Abstract: Advances in Modeling Hydrocarbon Migration in Compacting Sediments

Zhiyong He

A two-dimensional, two-phase fluid flow/compaction basin model, GENESIS-2D, has been developed. Some aspects of the model represent significant improvements over previous models.

Due to grid-size limitations of numerical basin models, bulk rock properties often must be derived for grids containing more than one rock type. Averaging may be satisfactory for simple properties such as density and porosity. However, for more complicated properties, such as the relationship between porosity and effective stress, more sophisticated mathematical techniques are

required. In GENESIS-2D, relationships of the individual constituents in a grid are combined mathematically to derive a new relationship that can be applied to the composite. This technique allows differential compaction of rock types within the composite.

A dynamic capillary-pressure model is used in GENESIS-2D. Capillary pressure is treated not only as a function of the saturation of the different phases, as in conventional reservoir simulators, but is also affected by the compaction process. The model allows the simulation of compaction-driven expulsion and migration of hydrocarbons. It also allows the prediction of the saturation profile and oil-water contacts in hydrocarbon accumulations. Such a formulation may significantly improve the ability to predict hydrocarbon expulsion and migration rates, probably the most important goal of multiphase modeling. Case histories will be presented to show various aspects of the model. Additional examples demonstrate that the model can predict the hydrodynamic effects on petroleum accumulations caused by compaction-driven and/or topographic-driven flow of water.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994