Carbonate Acidizing: A New Insight into Wormhole Propagation under Low Flow Rates

Wormholes are channels formed by the dissolution of carbonate rock due to interaction with acid solutions. These wormholes create pathways for fluid flow, playing a crucial role in applications such as production enhancement in petroleum engineering and geological CO₂ storage. However, the formation of wormholes at low flow rates is not well-explored. This gap is important because low injection rates frequently occur in field operations due to either reservoir constraints or operational limitations. Most models fail to accurately describe wormhole formation at low flow rates in systems with highly concentrated acids and high dissolution power, and experimental data remain scarce. In this study, acidizing experiments were conducted at low flow rates to investigate the pore volume to breakthrough (PVBt) and wormhole morphology behavior. Due to minimal pressure drop under these conditions, partial acidizing was systematically performed. Breakthrough was evaluated by analyzing micro-CT images and measuring the distance traveled by the wormhole in the sample to obtain PVBt estimates. The results suggest that the traditional models tend to overestimate PVBt values at low flow rates, leading to wormhole breakthrough occurring earlier than anticipated. A trend in the PVBt curve was detected at lower flow rates, stabilizing at a stoichiometrically derived limit rather than the indefinite increase predicted by earlier models. The findings of this study contribute to a deeper understanding of reactive flow at low flow rates, improving the accuracy of current models.