Polymer Effect on Gas/Water Flow in Porous Media

Abstract

Abstract The presence of hydrosoluble polymer or gel in porous media induces a selective reduction of permeability -called Disproportionate Permeability Reduction, DPR- i. e. a reduction of relative permeability to water much larger than the relative permeability to oil. Several experimental studies have been focused on oil/water systems with different cores, polymers and wettability conditions, confirming the DPR effect. The goal of our study is to investigate polymer effect on gas/water permeability in a wide range of flow rate, reproducing near well-bore conditions in water shutoff applications. The experimental study presented here proceeds to water and nitrogen injections into sandstone cores before and after polyacrylamide adsorption. Both low-rate Darcy regime and high-rate non-Darcy regime were investigated during gas flow, the later one being modeled using the classical Darcy-Forchheimer formalism. In the Darcy regime, the DPR effect induced by polymer adsorption is more significant when observed on gas/water systems than on oil/water systems investigated under comparable conditions during previous studies. Polymer induces both a strong reduction of the relative permeability to water while affecting very little the relative permeability to gas, and a significant increase of the irreducible water saturation. In the non-Darcy regime, taking into account water saturation and permeability modifications, we observe a reduction of inertial effects when gas is injected after polymer. Experimental data are discussed and confronted with the different hypotheses put forth to explain DPR. Both DPR effect and the reduction of inertial resistance coefficients during gas flow may have important applications in gas well treatments.