Propagation characteristics of optimum wormhole in carbonate matrix acidizing using micro X-ray CT imaging

This study aims to investigate the propagation characteristics of an optimum wormhole to make an efficient acid treatment in carbonate matrix acidizing based on wormhole visualization using micro X-ray computerized tomography (CT) with high resolution. Five cases comprising 25 core-flood experiments under different experimental conditions using Indiana limestone cores were carried out at various injection rates to obtain the optimum injection rates. From the results, the optimum injection rates tended to increase with permeability but was not related to acid concentrations. The pore volume to breakthrough (PVBT), the amount of acid consumption required to breakthrough, was lower at higher permeability and acid concentration. This means that less amount of acid is consumed to generate the wormholes. Wormhole visualization with X-ray CT imaging showed that the wormhole diameters were gradually reduced along with the wormhole propagation axis in all cases. In addition, the mean of wormhole diameter tended to increase according to the higher permeability and acid concentration. The tortuosity, which is the ratio of actual wormhole length to core length, was exceeded at least 1.35 in each case. This implies that the actual flow length of the optimum wormhole is much longer than the core length. However, previous studies of wormhole propagation regarding the configuration of optimum wormhole are sparse, more intensive research would be required. Therefore, these propagation characteristics of optimum wormholes should be considered to improve the wormhole prediction model, and the wormhole prediction results would be more accurate and realistic than those of the existing models. Further study is needed to develop a new wormhole prediction model considering the propagation characteristics, such as diameter reduction and actual flow length. •Core-flood experiments were performed under various permeabilities and acid concentrations.•Wormhole visualization was conducted by micro X-ray CT to analyze propagation characteristics.•Wormhole diameter can be reduced along with the wormhole propagation axis.•The actual wormhole lengths are at least 1.35 times longer than the core length.