Enhancing acid stimulation in low-permeability carbonate reservoirs through the development of an innovative microemulsion retarding agent

Reducing the acid-rock reaction rate is crucial for enhancing acid stimulation in low-permeability carbonate reservoirs. This study introduces a diluted non-ionic microemulsion retarding agent optimized via a pseudo-ternary phase diagram, which significantly slows the acid-rock reaction by forming a barrier on the rock surface. The study revealed that the retarding agent has an average droplet size below 12 nm, enabling complete miscibility with water and acid in any ratio while maintaining the stability of the microemulsion structure. Rheological analysis confirms that the agent behaves according to the Newtonian model, with acid concentration influencing only its viscosity. The microemulsion adsorbs onto the rock surface through hydrogen bonding and other forces, is consistent with the Langmuir isotherm, and the adsorption amount depends on the concentration and wettability, effectively reducing the acid-rock reaction rate by 80 %. Moreover, the microemulsion exhibits properties such as wettability modification, interfacial tension reduction, and enhanced oil dissolution, reducing the injection pressure by 10 % and increasing the oil relative permeability during flowback by 16.67 %. The optimal injection rate for the microemulsion acid was 0.75–1.5 mL/min, outperforming crosslinked acid. In field applications, this allows for forming a singular, elongated dominant wormhole over a wide range of injection rates, enhancing the acidizing effect. The formulation presented herein offers a straightforward, effective solution for acidizing in low-permeability carbonate reservoirs, enhancing treatment efficiency and operational outcomes.