Study on the Vertical Transport Capacity of Prematurely Failed Faults in Deep Oil and Gas Enriched Areas: A Case Study of Lufeng 13 Sag in the Pearl River Mouth Basin

     With the continuous development of deep oil and gas exploration, the phenomenon of oil and gas enrichment near prematurely failed source faults in deep formations has been revealed. However, the mechanism of how these prematurely failed faults open to transport hydrocarbon is not yet clearly understood, and there is a lack of quantitative evaluation of their transport capacity. This study takes the Lufeng 13 Sag in the Pearl River Mouth Basin as an example. Based on 3D seismic data, software simulation, and mudstone plastic deformation experiments, it analyzes the reactivation mechanism of prematurely failed faults and evaluates their vertical transport capacity, revealing the role of these faults in deep hydrocarbon enrichment. The study shows that the transport capacity of prematurely failed faults is negatively correlated with the normal stress on the fault plane during the reservoir-forming period and positively correlated with the ultimate pressure for mudstone plastic deformation. When the normal stress on the fault plane during the reservoir-forming period is less than 13.9 MPa, the buoyancy of hydrocarbon can overcome the normal stress on the fault plane at the upper interface of the source rock, allowing hydrocarbon to migrate upward along the fault. When the ultimate pressure for mudstone plastic deformation is greater than 18.5 MPa, the pressure on the fault plane is less than the ultimate pressure for mudstone plastic deformation, and the argillaceous components in the fault zone do not undergo plastic deformation and flow. The leakage spaces left in the fault zone are not blocked, and no seal is formed vertically. Based on the normal stress on the fault plane during the reservoir-forming period and the ultimate pressure for mudstone plastic deformation, a vertical transport coefficient (K) for prematurely failed faults is established. When K is less than 1.1, the prematurely failed fault has vertical transport capacity during the reservoir-forming period.