Application of pH-Triggered Polymers for Deep Conformance Control in Fractured Reservoirs

Abstract

AbstractWater injection is commonly employed to increase the average reservoir pressure and displace the oil. However, water flooding is not always successful. The most important problem is channeling of the injected water into high permeability zones which occur in heterogeneous reservoirs. This is particularly true in naturally fractured reservoirs.Injecting low viscosity pH-triggered polymers into the reservoir to block the already swept fractures and high permeability zones is a promising solution. No injection of high viscosity gels or triggering agents is needed is this process. Polyacrylic acid microgels can swell a thousand fold as the pH of the surrounding solution changes, with an accompanying large increase in viscosity. In this paper we studied the factors affecting the feasibility and the placement of pH-triggered polymers into fractured reservoirs by performing several coreflood experiments in fractured cores.Polymer treatment reduced the overall core permeability in all cases in contact with different minerals in various sandstone and carbonate fractured cores. At polymer concentrations of 1% or greater, the permeability reduction was more than a factor of ten. The polymer microgels showed excellent consistency after being one month in reservoir condition at 58°C and resisted flow at pressure gradients up to 80 psi/ft. The selection of polymer and salt concentration in polymer solution depends on the application and desired PRF value. However, the 1% polymer concentration and 3% NaCl concentration is recommended due to the ease of polymer preparation, injectivity, reasonable geochemical buffering time and PRF values.