FATE AND TRANSPORT OF FOUR ORGANIC COMPOUNDS FREQUENTLY USED IN HYDRAULIC FRACTURING FLUID IN LABORATORY COLUMNS CONTAINING AQUIFER SEDIMENTS

The use of hydraulic fracturing and horizontal drilling has resulted in the rapid development of oil and gas resources in many areas of the United States; however, the potential effects of hydraulic fracturing on shallow groundwater resources are not fully understood. There are several proposed groundwater contamination pathways, including compromised well integrity and fluid flow pathways caused by activating existing fractures and faults. The objective of our study was to assess the potential for contamination of a shallow aquifer by examining the environmental behavior of four organic compounds frequently used in hydraulic fracturing fluids. Four compounds were selected based on their frequent presence in fracturing fluids and their potential for transport in porous media: isopropanol, 2-butoxyethanol, ethylene glycol, and glutaraldehyde. Flow-through column experiments were used to measure breakthrough curves of the four organic compounds. Fate and transport parameters were determined by fitting the breakthrough curves to a one-dimensional advection-dispersion-first-order reactive transport model. The organic compounds were added to a synthetic groundwater mixture and simultaneously injected into two stainless steel columns containing sandstone collected from the Arapahoe Formation in the Denver-Julesburg Basin by drilling. One column was maintained as an abiotic control using sodium azide and biodegradation was observed in the other column. As expected for these water-soluble compounds, sorption in the flow-through columns was minimal. Anaerobic biodegradation was observed for ethylene glycol and glutaraldehyde (measured half-lives of 2.8 and 7.6 d, respectively). In the abiotic control column no removal was observed for ethylene glycol and some abiotic removal was observed for glutaraldehyde (measured half-life of 36 d). No significant removal in either column was observed for isopropanol and 2-butoxeythanol (biodegradation half life > 50 d). These experimentally-determined parameters of fate and transport may be applied to characterize transport potential in instances of suspected releases of hydraulic fracturing fluids at depths above the target formation and to identify candidate tracer compounds to assess evidence of suspected contamination of a shallow aquifer.