Study On The Natural Gas Accumulation Dynamics Mechanism In The Keshen Structural Belt

Keshen structural belt is a hydrocarbon enrichment zone,which is located in Kuqa foreland thrust belt.Exploration in keshen tectonic belt is still in its infancy.For this reason,the study of hydrocarbon accumulation mode in Keshen structural belt is helpful to the next hydrocarbon exploration.The source rock of Keshen structural belt includes Triassic and Jurassic strata,which are high thermal evolution degree and have generated a large number of dry gas.The reservoir of Keshen structural belt is Bashijiqike formation.The cap rock is the salt bed of Kumugeliemu group and its key sealed depth is 3000 m.With low porosity and low permeability,Bashijiqike formation develops a lot of fractures.The development of fractures improves the permeability of reservoir,which is benefit to the late filling of gas accumulation.As Keshen structural belt reservoir under salt bed is located in the superimposed area of fractures and favorable sedimentary facies belt,it is good for nature gas accumulation.The gas migration model in Keshen structural belt includes the vertical migration and the lateral migration.The shale formation exists between source rocks and reservoir with a thickness of 1 km,gas charges into the reservior through the faults,and migrates to sand body that has more developed fractures.Because the pore-fluid pressure is different between source rock and reservoir,the natural gas has the power of migrating from source rock to reservior vertically along the fracture,this can be the poor-forming dynamics.Based on the gas filling physical simulation and pressure evolution numerical simulation,the pattern of gas charging is a continuous process.The pressure difference between source rock and reservoir is 15 to 60 MPa.The pressure difference is one of the controlling factors of gas saturation in the reservoirs.