On the fate of hydraulic fracturing fluid additives: Thermochemical sulfate reduction reaction of sodium dodecyl sulfate

Hydraulic fracturing is a key technology for unlocking shale gas resources. While the compatibility and performance of fracturing fluid additives have been investigated, little research has been made on the post-fracturing fate of these components. Recently, the chemical additives used in hydraulic fracturing fluid were shown to undergo thermochemical sulfate reduction (TSR) reactions, leading to the delayed appearance of hydrogen sulfide (H2S) during production from a shale gas reservoir. Sodium dodecyl sulfate (SDS), an anionic surfactant used as a friction reducer and emulsion inhibitor, was shown to contain all the required reducing and oxidizing ingredients to participate in a TSR reaction. In this study, we demonstrate that the TSR reaction of SDS is an aqueous phase process with little dependence on the gas over-pressure. Furthermore, we demonstrate that presence of native sulfide (represented by sulfide anions) in the reservoir acts as a catalyst and significantly increases the rate of the produced H2S. Formation of organosulfur compounds also has been observed when SDS solution contains initial low concentrations (< 500 ppm) of sulfide anion.