Genesis of Carbonate Cement and Its Effect on Trap in Donghe Sandstone,Halahatang-Hadexun Area in Tarim Basin

ssociations. Slice and cathodoluminescence analyses show the carbonate cements include more calcite, some ferrocalcite and ankerite, and few dolomite. The carbonate cement usually deposits after quartz overgrowth, and fills in intergranular dissolved pore, feldspar and lithologic fragments dissolved pore, or occurs metasomatic processes of detrital grain. The results of carbon and oxygen isotope show δ13CPDB is –2.8～–7.7‰，average –4.7‰；δ18OPDB is –11.8～–16.6‰，average –14.7‰. With comprehensive analysis, the genesis of carbonate cement in Donghe sandstone has four types: organic acid decarboxylation, erosion and solution genesis of Ordovician carbonate, biogenesis and exposed sedimentogenesis. According to logging analysis, there is a significant negative correlation between the content of carbonate cement and porosity and permeability of reservoir. When the content of carbonate cement is more than 10%, the sandstone cements tight with poor physical property.The dense layers of carbonate cement distribute along unconformity, slope area or structural high part, which forms safeguard as the lateral sealing layers, local floor and cap rocks of hydrocarbon trap. This paper changes the opinion of people that Donghe sandstone as beach sand is not a strongly heterogeneous reservoir and the carbonate cement has no benefit to hydrocarbon trap.