TOTAL PETROLEUM SYSTEM CONCEPT FOR THE ASSESSMENT OF UNDISCOVERED PETROLEUM RESOURCES

The total petroleum system includes all genetically related petroleum that occurs in shows and accumulations (discovered and undiscovered) generated by a pod or by closely related pods of mature source rock. Total petroleum systems exist within a limited mappable geologic volume. They also include the essential mappable geologic elements of source, reservoir, seal, and overburden rocks. These essential geologic elements control the fundamental processes of generation, expulsion, migration, entrapment, and preservation of petroleum within the total petroleum system.

The total petroleum system serves as an excellent foundation for petroleum-resource assessments for the following reasons: (1) it offers a practical approach that standardizes and focuses the gathering and communication of relevant geologic knowledge; (2) the geologic and geochemical components of a total petroleum system can be scientifically tested; (3) petroleum geologists are generally familiar with the criteria used to identify and map total petroleum systems; and (4) new information that improves the understanding of the total petroleum system can be incorporated into an assessment. A total petroleum system might equate to a single unit for assessment, but can be subdivided into two or more units to keep each sufficiently homogeneous with respect to geology, exploration considerations, and risk.

Examples from the USGS World Petroleum Assessment 2000 illustrate the applicability of the total petroleum system concept. In that effort, 159 total petroleum systems around the world were analyzed and 149 were quantitatively assessed. This study revealed many trends among total petroleum systems. For example, recent generation and migration of petroleum greatly increases the likelihood of richness. Total petroleum systems with older times of generation generally avoid degradation only if significant evaporite seals are present. The study also demonstrated that some total petroleum systems are poorly understood, such as those in deltas.