Curtailing water production in oil wells: A case for anionic polymers

The influence of anionic polymers for reducing water production in oil wells under induced polymer adsorption is investigated. Cationic polymers are frequently used for polymer injection due to their positive ionic character and the negatively charged silica surface of most porous media. Results obtained for the anionic polymer used in this study, show that polymer adsorption is unaffected by the ionic character of polymers, provided the polymer is hydrophilic. Equally, previous studies on polymer adsorption in porous media have shown that static adsorption regime exists at low shear rate of injection. This results in thin polymer layer whose capability to reduce water permeability is marginal. However, polymer injection at increasing shear rates has revealed an increase in the adsorbed polymer layer and consequently, improved water permeability reduction.In this work, experimental results from sandpacks are presented to show that there is improvement in the adsorbed polymer layer with increased shear rates. This phenomenon is known as “flow-induced adsorption”. The experiments indicate that above a critical shear rate, there is a shift in permeability-reduction mechanism from static adsorption to flow-induced adsorption, resulting in a sharp increase in adsorbed polymer layer. Various scenarios were studied to investigate the effect of polymer residence time and increasing rate of brine flush after polymer injection. For comparison with the above experimental results, similar experiments were performed at increased polymer concentration and in Berea sandstone core. Results indicate that the permeability-reduction mechanism is constrained by increased polymer concentration and low-permeability porous media.