Understanding Organic Facies: a Key to Improve Quantitative Petroleum Evaluation of Sedimentary Basins

Alain Y. Huc

As the complexity of exploration problems increases, petroleum geologists tend to consider more carefully oil formation and migration in terms of quantity, quality, and timing, in order to assess more accurately the history of the hydrocarbons in source rocks in a given basin.

The present knowledge concerning the behavior of source rocks (quantity of hydrocarbons generated, composition of hydrocarbons, kinetics, expulsion efficiency) asserts the influence of factors related to organic matter in the sediments, such as organic matter content, organic matter quality, and pattern of the microdistribution of organic matter in the mineral fabric (layered, lens like, intergranular). All these properties are definitively inherited from the time of deposition of the source rocks. Moreover, field observations show the occurrence of organic facies changes at various scales in time and space, as a response to the variety of organic inputs, the variety of depositional environments, and to sedimentary processes.

The effects of these processes on source rocks emphasize, beyond the efforts to achieve comprehensive descriptions of source beds (Rock-Eval pyrolysis, microscopy, typing of organic matter, kinetic parameters measured on carefully selected kerogens, use of wireline logs, seismic information), the need to increase our understanding of organic-facies deposition to better predict the petroleum potential of sedimentary basins.

AAPG Search and Discovery Article #91032©1988 Mediterranean Basins Conference and Exhibition, Nice, France, 25-28 September 1988.