Measuring the Reaction Rate of Lactic Acid with Calcite Using the Rotating Disk Apparatus

Abstract

Abstract Lactic acid has been tested in various laboratories and applied in the field for acid fracturing. However, the rate of reaction of lactic acid with calcite has not been addressed before. This is mainly because of the complexity of the reaction kinetics and the thermodynamic equilibrium that limits the acid reactivity. Determination the reaction rate is a critical step for any successful matrix acidizing or acid fracturing. Therefore, the aim of this work is to conduct a detailed study on the reaction of lactic acid with calcite. Mass transport properties and the reaction kinetics are reported for such system for the first time using the rotating disk apparatus. Core samples of 1.5 in. diameter and 1 in. length were cut from Indiana limestone and were used in the reaction rate experiments. The effect of lactic acid concentration (1, 5, and 10 wt%), temperature (80–250°F), disk rotational speed (100–1800 rpm), and different inorganic salts on the reaction rate was investigated. The diffusion coefficient of 5 wt% lactic acid was determined at low rotational speeds and reported at 80, 200, and 250°F. The data of the reaction rate measured at 1500 rpm and in a temperature range 80–250°F was used to determine the reaction kinetics. The activation energy and the reaction rate constant for the reaction of lactic acid with Indiana limestone was reported at 80, 150, 200, and 250°F. The reaction of lactic acids with calcite was controlled by mass transfer at low disk rotational speeds (up to 500 rpm) and surface reaction limited at higher speeds. The acid diffusion coefficient increased with increasing the reaction temperature. The presence of inorganic salts significantly reduced the reaction rate.