Main controlling factors of new-type shale gas enrichment in Cambrian Qiongzhusi Formation, southern Sichuan Basin

Based on shale core, logging, and seismic data from the Cambrian Qiongzhusi Formation in the Sichuan Basin, the study used methods including thin-section analysis, scanning electron microscopy, organic and inorganic geochemistry, and adsorption–desorption tests. Combined with a comparative analysis of the Mancos shale in the San Juan Basin, North America, it systematically investigated the formation conditions and main enrichment controlling factors of new-type shale gas reservoirs. The results showed that: (1) The Qiongzhusi Formation in the Jingyan area was dominated by organic-bearing shale with total organic carbon (TOC) content < 1%. It developed sedimentary facies at the shallow-water gentle slope zone, which was favorable for the development of carrier beds. (2) The new-type shale gas reservoir exhibited the characteristics of "two lows, one large, and four highs": low TOC content, low Poisson's ratio, large pore size, high felsic content, high inorganic poro-sity, high gas content, and high Young's modulus. (3) Driven by source-reservoir pressure differences, natural gas generated from deep-water source rocks migrated and accumulated in the shallow-water organic-bearing shale carrier beds with more favorable pore structures. (4) The new-type carrier bed shale gas reservoir was different from the organic-rich continuous shale gas reservoir of the Longmaxi Formation, and exhibited a dual enrichment mechanism of source and reservoir controlled by sedimentation and diagenesis, and enrichment controlled by migration and preservation. The research results clarify the enrichment mechanism of new-type shale gas and provide a geological basis for the selection optimization of favorable exploration targets.