WHY DO GELS REDUCE WATER PERMEABILITY MORE THAN OIL PERMEABILITY

A capacity to reduce water permeability much more than oil permeabilit y ability is critical to the success of gel treatments in production w ells if zones cannot be isolated during gel placement. Although severa l researchers have reported polymers and gels that provide this dispro portionate permeability reduction, the explanation for the phenomenon was unclear. In this paper, we examine several possible explanations f or why some gels reduce water permeability more than oil permeability. Our experimental results indicate the disproportionate permeability r eduction is not caused by gravity or lubrication effects. Results also indicate that gel shrinking and swelling are unlikely to be responsib le for the phenomenon. Although wettability may play a role in the dis proportionate permeability reduction, it does not appear to be the roo t cause for water permeability being reduced more than oil permeabilit y. Results from an experiment with an oil-based gel suggest that segre gation of oil and water pathways through a porous medium (on a microsc opic scale) may play the dominant role in the disproportionate permeab ility reduction. However, additional work will be required to verify t his concept.