Analysis of shale gas accumulation conditions of the Niutitang Formation of Lower Cambrian in Sangzhi area, Hunan Province

The marine facies shales of Niutitang Formation are developed in Sangzhi area, with relatively few stu-dies on the shale gas accumulation conditions of Lower Cambrian in Paleozoic in this area. On the basis of literature research and combining with field survey and experimental analysis, the authors in this paper have studies the geological factors and reservoir-forming conditions of shale reservoir in the Niutitang Formation of Lower Cambrian in Sangzhi area, in order to provide reference for the next shale gas exploration and development in this area. The results show that the sedimentary facies in Niutitang Formation shale are shelf facies and slope facies, with good burial depth condition and large thickness. The abundance of organic matter is above 2% in terms of organic geochemical characteristics, with kerogen types of type II₁ and rare type I and organic matter maturity of 3.5%, which are the high-quality source rocks. The organic matter evolution and clay mineral diagenetic stage have a good corresponding relationship, and the diagenetic mineral transformation stage is basically the same as the organic matter oil and gas generation threshold, with the source rock in the stage of massive generation of dry gas and cracked gas. In terms of storage conditions, the porosity is 9% with primary pores, secondary pores, mineral pores, natural fractures, and structural fractures, which provide space for shale gas accumulation. The high content of brittle minerals makes fractures created easily. Overall, the shale of the Niutitang Formation is high-quality shale, and the accumulation conditions of shale gas are good, with great potential of exploration and development.