Determination and Fate of Formic Acid in High Temperature Acid Stimulation Fluids

Abstract

Abstract Formic acid is present in some corrosion inhibitors and is used as an intensifier in the acid treatment of oil and gas wells. This organic acid is important for the protection of low-carbon steels from acid corrosion at high temperatures and pressure. In this paper, the fate of formic acid used during acid treatments at temperatures up to 250°F in deep gas wells is investigated in detail. To the best of the authors’ knowledge, this is the first study of this type. The following conclusions were made from this work: Most of the commercial organic additives for corrosion inhibitors contain formic acid while one inhibitor intensifier contains both formic and acetic acids. Formic acid concentration in flow back samples from high temperature gas wells was higher than 85% of the injected value in most of the treatments. In concentrated HCl at 250°F, the amount of formic acid present in corrosion inhibitors and intensifiers decreased with time. After 8 hours corrosion inhibitors and intensifiers contained approximately 60% of the initial formic acid concentration. Acetic acid concentration did not significantly change with time in these tests. This work shows the fate of formic acid during acidizing of high temperature wells. Formic acid concentration in acid treatment flowback samples was near the injected value, showing that it remains available to act as a corrosion inhibitor intensifier. However, since it degrades with time, long shut-in times should be avoided. High formic acid concentrations in flow back samples may promote corrosion since the corrosion inhibitor concentration in these samples is significantly reduced.