The Geological Characteristics And Resource Assessment Of The Jurassic Tight Sandstone Gas Reservoirs In The Eastern Kuqa Depression

The discovery of Jurassic tight sandstone gas reservoirs demonstrates a huge unconventional resource potential in the eastern of Kuqa Depression.But its range,sweet spots,gas-bearing controllingfactors and resources are not clear,which shows the exploitation is in the initial stage.Dibei gas field,in the mature exploratory stage,has been scrutinized for obtaining reservoir characterizations,gas reservoirs type and gas-bearing controlling factors.The tight sandstone gas reservoir is evaluated for its resources potential and favorable areas in the eastern of Kuqa Depression based on above study.The following three results can be achieved:Interparticle dissolved pores,intraparticle dissolved pores and micropores are the main pores in the Jurassic tight sandsonte reservoir,Dibei gas field.The flaky and curved lamellar throat is the major proportion.And it mostly contains cross-interparticle fracture,interparticle-margin fracture and intraparticle fracture.The reservoir is low porosity and permeability and its property is apparently controlled by sedimentary microfacies and lithology.The experiments of geochemistry,fluid inclusion and quantitative fluorescence analysisdemonstrate the gas reservoirs have two stage of hydrocarbon charging.According to the reservoirs characteristics of geology,gas and water production and pressure distribution,combined with overseas gas reservoirs analogy,we consider that it may be a kind of conventional trap type tight reservoir rather than a deep basin gas reservoir understood by predecessors.The model of gas and water distribution is also predicted here.Based on the physical simulation experiment of gas charging into core samples saturated with water,mercury injection and gas-water twophase permeability experiment,we investigate the controlling factors of gas-bearing of tight sandstone reservoir,which is combined with the characteristics of physical property,fracture development and gas generation intensity.The gas saturation and flow production are determined by the physical property of reservoir.Natural fracture is favorable for preserving space and gas permeability of the reservoir,which controls natural gas accumulation and production.The gas saturation is determined by infill injection pressure difference with the same condition on physical property.The reservoir wettability would be altered by previous oil accumulation,which is benefit to gas charging and production.Some structural high parts are favorable area for natural gas enrichment and production.Considering about the latest exploration results and geological study,we analyze thefavorable zone of the Jurassic tight sandstone reservoirs in the eastern Kuqa Depression by using a method of key reservoirs forming factors superposition.Based on resource abundance analogy method and stochastic simulation method combined with volumetric method,the resource potential is 1.23×10¹²m³.And according to the relative potential and risk rank,we have chosen six favorable regions for tight sandstone gas exploration and development in the study area.The Dibei Slope region is the best for natural gas exploitation.Our study plays some guiding roles in the next step of tight gas exploration and strategic area selection in the eastern Kuqa Depression.