Hydraulic fracturing occurs via injecting water, sand, and select chemicals into a production well and pressurizing this mixture to crack the rock shale. Typical constituents of the chemical mixtures are biocides that are applied to inhibit growth of sulfate-reducing bacteria, which may cause pipe corrosion and production of hazardous gases. Among these biocides, glutaraldehyde is the most widely-used product. However, very little is known about the reactivity and fate of glutaraldehyde when subjected to down-hole conditions. While stable in aqueous phase under near-surface conditions, it is hypothesized that the extreme conditions typically found in deep subsurface environments enable transformation processes, likely through nucleophilic substitution reactions such as hydrolysis.  In this study, stainless steel reactors are used to simulate the high pressures and temperatures of down-hole conditions relevant for a wide variety of reservoirs around the United States. Under these conditions, the impacts of varying pH and salt concentration on glutaraldehyde degradation are investigated. HPLC/ESI-ToF-MS is used to track concentration, speciation, and degradation of glutaraldehyde as a function of time, elucidating its transformation kinetics and pathways. Additionally, field flowback samples are analyzed to validate that the laboratory simulations mirror real-life processes and results. Preliminary results suggest that the degradation kinetics for glutaraldehyde are significantly influenced by temperature. For instance, the observed half-life at pH 3 and 100 psi in DI water decreased from 5.3 days at 125� C to 0.5 days at 175� C, while no degradation was observed at 65� C over a 100 hour time period. The results from these experiments indicate so far that glutaraldehyde is not likely to persist at elevated temperatures relevant to many shales. Ongoing experiments ?will show the effect of shale material and complex aqueous geochemistry on the fate of glutaraldehyde.

Degradation of the biocide glutaraldehyde under down-hole conditions

247th National Meeting (2014)

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