Paleogeographic evolution of the middle and lower assemblages of the Majiagou Formation in the Ordos Basin and the pattern of reservoir distribution
Petrographic paleogeography study is the basis of reservoir delineation and hydrocarbon exploration.The results of the previous understanding of the petrographic paleogeography of the carbonate rocks in the Ordos Basin have effectively guided the exploration of the weathered crust reservoir at the top of the Ordovician Majiagou Formation,which has been proved to have nearly one trillion cubic meters of reserve size.However,limited to the data and the degree of understanding,the original reservoir distribution map can not meet the needs of the increasingly in-depth natural gas exploration work.Therefore,based on the latest geological data,the author comprehensively utilized petrographic paleogeographic analysis and reservoir prediction techniques,and clarified the main controlling factors and distribution rules of favorable reservoir development in the middle and lower part of Majiagou Formation by compiling sedimentary phase maps and reservoir distribution maps in the middle and lower part of the formation.The study shows that:1)the middle and lower part of Majiagou Formation mainly develops three major phases,namely evaporation plateau,confined plateau and plateau edge,as well as eight subphases and 16 microphases.Among them,the granular beach,microbial mound,granular beach at the edge of the platform,and gypsum-bearing dolomitite flats are favorable microphases for reservoir development.2)The microscopic storage space of the dolomite reservoirs in the middle and lower assemblages mainly consists of intergranular pores,intercrystalline pores,dissolution pores,microcracks,etc.,which are mainly controlled by three factors:deposition of mounds,beaches,and gypsum-bearing dolomitite flats,penecontemporaneous dissolution,and post filling effect.3)The reservoirs of Ma2,Ma4,Ma59 and Ma57 are mainly intergranular pores and intercrystalline pores of mound-shoal facies,and the reservoirs of Ma3 and Ma56 are mainly dissolved pores of gypsum-bearing dolomitite flats.It is concluded that the middle-lower assemblage reservoirs have various types,many strata and large thickness,which are the key strata of natural gas exploration in the next step.
万方数据
维普
