Hydraulic Fracturing Additives and the Delayed Onset of Hydrogen Sulfide in Shale Gas

As natural gas production has shifted further from deep prolific gas reservoirs to shale gas, several questions are being addressed regarding fracturing technologies and the fate of chemical additives. A less investigated issue is the unexpected increase in produced hydrogen sulfide (H2S) from hot shale gas reservoirs. Understanding the source of H2S in shale reservoirs and managing low-levels of recovered elemental sulfur affects plans for future treatment, corrosion mitigation, and fracture fluid formulations. In this work we demonstrate that some typical ingredients of hydraulic fracturing fluids are not as kinetically stable as one might expect. Surfactants and biocides such as sodium dodecyl sulfate and glutaraldehyde are shown to undergo hydrolysis and thermochemical sulfate reduction reactions under moderate reservoir conditions, with H2S as the final product accompanied with long chain alcohols and hydrogen sulfate as long-lived intermediate species. This finding suggests that fracture fluid additives can be responsible for the delayed production of natural reservoir H2S.