Strike-slip fault control on karst in ultra-deep carbonates, Tarim Basin, China

Karst reservoirs in the Ordovician carbonates of Tarim Basin are currently major targets of deep and ultra-deep hydrocarbon exploration and development in China. New drilling and seismic data show that these deep-buried carbonate karst reservoirs are spatially dependent on strike-slip faulting. Based on the geological and geophysical data, this study developed an attempt to determine the impact and spatial distribution of strike-slip faulting on carbonate karst reservoirs in the Tahe oil field. Strike-slip faults in the Taha area can be classified as first order, second order, and third order. Fault damage zones are distributed along the strike-slip faults, and their widths have a positive correlation with fault order. Influenced by strike-slip faults, fault-related fractures, and rock mechanical properties, the development degree and spatial distribution of carbonate karst reservoirs display strong heterogeneity. The horizontal heterogeneity of karst reservoirs is controlled by strike-slip faults with different scales and strikes, and the vertical heterogeneity is combined results of the strike-slip faulting and mechanical properties of carbonates. In the Tahe area, ultra-deep carbonate karst reservoirs are generally concentrated within 550 m (∼1800 ft) of the damage zone of north-northeast– and north-northwest–striking first-order and second-order strike-slip faults. Fewer and smaller-scale karst reservoirs are developed further away from the fault core. Additionally, fracture intensity is greater in more brittle facies enhancing the karstification. The results from this research provide an analogue for understanding the distribution of fault-controlled karsting in deep carbonate reservoirs around the world.