ORGANIC SUBSTANCES IN PRODUCED WATER FROM THREE UNCONVENTIONAL OIL PLAYS

Unconventional oil and gas (UOG) production has emerged as an important component of the U.S. and world energy supply. Technological innovations in the oil and gas industry, especially horizontal drilling and hydraulic fracturing, allow for enhanced release of oil and natural gas, making commercial exploitation of tight organic-rich reservoirs possible on a large scale. Although UOG is enormously successful, produced water from UOG extraction poses possible environmental and human health issues as a result of improper disposal, leakage, fluid spillage or other events that allow for fluid release into the surface environment. Organic compounds, salinity, radionuclides, and trace elements, present to varying degrees in UOG produced waters, may be environmentally relevant. Although lists of organic chemicals used in hydraulic fracturing are available, few studies have characterized the organics present in produced water, which could contain additional compounds mobilized from the formation itself. An understanding of the range of organic compounds present in produced water will allow for targeting specific compounds in studies of environmental contamination from UOG production.

In the present study, we determined organic substances in produced water from UOG oil production in the Permian Basin (TX), the Williston Basin (ND), and the San Joaquin Basin (CA). Previously, we observed a range of organic chemicals, including solvents, biocides, scale inhibitors, and other organic chemicals at mg/L concentrations for individual compounds in produced water from UOG gas production in the Marcellus Shale. Produced water collected at the well-head from UOG oil producing wells contains high levels of petroleum hydrocarbons (gas- and diesel-range alkanes and alkenes). Samples of produced water collected from open air separator tanks, however, have much lower levels of petroleum hydrocarbons, and organic chemicals similar to those from UOG gas production are observed. Specific organic compounds that might be targeted in environmental studies of impacts of UOG include: 2-butoxy ethanol (2BE) and derivatives, glycol ethers, and benzene and naphthalene derivatives.