In reservoir applications, due to their ability to restrict gas flow, foams are among the most promising and cost-effective means to alleviate the drawbacks associated with gas-based EOR processes. In porous media they can be seen as finely-textured bubbles of gas such as nitrogen, carbon dioxide, or/and methane, dispersed within a brine containing surfactants. The objective of this work is to probe the impact of the gas properties on foam efficiency and oil displacement.

Coreflood experiments were conducted on Fontainebleau and Clashach sandstones. The injected gases were mixtures in which CO2 fraction was changed from 12% to 100%. Different pressures were applied to evaluate the influence of gas density. Thus, the impact of oil saturation on foam efficiency could be assessed under both immiscible and miscible conditions. Simulations were performed to compare oil production improvement between Simultaneous Water And Gas injection (SWAG) and Foam-Assisted SWAG processes. A 1D horizontal model was adopted to evaluate the impact of gas mobility reduction, and a 2D vertical model to assess the impact of gravity override.

In the absence of oil and for each injected gas mixture, the impact of pressure on the steady state gas relative permeability in presence of foam, i.e. Krgf=vgμgas/(K∇Pfoam)⁠, revealed a unified behavior for the whole range of foam qualities. Regarding the effects of gas composition, Krgf was found to increase with the CO2 fraction. At the lab scale, the measured oil recovery factor does not take into account field scale heterogeneities. Thus, coreflood-calibrated simulations are essential to predict additional recovery at the reservoir scale. The numerical study provides helpful indications that may serve for selecting/designing a foam recovery process. It turns out that SWAG should be preferred to foam in reservoirs with low thickness and tilt, and/or with low vertical permeability. On the opposite, a foam process can be more efficient than SWAG in reservoirs that are subject to strong gas gravity segregation. In this situation, the economic success will essentially depend on the ability to minimize the surfactant adsorption.

Keywords:
gas injection method, displacement, relative permeability, oil saturation, flow in porous media, adsorption, composition, heterogeneous model, swag process, mobility reduction
Subjects:
Reservoir Fluid Dynamics, Improved and Enhanced Recovery, Flow in porous media, Gas-injection methods, Chemical flooding methods
Copyright 2016, Society of Petroleum Engineers
You can access this article if you purchase or spend a download.