Flow of Oil and Water Through Elastic Polymer Gels

High water production is one of the major problems faced by the petroleum industry. One method of controlling water production is to inject polymer gels into the near-wellbore formation. Unfortunately, polymer gel injections are not always successful, in part because the exact mechanisms by which they reduce water permeability more than oil permeability (i. e. , Disproportionate Permeability Reduction, DPR) are not understood. We have conducted a series of experiments on flow of water and oil through bulk polymer gels and through polymer-filled micromodels to elucidate the fundamental mechanisms involved in DPR. Flow experiments of oil and water through weak polyacrylamide-based gels have been performed to obtain the gel permeabilities under different test conditions. Oil and water permeabilities through the gel were each found to vary with flow rate according to a power-law, but with different pre-factors and exponents. The micro-scale flow experiments were conducted in transparent glass models to visualise clearly the flow events. Our observations enabled us to discount many previously-proposed explanations, and identify the fact that the oil and water can travel through the same pore channels, but in ways that differ, particularly at the pore scale. Water flows through the gel matrix as if flowing by diffusive flow through a porous medium, whereas the oil pushes its way in the form of immiscible drops or filaments. This difference in flow regime gives rise to the measured disproportionate permeability reduction.