Simulation and Experimental Studies of Foam for Enhanced Oil Recovery

by
Jianxin Shi, Ph.D.

University of Texas at Austin, 1996
Supervisors: William R. Rossen

Foams can improve sweep efficiency and oil recovery in miscible and steam enhanced-oil-recovery (EOR) processes. For a successful application of foam in EOR processes, a simulator that can predict foam performance under field conditions is highly desirable. In this study, a foam simulator that incorporates the "fixed limiting capillary pressure" model and some empirical foam models into a compositional miscible-flood simulator - UTCOMP - is implemented. This approach highlights the key foam mechanism that control foam behavior in porous media, offering unique insights into foam-process mechanism under reservoir conditions.

Simulations covering a wide range in reservoir properties and geometry, injection rate, foam quality, foam strength, and the mechanism of foam collapse suggest that a single dimensionless number, called the viscous-gravity ratio, can predict the ability of continuous-injection foam processes to overcome gravity override in homogeneous, anisotropic reservoirs. This result implies that foam can prevent gravity override by attaining a sufficient lateral pressure gradient at attainable injection rates. Simulations also show that Surfactant-Alternating-Gas (SAG) foam processes can achieve both high injectivity and improved performance in overcoming gravity override, demonstrating the potential advantages of SAG foam processes over continuous-foam-injection processes.

Our preliminary study shows that capillary cross-flow can grossly alter foam effectiveness in two layers in intimate contact; the extent of capillary cross- flow appears to depend on a ratio of viscous- and capillary-pressure gradients and reservoir geometry.

The sharp change of foam properties as a function of water saturation requires the use of fine simulation grids and small time steps to obtain quantitatively correct results. In SAG processes, fine grids are crucial for achieving results close to those predicted by fractional-flow theory.

Foam generation and foam stability in porous media at low pressure gradients or low flow rates are crucial to successful gas mobility control in EOR processes. The experimental study concludes that the heterogeneity of a porous medium, specifically, permeability variation in the flow direction, provides favorable conditions for the generating strong foams. Foam-stability experiments prove that, once foams are formed, they need not collapse at very low gas velocities or low (Delta)p in porous media.

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