Architecture of strike-slip fault zones in the central Tarim Basin and implications for their control on petroleum systems

Abstract

The strike-slip fault zones (SSFZs) of the central Tarim Basin have great potential for hydrocarbon exploration and development. They can both serve as hydrocarbon migration paths and host hydrocarbons. However, the complexity of SSFZ varies significantly along the fault strike, and strike-slip fault-controlled deeply buried carbonate reservoirs are often extremely heterogeneous, increasing exploration risks. Here, we reconstructed the architecture and setting of the SSFZ of the central Tarim Basin and analyzed the complex and heterogeneous hydrocarbon system that characterizes this exploration area.The integrated seismic and well datasets show that the development of SSFZs has led to the fracturing of tight carbonates and enhancements in the karstification process, secondary porosity and permeability due to the presence of open fractures. Based on the vertical height of the fault in the section and continuity, the SSFZs in the central Tarim Basin have been classified as 1st-order or 2nd-order faults. The 1st-order faults are found in the repeatedly reactivated vertical SSFZ, which is composed of sub-vertical strike-slip faults in the Paleozoic strata and en-echelon normal faults in the shallow layer. The 2nd-order faults develop only in Paleozoic strata without reactivated features. Continuous through-going, hard-linked 1st-order faults are a more valuable target for future exploration than soft-linked 2nd-order faults because 1st-order faults control larger-scale fracture-cavity reservoirs, and their fault activity periods correspond to hydrocarbon accumulation periods. We classified damage zones as wall-, and linking-damage zones, based on their location around the fault. There are two types of linking-damage zones, extensional steps and contractional steps, which develop in the extensional and contractional quadrants of the fault segment, respectively. Linking-damage zones are associated with more structural complexity than narrow and straight wall damage zones. Fractures in the contractional steps are generally closed and have low conductance, which is not suitable for fracture-cavity trap formation and hydrocarbon migration. Because opening-mode fracture development and permeability enhancement are greatest at the extensional steps, these locations are more likely to be important foci for strike-slip fault-controlled carbonate reservoirs. Our findings, in combination with previous research, indicate that fault zones in the central Tarim Basin, act as combined conduit-barrier systems, with damage zones typically featuring highly conductive fracture networks and fault cores acting as seals, resulting in heterogeneous reservoir distributions.