含裂隙碳酸盐岩酸化中超临界CO2对虫孔生长的影响初探

酸化是一种广泛应用于碳酸盐岩储层的增渗改造技术，其基本原理是将酸液注入储层裂隙，通过溶蚀反应使矿物溶解形成虫孔等通道，从而提高储层的渗透性和生产效率。以往的研究主要聚焦于优化注酸条件以提高成孔效率，忽略了碳酸盐岩酸化副产物CO2的影响。本研究针对三个含单裂隙的碳酸盐岩试样，开展不同浓度盐酸溶液的酸化实验，监测试样渗透率的变化；并在试验前后分别进行裂隙表面形貌激光扫描和内部空隙CT扫描，基于扫描结果对比分析了注酸条件对溶蚀效果的影响。研究结果表明：在流速、酸液浓度与种类等条件相同的条件下，CO2是否进入超临界态对虫孔形态有重要影响；超临界CO2可有效促进虫孔的生长，生成窄而长的虫孔，并显著提高溶蚀效果，试样的渗透率可提高3~9倍；而在CO2未进入超临界态的条件下，溶蚀形态接近面溶蚀或锥形虫孔，未贯通试样，试验前后渗透率没有显著变化，这是因为酸化反应产生的气态CO2会阻碍酸液的流动，从而降低酸化效果。本文结果揭示了在酸化中正面利用副产物CO2的可能性，有助于对现有酸化工程方案的优化和提升。

Effect of supercritical CO2 on wormhole generation in carbonatite acidification

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.