Dynamic equilibrium in hydrocarbon charging and leakage of an intensively overpressured reservoir

In active petroleum systems, hydrocarbon charging and leakage often occur simultaneously. Establishing the relative relationship between reservoir charging and leakage is crucial for hydrocarbon exploration and reserve assessment. This study investigates the dynamic equilibrium between gas charging and leaking in a sandstone reservoir using high-resolution seismic, wireline logging, and well testing data from the LD10 gas field in the Yinggehai Basin, South China Sea. Fluid migration pathways, including top seal breaches, are depicted by utilizing attribute extraction and volume rendering. The fluid pressure distribution is characterized through measured and predicted pressure data. The charging episodes are identified by carbon isotope compositions. Our results show that gas-bearing fluids were charged from source rocks into the channel sandstone reservoirs in the Upper Miocene Huangliu Formation through positive flower faults The fluids subsequently migrated to higher sandstone intervals via hydraulic fractures. Leakage occurred through normal faults developed at the top of the channels, penetrating the seal of the upper Huangliu Formation. Our findings provide insights into fluid migration mechanisms in deep overpressured environments in sedimentary sequences.