Abstract: The lateral sealing of small displacement faults determines the capacity of fault traps to accumulate oil and gas. With the development of oil and gas exploration technology theories, the role of small displacement faults, which were once overlooked, is becoming increasingly prominent in the process of oil and gas exploration and development. To clarify the internal structural characteristics of small displacement faults and the influence on the lateral sealing of faults, a self-developed high-pressure and low-speed circular shear device was applied. Taking the effective normal stress of the cross-section as a variable, it conducts circular shear physical simulation experiments on high porosity pure sandstone to analyze effective normal stress on the lateral sealing of faults. The results show that the fracture mechanism is mainly characterized by fragmentation in high porosity and pure sandstone, forming typical fragmented fault rocks. The significant decrease in permeability is the fundamental reason for the lateral sealing of the joint section of sandstone in the same formation. Under the condition that other factors remain unchanged, the larger the effective normal stress of the cross-section, the greater the degree of fragmentation of the fault rock, and the smaller the particle diameter and porosity; the fracture of rock particles and the filling of detrital matrix lead to a significant decrease in porosity and permeability of the fracture zone. The effective normal stress of the fault section is the main controlling factor of the lateral sealing capacity of the small displacement fault. Small displacement faults have the potential of oil and gas accumulating. The study results have guiding significance for the exploration and development of fault-block oil and gas reservoirs in rift basins.

Key words: small displacement fault, effective normal stress, circular shear, permeability, lateral sealing, Bohai Sea