The Influence of Equilibrium Reactions on the Kinetics of Calcite Dissolution in Lactic Acid Solutions



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Matrix acidizing has historically been a common means of removing formation damage and increasing the productivity of petroleum wells. Organic acids have been used in an effort to minimize the corrosion problem and the rapid reaction rate encountered when using strong acids, such as hydrochloric acid (HCl). The reaction of an organic acid with carbonates is reversible and thermodynamically limited by the presence of reaction products. This thermodynamic limitation must be considered when studying the reaction kinetics of organic acids with carbonates.

A kinetic model was developed to account for both the equilibrium reactions on the rock surface and the mass transfer of the reactants and products. This study provides both mass transport and reaction kinetics parameters, which can be combined with the reservoir temperature to determine treatment duration or soaking time. While lactic acid has been used successfully in the field, having a more detailed knowledge of the reaction between lactic acid and calcite will allow for optimized treatment design.

The kinetic model was also used to isolate the contributions of the transport of reactants, the surface reaction, and the transport of products to the overall resistance of the reaction. At all temperatures investigated, the transport of products away from the surface represented the largest contribution to overall resistance.

A coreflood experiment was also performed to observe and confirm the wormholing tendencies of lactic acid in calcite. Lactic acid formed a single dominant, minimally-branched wormhole through the core.