Effective evaluation of gas migration in deep and ultra-deep tight sandstone reservoirs of Keshen structural belt, Kuqa depression

Abstract The gas reservoir in the Keshen structural belt, Kuqa depression, Tarim Basin, Xinjiang, China is a typical deep and ultra-deep structural faulted anticline tight sandstone gas reservoir. This reservoir possesses abundant natural gas and exhibits a promising exploration and development prospective. However, the effectiveness of the gas migration (preferred migration pathway) and the contribution of gas source faults as a dominant migration pathway remains to be further investigated. Therefore, this paper examines gas-source correlation to determine the source of natural gas and uses fluid potential analysis combined with the tracer results of geochemical parameters to predict the predominant migration and accumulation pathways of natural gas. Next, the paper determines the contribution of gas source faults to the formation of the gas reservoir during the migration process by making a quantitative assessment of the gas source faults. The results show that the predominant source of natural gas from the deep and ultra-deep tight sandstone gas reservoir in the Keshen structural belt, Kuqa depression is Jurassic and Triassic source rock. Structural units with relatively low fluid potential represent the predominant migration pathway of natural gas. Gas source faults provide the predominant natural gas vertical transport pathway, with differences observed between zones in the south and north. The greater the contribution provided by a gas source fault during transport is, the higher the accumulation that results. The effectiveness of the natural gas migration deep and ultra-deep tight sandstone gas reservoir in the Keshen structural belt, Kuqa depression is as follows: Kela2 trap > Keshen6 trap > Keshen8 trap > Keshen2 trap > Keshen13 trap > Keshen9 trap. This method can be used in effective evaluation of the gas migration under the similar tectonic settings and reservoir formation conditions.