Abstract：The carbonates of the Member 5 of Majiagou Formation in the northern Shaanxi Province are important natural gas reservoir. In order to clarify the lithofacies palaeogeography evolution of each sedimentary period of Majiagou Formation in the study area,the lithofacies palaeogeography characteristics of M510-M51 submembers were restored based on the investigation of surrounding field outcrops,core observation of 98 wells,and well logging curve analyses. The results show that the marine carbonate platform is the major sedimentary microfacies in each layer of M510-M51,including three subfacies: restricted platform,open platform and evaporate platform,and further subdivided into 10 sedimentary microfacies: dolomite flat,gypsum-dolomite flat,gypsum-bearing dolomite flat,muddy dolomite flat,carbonate-dolomite flat,carbonate flat,grain beach,dolomite-carbonate flat,muddy carbonate flat and gypsum salt lake. The palaeogeography unit of M510-M51 is distributed in a ring belt shape from east to west with the central part located in Yanchang,Yanchuan and Qingjian. It is worth noting that the center of palaeogeography unit ring belt of M52 submember move northwestward to Jingbian and Zichang due to strong tectonic uplift in the south occurred in that period. Dolomite flat,gypsum-dolomite flat,gypsum-bearing dolomite flat,and grain beach microfacies are favorable for the formation of reservoir space. In vertical,M51+2,M54,M55,M57 and M59 submembers are relatively rich in these microfacies,which are the focused areas of regional hydrocarbon exploration and development.
Cao Hong-Xia,Li Wen-Hou,Wu Hai-Yan et al. Lithofacies palaeogeography evolution of the Member 5 of Ordovician Majiagou sedimentary stage in northern Shaanxi Province[J]. JOPC, 2021, 23(4): 723-734.
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