This study investigates, theoretically and experimentally, the effect of conventional and new chelating-agent-based acidizing fluid systems on carbonate formations. An initial assessment showed that an existing semi-empirical model used for hydrochloric (HCl) acid systems was not suitable for predicting wormhole growth and penetration for chelating agents.

With recent advances to acidizing and stringent environmental regulations, chelating agents have begun to replace conventional acid systems for well stimulation. They are more environmentally acceptable and can work in high-temperature wells. One crucial aspect for successful well stimulation of carbonate matrix acidizing is acidizing models. Yet, there have been few attempts to model wormhole growth and penetration for these newer chelating agents.

A semi-empirical mathematical model is proposed for chelating agents based on published experimental data. The results were compared with HCl acid systems.

The predicted wormhole growth was in good agreement with laboratory data for a wide range of temperatures and concentrations. A comparative study with chelating-agent and HCl-acid systems is also discussed. Results showed that pore volume to breakthrough (PVbt) for the chelating-agent-based system increased more steeply compared to the HCl-acid-based system with injection rate. This would translate into higher pumping volumes in the field for a given wormhole penetration if not optimized. This could be attributed to the slower reaction rate of the chelating agent and might require adjustment in transport phenomena for optimized treatment design.

The model developed in this work should help field engineers design treatments with optimum rates and volumes, helping minimize the cost of stimulation treatments. It should also further facilitate understanding of the wormhole formation mechanism for chelating agents.

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