pH-Responsive Profile Agent for Alkaline Conditions in Daqing Oilfield

Abstract Enhanced oil recovery technologies, such as alkali–surfactant–polymer (ASP) flooding, have been widely applied in mature oilfields to improve oil recovery rates, especially for the Daqing Oilfield. However, the strong alkaline conditions induced by ASP processes significantly affect polymer viscosity, thereby limiting mobility control and oil displacement efficiency, especially in heterogeneous reservoirs. To address this challenge, we developed a series of pH-responsive copolymers based on 2-(diethylamino)ethyl methacrylate (DEAEMA) and acrylamide (AM) via micellar polymerization, specifically tailored for application in strongly alkaline environments such as the Daqing Oilfield. The synthesized copolymers were characterized by FTIR and 1H NMR, confirming the successful incorporation of DEAEMA monomers. Rheological tests were conducted at 45 °C with a polymer concentration of 800 mg/L and a salinity of 4500 mg/L NaCl. Under these conditions, the copolymer solutions exhibited remarkable pH-responsive thickening behavior: at pH 9, the viscosity was 24 mPa·s; upon increasing the pH to 13, the viscosity increased to 512 mPa·s, achieving a 20-fold viscosity enhancement (defined as the ratio of viscosity at pH 13 to that at pH 9 under identical temperature, salinity, and polymer concentration). This thickening effect is driven by reversible physical crosslinking networks formed through hydrophobic associations. Core flooding experiments further validated the superior profile control performance of the pH-responsive polymers, which effectively redirected fluid flow into low-permeability layers, enhanced sweep efficiency, and increased oil recovery rates by 24.32% compared to conventional polymers. This study highlights the potential of pH-responsive polymers as effective chemical profile control agents for addressing the challenges of heterogeneous reservoirs and strongly alkaline environments. The developed polymers provide a promising solution for improving oil recovery efficiency and mitigating water channeling in mature oilfields, paving the way for future advancements in oilfield chemistry and enhanced oil recovery technologies.