Genetic Classification of Petroleum Systems

DEMAISON, G., Consultant, Capitola, CA, and B. J. HUIZINGA,* Chevron Oil Field Research Co., Richmond, CA

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

The charge factor is estimated on the basis of the richness and volumetrics of mature source rocks. The source potential index (SPI), which combines source-rock richness and thickness into a single parameter, is a convenient shortcut for comparing the petroleum

potential of different source rocks containing dissimilar kerogen types and for rapidly estimating a basin's regional charging capacity. On a global scale, a general correlation exists between the magnitude of SPI and basinwide petroleum reserves.

The dominant migration drainage style can be predicted from the structural and stratigraphic framework of a basin. Vertical-migration drainage, which occurs mainly through faults and fracture systems breaching a seal, is characteristic of rift basins, deltaic sequences, salt-dome provinces, and fold-and-thrust belts. Lateral migration drainage dominates wherever continuous seal-reservoir "doublets" extend over large areas in a tectonically undisturbed regime (e.g., commonly found in 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 "hydrocarbon kitchens."The entrapment style, which is also dependent on the structural framework and the presence of seals, describes the degree of resistance (i.e., impedance) working against dispersion of the petroleum charge.

Application of these working concepts should help significantly reduce geologic risk, particularly in new ventures-type exploration.

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)