Lithofacies distribution and gas-controlling characteristics of the Wufeng–Longmaxi black shales in the southeastern region of the Sichuan Basin, China

Abstract

The Wufeng–Longmaxi (WF–LMX) black shales in the southeastern region of the Sichuan Basin are currently the focus of shale gas exploration and development in China. In this study, field surveys and laboratory analyses of the Shuanghe (SH), Qilongcun (QLC), and Guanyinqiao (GYQ) outcrop profiles located within this region were conducted. Field data from the Jiaoshiba (JSB) gas field were also analyzed and interpreted. A systematic study of the distribution and evolutionary succession of the region's sedimentary microfacies and shale lithofacies, as well as the interrelationships between these facies, was conducted. An improved shale lithofacies classification scheme was developed. Fourteen lithofacies were identified, and variations in the types of shale lithofacies were found at different locations within the same sedimentary microfacies or member. Various shale lithofacies were found to have significantly different characteristics of total gas content and open flow rate, and certain lithofacies in the study area had very strong gas-controlling characteristics. This region has four dominant types of shale lithofacies: argillaceous, siliceous shale with rich total organic carbon (TOC) content; argillaceous, silty shale with high TOC content; argillaceous, silty shale with medium TOC content; and silty clay shale with low TOC content. Among these four lithofacies, the argillaceous, siliceous shale with rich TOC content and the argillaceous, silty shale with high TOC content facies are the best and second-best shale lithofacies, respectively, in terms of total gas content and open flow rate. These results of lithofacies distribution and gas-controlling characteristics in this region help provide useful reference information for predicting favorable targets for shale gas development.