Genetic Mechanism of T₂ Reflector Fault Dense Zones in Northern Songliao Basin

The relationship between T₂ reflector fault and hydrocarbon accumulation reservoir of middle-shallow layer is close, which proves genetic mechanism of T₂ reflector fault dense zones is important for hydrocarbon exploration. Based on the northern Songliao basin regional seismic interpretation, the analysis of the development characteristics and the formation and evolution of fault, we systematically analyze fault deformation mechanism at different stages, which reveal formation mechanism of T₂ reflector fault dense zones and indication of hydrocarbon exploration. This study shows that T₂ reflector fault dense zones have been formed through the following three preriods, namely, the initial faulted period, pre-structure in faulted period, and level detachment of plastic mudstone cap rock and EW tension stress field in Quanyi member. Stretch dense zones of SN tension stress mechanism dominates the region. Accommodation and strike slip accommodation dense zones of NE, NW and EW oblique stretch mechanism is fragmentary in distribution. Sinistral compresso-shear deformation field, half grabens during faulted period and basal huge faults jointly control the formation of subprime anticlines and structural inversion belts during reversed period, meanwhile, fault dense zones of structural inversion belts reform and setting as main NW-NNW by counterclockwise rotation. Edge fault in T₂ reflector NW-NNW fault dense zones of structural inversion belts and SN fault dense zones of structural non-inversion belts are long-term activity, of which matches with hydrocarbon generation and expulsion phase in time. They are oil-migrating faults of hydrocarbon accumulation reservoir in middle-shallow layer.