This study describes a pore level approach taken to investigate the complex flow of foamed gels in porous media. Foamed gels can be used as blocking agents to control excessive gas or water production in oil reservoirs. Although the use of foamed gels as plugging agents has been studied for some time, the mechanisms of foamed gel flow in porous media are not so clear. Through visual observation in transparent etched-glass micromodels, the effect of foamed gel microstructure or texture on blockage effectiveness and on trapping mechanisms in porous media are evaluated. The experimental observations demonstrate that foamed gels provide a higher flow restriction capability than conventional aqueous foams. Photographs and videotapes of flooding tests in a micromodel show very high oil recovery, as a result of foamed gel flooding. Visual observations of pore-level behavior indicate that foam bubbles are regenerated and reshaped within the porous media by snap-off, which seems to be the predominant mechanism. To achieve effective fluid flow restriction using foamed gels, it seems important to keep within the porous media a balance between the saturation of trapped discontinuous gas phase, and the gel configuration in the pore space.
Foam is applied broadly as a mobility-control and profile modification agent for flow in porous media. Foam is a dispersion of a relatively large volume of gas in a small volume of a liquid. It is generated inside a porous medium when a liquid containing a foaming agent is mixed with either an externally injected or an in situgas (1), with the gas occupying typically 50%to 99% of the total volume. Foam mobility measured in porous media is many orders of magnitude smaller than that of the constituent gas. This mobility reduction is achieved primarily because the gas phase is dispersed into bubbles, which are generally about the size of the pore channels(2). Additionally, flowing lamellae encounter significant drag because of the presence of pore walls and constrictions(3). This performance makes foams suitable for three potential applications; 1) Mobility control, improving the displacement efficiency of gas drive processes; 2) Mobility control and flow impediment, improving the sweep efficiency of other fluid injection processes; 3) Partial or total pore blockage, restricting the flow of undesired fluids and plugging of high permeable oil "thief" zones(4).
Performance of foam that is already capable of strong mobility control may be further improved by addition of suitable polymer or gelant(5). A foamed gel is created by means similar to those used for aqueous foam generation. The major difference between foamed gels and aqueous foams is that the external phase of the foamed gel crosslinks, greatly enhancing the mechanical stability of the foam system (6). The feasibility of using foamed gels for profile modification has been demonstrated by Miller and Fogler(6). Their findings verified that foamed gel is suitable for diversion of injected water into the lowpermeability zone of a parallel, non-communicating arrangement of cores. Later on, Wassmuth et. al,(7) evaluated an effective near wellbore blocking and diverting gel-foam treatment to control gas channeling.