Major factors controlling the shale gas accumulations in Wufeng-Longmaxi Formation of the Pingqiao Shale Gas Field in Fuling Area, Sichuan Basin, China

Abstract

Pingqiao Shale Gas Field in Fuling Area of Sichuan Basin in China is located in a narrow-abrupt fault anticline of the Fenglai Syncline. Presently, the proven geological reserves of shale gas are 138.917 × 109 m3 in the Pingqiao Shale Gas Field, suggesting good potential for shale gas exploration in the Pingqiao Shale Gas Field. According to the drilling, logging, as well as the seismic and experimental data, the basic features of the Pingqiao Shale Gas Field with the narrow-abrupt fault anticline structure is outlined. Herein, the major factors controlling the accumulation and the high productivity, as well as the reasons for the differences in the production in the Pingqiao Shale Gas Field are also analyzed. The studies show the following: (1) The thickness of the shale gas layers (TOC ≥ 1%) is 115–155 m, the thickness of quality shale layers (TOC ≥ 3%) at the bottom of Wufeng-Longmaxi Formation in the Pingqiao Shale Gas Field is 36–40 m, which is featured by the high abundance in reserves (1.268 × 109 m3/km2), high pressure of shale gas accumulation (pressure ratio 1.56) and the high production value (average testing production 219.9 × 103 m3/d). (2) Main factors controlling shale gas accumulation and production in the Pingqiao Shale Gas Field include developed quality shales in the deep shelf, no faults stretching to the surface, weak slipping, good sealing, no outcrops and no obvious pressure-released belts in the surrounding area. (3) The development degree of the micro-fractures, structure position and depth are the key factors for the differences in production when shale gas layers have similar enrichment conditions.