Fate And Transport Of 8 Hydraulic Fracturing Fluid Organic Compounds
Dehart, Jessica N 1 ; Ryan, Joseph 2
1 University of ŷڱƵ, Boulder
2 University of ŷڱƵ, Boulder
Many areas in the United States are currently experiencing rapid development of natural gas production wells employing the method of hydraulic fracturing to extract the gas out of shale formations. The potential impact of hydraulic fracturing on shallow groundwater resources, however, is not yet fully understood. One recent study found evidence of thermogenic methane migration to shallow drinking water wells in “active gas-extraction areas,” defined as one or more wells located within 1 km, indicating that fluid migration pathways may exist (Osborn et al., 2011).
Our work seeks to understand the potential for migration of hydraulic fracturing fluids into shallow groundwater via unintended release pathways such as faulty well casings, as well as examine the suitability for organic fracturing fluid additives to be used as tracers to identify instances of fracturing fluid migration. The initial project stage used available physiochemical data for 200 identified fracturing fluid chemical additives to construct a fate and transport model with the objective of predicting which organic compounds may be observed at significant quantities (>10% initial concentration remaining) with distance from a gas production well.
This initial analysis was used to identify 8 priority organic compounds: benzene, 2-butoxyethanol, ethylene glycol, triethylene glycol, isopropanol, glutaraldehyde, acrylamide and polyacrylamide. These compounds are all fairly soluble and represent a large range in both environmental persistence and human toxicity (Howard et al., 1991). Additionally, most of these compounds are frequently used in hydraulic fracturing fluids at relatively high concentrations (GWPC & IOGCC, 2012).
Large scale column tests will be used to measure retardation factors and degradation half lives of the 8 priority organic compounds. The 8 organics will be injected simultaneously into a synthetic groundwater and pumped through 1 m length, 0.1 m diameter stainless steel columns packed with sandstone sediments collected from the Arapahoe Aquifer, at a depth of approximately 120 m. One column will be maintained as an abiotic control to distinguish sorption and chemical degradation from biological degradation processes.
The experimentally determined removal rates of the 8 organic compounds may have applications in characterizing transport potential in instances of suspected releases of hydraulic fracturing fluids at depths above the target formation, such in the instance of a faulty well casing.
Groundwater Protection Council (GWPC), & Interstate Oil & Gas Compact Commission (IOGCC), 2012, FracFocus chemical disclosure registry, Accessed at http://fracfocus.org
Howard, P. H., Bosthling, R.S., Jarvis, W. P., Meylan, W. M., & Michalenko, E. M., 1991, Handbook of environmental degradation rates, Boca Raton, FL, CRC Press LLC.
Osborn, S.G, Vengosh, A., Watner, N. R., & Jackson, R. B., 2011, Methane contamination of drinking water accompany gas-well drilling and hydraulic fracturing: Proceedings of the National Academy of Science of the United States of America, 108(20), 8172-76.