Our genetic classification of petroleum systems is founded on a simple working nomenclature that consists of combining qualifiers from each of the following three categories: (1) charge factor (supercharged, normally charged, or undercharged), (2) migration drainage style (vertically drained or laterally drained), and (3) entrapment style (high impedance or low impedance).

The charge factor is estimated using the initial richness of the source rock and the volume of mature source rock. The source potential index (SPI), which combines source rock richness and net source rock thickness into a single parameter, is a convenient shortcut for comparing the petroleum potential of diverse source rocks containing dissimilar kerogen types and for rapidly estimating regional charging capacity. In extensively explored petroleum provinces that contain a single petroleum system, a positive correlation exists between the magnitude of the SPI and provincewide petroleum reserves.

Migration drainage style is determined from the structural and stratigraphic framework of the basin fill. Vertical migration drainage, which occurs mainly through faults and fractures that breach a seal, is characteristic of petroleum systems in rift basins, deltaic sequences, salt dome provinces, wrench basins, and fold and thrust belts. In contrast, lateral migration drainage is dominant wherever stratigraphically continuous seal-reservoir “doublets” or carrier beds extend over a large area in a tectonically stable province (e.g., foreland or intracratonic platform basins). Recognition of the dominant migration style helps to predict the location of zones of petroleum occurrence in relation to the pod of mature source rock.

Entrapment style, which is also dependent on the structural framework and the presence and effectiveness of seals, describes the degree of resistance (impedance) working against dispersion of the petroleum charge. Application of these working concepts should help to reduce geologic risk significantly, particularly in new ventures exploration.