ABSTRACT: Modeling the Hydrodynamic Effects on Hydrocarbon Accumulation

He Zhiyong, John Pantano

Oil and gas migration and accumulation occur in sedimentary basins in water-saturated environments Understanding the process of movement and entrapment of hydrocarbons in such environments is of primary scientific and economic importance.

Based on fluid mechanics and the potential theory that describes movement and entrapment of hydrocarbons under hydrodynamic conditions, the influence of structural configuration, stratigraphic variation, and carrier bed inhomogeneity on the flow regime and, in turn, on the hydrocarbon accumulation patterns is investigated using a two-dimensional numerical model.

The model incorporates hydrodynamic effects due to spatial variations of permeability and capillary properties. A finer scale for mapping the aquifer is used in this model relative to the scale used in conventional two-dimensional fluid-flow models. This finer scale allows further insight into the question of what is the appropriate modeling scale for different phenomena.

Tests show that the location, extent, and shape of hydrocarbon accumulations may be predicted based on regional potentiometric observations once a primary migration input is estimated.

Examples demonstrate that in addition to permeability and capillary pressure changes, structural variations also influence the oil-water interface. Further, the hydrocarbon accumulation exerts a feedback on the local hydrodynamic flow owing to reduced conductivity of the carrier bed. It may increase the tilt and cause distortion of the oil-water contact even if the gradient of the regional potentiometric surface is small (e.g., 1 m/km). In such cases, casual use of the widely documented Hubbert's equation may lead to error in the estimate.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990