Anionic amphiphilic copolymers as potential agents for enhanced oil recovery

To develop “smart fluids” for enhanced oil recovery from reservoir rocks, comb-type amphiphilic copolymers were synthesized through free radical polymerization (FRP) of: (i) the hydrophilic, anionic monomer 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPSA) that offer a hydrophilic character to the final copolymers; (ii) the weakly acidic hydrophilic monomer acrylic acid (AA); (iii) the hydrophobic monomer dodecyl methacrylate (DMA). The polymers were characterized by Proton Nuclear Magnetic Resonance (1H NMR), Attenuated Total Reflection Fourier Transform Infrared Spectroscopy (ATR-FTIR), fluorescence probing, Dynamic Light Scattering (DLS) and electrophoresis. Stable polymer solutions were prepared without and with the presence of salts (NaCl, CaCl2, MgSO4). The dynamic air/water surface and oil/water interfacial tensions were measured by the pendant drop method, and their steady-state values were estimated with fitting to asymptotic relations predicting the long-time behavior. Moreover, the wettability of water/air and water/oil to glass or poly(methyl methacrylate) (PMMA) surface was quantified by measuring the contact angles. Oil-in-water Pickering emulsions were prepared by mixing n-dodecane with polymer solutions and their stability was evaluated macroscopically with optical inspection, and microscopically by measuring the oil drop size distribution and shear viscosity. Polymer solutions and Pickering emulsions were tested as agents for the displacement of the residual n-dodecane from a glass-etched pore network. The long-lasting retention of polymer solution in the pore network makes the solid surface more hydrophilic, facilitating the fission of oil ganglia into smaller ones which are mobilized easier, resulting in a final EOR efficiency between 10% and 18%. When using an emulsion as displacing fluid, the viscosity ratio and capillary number increase by orders of magnitude, the viscous forces prevail against the capillary ones, and the growth pattern becomes a frontal drive leading to a high EOR efficiency of ∼94%.