Progress and direction of exploration and development of normally-pressured shale gas from the periphery of Sichuan Basin

This study firstly introduces the geology and production characteristics of the typical normally-pressured shale gas plays in the U.S. and analyzes the origins of normal pressure and under-pressure. The normally-pressured shale gas reservoirs from the periphery of Sichuan Basin are then characterized using the E & P cases of the Upper Ordovician Wufeng to Lower Silurian Longmaxi formations in the Wulong, Pengshui and Daozhen areas. The comparison between normally- and under-pressured shale gas reservoirs in the U.S. and China reveals that: (a) U.S. shales with large thickness are widely distributed; (b) U.S. shales have relatively lower maturity compared to Chinese marine shales; and (c) U.S. shales experienced fewer tectonic events after deposition. Nitrogen foam and ultra-light proppant have been successfully used for the hydraulic fracturing of the under-pressured Ohio shale in the Big Sandy area. Based on the analysis of the exploration and development progress of three residual synclines, it is apparent that the tectonic period and strength, burial depth and distribution area are the main factors for the difference of preservation conditions of residual synclines outside the basin, and are also the main reasons for the difference of formation pressure coefficient and production. Based on this, the paper puts forward some suggestions for further theoretical and technical research on normally-pressured shale gas from the periphery of the basin.