川东北元坝西部须二段—须三段沉积相及其对储层控制作用OA北大核心CSTPCD

The Upper Triassic Xu-2-Xu-3 Member in the western Yuanba of Northeast Sichuan is an important oil and gas reservoir.In this study,we used drilling cores,logging data,and 3D seismic data to study the sedi-mentary facies,sedimentary characteristics,depositional models,and their effects on the reservoir development of the Upper Triassic Xu-2-Xu-3 Members,as to guide the deployment of oil and gas exploration in the region.The results show that Xu-2-Xu-3 Members are mainly braided river delta facies and lacustrine facies.Four subfacies have been recognized,as delta plain,delta,front delta,and coastal shallow lake,which can be fur-ther divided into 9 microphases.Two depositional models were developed during the depositional period of Xu-2-Xu-3 Member.Xu-2 Member shows a model of gentle slope wide channel braided river delta deposition,and mainly develops wide river channels with overlapping sand bodies.Xu-3 Member shows a model of steep slope narrow channel braided river delta deposition,and mainly develops narrow river channels,and the sand bodies are distributed as strips along the river channel.Xu-2 Member mainly develops two favorable reservoir rock types,medium feldspar sandstone and medium-grained quartz sandstone.Xu-3 Member also develops two favor-able reservoir rock types,medium-coarse calcareous sandstone and fine sandy conglomerate.The high-quality reservoirs of Xu-2 Member are mainly distributed in the sand bodies of the underwater distributary channel of the delta front.The high-quality reservoirs of Xu-3 Member are mainly distributed in the sand bodies of the braided channel-delta front of the underwater distributary channel transition zone in the delta plain.The physical proper-ties and pore structure of feldspar sandstone and quartz sandstone are significantly better developed than those of the calcareous sandstone and sandy conglomerate.