Experimental study and application of anti-salt polymer aqueous solutions prepared by produced water for low-permeability reservoirs.

Abstract Hydrolyzed polyacrylamide (HPAM) has been widely used in chemically enhanced oil recovery (EOR) processes. However, the sensitivity to salinity limited the utility of HPAM polymers for many potential EOR applications in high-salinity reservoirs. To overcome the HPAM salinity sensitiviy shortcoming, the authors developed anti-salt polymers (ASPs) with high salt-tolerance to be used for mobility-control. ASP is an electrolyte-responsive terpolymer of an acrylamide (AM) with 2-acrylamido-methylpropane-sulphonic acid sodium salt (NaAMPS) and a monomer that is much like N-(4-benzoylphenyl) acrylamide (BPAm). Generally, for reservoirs that have high total dissolved solids (TDS) in water, ASP solutions are projected to generate a high-viscosity injected fluid. However, debates are ongoing as to whether ASP can be successfully applied to low-permeability reservoirs if produced water is used as the polymer mixing water. In this study, produced water taken from block 2 of the Pubei Oilfield development zone in Daqing with a TDS of 12910 mg/L was used to prepare and dilute the polymer aqueous solutions. Comparative experiments with ASPs and HPAM were conducted in regard to their viscosity, stabilities, hydrodynamic radii, and core flooding feasibilities. ASPs had better thickening ability compared with HPAM in produced water. Even with low retention rates, ASP aqueous solutions still held a favorable viscosity after aging for 15 days. Core flooding experiments demonstrated that ASPs has good propagation in porous media and acceptable behavior as a displacing fluid. Improved oil recoveries of 9.54, 13.34, and 15.64% were achieved during the injection of ASP solutions and subsequent water flooding. Furthermore, the result from the pilot test showed that ASP was successfully used in block 2 of the Pubei Oilfield development zone in Daqing, which provides a reference for other oilfields' mobility-control. Highlights • Anti-salt polymer have good thickening behavior when being mixed with produced water. • Anti-salt polymer solution shows acceptable transportation in low-permeability cores. • Anti-salt polymer can significantly improve the oil recovery. • Anti-salt polymer achieved success in pilot test in Pubei development zone in Daqing oil field. [ABSTRACT FROM AUTHOR]