Filling characteristic and formation mechanism of strike-slip fault-controlled reservoirs in the Mangar Sag, Tarim Basin

Abstract The formation and preservation mechanism of ultra-deep carbonate reservoirs are crucial fundamental scientific issues that constrain the exploration and development of ultra-deep oil and gas. This study focuses on the strike-slip fault-controlled reservoirs in the Mangar Sag of the Tarim Basin, using core samples, thin sections, geochemical data, and production data as the basis. By analyzing the characteristics and genetic mechanism of the fillings in carbonate reservoirs, we investigate the impact of faulting and diagenesis on fault-controlled reservoirs. The results show that the fillings in ultra-deep fault-controlled reservoirs mainly consist of clay, silica, and carbonate materials. These fillings indicate multiple stages of faulting and diagenesis, including dissolution, filling, cementation, and recrystallization processes. Fault-related diagenesis is primarily developed during the early diagenetic stage, with some occurrences during the later hydrothermal burial stage. The faulting, diagenesis, and hydrodynamic conditions control the upper and lower stratified karst reservoirs. Large-scale karst reservoirs are mainly formed during the early diagenetic stage, while later hydrothermal dissolution and filling processes only inherit and modified the early reservoirs. This study provides a case for the formation timing and mechanism of ultra-deep carbonate reservoirs in the Tarim Basin and offers insights into the research of ultra-deep carbonate reservoir mechanism.