Fault seal behavior in porous sandstones: A case study from the Bozhong subbasin, Bohai Bay Basin, China

ABSTRACT Faults in porous sandstone were previously considered ill-suited for sealing hydrocarbons, which resulted in many promising fault-related hydrocarbon exploration targets being overlooked. This study investigates the sealing properties of faults within porous sandstone in the Bozhong subbasin using well drilling data and repeat formation test pressure measurements from both sides of the faults. The results demonstrate that the faults in the porous sandstone could seal hydrocarbons, with the maximum sealable hydrocarbon column height reaching 83 m and the buoyancy pressure reaching 0.223 MPa. Owing to the low clay content (<10%), high porosity (>15%), and moderate burial depth (1–3 km) of the host rock, cataclasis associated with fault deformation may generate low-permeability cataclasite, which is regarded as the most probable sealing mechanism for faults in porous sandstone. Increased effective fault normal stress during fault movements intensifies sandstone grain cataclasis, further reducing fault permeability and enhancing the fault sealing capacity. A positive correlation was identified between fault sealable buoyancy pressure and effective fault normal stress. These findings highlight the importance of considering stress effects, in addition to clay content, when evaluating the sealing capacity of faults in sand–mudstone sequences. Neglecting the role of stress may lead to underestimation of the fault sealing potential, particularly for faults in porous sandstones. More research is needed to evaluate the sealing capacity of faults in porous sandstone. In addition, data sharing and cooperation between industry and academia should be encouraged so that, in the long run, workflows can be developed specifically for faults in porous sandstones.