Logging Characterization Of Sedimentary Facies Of Carbonate Reservoir Of Ma5₅-Ma4 Member In Ordos Basin

The development of the middle-lower combination of Ordovician Majiagou Formation in Ordos Basin is controlled by the sendimentary facies belts.So studying the disturibution of sendimentary microfacies belts can predict the distribution of reservoir efficiently.Based on core,thin section,conventional logging and image logging data,the methods of previous researchers,the sedimentary microfacies of the middle-lower combination of Ordovician Majiagou Formation in Ordos Basin were classified.There are two facies,open platform and restricted platform.The open platform develops 2 subfacies,intraplatform bank subfacies and interbank sea subfacies.There is one sedimentary microfacies in the intraplatform bank subfacies,which is bioclast bank microfacies.There are 4 sedimentary microfacies in the interbank sea subfacies,which are interbank sea dolomite microfacies,interbank sea limy dolomite microfacies,interbank sea dolomitic limestone microfacies,interbank sea limestone microfacies.The restricted platform facies developes 3 subfacies,which are grain bank subfacies,tidal flat subfacies,lagoon subfacies.Grain bank subfacies developes psammitic bank microfacies.Tidal flat subfacies developes 6 subfacies,which are mud flat microfacies,muddy dolomite flat microfacies,muddy limestone flat microfacies,dolomitic limestone flat microfacies,limy dolomite flat microfacies,dolomite flat microfacies.Lagoon facies develops 2 subfacies,which are gypsum-dolomite lagoon microfacies and salt lagoon microfacies.Conventional and image logging data are calibrated by core and thin section.The qualitative characterization method of sedimentary microfacies using image logging was established by identifying the image mode and observing response characters of GR,PE,RLLS curves.And the quantitative characterization method using conventional logging was established by PE-GR crossplot and PE-RLLS crossplot.Quantitative conventional logging identification standards are established.Applying the newly built logging characterization method,sedimentary facies of single well are divided,well sections and sedimentary microfacies distribution maps are drawn,and distribution pattern of sedimentary facies of the target layer in the study area were summarized.Based on the sedimentary microfacies distribution maps,the sedimentary models of Ma56 and Ma57 submember are analyzed,which can support the prediction of the distribution of reservoir in the target layer of the study area.