Design of polymer boron crosslinking agents based on scale effects and study of the crosslinking mechanism of guar gum at ultra-low concentrations.

Research on guar gum-based fracturing fluids reveals a scale disparity of approximately ten thousandfold between their molecular chains and conventional boron crosslinkers, leading to pronounced scale and structure effects. Traditional crosslinking theories focus solely on group interactions, lacking a holistic molecular structural perspective. To address this, this study proposes synergistically optimising scale and structural effects to overcome theoretical limitations. Targeting the core issue of low crosslinking efficiency at low concentrations, a novel polymeric boron crosslinking agent, PCAAP (with acrylamide as the primary monomer and 3-acrylamidophenylboronic acid and 2-acrylamido-2-methylpropane sulfonic acid as functional monomers). Its innovation lies in achieving molecular scale matching (PCAAP size: 129 nm, reducing scale disparity to one ten-thousandth) and synergistic multi-crosslinking sites, thereby overcoming traditional limitations. Based on this, highly efficient cross-linking of hydroxypropyl guar gum at an ultra-low concentration of 0.15 wt% was successfully achieved at 160 °C. Results indicate that after 120 min of shearing at 170 s-1, the system maintained a viscosity of 57 mPa·s, representing an improvement of over 256 % compared to traditional boron cross-linking agents, with gel-breaking residue of only 115.3 mg/L. Molecular dynamics simulations revealed that the reinforcement mechanism stems from significantly enhanced HPG-crosslinker interaction energies and restricted high-temperature water molecule migration. PCAAP enables a reduction in guar gum dosage exceeding 60 %, offering a novel solution for low-damage fracturing and establishing a theoretical foundation for developing highly efficient, low-cost crosslinking agents.