Fracture Diagenesis in Strike-Slip Fault Zones and Its Implications for Reservoir Development in the Central Tarim Basin, NW China

It remains highly challenging to decipher the coupling between multistage fracturing and diagenesis in subsurface strike-slip fault zones. Based on seismic fault analysis, core and thin-section observations, and compiled calcite-cement U–Pb ages and fluid-inclusion data, this study investigates fracture diagenesis and its implications for Ordovician carbonate reservoirs along strike-slip fault zones in the central Tarim Basin. Seismic interpretation shows that faults terminate upward at the tops of the Ordovician carbonate, Silurian–Devonian, and Permian strata, broadly constraining three stages of fault and fracture activity. The fault zones are characterized by multiple fracture sets, variable diagenetic compaction and pressure solution, and multistage cementation and dissolution. The main fracture-diagenetic processes include argillaceous filling, multistage dissolution, calcite cementation, and minor infiltration of hydrothermal minerals, including fluorite, dolomite, and pyrite. Fractured reservoirs are strongly heterogeneous and are mainly confined within fault damage zones. Fracture density, reservoir porosity, and oil and gas production generally decrease with increasing distance from the fault core, although the trends are highly scattered. Integrated geochronological and regional tectonic data indicate that multiple fracture-diagenetic events initiated in the Middle Ordovician and were largely completed before the Carboniferous. These events include Middle Ordovician fracturing, contemporaneous dissolution and karstification, and long-lasting burial and hydrothermal diagenesis during the Late Ordovician, Silurian, Devonian, Carboniferous, and Permian. The results suggest that penecontemporaneous to shallow-burial meteoric dissolution contributed substantially to reservoir porosity in the Ordovician carbonates, whereas early compaction and cementation destroyed most primary porosity. Later multistage fracture diagenesis further modified reservoir quality and enhanced reservoir heterogeneity. These results indicate that intensive fracturing, dissolution, and cementation during early faulting stages, rather than late burial dissolution or hydrothermal activity alone, primarily controlled the formation and distribution of fractured reservoirs. This study highlights fracture diagenesis as an effective approach for reconstructing and evaluating deep ancient fractured reservoirs along fault zones.