Foam generation and propagation in heterogeneous porous media
Miller, Clarence A.; Hirasaki, George J.
Doctor of Philosophy
This thesis addresses several key issues in the design of foam processes in porous media. Laboratory experiments were performed to identify the conditions for the generation of strong foam. They demonstrated that strong foam in homogeneous porous media is obtained above a critical dimensionless number that represents the point when there are sufficient lamellae to create discontinuity in all flowing gas paths. The critical number corresponds to a critical pressure drop that scales inversely with the square root of permeability. The results imply that mobilization and division is the primary mechanism for the generation of strong foam in homogeneous media. Effects of heterogeneity on foam generation and propagation are studied. Steady-state analysis suggests snap-off occurring near permeability increase due to the drop in capillary pressure. Experiments in homogeneous and heterogeneous sand-packed columns revealed that the foam mobility in the two cases could indeed differ by two orders of magnitude, due to snap-off for flow across an abrupt increase in permeability. This mechanism of foam generation is dependent on the degree of permeability contrast and the gas fractional flow. At low gas fractional flow, a permeability contrast of at least about 4 is necessary. Snap-off also occurs when the increase in permeability is gradual. In this case, small capillary number (e.g. low flow rate) is required. A simple foam model was developed and incorporated into an existing reservoir simulation package. In addition to a fixed increase in foam effective viscosity---a feature that is common in many previous models, the increase in trapped gas saturation during imbibition is included. The latter is critical to model diversion in surfactant-alternating-gas processes. Observations from a field-scale foam application for aquifer remediation were reviewed. The reservoir simulator that included the foam model was successfully utilized to simulate the process and interpret its results. The field results are consistent with the conditions for strong foam and the effects of heterogeneity identified in the laboratory. Simulations indicated that foam mobility in the vertical direction, which is generally perpendicular to stratification, was about 1 to 2 orders of magnitude less than its horizontal mobility. The reduction in vertical mobility due to snap-off in stratified media implies that foam in field-scale processes should propagate farther than previously thought.
Chemical engineering; Petroleum engineering; Environmental science; Environmental engineering