The Origin And Distribution Of Dolomite Reservoir In The Qixia Formation Of Lower Permain,Sichuan Basin

This paper aims at Qixia formation,lower Permian,Sichuan Basin,utilizing field outcrop data,core data,thin section data,geochemical data and previous research data,based on principal theories sequence stratigraphy,sedimentary petrology and Reservoir sedimentology,taken field profile and drilling cores as research object,series of investigations have been studied on the stratigraphic and sedimentary features,reservoir characteristics and its main controlling factors of Qixia formation's karstic dolostone reservoirs which is control by grain beach facies.The present work ends with several following conclusions:(1)Through the identification of sedimentary facies symbols,including the lithology,palaeontology and geophysics,the sedimentary facies types and characteristics of the SQ1-HST are established.The transgressive system of Qixia Formation of the Lower Permian in the Sichuan Basin(SQ1-TST)is the open-platform facies,and the high level system(SQ1-HST)is the flanger type carbonate platform depositional system,including the facies belts of shallow open platform,deep platform,platform margin,slope and basin.On the basis of single well and well-tie facies analysis,with the guidiednce of the depositional models,the author drawed sequence lithofacies paleogeographic maps and describe the distribution and evolution features of paleogeography.(2)The rock types of dolomite reservoirs are mainly divided into crystalline dolomite and leopard limestone.Reservoir space mainly consists of intercrystalline solution pores,solution vugs,intercrystalline pores and cracks.Dolomite reservoirs can be divided into pore-caveat-fractur type and pore-fracture type.Qixia formation had undergone several types of diagenesis.Compaction and cementation which are destructiveness diagenesis.Shallow-buried dolomitization and multistage dissolution which are constructive diagenesis.(3)The sedimentary microfacies of the high-energy biodetritus beach are thematerial basis of the formation of the dolomite reservoirs in the Qixia Formation.The exposed dissolution of the syngenetic period is a prerequisite for the high quality reservoir.The sea level eustasy have influence on reservoir physical property in the longitudinal direction.TheShallow-buried dolomitization makes the reservoirs initially formed and preserved at a later stage,and the dissolution of fractured and buried corrosive formation water plays a key role in the improvement of reservoirs.Based on the main controlling factors of reservoirs,the Jixian-Ya'an area in western Sichuan is forecasted as the most favorable reservoir development area.