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Proposed Revision of the Petroleum System Concepts and the Petroleum System Events Chart

Dr Fivos Spathopoulos¹ and Prof Kerry Gallagher²
¹Imperial College, London, UK
²Université de Rennes, France

Some issues with the Petroleum System and Total Petroleum System concepts:

  1. The Petroleum System concept, at its initial form, deals only with known accumulations and shows and tries to verify their provenance. It is a great way to organise information and make good use of geochemistry, but it does not deal with unknown accumulations, especially in frontier areas.
  2. The method of naming Petroleum Systems, using the source rock in the mature pod plus the main reservoir, may cause problems: what should we do in basins with one major source rock and several important reservoirs? The Central North Sea basins are a particular example: one Kimmeridge Clay pod can charge a number of producing major reservoir units (Triassic, Upper Jurassic Fulmar, Upper Cretaceous Chalk, Tertiary Forties).
  3. The current Petroleum System Events Chart is adequate to express the original Petroleum System concept: as it deals only with known accumulations, the “preservation” is a given. The use of this chart to explore for unknown accumulations may create a false sense of security.
  4. An additional shortcoming is that the generation & migration volume is assumed to be uniform in time. However, there is a specific time period when most of the oil is generated and expelled, while the rest of the time very little oil leaves the source rock.
  5. The concept of the Total Petroleum System was introduced by USGS to be used in exploration of undiscovered petroleum pools in areas with known source rocks. In this case, however, the “preservation” of a prospect is not known and it has to be evaluated.
  6. In exploration, we mostly deal with evaluation of Total Petroleum Systems, as we often try to discover petroleum in less explored or frontier areas. It is proposed, therefore, that a revised Petroleum System Events Chart must be used; one that it will take into account any events that may cause disruption of “preservation” and create an objective view of the prospectivity of a basin.

Finally, a revised Petroleum Systems Events Chart is proposed, in which two more rows (destruction of trap and biodegradation) have been added and the term “preservation” is replaced by “accumulation integrity”.

AAPG Search and Discovery Article #120098©2013 AAPG Hedberg Conference Petroleum Systems: Modeling the Past, Planning the Future, Nice, France, October 1-5, 2012