Synthesis of a salt-responsive hydrophobically associating polymer for fracturing fluid based on self-assembling transition

Abstract

A salt-responsive hydrophobically associating polymer (HSRP) with a molecular weight of 1.21 × 106 g/mol was synthesized and characterized. It has the characteristics of strong association and low molecular weight by choosing monomers and adjusting the polymerization system. HSRP exhibited a high sensitivity to salt ions owing to the peculiarities of its molecular structure. Through various experimental tests, this study further expanded and complemented the salt-thickening effect of hydrophobic association water-soluble polymers. In brine, HSRP exhibited low apparent viscosity and shear stress. In addition, HSRP demonstrated better thixotropic properties and viscoelastic behavior as the salinity increased, which was attributed to a self-assembling transition. The effect of salinity on self-assembling behavior of supermolecules and rheological properties of HSRP was examined through macroscopic properties and microscopic mechanisms. A reasonable core–shell model was proposed for the salt-responsive behavior: The hydrophilic backbones curled up, forming a shell, and the hydrophobic branched chains interassociated to form a core. In brine, HSRP displayed excellent viscoelasticity and low friction. It is expected to find wide applications in tertiary recovery and fracturing in saline reservoirs based on its excellent salt-responsive properties.