The Petroleum System

L. B. Magoon, W. G. Dow

Sedimentary basins, petroleum systems, plays, and prospects may be viewed as separate levels of investigation, all of which are needed to understand the genesis and habitat of hydrocarbons. Sedimentary basin investigations emphasize the overall stratigraphic and structural evolution of sedimentary rocks. Petroleum system studies describe and map the genetic relationship between a pod of active source rock and the resulting discovered oil and gas accumulations. Investigations of plays describe the present-day geological similarity of a series of present day traps, and studies of prospects describe an individual present day trap. The sedimentary basin and petroleum system occur in nature regardless of economics. However, the play and prospect exist only when undiscovered co mercial accumulations of petroleum are thought to Occur.

A petroleum system encompasses a pod of active source rock and all genetically related oil and gas. Additionally, a petroleum system includes all the essential elements and processes that are needed for oil and gas accumulations to exist. The essential elements are the source rock, reservoir rock, seal rock, and overburden rock, and the processes include trap formation and the generation-migration-accumulation of petroleum. All essential elements must be placed in time and space such that the processes required to form a petroleum accumulation can occur. Characterization Of petroleum systems include the procedures to identify, characterize, name and determine the levels of certainty.

The petroleum system has a stratigraphic, geographic, and temporal extent. The system name combines the names of the source rock and the major reservoir rock and also expresses a level of certainty-known, hypothetical, and speculative. For example, the Mandal-Ekofisk(!) petroleum system. Four figures and a table that best depict the geographic, stratigraphic, and temporal evolution of the petroleum system include a burial history chart to establish the critical moment for the system, a map and cross section drawn at the critical moment, an events chart to summarize the formation and history of the petroleum system, and a table of related accumulations. The petroleum system concept is used to investigate discovered hydrocarbon accumulations and as a basis for proposing plays and prospe ts.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995