Temperature-Activated Acid Thickening Agent Based on Grafted Cellulose Derivatives for Stimulation of High-Temperature Carbonate Reservoirs

Abstract

To address the challenges of rapid acid depletion and limited stimulation range caused by high temperatures during acid fracturing in deep carbonate reservoirs, this study synthesized a temperature-responsive smart acid thickener, CMHM (cationic-modified hydroxypropyl methylcellulose), based on renewable cellulose derivative hydroxypropyl methylcellulose (HPMC). By grafting hydrophobic and cationic monomers, this material exhibits thermally induced thickening properties alongside acid and salt resistance. Characterization experiments confirmed successful grafting and excellent thermal stability. Rheological and microscopic studies revealed that CMHM forms a 3D network through hydrophobic association and electrostatic interactions at high temperatures. Hydrophobic association drives interchain aggregation, while the electrostatic repulsion of cationic groups and ionic bridging jointly regulate the stability of the network structure. Macroscopically, this results in a “thermal thickening” phenomenon, and this mechanism is enhanced in strong acid and high salt environments. Rock dissolution tests under simulated deep-earth conditions (120°C, 30,000 ppm mineralization) demonstrated that CMHM reduced acid-rock reaction rates by 82.3% compared with conventional thickeners. Acid consumption within 1 hour was less than 30% of conventional systems, significantly delaying acid depletion. This breakthrough addresses the technical limitation of conventional thickened acids experiencing “heat-induced viscosity reduction” at the mechanistic level. This study presents an exploration of thermosensitive smart materials in carbonate thermal reservoir acidizing, achieving a reverse response of “low viscosity at low temperatures, high viscosity at high temperatures” and elucidating the self-assembly behavior and thermally induced thickening mechanism of polymers under challenging conditions.