Reservoir characteristics and control factors of the fifth member of Majiagou formation in the west side of Jingbian gasfield,Ordos basin

There are 3 types of dolomite reservoir space in the upper group of the fifth member of Majiagou formation including cavity,pore and fissure.The main reservoir space is anhydrite nodules dissolved pore and crevice,followed by cave,intergranular pore and dissolved pore.There are 4 types of dolomite reservoir space in the middle group including dolomite intercrystal pores,intergranular micropores,intergranular dissolved pore and dissolved pores.The development of fissure is beneficial to improve the porosity and permeability of reservoir.The distribution of the fifth member of Majiagou formation dolomite reservoir is controlled by sedimentary facies belt and ancient karst landform: gypsum-dolomite flat and gypsodolomite flat are the best reservoir belts for development of Paleokarst reservoir in upper group,the best belts for dolomite reservoir in upper group are grain beach and dolomitic flat.The study area is located in the slope area of ancient weathering crust karst,Erdos basin,it is beneficial for reservoir development.