Carbonate acidizing – A review on influencing parameters of wormholes formation

Acidizing is a well-stimulation operation that consists of injecting a reactive fluid into the rock formation. When in carbonate rocks, the dissolutions create conductivity channels called wormholes. The pattern formed depends on the flow rate, thermodynamic conditions, and several rock-fluid interaction parameters. Despite acidizing operations being well-known, several factors or conditions affecting wormhole formation are not thoroughly tested in the laboratory. We observe a difficulty in the literature to summarize the main aspects involved in wormhole formation. At the same time, understanding how each parameter could affect the wormholing process can help to optimize the acidizing design, maximizing the financial return. Therefore, this review article discusses the main studies about the parameters affecting the wormhole's formation: acid concentration, reaction rate, flow rate, temperature, core sample dimension, and heterogeneity. The main idea here is to provide a resume of the most relevant works founds in our literature review and a reference base for researchers interested in carbonate acidizing. The pore-volume-to-break-thought (PVbt) plotted as a function of the flow rate is the most common approach to evaluate the dissolution pattern observed for each reactive fluid-rock combination. However, PVbt should be seen more comprehensively as a consequence of advection-diffusion-reaction balance. Other essential aspects that need to be considered to obtain a significant representation of the PVbt plots are sample geometry and the initial rock saturation.