Carbonate Diagenesis Of Member5₄～6of Majiagou Formation In Fuxian Region, Ordos Basin

The study area of this paper is Fuxian area, located in the southeast of Shanbei slope inOrdos basin. And the study section is member54～6of Ordovician Majiagou Formation. Inorder to figure out its lithologic character and main diagenesis, this paper adopts manyresearch methods and means, such as core description, thin section identification,cathodeluminescence, scanning electron microscopy, electron probe, and carbon and oxygenisotope analysis. The study result shows that the main rock types of member54～51includedolomicrite, corrosion carneule, dolarenaceous, dolorudite, sparry oolitic dolomite, andsecondary limestone, while the main rock types in member6are micritic limestone andbrecciola. And these rocks experienced near surface diagenesis environment, shallow burialdiagenetic environment, epidiagenetic environment and deep burial diagenetic environment.The diagenesis includes constructive diagenesis and destructive diagenesis.Penecontemporaneous dolomitization, seepage reflux dolomitization, dissolution, anddedolomitzation are called constructive diagenesis, since they are beneficial to thedevelopment of reservoir pores, while destructive diagenesis such as pressure solution,cementation, and recrystallization has negative effect on the development of reservoir pores.The reservoir space of carbonate rocks is mainly intercrystalline pore, intercrystalline solutionpore, gypsum mould hole, salt mould hole, karst cave and crack.The reservoir is characterized by ultra-low porosity, low permeability and strongheterogeneity.