Thermal anomaly profiles inferred from fluid inclusions near extensional and strike-slip faults of the Liaodong Bay Subbasin, Bohai Bay Basin, China: Implications for fluid flow and the petroleum system

Different types of faulting may greatly impact the flow of hot fluids and related thermal anomalies, which may substantially affect the migration and accumulation of petroleum. However, little is known about the effects of fault types. In this study, 64 core samples were collected from localities controlled by extensional and strike-slip faults in the Liaodong Bay Subbasin, Bohai Bay Basin, and fluid inclusions in these samples were used as thermal indicators of paleo-fluids. The results show strong thermal anomalies near the extensional and strike-slip faults due to the flow of hot fluids. The highest anomalies were recorded at localities proximal to the faults: 134.4 °C at a distance of 375 m from an extensional fault and 145.5 °C at a distance of 262.5 m from the strike-slip fault. However, these anomalies are all local and decrease with increasing distance from the faults, up to a maximum distance of approximately 3000 m. Compared with those near the strike-slip fault, the anomalies near the extensional faults decrease more slowly and typically exhibit higher anomalies at similar distances, which indicates that the extensional faults are better pathways for the flow of hot fluids. The thermal effects of hot fluids have enhanced the maturation of organic matter and shifted the threshold depth for petroleum generation upward by approximately 300 m. Such effects on source rock maturation decrease with increasing distance from the faults, up to a maximum distance of approximately 3000 m. Most Ro values near the extensional faults are clearly higher than those near the strike-slip fault. Thus, the extensional faults play a more efficient role in the enhancement of source rock maturation and are interpreted as preferential pathways for the migration of generated hydrocarbons in the Liaodong Bay Subbasin.