Characteristics and evolution of sub-member Ma45 of Majiagou Formation in southern Jingbian gas field,Ordos Basin
As one of the critical replacement production layers following the Sub-member Ma55 of the Ordovi-cian Majiagou Formation in the Jingbian gas field,the sub-member Ma45 is limited in the reasonable and accu-rate prediction for the carbonate reservoir development and natural gas distribution because of the weak analy-sis on the sedimentary microfacies.Taking the southern Jingbian gas field as an example,the sedimentary mi-crofacies type were identified and the planar distribution law was described,and the evolution law of sedimen-tary microfacies of different layers from the sub-member Ma45 was made clear in this paper through core obser-vation,thin section identification and logging interpretation for sedimentary facies.The results show that the sedimentary subfacies of the sub-member Ma45 is dominated by restricted platform in the central and western study area,including lime-bearing dolomite flat,calciferous dolomite flat,mud-bearing dolomite flat,argilla-ceous dolomite flat,dolomitic mud flat,and mud-lime bearing dolomite flat.The evaporation platform is main-ly distributed in the eastern study area,and dominated by gypsiferous dolomite flat and gypsiferous lake.The Ma4-35 layer is dominated by restricted platform,with the largest area of mud-bearing dolomite flat and mud dol-omite flat development.During the sedimentary period of Ma4-25 layer,the evaporation platform area in the east-ern study area increased.The content of terrigenous mud increases again when in the Ma4-1b5 layer sedimentary period resulting in the extensive development of mud dolomite flat in the central study area,while decreases during the Ma4-1a5 layer sedimentary period resulting in the extensive distribution of calciferous dolomite flat de-velopment with local development of evaporation platform.The natural gas distribution is controlled obviously by sedimentary microfacies.The calciferous dolomite flat and mud-bearing dolomite flat are the favorable sedi-mentary microfacies for natural gas distribution of sub-member Ma45 in the study area.The research results is helpful for the prediction of favorable carbonate reservoir distribution areas and the deployment of natural gas exploration and development scheme in Jingbian gas field.
sedimentary microfaciescarbonate rockMajiagou FormationJingbian gas fieldOrdos Basin
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