Synergies of Alkali and Polymers - Decreasing Polymer Costs and Increasing Efficiency

Abstract

Abstract Alkali injection leads to in-situ soap generation of high TAN number oil and residual oil reduction accordingly. We are showing that the performance of AP floods can be optimized by making use of lower polymer viscosities during injection but increasing polymer viscosities in the reservoir owing to "aging" of the polymers at high pH. Furthermore, AP conditions enable reducing polymer retention in the reservoir decreasing the Utility Factors (kg polymers injected / incremental bbl. produced). Phase behavior tests were performed to understand the oil/alkali solution interaction and interfacial tension (IFT) was measured. Micromodel floods addressed displacement effects while two-phase core floods covered the displacement efficiency of alkali polymer solutions. We used aged polymer solutions to mimic the conditions deep in the reservoir and compared the displacement efficiencies and the polymer adsorption of non-aged and aged polymer solutions. IFT measurements showed that saponification (41 μmol_g saponifiable acids) at the oil-alkali solution interface is very effectively reducing the IFT. Alkali phase experiments confirmed that emulsions are formed initially and supported the potential for residual oil mobilization. Aging experiments revealed that the polymer hydrolysis rate is substantially increased at high pH compared to polymer hydrolysis at neutral pH resulting in 60 % viscosity increase in AP conditions. Within the reservoir, the fast aging of polymer solutions in high pH results in increase to target viscosity while maintaining low adsorption owing to alkali and softened water. Hence, injectivity of alkali polymer solutions can be improved over conventional polymer flooding. The two-phase experiments confirmed that lower concentration polymer solutions aged in alkali show the same displacement efficiency as non-aged polymers with higher concentrations. Hence, significant cost savings can be realized capitalizing on the fast aging in the reservoir. Due to the low polymer retention in AP floods, less polymers are consumed than in conventional polymer floods significantly decreasing the Utility Factor (injected polymers kg/incremental bbl. produced). Overall, the work shows that Alkali/Polymer (AP) injection leads to substantial incremental oil production of reactive oils. A workflow is presented to optimize AP projects including near-wellbore and reservoir effects. AP flood displacement efficiency must be evaluated incorporating aging of polymer solutions. Significant cost savings and increasing efficiency can be realized in AP floods by incorporating aging of polymers and taking the reduced polymer adsorption into account.