Research On The Geological Conditions Of Carboniferous Tight Sandstone Gas In The Eastern Section Of Delingha Depression,Qaidam Basin

With the deepening of exploration in recent years,the Carboniferous of Delingha Depression in Qaidam Basin is considered to have great potential for forming tight sandstone gas reservoirs.In this paper,the core and peripheral outcrop profiles of Wells QDC1 and QDD1 are used to systematically study the Carboniferous stratigraphic characteristics,rock assemblages and sedimentary facies distribution characteristics,and carry out petroleum geological evaluation for tight sandstone gas to obtain relevant knowledge.There are 12 types of rock assemblages in the Carboniferous in the Delingha Depression.Among them,the sandstone-mudstone combination of the Chengqianggou Formation,the siltstone-clastic limestone combination of the Keluke Formation,and the Limestone-fine sandstone combination of the Zabusagaxiu Formation.Drilling core test data shows that the organic matter type of the Keluke Formation source rocks is mainly type ? organic matter,mainly gas generation,and the thermal evolution is in the stage of maturity to high maturity,which can provide hydrocarbon source supply for tight sandstone gas reservoirs.The rock types of tight sandstone reservoirs are mainly detrital sandstone and detrital quartz sandstone,followed by quartz sandstone and feldspar quartz sandstone.The sandstone pores of the Keluke Formation are well developed,with poor pore connectivity.Tight sandstone reservoirs and source rocks are developed in a thin layer,and are easily eroded and transformed by organic acids generated during hydrocarbon generation,which is conducive to the adsorption of natural gas.The parameters such as the breakthrough pressure and mud-to-ground ratio of the Keluke Formation mudstone show good sealing ability.There are three favorable types of source-reservoir-caprock assemblages in the Carboniferous in the study area.The combination types existing in the Keluke Formation and Chengqiangou Formation are most conducive to the formation of tight sandstone gas reservoirs.The evolution model of oil and gas migration and accumulation in Well QDC1 was proposed.