Basic characteristics and exploration potential of shale gas in Longtan Formation of Upper Permian in eastern Sichuan Basin

Abstract

Various types of sedimentary facies were developed during the Longtan period of the Late Permian, Sichuan Basin. To discover the shale gas exploration potential of belts with different sedimentary facies, a systematic analysis of shale gas generation conditions was carried out on the basis of different typical wells. The organic-rich shale developed in the Sichuan Basin during the Late Permian Longtan period was mainly distributed in tidal flat-lagoon and shelf facies. With complex lithological combinations, the tidal flat-lagoon facies shale was distributed in the Ziyang-Yongchuan-Qijiang areas. Mudstone, shale, and argillaceous carbonate rocks were interbedded with varying thickness and coal seams were also developed in all sections. Furthermore, it has the characteristics of "high TOC, clay and gas contents, and high porosity". The main organic matter type is type Ⅲ. The shallow water, mixed shelf facies in the Longtan Formation was mainly distributed in the Guang'an-Changshou-Nanchuan area, with reduced coal seams and increased ash content. Coal seams were barely developed in the second member of the Longtan Formation. Its organic matter type is Ⅱ2-Ⅱ1, with stable thickness as well as medium TOC and brittle mineral contents. Gas logging was anomalous. The deep-water shelf facies in the Wujiaping Formation were mainly distributed in Shizhu-Wanxian and Guangyuan-Liangping. Coal seams were only developed at the bottom of the Wujiaping Formation. Moreover, the second member of the Wujiaping Formation is composed of siliceous shale and mudstone, which has the characteristics of "high TOC content, high brittle mineral content, high porosity, high gas content, and high gas saturation". Its organic matter type is Ⅱ1, with widespread organic pores. It is currently the main strata for the exploration and development of Permian shale gas in the Sichuan Basin.

Keywords

• shale gas
• longtan formation
• wujiaping formation
• permian
• exploration potential
• eastern sichuan area