Discovery of strike-slip faults and their evolution on Trakes Slope, Termit Basin in Niger

Research on strike-slip faults and their control on the accumulation and distribution of oil and gas in petroliferous basins plays an important role in guiding oil and gas exploration activities. Based on the interpretation and analysis of seismic and drilling logging data, the geometry, evolution process, genetic mechanism and control on the accumulation of oil and gas of strike-slip faults in the Termit Basin are studied by applying coherent techniques. The results show that the strike-slip faults in the Termit Basin are mainly developed in the Trakes Slope in the eastern margin of the basin. The principal displacement zone of these strike-slip faults extending mainly in NNW-SSE and NW-SE, their en-echelon extension fractures (T fracture) are in south-north trending with dextral movement and right-lateral stepping. Most of these strike-slip faults are transtensional faults with few transpressional faults. Negative flower structures and Y-style fault combinations are widely developed, while straightly steep faults andpositive flower structures are locally developed. These strike-slip faults are the result of Cretaceous normal faults subjected to later shear stress in Paleogene Eocene Oligocene. The strike-slip mechanism is that differentially transverse compressive stress between blocks induces shear deformation of early normal faults. Since the Paleogene, the collision accumulation effect of the Eurasian plate and the African plate has formed a near-EW compressive stress inside the African plate. The nonhomogeneous distribution of stress at the northern boundary of the African plate caused differential movement between the Northwest African block and the Northeast African block, which induced the transformation of the Early Cretaceous normal faults on the Trakes Slope into a transtensional strike-slip faults. This series of strike-slip faults formed a group of antithetic fault block traps in Paleogene Sokor1 Formation,Sokor2 Formation and the Upper Cretaceous Yogou Formation, and these strike -slip faults are also vertical migration channels for oil and gas, which are beneficial for the hydrocarbon generated by Upper Cretaceous source rocks to migrating upward and accumulating in the Paleogene reservoirs.