Stimulation of high temperature oil and gas wells with HCl could cause significant corrosion to tubular goods. Organic acids are viable alternatives to HCl. However, conventional wisdom teaches that organic acids do not spend to its full capacity due to CO2 in solution. This leads to reducing their carbonate dissolving capacity further. Another potential drawback of using organic acids is the precipitation of the salt of calcium and organic ligands. Consequently, the concentration of the organic acid has to be confined to prevent the precipitation. Due to the above reasons, along with their cost per mass of rock dissolved, organic acids often have limited use in well stimulations.
Recent thermodynamic modeling studies have shown that when an organic acid or a mixture of HCl and an organic acid reacts with calcite, a previously unrecognized reaction occurs. This reaction enhances the calcite's dissolving capacity by the organic acid. The model provided new insight into the reaction equilibrium between organic acids with calcite, and gave a better understanding of which chemical species plays the dominant role in driving the overall dissolution reaction. In the case of acetic acid reacting with calcite, the model found that a chemical species, ca-monoacetate (Ca(CH3HCOO)+), exists because of the association of acetate and calcium ions. This species cannot be ignored. When quantitatively concentrated, it results in higher acetic acid dissolving capacity. Furthermore, mixing acetic acid with HCl can increase the conversion of acetic acid by the same calcium and acetate ion association and lead to more complete spending of acetic acid. The objective of this paper is to present the evidence of the existence of calcium monoacetate through experimental studies using Raman spectroscopy. Results showed that ca-monoacetate does exist during acetic acid dissolving of calcium carbonate. However, quantitative match between the experimental data and thermodynamic model prediction remains uncertain.