Retarded Gelled Acid for High-Temperature Carbonate Reservoir Acidizing: Retardancy and Mechanism Study

Carbonate reservoirs, characterized by deep burial, high temperatures, strong heterogeneity, and extensive fracturing, pose challenges for effective acidizing stimulation. Gelled acid treatment offers a solution to issues such as severe acid fluid loss and limited penetration in high-temperature carbonate reservoirs. However, current gelled acids often lack sufficient temperature resistance, and the retardation effect of single gelled acids remains limited. In this study, a temperature-resistant gelled agent was synthesized using acrylamide (AM), methacryloyloxyethyl dimethyl octadecyl ammonium bromide (DM-18), dimethyl diallyl ammonium chloride (DMDAAC), and 2-acrylamido-2-methylpropanesulfonic acid (AMPS), achieving the designed molecular structure. Additionally, the zwitterionic surfactant dodecyl betaine (BS-12) was selected as a retardation synergist, forming a retarded gelled acid with excellent stimulation performance and effective rock etching. Static retardation rate tests and high-temperature, high-pressure acid-rock reaction kinetic experiments were conducted to compare the retardation effects of gelled acid and retarded gelled acid. The kinetics equations and activation energies for hydrochloric acid, gelled acid, and retarded gelled acid under varying temperatures and concentrations were determined. Results demonstrated that the retarded gelled acid exhibited superior retardation efficiency compared to single gelled acid, achieving a retardation rate exceeding 80% within 1 h. Its kinetic reaction rate and activation energy at high temperatures were lower than those of single gelled acid, highlighting its stability and effectiveness in high-temperature environments. Scanning electron microscopy and infrared spectroscopy analyses revealed the retardation mechanism: the polymer network hindered hydrogen ion transfer, while the adsorption film prevented direct contact between hydrogen ions and the rock surface.