Strike-slip faults and hydrocarbon accumulation in the eastern part of Fuman oilfield, Tarim Basin

The strike-slip faults in the eastern Fuman oilfield have been targeted for Ordovician ultra-deep carbonate reservoirs in the Tarim Basin. However, they are difficult to be identified and interpreted with available data due to their weak activity, thus it is essential to deeply understand their development, evolution and reservoir-controlling characteristics. Based on the newly acquired 3D seismic data of the oilfield, three typical trunk faults (F_I10, F_I12 and F_I17) are selected for a fine interpretation to clarify the activity characteristics and main faulting stages of the strike slip faults. Combined with oil and gas properties and reservoir-forming stages, the study analyzed the relationship between fault activity characteristics and hydrocarbon accumulation to deepen the understanding of fault development characteristics and hydrocarbon distribution in the area as well as clarifying the coupling relationship between multi-stage evolution of faults and multi-stage accumulation of hydrocarbons. The results show that the strike-slip faults in the Fuman oilfield has the characteristics of vertical stratified differential deformation, which can be divided into four tectonic deformation layers from bottom up: the subsalt basement tectonic layer (below T ${-\mathrm{C}}_2$), salt tectonic layer (T ${-\mathrm{C}}_2$-T ${-\mathrm{C}}_3$), carbonate rock tectonic layer (T ${-\mathrm{C}}_3$-TO₃t) and clastic rock tectonic layer (above TO₃t). The active faulting can be divided into three stages: the early Caledonian, the third episode of the middle Caledonian and the late Caledonian-Hercynian, among which the third episode of the middle Caledonian is the main active faulting stage. Combined with the coupling relationship between the difference of oil and gas properties, the production performance of oil wells, the characteristics of fault activity and the period of hydrocarbon accumulation, comprehensive analyses show that faulting affects the opening of vertical migration pathway and controls the vertical hydrocarbon migration. The faulting lasts for a long time, which keeps the hydrocarbon migration pathways open and is conducive to the continuous charging of late highly mature oil and gas, resulting in fault-controlled reservoirs characterized by high hydrocarbon charging intensity, high maturity and high gas-oil ratio.