Evaluation of pH-Sensitive Hydrogels to Control the Permeability Anisotropy of Oil Reservoirs

摘要

In stratified or fractured oil reservoirs, the oil recovery efficiency tends to be low as the injected fluid flows mainly through the matrix's most permeable regions, leaving behind part of the displaceable oil in the matrix's unswept zones. Given this issue, this study aims to evaluate the potential of applying seven commercial samples, based on poly(acrylic acid), to control the anisotropic permeability profile of reservoirs. To perform this study, first, continuous and oscillatory shear tests were conducted to characterize the hydrogel's rheological and viscoelastic behavior in various subsurface conditions (salinity, temperature, and/or pH value). Second, polymer dispersion elution tests were performed in a porous medium to evaluate the matrix's permeability reduction after treatment with hydrogels. The seven commercial samples were classified as pseudoplastic fluids at pH values ranging from 1 to 10. Under typical reservoir conditions, PAAr 70 (which has intermediate molar mass and intermediate number of crosslinks) was the only sample to behave as a strong gel (G'/G'' >10). Elution tests confirmed that the PAAr 70 hydrogel gelified inside the consolidated sandstone plugs and reduced the matrix's permeability four-fold. Therefore, samples based on poly(acrylic acid) with high crosslink density proved to be the most promising for controlling the anisotropic permeability profile of heterogeneous oil reservoirs.