Geologic Distribution of Oil: ABSTRACT

Abstract

A model for the worldwide distribution of oil can be constructed using only geologic variables. Three joint probabilities are required to explain the known distribution of giant oil fields in time. These probability functions are (1) that an adequate source has been deposited, (2) that oil has been generated and entrapped, and (3) that accumulations have not been destroyed nor the accumulation process aborted. The tectonic setting strongly affects the probability values. For cratonic areas, the probability of adequate source can be modeled by the published curves for changes in sea level, because times of maximum transgression are most favorable for deposition of source sequences. Adequate thermal maturation varies with the geothermal gradient and is, therefore, extremely dependent on tectonic setting. Generally, Tertiary fields are in tectonically active areas whereas pre-Tertiary fields are in more passive areas. Oil fields in tectonically active areas are destroyed rapidly, whereas older fields which are in generally passive areas are destroyed more slowly. This model predicts the large concentration of Cretaceous and Jurassic oil as the result of (1) maximum source availability because of extensive transgression, (2) adequate thermal maturity, and (3) very little destruction. End_of_Article - Last_Page 428------------