ABSTRACT: Oil Expulsion: A Sensitivity Analysis

WAPLES, DOUGLAS W., and AKIHIKO OKUI, Japan National Oil Corp., Chiba, Japan

We have performed sensitivity analysis on the phenomenon of oil expulsion by systematically varying a number of input parameters in a computer model that simulates hydrocarbon generation and expulsion as a three-phase flow process. We examined the following parameters: porosity, critical and end points for relative-permeability curves, shapes of relative-permeability curves, expulsion forces, adsorption of oil in kerogen, oil viscosity, and hydrogen index. These parameters were examined for a broad range of burial histories, as well as for a range of TOC values (0.5%-60%) and kerogen types (II, III, II-S).

For type II and II-S kerogens in reasonably rich source rocks, results are generally not very sensitive to the anticipated uncertainties in any of the parameters. For source rocks with less than about 3% TOC, uncertainties in porosity and relative-permeability curves are most important, but in richer rocks adsorption of oil on kerogen becomes dominant. For type III kerogens and for coals, uncertainty about oil adsorption on kerogen is extremely important; all other factors are of little or no importance.

These results indicate that to improve modeling of oil expulsion, more effort must go into (1) accurately specifying the porosity of source rocks as a function of burial, and (2) better constraining the amount of oil adsorption on kerogen and coal. The problem of specifying critical values and end points for relative-permeability curves for source rocks is also important but is particularly difficult since such curves cannot be established by laboratory measurements.

When two or more phases are present in significant amounts, total fluid mobility decreases drastically compared with that of a one-phase system. This phenomenon may be important in the development of overpressuring in active source rocks.

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)