Sedimentary Microfacies And Reservoir Prediction Of The Third And Fourth Member Of The Middle East Of Ordos Basin

Carbonate rocks in the Lower Paleozoic in the Ordos Basin are very important oil and gas exploration strata in China,and some important exploration progress has been made.The Majiagou Formation is an important exploration stratum in the Ordos Basin.The reservoirs are controlled by sedimentary facies,so studying the distribution of sedimentary facies can effectively predict the distribution of reservoirs.Therefore,based on the data of field outcrop,core,well logging,seismic,experimental analysis and related research results,the sedimentary microfacies and reservoir characteristics of the Ma3 and Ma4 in the study area were analyzed in depth,and the following insights were obtained:(1)Sub-level sedimentary cycles still develop in the Ma3 and Ma4.Ma3 and Ma4 can be divided into six small layers,Ma3-1,Ma3-2,Ma3-3 and Ma 4-1 Ma4-2,Ma4-3.(2)By studying the sedimentary microfacies of each small layer,the classification scheme of the sedimentary microfacies of the Ma3 and Ma4 was determined.The type of sedimentary microfacies at the target layer in the study area was systematicall y summarized,and the sedimentary facies model was established.The study suggests that Ma 3 and Ma 4 have two types of sedimentary facies,namely open platform facies and evaporative platform facies.The open platform facies can be further subdivided into five types of sedimentary microfacies: sandy debris sedimentary microfacies,lime flat sedimentary microfacies,lime cloud flat sedimentary microfacies,dolomite flat sedimentary microfacies and limestone depression microfacies.The evaporative platform facies can be subdivided into five types of sedimentary microfacies including niyunping,anhydrite-containing nodular dolomite ping,gypsum-containing yunping,gypsum-yunping,and gypsum-salt lagoon.(3)Through analysis and research on core,thin slices and other data,it is believed that Masan and Masi develop three types of reservoirs,namely,grain beach facies dolomite reservoirs,gypsum-dissolved pore dolomite reservoirs,and biologically disturbed dolomite reservoirs.(4)Sedimentation plays an important role in controlling the development of carbonate reservoirs.The reservoir at the target horizon in the study area is a typical phase-controlled reservoir,and the quality of the reservoir is strictly controlled by the sedimentary microfacies.A comprehensive study of drilling cores and microscopic slices shows that the granular beach facies,dolomite flats and anhydrite-containing nodular nodular dolomite flats are favorable reservoir facies belts of the Ma3 and Ma4 members,developing high-quality reservoirs.By superimposing sedimentary facies maps,the distribution of favorable reservoir areas can be predicted.