Intracratonic strike-slip faults have been recognized as a major factor controlling the formation of fracture-cave carbonate reservoirs in deep buried basins, yet which properties and how the strike-slip faults influence reservoir distribution and their connectivity are still ambiguous. This uncertainty significantly restricts hydrocarbon exploration and development, such as in the Fuman oilfield, northern Tarim Basin, NW China. Using a high-resolution 3D seismic reflection survey and borehole data, we investigated the geometry and kinematic evolution of the F_I17 fault zone in the Fuman oilfield. This fault zone is characterized by a single fault zone, pop-up or pull-apart structures, right-stepping en echelon normal faults, and much smaller displacement (<30 m) normal fault arrays from bottom to top. The F_I17 fault zone consists of four genetic segments, including the extensional strike-slip duplex, Riedel left-lateral shear, right-stepping horsetail splay, and horizontal slip segments in map view. In particular, the formation of the ∼18 km Riedel shear zone is characterized by the growth and linkage of segmented shear faults (synthetic and secondary synthetic shears). We observed that the large-scale fault-controlled fracture-cave reservoirs are distributed in positions with wider fault zones, which are characterized by overlapping of neighboring secondary shear faults. Furthermore, the reservoir width examined in this study is natural logarithmic correlated (positively) to the fault zone width. The reservoirs linked by the same shear faults show better internal connectivity. The spatial coherence between fault geometry and reservoir features indicates that segmentation and lateral growth of intracratonic strike-slip faults controls the occurrence of fracture-cave reservoirs, which may provide support for reservoir prediction in the Fuman oilfield and other deeply buried fault-controlled carbonate reservoirs in general.

Siliceous minerals with the property of resistance to diagenetic alteration precipitate during the migration of hydrothermal fluids through strike-slip faults and the interaction of these fluids with host rocks during fault activity. Based on petrological analyses and U-Pb dating of siliceous minerals, the stages of strike-slip faulting of the ultra-deep-burial Ordovician in the Fuman oilfield were subdivided and their evolutionary process was discussed in combination with seismic interpretation. The results reveal the following: (1) the strike-slip faults contain hydrothermal siliceous minerals, including cryptocrystalline silica, crystalline silica, and radial silica. (2) Based on the twelve U-Pb ages of siliceous minerals (ranging from 458 ± 78 Ma to 174 ± 35 Ma) and five U-Pb ages of calcite, the activity of the strike-slip faults was divided into six stages: the Middle Caledonian, Late Caledonian, Early Hercynian, Middle Hercynian, Late Hercynian, and Yanshanian, corresponding to twelve siliceous U-Pb ages ranging from 458 ± 78 Ma to 174 ± 35 Ma, and five calcitic U-Pb ages. The Late Caledonian and Early Hercynian were the main periods of strike-slip fault activity, while the Late Hercynian period marked the final period of the fault system. (3) Later-stage faults inherited and developed from pre-existing faults. Steep linear strike-slip faults formed during the Middle and Late Caledonian movements. During the Late Hercynian and Yanshanian movements, mid-shallow faults, branch faults, and shallow echelon faults developed on the foundation of these linear faults. The methods and results of this study can guide future hydrocarbon exploration in the Fuman oilfield and can be applied to areas with similar tectonic backgrounds.