Rock/Fluid/Polymer Interaction Mechanisms: Implications for Water Shut-off Treatment

Several disproportionate permeability reduction (DPR) mechanisms have been proposed in the literature for water shutoff treatment using polymer relative permeability modifiers (RPM). However, none appear to be universally accepted. The lack of agreement may be because no single factor determines the success of DPR treatment. Moreover, there is still a lack of understanding of DPR mechanisms and the order of how these mechanisms work together. This paper provides a comprehensive review of the mechanisms behind the RPMs. We identify that sufficient polymer adsorption onto the rock surface is a primary condition for water shutoff treatment, while rock surface initial wettability and fluid-polymer-rock interaction/attraction plays a significant role in polymer adsorption. Furthermore, polymer concentration, polymer molecular weight, aging time, polymer injection volume, polymer injection rate, and reservoir temperature are also vital for polymer adsorption. After polymer adsorption, the mechanisms such as fluid segregation and wall effect help accomplish the required DPR. We also find that there is a more consistent agreement among the published studies on the order of DPR mechanisms e.g. initial rock wettability effect comes first, followed by initial segregation, adsorption wall effect (i.e., steric, lubrication, wettability alteration, and swelling/shrinkage), and then the final segregation. Depending on the RPM implementation, which depends on pore size, the polymer layer thickness can be adjusted after the placement permanently or temporarily by controlling swelling/shrinkage. The subject matter investigated in this review helps us understand the factors responsible for optimal performance of polymer solutions in controlling excess water production from hydrocarbon reservoirs-thus assisting in more efficient oil/gas production.