Downhole Decomposition of Biocide Dazomet and Implications in the Delayed Onset of Hydrogen Sulfide in Hot Shale Gas Production

The unexpected presence of H2S in hot shale gas was previously attributed to Sulfur-reducing bacteria contamination. However, in recent years we have shown how sulfur containing chemical additives, used during the hydraulic fracturing procedures, could readily decompose and/or react under high-temperature and pressure (downhole conditions), producing H2S along with organosulfur compounds. In this abstract, we present evidence of the delayed souring of shale gas caused by Dazomet (commonly used biocide) which undergoes several reactions that leads to H2S and methyl thiol, exemplifying a case in which a chemical additive has the potential to sour hot shale gas production.