The Mineral Geochemistry Identification and Its Influence on the Pore Evolution of the Upper Ordovician Carbonate Cements in Tazhong Oil Field

According to the crystal morphology and cementation sequence of the calcite cements, with the aid of cathode luminescence and microelement analysis methods, 11 categories of calcite cements are identified in the fracture cave of upper Ordovician Lianglitage Formation in Tazhong Oil Field in the Tarim Basin; three diagenetic environments, that is, submarine diagenetic environment, the meteoric freshwater diagenetic environment, and buried diagenetic environment are determined. The submarine diagenetic environment is Phase I cementation which mainly produces microcrystalline, fibrous, radial fibrous, fasciculate, and radial-axial calcites and subspherical aragonites with a pore filling of 0–30 %. The meteoric fresh water environment is Phase II cementation and its main cements are crescent or pendant calcite, vadose silt, and syntaxial cement with a pore filling of 5–100 %; Phase III cementation occurs in burial diagenetic environment. The crystals of cement are bright and massive and the main categories are calcsparite and poikilotopic calcite with a pore filling of 5–100 %.