Preparation and Properties of a Novel Quaternary Thickener for Low Damage Fracturing

ABSTRACT In this study, a novel quaternary thickener (S−D−HPAM) for low−damage fracturing was successfully synthesized by using acrylic acid (AA) and acrylamide (AM) as the copolymer backbone and synchronously introducing octadecyldimethylallyl ammonium chloride (DMCAAC−18) and methacryloyloxyethylsulfobetaine (SBMA) as the bifunctionalized monomer. The structure of S−D−HPAM has been confirmed by Fourier transform infrared spectroscopy, hydrogen nuclear magnetic resonance, thermogravimetric analysis, scanning electron microscopy, and matrix−assisted laser desorption−ionization−time−of−flight mass spectrometry. Compared with hydrolyzed polyacrylamide (HPAM) directly polymerized with AA and AM, S−D−HPAM exhibited superior performance in terms of thickening ability, salt tolerance, temperature resistance, shear resistance, sand−suspending capability, and degradation. Specifically, the introduction of long−chain alkyl groups in DMCAAC−18 could generate dynamic reversible hydrophobic interactions between the polymer main chains, resulting in an apparent viscosity of 471.5 mPa·s for S−D−HPAM solution at 3500 mg/L, which was about 1.7 times higher than that of the HPAM solution (282.5 mPa∙s) with the same concentration. In addition, the hydrolysis of the ester bonds in SBMA led to the shedding of the sulfonic acid group (−SO 3 − ) from S−D−HPAM, which enhanced the degradation rate (83.10%) of S−D−HPAM by 21.81% compared to that of HPAM (61.29%). Moreover, the sulfonic acid group and quaternary ammonium group can synergistically form a strong hydration layer and reduce the adsorption and retention of the thickener on the core surface, which results in a permeability recovery rate of 91% and a low core damage rate (8.60%) for S−D−HPAM, which were better than those of HPAM (88% and 11.64%). Thus, the strategy of introducing dual monomers enables S−D−HPAM to simultaneously improve the thickening ability and reduce the damage to the reservoir. Meaningfully, the technical bottleneck of traditional thickeners, which inevitably increase viscosity at the expense of damaging the reservoir, can be effectively broken through. In addition, the successful synthesis of S−D−HPAM using the strategy of introducing dual monomers into the polymer opens a new prospect for the development of more new novel fracturing thickening agents.