Four basic types of whole petroleum systems and their major plays

Although the fundamental principles behind the basic hydrocarbon accumulation and distribution patterns within a whole petroleum system (WPS) are universal, these patterns tend to vary in actual geological settings, reflecting the dialectical relationship between theoretical universality and geological particularity. To address this challenge, we systematically analyze the differences in the hydrocarbon enrichment characteristics of WPSs under varying conditions. The results indicate that the differences in the hydrocarbon accumulation characteristics are determined by three fundamental conditions, i. e., geodynamic setting, reservoir medium, and source rocks, as well as their coupling relationships. Based on the combinations of key hydrocarbon accumulation factors in the three conditions, we classify WPSs into 48 types and propose a nomenclature rule. The results highlight four practically significant WPS types: those with clastic rock sequences, carbonate sequences, coal-bearing sequences, and near-surface special sequences as reservoirs, which are particularly important for further hydrocarbon resource development. Accordingly, we systematically elucidate the fundamental characteristics, hydrocarbon enrichment patterns, and resource potential of the four types of WPSs, demonstrating their respective resource development directions and major plays. Specifically, reservoirs of clastic sequences are governed by diagenesis dominated by typical tightening laws and exhibit shallow buoyancy-driven hydrocarbon accumulation depths (BHADs). In these reservoirs, deep unconventional tight hydrocarbon resources show extensive plays, suggesting broad exploration prospects. Carbonate reservoirs are primarily of the hypergene weathering-related vuggy type, with high-quality intervals potentially preserved in deep to ultra-deep strata. These reservoirs contain a high proportion of conventional resources and hold huge potential for deep to ultra-deep resource development. In coal-bearing sequences, coals exhibit high gas generation and expulsion capacities, while natural gas in peripheral reservoirs shows a wide and continuous distribution. Furthermore, coals with high thermal maturity develop abundant cleats and exhibit anomalously high porosity and permeability, while their peripheral reservoirs demonstrate high sealing performance after gas accumulation. These factors are conducive to free gas enrichment in coal-bearing sequences. The near-surface special sequences, although characterized by complex hydrocarbon accumulation conditions, hold vast resource potential, including heavy oil bitumen, natural gas hydrates, and water-soluble natural gas. Advancing research and development of key technologies, alongside reducing exploitation costs, will facilitate the efficient utilization and rapid development of these resources.