Main factors controlling shale gas accumulation and exploration targets in the Lower Cambrian, Sichuan Basin and its periphery

We studied the basic geological conditions and main controlling factors for shale gas accumulations in the Sichuan Basin and its periphery based on the latest theories for shale gas exploration and modeling results. Dark shale deposited in the Lower Cambrian can be defined as passive continental shale and tensional trough shale. The passive continental shale has good quality, great thickness and wide distribution. It has favorable basic conditions for shale accumulation, but the bottom plates are unfavorable and the structural deformation is extensive, thus the preservation conditions for shale gas are unfavorable. Tensional trough shale has reached the standard of basic hydrocarbon rocks, though the thickness of single shale interval is limited. It developed many vertical layers with good top and bottom plates and weak structural deformation. High thermal evolution degree restricted the gas-bearing capacity of dark shale, which was unfavorable for shale gas enrichment. Top and bottom seals are necessary when shale gas reservoirs were formed during the early stage. Tectonic conditions are important for the preservation of shale gas during the late stage. The favorable area for shale gas exploration is Mianyang-Lezhi-Longchang-Changning in the Sichuan Basin, Chengkou-Wuxi in the northeastern Sichuan Basin, Yien-Hefeng in the western Hubei, Huayuan-Zhangjiajie in the western Hunan, and Zhenyuan in Guizhou.