Origin of Overpressure and Its Influence on Hydrocarbon Leakage in Mosuowan Uplift of the Junggar Basin, NW China

ABSTRACT The Junggar Basin is one of the main petroliferous basins in Western China. The Mosuowan Uplift, located in the central part of the Junggar Basin, is a favourable hydrocarbon accumulation zone. The overpressure is widely developed in the strata below the Jurassic, and the pressure coefficient gradually increases with the buried depth, up to 2.15. Based on the multi‐logging combination method, Bowers method, sonic velocity–density cross‐plot method and combined with geological setting, using porosity data of sandstone, geochemical data of source rocks, acoustic transit time ‐resistivity cross plots and so on, the origins of overpressure in each stratum of the Mosuowan Uplift are analysed. The results show that disequilibrium compaction, pressure transfer and tectonic compression are the main reasons for the development of deep overpressure. Disequilibrium compaction is considered to be an important reason for overpressure in Jurassic, Triassic, Upper Permian Upper Wuerhe Formation and Middle Permian Lower Wuerhe Formation due to the development of multiple sets of mudstone in deep strata. The Jurassic is charged by deep overpressure fluid, and the pressure transfer also has a significant contribution to the overpressure of Jurassic. The tectonic inversion occurred in the central part of the basin at the end of the Early Permian, and the overpressure in the Middle Permian Xiazijie Formation was closely related to tectonic compression. The hydrocarbon generation of the Permian and Jurassic source rocks has little contribution to the overpressure of the Mosuowan Uplift due to the poor source rock. The Mosuowan Uplift is an inherited anticline, adjacent to hydrocarbon generation sag, which is the dominant direction of oil and gas migration, but drilling confirmed that the deep reservoir is water layer. Comprehensive analysis of maturity parameters, logging fluorescence show and quantitative fluorescence analysis indicates that overpressure caused oil and gas leakage and destroyed hydrocarbon reservoirs.