| Foam is used in stimulation treatments and enhanced oil recovery to aid diversion and to improve sweep efficiencies. When they are used as diverting agents during matrix-acidizing treatments, they direct acid flow to low-permeability or oil-saturated zones. However, foam mechanisms in rock are complex and not well understood. Foam mobility is controlled by foam texture, which itself is a complex function of many variables. Capillary pressure and the relation between the pore-size distribution of the rock and the texture of the foam, especially, play important roles in foam behavior.;This work explores the mechanisms of foam diversion in two ways. The first is mathematical modeling. A theoretical model of foam in rock can be derived from first principles, using a material balance on each component and a population balance on the foam bubbles. However, this method involves the description of processes that are not well understood. Our investigation focuses on a simpler approach, which was introduced in an earlier work and that describes the dominant mechanism of foams in a rock, applying fractional-flow methods under the assumption of a limiting capillary pressure. We show that the predictions of foam flow using this model are comparable to the other approach, in spite of its simplicity.;A second focus of this work is an experimental investigation of the bubble-size distribution in foam. Foam-acid treatments in the field and experimental work published in the literature suggest that foam texture depends on parameters such as the permeability and the pore-size distribution of the porous medium, which reconfigures foam texture. We have built an apparatus that measures both bubble-size distribution as foam exits the medium and the pressure drop caused by the foam in a variety of sandpacks and rock samples. |
