Permeability enhancement via acid has drawn broad attention in mining and oil industries to treat low-permeability formations to increase the resource recovery rate. In this study, experiments including static acid permeability enhancement tests, flooding acid permeability enhancement tests, and micro-CT scanning were conducted to investigate the mechanism of permeability enhancement and changes in pore structure during acid treatment. First, the extent of reaction between low-permeability sandstone samples and four different acids was evaluated by static tests. The hydrochloric and formic acids exhibited good performance to dissolve filling minerals during static tests. Second, acid flooding in sandstone cores was carried out under reservoir conditions. After acid flooding, the porosities of sandstone cores were significantly increased and a decrease in pressure difference was observed, demonstrating a permeability increase. The pressure difference of hydrochloric acids was lower than that of formic acids at the end of flooding, and the permeability results indicated that the percentage of permeability increase by hydrochloric acid treatment and formic acid treatment were 283% and 120%, respectively. Third, all samples were scanned by micro-CT before and after acid permeability enhancement tests, and CT images were analyzed to study changes in pores, pore throats, and coordination numbers using Avizo software. The mineral compositions and 2D micromorphology were characterized by SEM-EDS, XRD and ICP. After acid treatment, the number of interconnected pores, pore throats, and their equivalent radii all increased, leading to a higher permeability. The improved permeability was mainly due to the dissolution of dolomite, which was identified by SEM-EDS and ICP.

通过酸提高渗透率已引起采矿和石油工业的广泛关注，以处理低渗透率地层以提高资源回收率。本研究通过静态酸促渗试验、驱替酸促渗试验、显微CT扫描等实验，探讨酸处理过程中的增透机理和孔隙结构变化。首先，通过静态试验评估了低渗透砂岩样品与四种不同酸之间的反应程度。盐酸和甲酸在静态测试中表现出良好的溶解充填矿物的性能。二是在油藏条件下实施砂岩岩心酸驱。酸驱后，砂岩岩心的孔隙度显着增加，压差减小，表明渗透率增加。驱油结束时盐酸压差低于甲酸压差，渗透率结果表明，盐酸处理和甲酸处理的渗透率增加百分比分别为283%和120%。第三，在酸渗透增强试验前后对所有样品进行显微 CT 扫描，并使用 Avizo 软件分析 CT 图像以研究孔隙、孔喉和配位数的变化。通过SEM-EDS、XRD 和ICP 对矿物成分和二维微观形态进行了表征。酸处理后相互连通的孔隙、孔喉和等效半径均增加，导致更高的渗透率。渗透率的改善主要是由于白云石的溶解，这是通过 SEM-EDS 和 ICP 确定的。