The Reservoir Formation Mode and Mechanism of Longmaxi Formation Shale Gas in the Yuxi area of the Sichuan Basin

Abstract

The study on the reservoir formation mode and mechanism of Longmaxi Formation shale gas in the Yuxi region of the Sichuan Basin is a fundamental basis for understanding the enrichment law and development potential of shale gas in this area. The shale layers of the Wufeng Formation to Longmaxi Formation in the Yuxi region are buried at depths ranging from 3900 to 4500 meters, with high Total Organic Carbon (TOC) content ranging from 1.96% to 7.88%. The organic matter is of Type I kerogen and is in an overmature stage, exhibiting excellent hydrocarbon generation potential. Research indicates that the gas content in shale increases with burial depth, with the Long11-Long13 layers showing higher gas content, making them the main high-quality gas layers. The ratio of free gas to adsorbed gas is high, indicating significant development potential.The mineral composition of the shale is primarily quartz and clay minerals, with high quartz content facilitating pore development and fracturing, while clay minerals mainly affect adsorbed gas content. Pore types include organic pores, intergranular pores of pyrite, and microfractures, with the Long11 sub-layer exhibiting optimal micro-porosity and superior adsorption and storage performance. Shale gas reservoirs in the Yuxi region have favorable preservation conditions, with few fractures leading to minimal gas loss.Based on regional structural characteristics, a shale gas reservoir formation model of "narrow steep anticlines + fault sealing and covering by wide gentle synclines" is proposed. The study demonstrates that the TOC content, mineral composition, reservoir properties, and preservation conditions collectively influence the enrichment and accumulation of shale gas in the Wufeng Formation to Longmaxi Formation in the Yuxi region, providing important reference for the development of shale gas resources.