Foam for mobility control in alkaline/surfactant enhanced oil recovery process
AbstractThis thesis addresses several key issues in the design of foam for mobility control in alkaline-surfactant enhanced oil recovery processes. First, foam flow in fracture systems was studied. A theory for foam flow in a uniform fracture was developed and verified by experiment. The apparent viscosity was found to be the sum of contributions arising from liquid between bubbles and the resistance to deformation of the interfaces of bubbles passing through the fracture. Apparent viscosity increases with gas fractional flow and is greater for thicker fractures (for a given bubble size), indicating that foam can divert flow from thicker to thinner fractures. The diversion effect was confirmed experimentally and modeled using the above theory for individual fractures. The amount of surfactant solution required to sweep a heterogeneous fracture system decreases greatly with increasing gas fractional flow owing to the diversion effect and to the need for less liquid to occupy a given volume when foam is used. The sweep efficiency's sensitivity to bubble size was investigated theoretically in a heterogeneous fracture system with log-normal distributed apertures.
Second, the foam application in forced convection of alkaline-surfactant enhanced oil recovery processes was studied. From sand pack experiments for the alkaline-surfactant-polymer process, a 0.3 PV slug of the surfactant blend studied can recover almost all the waterflood residual crude oil when followed by a polymer solution as mobility control agent. But this blend is a weak foamer near its optimum salinity while one of its components, IOS, is a good foamer. Two types of processes were tested in sand packs to study possible process improvements and cost savings from replacing some polymer by foam for mobility control. The first used IOS foam as drive after the surfactant slug, while the second, which is preferred, involved injecting gas with the surfactant slug containing polymer followed by IOS foam. It was found that foam has higher apparent viscosity in high than in low permeability region. Thus, use of foam should be more attractive in heterogeneous system to get better sweep efficiency