Multiple fracture, dissolution, and cementation events of Ordovician carbonate reservoirs in T-SH Oilfield, Tarim Basin

Strike-slip fault plays an important role in reservoir development in T-SH area of Tarim Basin. The fractures and calcite cements of Ordovician reservoir in strike-slip fault are identified and divided through core and thin section observation, and the diagenetic stage and environment are determined through isotope analysis and fluid inclusion temperature measurement. The study shows that mottled fabric is a distinctive characteristic of Ordovician reservoir and the basis for identifying fractures and internal cements. Ordovician reservoir in T-SH area has four stages of diagenesis, which can be further divided into shallow diagenetic environment (stage 1), middle diagenetic environment (stage 2), and deep diagenetic environment (stages 3, 4). The development characteristics of asphalt and fluid inclusions in the reservoir reveal that there are two stages of hydrocarbon filling in the study area. The first hydrocarbon filling occurred in the stage 2, which began in the late Caledonian and was destroyed in the Early Hercynian. The second hydrocarbon filling occurred in the stage 4 (from late Hercynian to Indosinian), which is the main hydrocarbon accumulation period of Ordovician reservoir in T-SH area. Through comprehensive analysis of petrology and geochemistry, it is considered that the main diagenetic fluid of the reservoir is upward deep-buried diagenetic and hydrocarbon fluid caused by strike-slip fault. The period of hydrocarbon filling is closely related to the period of fault movement, indicating that fault movement and diagenesis are the key factors controlling the period of hydrocarbon accumulation.