蜀南地区东部上二叠统长兴组沉积特征及有利储层分布OA

In recent years,driven by the reef-shoal hydrocarbon accumulation theory,it has been confirmed that the intra-platform shoals of the Changxing Formation in the eastern part of southern Sichuan Basin have good gas-bearing properties.However,the sedimentary system and reservoir distribution of the thick-bedded limestone reservoirs remain unclear,thus restricting the deployment of oil and gas exploration.Based on outcrop,thin section,and well-seismic data,this paper carries out sequence division and third-order framework construction of the Changxing Formation,identifies sedimentary facies by integrating lithofacies,logging facies,and seismic facies,and accordingly analyzes the dominant facies belts of high-quality reservoirs and their favorable distribution areas.The results show that:(1)Three sequence boundaries(SB1,SB2 and SB3)are identified in the Changxing Formation in the eastern part of southern Sichuan Basin,which can be further divided into two third-order sequences(Sq1 and Sq2)from bottom to top.In the early stage,carbonate deep-shallow ramp developed;in the middle-late stage,ramp-type carbonate platform developed.Among these,the intra-platform shoal subfacies of the open platform facies mainly developed during the Sq1-HST and Sq2-HST depositional periods,with the most extensive development occurring particularly in the Sq2-HST period.The shoal bodies exhibite a lateral migration trend in the planar distribution and are only locally superimposed vertically.(2)The reservoir lithology is predominantly bioclastic limestone,with pore spaces and fracture-vug systems serving as the main reservoir spaces.The formation of reservoirs is primarily controlled by sedimentary facies and dissolution processes,and favorable reservoir zones concentrated in the intra-platform shoal subfacies,displaying a scattered patchy distribution.(3)According to the sedimentary facies,the development location and thickness of shoal bodies,and the development thickness of reservoirs,three favorable reservoir development areas and two potentially favorable reservoir development areas are evaluated and predicted:the area around Z207-Z201-Z202 well area,the B28-B61 well area,the B24-G11 well area are classified as favorable reservoir development zones;the BH2-BH3 well area and F7-N49 well are the potential favorable reservoir development zones.The systematic study on the sedimentary facies and reservoir characteristics of the thick-bedded limestone of the Upper Permian Changxing Formation in the eastern part of southern Sichuan Basin provides strong guidance for the next step of oil and gas exploration in the reef-shoal field of this area.