Study on characteristics and source of tight gas in the Shahezi formation, Xujiaweizi Fault Depression, Songliao Basin, China

Abstract

The Xujiaweizi fault depression is rich in natural gas resources in Lower Cretaceous and a major fault depression of the deep strata in northern Songliao Basin. In this study, the tight gas is coaliferous gas in the K1sh Formation of the Xujiaweizi Fault Depression. The methane carbon isotope value of tight gas is controlled by mature evolution. The cause of reversed sequence and partially reversed sequence of gas components carbon isotope is carbon isotope fractionation with hydrocarbon generation evolution of high-overmature stage source rock. The carbon isotope values of the low content components are obviously lighter with the increase of buried depth at the late stage of mature evolution. The carbon isotope values of adsorbed gas show similar characteristics, whether mudstone, carbargilite or coal in the same well. The tight gas reservoir is self-generation and self-accumulation gas reservoir by vertical diffusion and short distance migration in the K1sh Formation of the Xujiaweizi Fault Depression. It is important to study on the geochemical characteristics and the genesis of tight gas for guiding the exploration and deployment in the future.