about 30 m) and high TOC (greater than 4.00%), thus still possessing good shale gas accumulation potential. The research results can provide geological basis for the construction of a shale gas exploration and development demonstration area in western Hubei-eastem Chongqing.

Key words: black shale, reservoir characteristics, accumulation potential, Wujiaping Formation, eastern Chongqing

CLC Number:

TE122

CHEN Miankun, XU Lulu, YAO Mingjun, LIU Zaoxue, WEN Yaru. Geological characteristics of the second member of the Permian Wujiaping Formation in the Longmenba Section, eastern Chongqing[J]. Special Oil & Gas Reservoirs, 2024, 32(5): 66-75.

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