Application of citric acid in acid stimulation treatments

Abstract

Mass transfer process during the reaction of citric acid with calcite was investigated using the rotating disk apparatus. The effects of disk rotational speed, initial citric acid concentration, and temperature on the effective diffusion coefficient of citric acid were examined. Using various citric acid concentrations (1, 2, 5, 7.5 wt%), the diffusion coefficient of citric acid was calculated at 25, 40, 50°C. The effective diffusion coefficient of citric acid was found to be a function of the interplay between the calcium citrate precipitation and the presence of the counter calcium ions. At high initial acid concentration, (5, 7.5 wt%), the effects of calcium citrate precipitation and counter calcium ions were significant and the calculated citric acid diffusion coefficients were not comparable with its measured effective diffusion coefficients using the rotating disk. However, the effects of both the calcium citrate precipitation and the counter calcium ions on the citric acid diffusivity were minimal at low initial citric acid concentrations. The effect of temperature on the diffusion coefficient of citric acid at a constant citric acid concentration was found to follow Arrhenius law, and the activation energy is equal to 37.9 kJ/mol.