Salt Resistance Study of Different Monomer Combinations of Polyacrylamide-Based Slickwater Drag Reducers

Summary Slickwater fracturing fluids are commonly used in the extraction of unconventional oil and gas reservoirs. However, their efficacy is significantly diminished in the presence of elevated salt concentrations. A pivotal component of slickwater fracturing fluids, the salt resistance of a drag reducer determines its overall performance. In this paper, we focus on the salt resistance of different monomer combinations of polyacrylamide (PAM)-based slickwater drag reducers using a selection of common drag-reducer functional monomers, including acrylic acid (AA), 2-acrylamido-2-methylpropanesulfonic acid (AMPS), and methacryloyloxyethyltrimethylammonium chloride (DMC). Reverse-phase emulsion polymerization was used to synthesize 30 PAM-based drag reducers of six types with different monomer combinations. The successful synthesis of the product was confirmed by Fourier transform infrared (FT-IR) spectroscopy. The viscous averaged molecular weights were all greater than 2.4×106 g/mol, and the monomer conversion rate was greater than 90%. The dissolution experiments showed that the acrylamide (AM)/DMC monomer combination achieved the best dissolution performance at a dissolution time of 40 seconds. The steady-state shear viscosity test showed that in clean water, the monomer combination AM/AA had the best viscosity-increasing performance, with a viscosity of 328.9 mPa·s after steady-state shear. In salt solution, the monomer combination AM/AMPS/DMC showed the best salt resistance, with a viscosity retention rate of 39.30% in 20×104 mg/L CaCl2 solution. The amphoteric ionic drag reducer exhibits excellent salt resistance. It was shown in the drag reduction performance test that the AM/DMC monomer combination had the best drag reduction performance in clean water, with a drag reduction rate of 80.1%. In salt solution, the monomer AM/AMPS/DMC exhibited the highest drag reduction with a retention rate of 92.15%. The microscopic effects of salt concentration on the molecules of the drag reducer were illustrated using hydrodynamic radii and zeta potentials. The results of this research are of great significance for the development of salt-resistant drag reducers that can facilitate the efficient development of unconventional oil and gas reservoir resources.