Modeling Fate And Transport Of Hydraulic Fracturing Fluid Organic Compounds
Dehart, Jessica 1
1 University of Colorado, «Ƶ
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 study seeks to understand the potential for migration of hydraulic fracturing fluids into shallow groundwater as well as examine the suitability for organic fracturing fluid additives to be used as tracers to identify instances of fracturing fluid migration. Using available physiochemical data for 200 identified fracturing fluid chemical additives, a fate and transport model was constructed 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. The model takes hydrogeologic data as an input and therefore can be applied to the conditions specific to individual sites. The model was run under several different conditions to predict highly persistent compounds at those sites.
When compared to published groundwater samples from deep monitoring wells 100-200 meters away from production wells in Pavilion, Wyoming, the fate and transport model prediction of environmental behavior reasonably agreed with observed concentrations of nine out of eleven organic compounds (Fig 1-2). Under all varying hydrogeologic conditions, the model returned that compounds with a risk to human health, including some regulated under the Safe Drinking Water Act, may be present in significant quantities at distances >1 km from a gas production well.
The results of this study are designed to prioritize categories of potential hydraulic fracturing fluid compounds on the criteria of toxicity and persistence. Results from the model indicate that organic compounds may be likely candidates to be used as tracers to observe any migration of fracturing fluids away from the gas production well. This is due to the environmental persistence of some of the organic compounds and the fact that the presence of the compounds may not be explained by the natural geochemistry or alternative anthropogenic sources.
DiGiulio, D. C., Wilkin, R. T., Miller, C., & Oberley, G. United States Environmental Protection Agency, Office of Research and Development. (2011). Investigation of ground water contamination near pavillion, wyoming (EPA 600/R-00/000). Retrieved from website: http://www.epa.gov/region8/superfund/wy/pavillion/
Osborn, S. G., Vengosh, A., Warner, N. A., Jackson, R. B., 2011, Methane contamination of drinking water accompanying gas-well drilling and hydraulic fracturing: Proceedings of the National Academy of Sciences of the United States of America, v.108, p. 8172-8176.