Abstract
Acid stimulation of carbonate rocks aims to create channels within the rock, known as wormholes, to restore or enhance permeability, increasing production. Among the acids used in this type of treatment, 15 wt % hydrochloric acid (HCl) stands out due to its high reactivity, formation of soluble reaction products in aqueous media, and cost-effectiveness. To minimize corrosion of metallic structures and avoid emulsion formation after contact with formation oil, acid solutions are commonly prepared with additives such as corrosion inhibitors and emulsion preventers. To evaluate the influence of these additives on wormhole formation, this study performed core flooding experiments at different injection rates to construct pore volume to breakthrough (PV(bt)) curves, both in the presence and absence of these additives. The tests employed 15 wt % HCl solutions, with and without additives, using Indiana Limestone rocks containing 98.57% calcite. The experiments were conducted in a core flooding system under an injection rate range of 0.25-16 mL/min, at 25 °C, with a confining pressure of 2000 psi and back pressure of 1200 psi. After the tests, the cores were analyzed by X-ray microcomputed tomography to evaluate wormhole formation. The results indicated that additives reduced PV(bt) values at low flow rates, suggesting slower reaction kinetics and higher wormhole formation efficiency. The presence of additives decreased the optimal interstitial velocity by approximately 77% (from 0.91 to 0.21 cm/min), indicating that they provide better reaction control and enhance treatment efficiency. Moreover, micro-CT images confirmed the formation of dominant wormholes at almost all flow rates in the presence of additives, whereas in their absence (e.g., at 0.5 mL/min), the sample collapsed before breakthrough. The Buijse-Glasbergen model provided a good fit to the experimental data (R (2) = 0.99) for the additive-free curve. For the additive-containing system, however, an empirical adjustment of the model exponent was required to improve the correlation (from R (2) = 0.85 to R (2) = 0.93). The results demonstrate that these additives not only inhibit corrosion and prevent emulsions but also controlled the reactivity effect. This behavior significantly broadens the scope of their application, reinforcing their strategic importance in carbonate reservoir treatments.