Exploring the evolution of antithetic normal fault architecture and its constraints on fault transmissibility: Evidence from sand–box simulation experiments

Antithetic normal faults play an important role in the tectono–stratigraphic evolution of extensional basins. These faults also control the regional accumulation and distribution of oil and gas, and form an important channel for oil and gas longitudinal migration. However, the evolution of such faults architecture and their hydrocarbon conduction and accumulation are not well constrained. This work examines the evolution of such fault zones and their oil conduction process by employing sand–box simulations based on the actual antithetic normal fault with coring in the Dongying depression. The study reveals that the antithetic normal fault in semi–consolidated strata evolves from initial small faults based on drag folding, the drag in their damage zones effect also makes some fault properties reverse, and the intermittent dilation zone indirectly improves the physical properties of the secondary fault. The fault displacement controls the longitudinal oil–bearing layers and their saturation in the whole fault zone. The number of oil–bearing layers and their oil saturation decrease with decreasing of the total fault displacement. The longitudinal conduction of the fault is controlled by the displacement of the secondary faults in the damage zone. In semi–consolidated strata, the fault further evolves from drag folds, forming extensional fault–related folds overlapped with secondary faults in the damage zone. The secondary faults control the longitudinal conduction of oil and the drag folds become favorable reservoir space. Thus, the mudstone sealing of the main fault and conduction of the entire fault zone are two co–existing but not contradictory geological processes. The results of this study provide a new way to evaluate the transmissibility of the growth fault in extensional basins.