Sedimentary Facies And Sandbody Distribution Of The Mesozoic Sequence In Huanghua Depression

This paper takes the Mesozoic in Huanghua Depression as the main research object,and the stratigraphic characteristics,sedimentary facies characteristics,sedimentary facies distribution and favorable sand body distribution of the Mesozoic in Huanghua Depression are systematically studied by synthesizing regional geological,core,well logging,seism,sporopollen data and previous research results.The Mesozoic in Huanghua Depression is divided into four strata.Middle-Lower Triassic,Middle-Lower Jurassic,Upper Jurassic and Lower Cretaceous,through the analysis of logging response,logging data and seismic response characteristics,core observation and analysis,sporopollen data and volcanic rock dating data.Among them,the middle and lower Triassic mainly developed purple-red sand-mudstone interbeds with finer grain size.Logging curves are mainly toothed box type and toothed line type.In the Middle and Lower Jurassic,massive sandy mudstones and interbedded sandy mudstones are mainly developed,and coal is locally visible.Logging curves are mainly middle-high amplitude microtoothed box-bell and toothed funnelbox-finger.Upper Jurassic mainly developed purple-red sand-mud interbeds,and thin layers of intermediate-basic volcanic rocks were found at the bottom of some areas.Logging curves are mainly high-amplitude toothed box-shaped and funnel-shaped,micro-toothed straight,lowamplitude toothed-toothed box-shaped and high-amplitude funnel-shaped.The Lower Cretaceous mainly developed purple mudstone and siltstone,grey-white sandstone,coarse sandstone and calcareous sandstone in some areas,and volcanic rocks in the bottom.Logging curves are micro-toothed bell-box,micro-toothed flat,toothed funnel-box-finger.By sorting out the borehole logging data in the depression and summarizing the residual thickness of each stratum,it is found that the Mesozoic residual strata are obviously thin in the north and thick in the south.The Middle and Lower Triassic is mainly distributed in the south,with a small amount of distribution in the middle,and the whole is thinner;the Middle and Lower Jurassic is mainly distributed in the South and the strata are thick and thin in the south;the Upper Jurassic is less distributed,sporadically distributed and thinner in each area;the Lower Cretaceous is mainly distributed in the north and there are many distribution areas,and the middle area is better.Through identification of lithology,sedimentary structure and logging curve,it is considered that there are four main sedimentary facies in Mesozoic: meandering river facies,braided river facies,lake facies and alluvial fan facies.In the early and middle Triassic,large-scale dry river-lake depositional systems were mainly developed in the depression.The fluvial facies was dominated by floodplain deposits,while the lacustrine facies was dominated by shore-shallow lake deposits.In the early and middle Jurassic,meandering and braided river facies were mainly developed in the study area,and lake facies and alluvial fan facies were developed in some areas.Through single well sedimentary facies analysis and continuous well sedimentary facies analysis,the plane facies distribution characteristics of Mesozoic Middle-Lower Triassic and Middle-Lower Jurassic in Huanghua Depression are analyzed.On this basis,the types and distribution of favorable sand bodies in the Mesozoic are studied.It is found that there are three different provenances and river sedimentary systems in the Middle and Lower Jurassic.The structure of each system is "lower braided upper curvature".The favorable sand bodies are braided channel massive sandstones in the lower part of each sedimentary system.The lower massive sand bodies are mainly distributed in Chenghai area.The grain size of the sand bodies is coarse and the lithology is mainly lithic feldspar sandstone.The middle massive sand bodies are distributed in Wangguantun-Zaoyuan and Chenghai areas,with fine grain size and lithology of lithic feldspar sandstone.The upper massive sand bodies are distributed in Shenusi area,with medium grain size and mainly feldspathic lithic debris sandstones.