A novel two-phase thermal-hydraulic-chemical two-scale carbonate matrix acidizing model and effect of CO2

During matrix acidizing in carbonate reservoirs, the reaction between acid and rock minerals generates carbon dioxide (supersaturated CO 2 ), resulting to multiphase flow and reducing the effective surface area available for acid-rock reaction. Under typical reservoir conditions, CO 2 often exists in a liquid or supercritical state, where temperature and pressure significantly influence its physical properties. However, existing models lack the capability to efficiently and accurately simulate these complex processes. To address this gap, we develop a two-phase thermal-hydraulic-chemical two-scale model that incorporates CO 2 generation. The model is solved by sequential iterative solution method for computational efficiency and convergence issues associated with strong non-linearities in fully coupled approaches. The model is validated with existing models and analytical solutions. Simulation results demonstrate that produced CO 2 by the reaction leads to wormhole structures with sparser branching, shorter branch lengths, and smaller diameters. CO 2 facilitates acid transport to the wormhole tip, improving wormhole propagation efficiency and reducing the pore volume to breakthrough (PV bt ). Elevated injection temperatures accelerate reaction rate, further decreasing PV bt and increasing the optimal injection rate. Due to the reaction heat, the temperature around and at the top of the wormhole, as well as the surface reaction rate, are respectively 2–7K higher and increase by 20%–60% compared to those inside the wormhole. However, pressure exerted negligible effects on PV bt . Both PV bt and the optimal injection rate decrease with increasing initial average porosity. A greater horizontal-to-vertical spatial correlation length ratio enhances the directionality of wormholes. PV bt remains stable at low porosity variation coefficients but drops sharply beyond a specific threshold. This study provides a theoretical framework for optimizing acidizing design and process efficiency in carbonate reservoirs.