Research On Eogenetic Karst Of Marine Carbonate And Its Reservoir In The Three Major Basins,Western China

As oil and gas explorations of the carbonate reservoir in Sichuan,Ordos and Tarim Basin get into deeper,more and more landscapes formed by dissolution of carbonate rocks are hard to explain by the traditional theories of telogenetic karst or weathered crust karst.Combining with the new advance of eogenetic karst from abroad,we consider the carbonate reservoir seems to be related with the eogenetic karstification.Therefore,this paper studies eogenetic karst and its carbonate reservoir.Based on the massive relevant literatures,combining with multi-angle,including the karst host rocks,geographical settings,exposure time and the controll of carbonate sequence stratigraphy on karstification time,we try to classify the eogenetic karst to two parts,ie.syngenetic-penecontemporaneous karst and early-supergene karst.Through living example of multi-layer in three basins of western China,we discuss the identification,feature,spatial distribution and controlling factors of syngenetic-penecontemporaneous karst and early-supergene karst,summarize meteoric fresh water len model of syngenetic-penecontemporaneous karst,inland facies-controlled model and coastal mixing dissolution model of early-supergene karst.Combining theory with practice,we discuss the characteristics and distributions of reservoir,karstification contribution to the reservoir and the superposition reconstruction of late diagenesis,summarize the forming models of different eogenetic karst reservoir.The fonning models of syngenetic-penecontemporaneous karst reservoir can be divided into the sedimentary-preservation type and the modified-preservation type,and that of early-supergene karst reservoir can be classified as the karstification modified type,karstification-dolomitization modified type and tectonism-karstification-dolomitization modified type.Finally,the exploration status of three basins in western China indicate that the eogenetic karst reservoir is developed "well and has a great exploration potential.The intense research for eogenetic karst is of great significance for studies of the subject and oil&gas geology.