The most important success key in waterflooding and other EOR processes is to properly inject fluids into a reservoir without channeling. The selective plugging technique by forming gel is one good approach where polymer with a crosslinker is injected into the reservoir. In this paper, CAG (CO₂-Water Alternating Gelant Injection Process) is proposed as a new polymer gelation scheme for permeability profile modification. This method is comprised of alternate injection of the two solutions: carbon dioxide-saturated water and gelant (aqueous solution of polyacrylamide, sodium aluminate and sodium hydroxide). Theoretically, the two different slugs injected into the reservoir are mixed by viscous fingering and dispersion, and pH of the gelant can be lowered. It leads to generation of aluminum ions which crosslink the partially hydrolyzed polyacrylamide, and forming high viscous gel to plug the high permeable streak.
To verify the efficacy of the CAG laboratory experiments were performed. The optimum concentrations of polyacrylamide, sodium aluminate and sodium hydroxide in gelant were selected to be 250mg/l from beaker tests. The experiments using glass-bead packed cores have revealed that the CAG could reduce the core permeability by about 1/60 to 1/360 of its original permeability. The slug size of gelant and CO₂ water, gelant concentration, and core permeability were found to influence the behavior of gel formation.
This method has only been verified by laboratory experiments, but is thought to be promising for future field application because of simplicity in theory and operation.