Geochemical Impacts on the Degradation of the Hydraulic Fracturing Biocide Glutaraldehyde Under Downhole Conditions.

Glutaraldehyde is one of the most prevalent biocides in hydraulic fracturing fluids, used in 11% of all registered wells nationwide and representing 27% of total biocide use in the continental United States.  Biocides, often a key component of hydraulic fracturing fluids, are necessary to prevent microbial-induced souring and/or corrosion in any well where underground temperatures are favorable towards bacterial growth (typically under 121ºC).  Despite the widespread use of glutaraldehyde, very little is known about its chemical behavior underground, when subjected to the high pressures, temperatures, salinity, and varying pH experienced down-hole during a hydraulic fracturing event.  Current studies reveal that increased degradation is observed with increasing temperature and pH.  Here we use stainless steel reaction vessels with sampling ports to simulate underground conditions while employing analytical methods (HPLC with UV-vis and ToF-MS detection) to track degradation of glutaraldehyde over time while simulating down-hole conditions, providing for the first time kinetic constants detailing these relationships.  This study covers a range of relevant temperatures and pH values as well as the effects of both salinity and pressure.  Furthermore, major degradation products are revealed using mass spectrometry and NMR techniques.  The work presented here not only provides a novel look at down-hole behavior of glutaraldehyde but may also serve as a model for future studies focused on elucidation of underground behavior of other organic chemicals present in hydraulic fracturing fluids.