Carbonate Acidizing: Effect of Additives on Reactivity and Wormhole Development

Abstract

The reduction in productivity in carbonate reservoirs is often associated with near-wellbore formation damage, making matrix acidizing an essential strategy to restore permeability. In this context, treatment efficiency depends on the balance between reaction kinetics and mass transport, which governs the formation of dominant wormholes. Although additives such as corrosion inhibitors and emulsion preventers are widely used for operational purposes, their effects on the reactive behavior of acid systems remain poorly understood. This study investigates the influence of commercial additives on HCl-based acid systems, using an additive-free system (NA) as a reference. An emulsion preventer (EP), a corrosion inhibitor (CI), and a formulation containing both additives (BA) were evaluated. The EP and CI were used at concentrations of 0.2 and 0.5 vol %, respectively, and the BA formulation contained both additives at the same concentrations. The formulations were evaluated through physicochemical characterization, carbonate dissolution kinetics, and reactive-flow experiments performed on Indiana Limestone samples (18.4% average porosity and 123 mD average permeability) during the injection of 15 wt % HCl until breakthrough. The presence of additives led to a significant reduction in surface tension, suggesting changes in interfacial conditions. Batch reactor experiments showed a pronounced retardation in dissolution kinetics, with reaction times increasing by approximately 4.5-fold, 30.6-fold, and 18.2-fold for the EP, CI, and BA systems, respectively, compared with NA. In reactive-flow experiments, the minimum pore volume to breakthrough (PVbt) was reduced from 0.40 PV for the additive-free system (NA) to 0.30, 0.21, and 0.34 PV for the EP, CI, and BA systems, respectively, indicating lower acid consumption to achieve breakthrough under the evaluated laboratory conditions, with the most pronounced effect observed for the CI system. Microcomputed tomography analysis revealed that acid systems containing additives promoted the formation of dominant wormholes at lower interstitial velocities, shifting the optimal acidizing condition toward lower injection rates. Under the evaluated laboratory conditions, this behavior is likely associated with reaction retardation induced by the additives, which may reduce premature acid consumption and enable deeper wormhole propagation before significant radial enlargement occurs. The results demonstrate that acid formulation plays a key role in controlling the dissolution regime and wormhole development. Even at low concentrations, the commercial additives modified dissolution kinetics, reduced the pore volume required to achieve breakthrough, and altered wormhole development, shifting the optimum acidizing condition toward lower injection rates under the evaluated laboratory conditions. These findings demonstrate that commercial acidizing additives should be considered as active formulation components capable of modifying dissolution kinetics, acid consumption, and wormhole development under reactive-flow conditions.