Characteristics, Distribution Patterns, and Classification of Volcanic Reservoirs in the Huanghua Depression, Bohai Bay Basin, China

Identifying volcanic reservoir types and their distribution patterns in volcanic edifices is important for accurate prediction and exploration of hydrocarbon reservoirs. Herein, we analyzed the distribution patterns of different reservoir levels in volcanic edifices, discussed controlling factors, and reclassified reservoir types. This was done using core observations, whole-rock geochemistry, and reservoir physical property analysis, combined with logging, drilling, seismic, and oil-gas test data. Reservoirs can be divided into three classes based on their physical properties. The Mesozoic intermediate and basic rocks formed Class I reservoirs, most lithologies formed Class II reservoirs, and diabase intrusions and tight volcanic rocks formed Class III reservoirs. Reservoirs form in different lithologies in the Huanghua depression due to weathering. Tectonic faults deepen the influence of weathering leading to the formation of reservoirs in tight. Additionally, volcanic rhythms and fractures control the vertical distribution of Cenozoic basaltic reservoirs. Volcanic reservoirs are classified into five types based on the main controlling factors and distribution patterns in volcanic edifices: tectonic-alteration, vesicle-fracture, weathered-effusive, weathered-eruptive, and weathered-tectonic types. Among these, the weathered-eruptive type can easily form Class I reservoirs, making it the best target for exploration. Whereas the weathered-tectonic and vesicle-fracture types tend to develop Class II reservoirs and can be potential targets. The new classification takes into account the relationship between reservoir levels and their distribution in volcanic edifices, it is more conducive to igneous reservoir prediction in the Huanghua depression. This study provides a novel idea for the classification and comparative study of igneous reservoirs in petroliferous basins.