Main Controlling Factors and Evolution Models of Bioclastic Shoal Reservoirs of Permian Changxing Formation in Zhongjiang-Moxi Region

Abstract

The Changxing Formation of the Upper Permian in the Sichuan Basin remains a focal area for natural gas exploration. Previous research on this formation has predominantly focused on platform-margin reefs in northeastern Sichuan Basin, while reservoirs within the platform have received limited attention. This study addresses this gap by systematically analyzing bioclastic shoal reservoirs in the Zhongjiang-Moxi region of central Sichuan Basin, using integrated methods including core observations, petrographic analysis, well log interpretation, and 3D seismic data. Results reveal that the study area primarily hosts porous bioclastic limestone reservoirs, characterized by storage spaces dominated by intragranular and interparticle dissolution pores. These reservoirs exhibit distinct facies-controlled attributes. Key controlling factors include: (1) syn- to penecontemporaneous karstification, (2) sea-level fluctuations governing reservoir thickness and stacking patterns, (3) micro-paleogeomorphic variations influencing early exposure dissolution, and (4) dolomitization enhancing reservoir quality. Based on these findings, two depositional evolution models for intraplatform reservoirs of the Changxing Formation are proposed.

Keywords

Zhongjiang-Moxi region / Changxing Formation / bIoclastic shoal / reservoir characteristics / geomorphology evolution / natural gas / petroleum geology

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