Acidification is a widely used reservoir remediation technology in carbonate formations. Injecting acids into a carbonate formation can significantly improve the permeability and production efficiency of a reservoir by dissolving rock minerals and forming wormholes. Previous studies mainly focused on optimizing acid injection conditions to improve pore forming efficiency, but little attention was paid on the effect of CO₂, a by-product of carbonatite acidification. In this study, acid solution injection experiments with different concentrations of hydrochloric acids were applied to three carbonatite samples containing a single fracture. The permeability was monitored, and the internal voids and surface topographies of each sample were measured to investigate the influence of injection conditions on erosion. The results show that whether CO₂ enters the supercritical state has an important impact on the wormhole generation under the same conditions such as flow rate, acid concentration and type. When entering the supercritical state, supercritical CO₂ can promote the growth of wormholes, help generate narrow and long wormholes, and effectively improve the erosion. The permeability can be increased by 3~9 times. In contrast, when CO₂ is under the gas state, the erosion form is close to surface dissolution or conical wormholes. The generated wormhole does not penetrate the sample, and thus there is no obvious change in the permeability before and after the experiment. This is because CO₂ in the gas state can hinder the flow of acid solution and undermine the acidification effect. This study provides an implication of positively utilizing CO₂ to improve the acidification technique in engineering practices.