Peculiar accumulation conditions for shale gas in the Lower Cambrian in Qianzhong uplift and its periphery

The Lower Cambrian Niutitang Formation shale is characterized by large thickness, high organic carbon content, high thermal evolution degree and high brittle mineral content in the Qianzhong uplift and its periphery. It has the basic geological conditions for shale gas accumulation. However, after many years of exploration, the study area has not made a substantial breakthrough, and some peculiar conditions for shale gas accumulation are the main controlling factors. Through the systematic analysis of outcrop sections and the data from wells including Huangye 1, Longye 1 and Dingshan 1, this paper focuses on the study of the basic geological characteristics of shale, including sedimentary facies, shale distribution, organic carbon content, thermal evolution degree, and the shale reservoir characteristics, including reservoir types, reservoir physical properties and gas content. The peculiarities of shale gas accumulation conditions are mainly manifested in two aspects: (1) The particularity of high shale thermal evolution degree, with complex hydrocarbon generation and expulsion history, is not conducive to gas occurrence and enrichment. (2) The particularity of the shale reservoir. Complex thermal evolution and strong diagenesis resulted in low porosity, especially little organic matter pores and small diameter, which made the reservoir property of shale very poor. On this basis, some parameters for shale gas exploration were selected, and some favorable areas for shale gas enrichment were evaluated. The Huangping region in the Qiannan Depression is a type Ⅰ favorable area of shale gas exploration in the Qianzhong uplift and its periphery, with relatively stable structure, moderate depth, relatively low thermal evolution degree of organic matter, favorable preservation conditions and good gas-bearing capacity. The exploration risk of the Huangping region is relatively low. Because of high maturity, the Qianxi region is a type Ⅱ favorable area to explore for shale gas reservoirs with high thermal evolution degree.