Mechanisms and models of conversion between conventional and unconventional hydrocarbon reservoirs during the formation and evolution of the whole petroleum system

The theory of the whole petroleum system (WPS) defines the orderly distribution of conventional, tight, and shale reservoirs, providing an important theoretical basis for the combined evaluation, exploration, and exploitation of conventional and unconventional hydrocarbon reservoirs. However, during the evolution of the WPS, complex hydrocarbon reservoirs are formed by the superimposed, composite hydrocarbon accumulation processes characterized by multiple driving forces, multiple stages, and diverse elements. It’s hard to identify and explain these complex reservoirs using the orderly distribution pattern of various hydrocarbon reservoirs. Based on dynamic hydrocarbon accumulation processes, we categorize and analyze typical hydrocarbon reservoirs across six major basins of China. Furthermore, we explore the mechanisms controlling the conversion between conventional and unconventional hydrocarbon reservoirs during the evolution of the WPS. The results indicate that all types of hydrocarbon reservoirs exhibit genetic correlations according to the basic principle of the WPS. As hydrocarbon dynamic fields evolve, the formation and development of deep media (especially carbonate reservoirs) are governed by compaction and diagenesis, while intensively reformed by geofluid activities and tectonic stress, among others. A distinctive distribution pattern of hydrocarbon reservoirs occurs as a result. Systematic analysis reveals four conversion models between conventional and unconventional hydrocarbon reservoirs, namely, compaction-induced tightness, stress reformation, geofluid reformation, and special medium reformation. The combined effects of multiple geological processes lead to more complex hydrocarbon accumulation characteristics and reservoir distribution patterns. This study holds great significance for deepening the understanding of the dynamic evolution process and mechanisms of the WPS, providing a theoretical basis for determining the formation and distribution patterns of hydrocarbon reservoirs in the WPS under complex geological conditions.