Study on the genesis of carbonate cements in tight and non-tight sandstone reservoirs in Fukang Sag

Carbonate cements characterization and reservoir genesis mechanism are the key geological issues constraining the current deep oil and gas exploration. The relationship between carbonate cementation and oil and gas filling time can affect reservoir reserves. In this paper, the tight and non-tight sandstone reservoirs of the Middle Jurassic in Fukang Sag of Junggar Basin are taken as the research object. The petrology, sedimentary microfacies, diagenesis, porosity and carbonate cements of tight and non-tight reservoirs are compared by means of casting thin sections, scanning electron microscope (SEM) and carbon and oxygen isotopes. The research shows that the tight reservoirs and non-tight reservoirs of deep sandstone in Fukang sag are similar in rock type and sedimentary microfacies, they are all feldspar lithic sandstone. The reservoirs are mainly developed in underwater distributary channels and estuary sand dams. There are obvious differences in the strength of compaction and pore types. Although they all contain carbonate cements, their genesis and formation time are obviously different. The results show that the carbonate cements in the non-tight sandstone reservoirs of the Toutunhe Formation are mainly of Microbial sulfate reduction (BSR) origin, which are formed in the process of reservoir failure. The formation of carbonate mineral cements in tight sandstone reservoirs of the Badaowan Formation and Sangonghe Formation is mainly related to the decarboxylation of organic acids, which are mainly formed in the process of hydrocarbon accumulation. The research in this paper can provide theoretical guidance for exploration and development in the future of the 4th Block of central Junggar Basin and similar research areas.