Sandy-conglomerate reservoir has gradually become a major target of oil and gas explora-tion.Complex diagenetic process and diagenetic fluid play a significant role in affecting reservoir hetero-geneity.Carbonate cements form at various stages of the diagenesis process and record various geological fluid information.Recently,one-billion-ton sandy conglomerate oil field was exposed in Triassic Bai-kouquan Formation,Mahu sag,Junggar Basin.Therefore,an integrated study applying casting thin sec-tions,cathodeluminescence,fluorescence,carbon and oxygen stable isotopes,electronic probe microanal-ysis and aqueous fluid inclusions measurements was performed in order to identify the types of carbonate mineral and its representative diagenetic environment and discuss the influences of different CO2 injec-tions on reservoir quality.The main findings are as follows:The reservoir is mainly composed of 70.33％conglomerate and 16.06％coarse-grained sandstone.They are characterized by low compositional ma-turity and abundant lithic debris.Four types carbonate cements are identified according to the petrological and geochemical characteristics,including two types of Mn-rich calcite,ferroan calcite,siderite and daw-sonite.They display an unusual broad spectrum of δ13C values(-54.99‰ to+8.8‰),suggesting both or-ganic and inorganic CO2 injections.The δ13C values of siderite are close to 0,and its formation is related to meteoric water.The δ13C values of ferroan calcite and the occurrence of dawsonite indicate the trace of inorganic mantle-derived magmatic fluids.The δ13C values and trace elements of Mn-rich calcite record the information of hydrocarbon-bearing fluids.The fluid inclusions measurement data and reservoir prop-erties and oil-test data show that the oil content of reservoir is not only affected by the formation time of different cements,but also by the relative content of dissolution and cementation.For these reservoirs altered by carbonate cements,it does not cause poor oil-bearing due to blockage of secondary minerals.