Determination of the Diversion Period of Hydrocarbon Migration from Faults to Sand Bodies: A Case Study of the Nandagang Fault in the Southern Qikou Sag of the Bohai Bay Basin

In order to accurately portray the oil and gas enrichment patterns near oil source faults in the "lower generation and upper storage" in petroliferous basins, we put forward a methodology for ascertaining the diversion period of hydrocarbon migration from fault to sand body, with the Nandagang Fault in the southern Qikou Sag in the Bohai Bay Basin serving as a case in point. The initial step was to couple the period of active faults with hydrocarbon supply to the accumulations inside and outside of the underlying source rock, with the objective of determining the hydrocarbon transport period of faults. Subsequently, the sand body's oil and gas transport period was determined based on the time taken to form a seal in the overlying regional mudstone cap rock. Finally, the coupling period between the two was employed to ascertain the diversion period. The results indicate that the hydrocarbon transport period of the Nandagang Fault extends from the early to the late stages of the Neogene Minghuazhen Formation's (Nm) deposition. The sand body's oil and gas transport period spans from the end of the Paleogene Shahejie Formation's (Es) deposition to the present day. The hydrocarbon diversion migration from the Nandagang Fault to the sand body occurred from the early to the end of the deposition period of the Nm Formation. This relatively long diversion period is conducive to hydrocarbon transport, which coincides with the magnitude and extent of actual hydrocarbon enrichment. This study contributes to effectively guiding oil and gas exploration in the vicinity of faults.