Biocides represent a key class of chemicals within hydraulic fracturing fluids which are included to prevent microbial-induced souring and/or corrosion in wells where underground conditions may favor bacterial growth. This presentation will first give a brief overview of these chemicals’ fate, toxicity and mobility as used in hydraulic fracturing. The remainder of the talk will focus on elucidating the transformation kinetics and pathways of glutaraldehyde, the most commonly used biocide in hydraulic fracturing fluids. Despite the widespread use of glutaraldehyde, very little is known about its fate when subjected to the high pressures, temperatures, salinity, and varying pH experienced downhole during a hydraulic fracturing event. Thus, we employed stainless steel high temperature/pressure reaction vessels to simulate various underground conditions while utilizing HPLC-UV-vis and mass spectrometry to track transformation of glutaraldehyde over time. We observed faster transformation of glutaraldehyde at high pH (t1/2 = 38.2 h at pH 6; 5.8 h at pH 7; 1.1 h at pH 8) and high temperature (t1/2 = 153 h at 65 ºC; 5.8 h at 100 ºC; 0.4 h at 140 ºC), but slower transformation in the presence of salt (t1/2 = 5.8 h in absence of NaCl; 21.0 h at 1 M NaCl; 31 h at 2 M NaCl; 40 h at 3 M NaCl). We did not observe any effect of pressure up to 2000 psi. Several major transformation products are revealed as polymers with varying degrees of hydration resulting from the symmetrical aldol condensation(s) of glutaraldehyde. In conclusion, transformation of glutaraldehyde is greatly affected by down-hole conditions and the bulky polymeric products are not likely to return to the surface with flowback water.

Transformation kinetics and pathways of hydraulic fracturing biocides under downhole conditions: Focus on glutaraldehyde

249th National Meeting (2015)

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