Downhole chemical degradation of corrosion inhibitors commonly used in shale gas fracturing and stimulation

Abstract

Hydraulic fracturing combined with horizontal drilling and acid stimulation has allowed for the development of vast shale gas reserves, an important low-carbon energy source. Recent studies have focused on understanding the decomposition rate and products of chemical additives when exposed to laboratory hydraulic fracturing or acid stimulation conditions. Among common additives, corrosion inhibitors are necessary to protect the integrity of the wellbore materials (tubing) and eventually the production facilities. In this study, we report the hydrolysis rates for three common sulfur-containing corrosion inhibitors (2,5-dimercapto-1,3,4-thiadiazole, 2-amino-1,3,4-thiadiazole and 2-aminobenzothiazole), where the first two were found to decomposed to H2S and CO2. 2-amino-1,3,4-thiadiazole was found to decompose slower than 2,5-dimercapto-1,3,4-thiadiazole, but with a similar activation energy. Increased ionic strength accelerated the H2S formation rate for these systems while preloading with H2S showed no impact when compared to normal conditions. The third corrosion inhibitor, 2-aminobenzothiazole, did not decompose under the conditions tested (T = 150 °C and p = 140 bar). Data presented here provide insight into the degradation mechanisms and perhaps future designs of corrosion inhibitors.