Oil Displacement Efficiency of Salt-Tolerant Polymers: A review

Salt tolerant polymers are being considered increasingly for polymer flooding in reservoirs where conventional HPAM would lose viscosity from high salinity, divalent ions, high temperature, and lengthy contact to chemistries. However, salt tolerance does not guarantee an enhanced oil recovery (EOR) value: the essential query becomes whether or not the polymer is able to propagate through porous media and optimize the displacement at a pressure cost that is acceptable both technically and economically. This review critically assesses the oil displacement efficiency of salt tolerant polymers as described in the literature from the years 2015–2025 and makes relationship between the molecular class of the polymers described to their mobility control, pore-scale displaceability of oil at acceptably low levels of pressure cost. Evidence from core floods, sand packs, micromodel studies, computed tomography studies, and field pilot tests is compared while carefully noting differences in the baseline waterflood recovery factor, rock type, permeability, oil viscosity, brine composition, polymer concentration, slug size, and flow rate. Sulfonated AMPS/ATBS copolymers exhibit effective mobility control with relative efficiency, even under moderately extreme conditions, while using hydrophobically associating, amphiphilic, and amphoteric/zwitterionic polymers can have non-displacement enablement when viscosity is maintained or amplified under higher salinities, and could manifest stronger viscoelastic or associative effects. Studies indicate considerable increases in recovery for high-temperature/high-salinity processing, but comparisons across studies remain unknown as there are no standardization protocols or definitions. Increased apparent viscosity can also cause injectivity loss, while adsorption and mechanical retention lower the effectual concentration of polymers, potentially damaging formation. Accordingly, the review suggests a displacement efficiency framework that fractures the benefit of the mobility control, microscopic mobilization, propagation efficiency, operational penalty, etc. Future work should include matched-condition polymer comparisons, retention based on mass balance, in situ rheology, imaging of saturation redistribution, long duration injectivity tests, and transparent field-scale reporting. These measures are needed to move promising lab-scale salt-tolerant polymers into defensible field EOR technologies.