Exploration Potential of Shale Gas in Lower Permian Liangshan Formation of Lianyuan Depression, Central Hunan

Based on outcrops and drilling data of Lower Permian Liangshan Formation shale in Lianyuan depression, its geological and geochemical characteristics, mineral composition, pore structure as well as gas adsorption capacity have been studied and discussed in this paper through using the organic geochemical test, X-ray diffraction mineral analysis, electron microscopy scanning, and methane isothermal adsorption. The results show that the shale reservoir of Liangshan Formation is 6.15-35.18m thick. The abundance of organic matter is mostly greater than 1%, with an average of 1.77%, and the organic matter type is mainly type I. The temperature of maximum pyrolysis output T_max (450-533℃) and vitrinite reflectance R_o (1.51%-1.83%) indicate that the shale belongs to organic-rich shale in post-mature stage. The shale minerals are dominated by quartz and followed by clay minerals. The clay minerals are mainly illite, which is beneficial to improve the shale reservoir performance. With diverse pore types, the organic pores, intergranular pores and micro-cracks provide space for shale gas. The adsorption gas content of shale is 0.65 m³/t, and it has a good gas adsorption capacity. In a word, Liangshan Formation shale is generally developed and large in Lianyuan Sag, especially in the south of syncline areas, which are favorable for shale gas exploration.