Analysis of Fault Sealing Capacity with Low-Offset in High Net/Gross Ratio Sequences: Insight from a Field of Bohai Bay Basin

Low-offset faults usually exhibit weak sealing in sand‒clay sequences. To evaluate the lateral sealing mechanism of low-offset extensional faults in high net/gross ratio sequences, a case study of a production field is introduced in this paper. The analysis of oil and water drilling data indicated that the fault in the JZ23-2 region separates oil and water on both sides of the fault. Based on the empirical fault seal calibration workflow, we investigated the lateral sealing capacity of low-offset faults in sand-dominated sequences in this study. The lithology juxtaposition triangle diagram shows that the fault sealing type mainly encompassed fault rock sealing. By establishing the relationship between the shale gouge ratio (SGR) and across fault pressure difference (AFPD), it could be observed that the fault sealing ability linearly increases with increasing SGR of the fault zone. The calculated AFPD varies between approximately 0 and 0.1 MPa, and the maximum hydrocarbon column height reaches up to 90 m. The lower limit of the critical SGR for lateral sealing of the control fault is 9.2%, which differs from the critical value published. Combined with reservoir core microscopic characteristics, it was demonstrated that under the condition of a low critical SGR, the internal fragmentation and cataclasis of the host rock are the main controlling factors influencing the fault lateral sealing ability and determining the pressure difference between both sides of the fault. With this research, the study of the lateral sealing capacity of small-scale faults is extended, which provides a certain sealing capacity and exploration value.