Genetic Classification of Petroleum Basins

Gerard Demaison, Bradley J. Huizinga

Rather than relying on a descriptive geologic approach, this genetic classification is based on the universal laws that control processes of petroleum formation, migration, and entrapment. Petroleum basins or systems are defined as dynamic petroleum-generating and concentrating physico-chemical systems functioning on a geologic space and time scale.

A petroleum system results from the combination of a generative subsystem (or hydrocarbon "kitchen"), essentially controlled by chemical processes, and a migration-entrapment subsystem, controlled by physical processes.

The generative subsystem provides a certain supply of petroleum to the basin during a given geologic time span. The migration-entrapment subsystem receives petroleum and distributes it in a manner that can lead either to dispersion and loss or to concentration of the regional charge into economic accumulations.

Key factors controlling petroleum proliferation in a basin are charge volume, migration drainage, and trap availability.

The charge factor can be estimated on the basis of mature source rock volumetrics expressed as an organic facies-weighted ratio between the volume of active source rocks and the overall sealed-in, drained sedimentary volume. Furthermore, the source prolificity index (SPI), a number that integrates average hydrocarbon yield and source rock thickness, allows sedimentary basins to be ranked according to their petroleum charging ability.

In the drainage factor, combinations of vertical and lateral migration drainage always exist. The point is to recognize which is dominant in controlling regional petroleum concentration mechanisms. Vertical-migration drainage, through faults and fractures, often predominates in rift basins, Tertiary deltas, hanging-wall plays in thrust belts, and salt-dome provinces. Lateral-migration drainage predominates wherever stratigraphically continuous seal-reservoir doublets extend over very large areas in tectonically simple, relatively stable regimes (e.g., platform basins, either foreland or intracratonic).

The entrapment factor is directly proportional to the degree of resistance (i.e., impedance) against physical dispersion of the petroleum charge. Impedance is dependent on both tectonic style and stratigraphic variability.

Our classification scheme for petroleum basins rests on a simple working nomenclature consisting of the following qualifiers: (1) charge factor: undercharged, normally charged, or supercharged, (2) migration drainage factor: vertically drained or laterally drained, and (3) entrapment factor: low impedance or high impedance. Examples chosen from an extensive roster of documented petroleum basins are reviewed to explain the proposed classification.

AAPG Search and Discovery Article #91022©1989 AAPG Annual Convention, April 23-26, 1989, San Antonio, Texas.