Strike–Slip Fault-Associated Paleokarst Systems: A Comparison Between the Tarim Basin, NW China, and Monts de Vaucluse, SE France

Important hydrocarbon resources are preserved in deeply buried (>6500 m), intensely karstified Ordovician carbonates of the Tarim Basin, where reservoir development is closely associated with strike–slip fault systems. However, the links among faulting, karstification, reservoir formation, and subsequent diagenetic modification remain poorly understood because of the complex tectonic and burial history of the basin. In this study, we compared deeply buried Ordovician karst reservoirs from the Halahatang oil field in the Tabei Uplift, Tarim Basin, with near-surface Cretaceous karst systems at Fontaine de Vaucluse, southeastern France. Both of these systems were influenced by multiphase strike–slip faults. Despite their contrasting deposition timing and burial histories, the two systems exhibited comparable linear reservoir distributions controlled by a sequential evolution process that formed under compressional stress. In both cases, diagenetic fluids were characterized by mixing between two end-members, meteoric water and formation water, although they may have been circulated to different depths. Moreover, epigenic karstification was the principal mechanism of reservoir formation in both cases, although hypogenic products occur locally. These similarities indicated that the deeply buried (>8000 m) Ordovician paleokarst reservoirs of the Halahatang area formed primarily because of fault-controlled epigenic karstification and associated meteoric-water diagenesis. This comparative framework increases our understanding of the evolution of ultradeep carbonate reservoirs and has implications for hydrocarbon exploration in the Ordovician carbonates of the Tabei Uplift.