四川盆地高磨地区震旦系灯影组四段微生物丘滩叠置样式及沉积演化特征OA

The reservoirs in the 4th member of the Sinian Dengying Formation(Deng 4 Member),Sichuan Basin are facies-controlled karst reservoirs formed by microbial mound-shoal deposits superimposed with dissolution and karstification.Clarifying the distribution and evolution characteristics of these microbial mound-shoals is essential for refined reservoir characterization.This study identified mound-shoal sedimentary microfacies types,characterized their stacking patterns and distribution characteristics across depositional stages,and clarified their sedimentary evolution processes and controls on reservoir development in the Deng 4 Member of the Gaomo area,Sichuan Basin,using integrated core,outcrop,well-log,and 3D seismic data.As indicated by the research results,(1)three types of mound-shoals developed in the Deng 4 Member under the control of relative water depth:vertically stacked,laterally migrating,and isolated types.The vertically stacked mound-shoals are characterized by massive aggradational geometry,displaying multi-layer parallel seismic events with moderate-to-weak amplitude and moderate-to-weak continuity.The laterally migrating type forms tabular laterally accreted or progradational mound-shoals,showing shingled seismic events with moderate-to-weak amplitude and moderate-to-weak continuity.The isolated type occurs as sheet-like mound-shoals,showing mound-shaped weak seismic reflections.(2)Temporally,mound-shoals were initially confined in distribution during the early depositional stage,dominated by migrating and isolated types.In the late stage,these complexes expanded,encompassing all three stacking patterns.(3)The average porosities of vertically stacked and laterally migrating mound-shoals are 5.2%and 3.3%,respectively.These two types contain well-developed high-quality reservoirs and are favorable exploration targets.In contrast,isolated mound-shoals have an average porosity of only 2.2%,with poorly developed high-quality reservoirs.The Deng 42 and Deng 43 sublayers in the platform-margin zone are dominated by vertically stacked mound-shoals and have relatively high development potential,whereas the intraplatform area is dominated by isolated mound-shoals,exhibiting poor reservoir performance.