Join us for the 2025 Adrian Smith Lecture featuring
Douglas B. Kent
Scientist Emeritus
Earth Systems Process Division U.S. Geological Survey
Findings from studies of the environmental geochemistry of wastewater from oil and gas production
Oil and gas (OG) development in the United States generates more than two million cubic meters of co-produced water (herein called “wastewater”) annually, more than six times the annual production of petroleum hydrocarbons. Most of this wastewater is disposed of by injection into the subsurface, but some reaches surficial environments through land-surface application for beneficial uses (such as road deicing) or accidental releases (leaks and spills). We have been conducting research on potential water-quality impacts on the health of humans and aquatic ecosystems through the examination of wastewater and of surficial systems where accidental releases occurred. Changes in wastewater composition were examined at a shale-gas well completed in the Devonian-age Marcellus formation (Marcellus Shale Energy and Environment Laboratory, MSEEL, near Morgantown, West Virginia, United States) for over three years after the well went into production. As typically observed, dissolved salt concentrations increased with time in production, eventually reaching 200 grams per liter (g/L, ionic strength 4.0). Dissolved salt concentrations decreased substantially during prolonged shut in periods, but rebounded within weeks of going back into production. The wastewater compositions can be classified as a sodium-calcium-chloride brine, with elevated concentrations of barium, strontium, ammonium, and radium. Wastewater collected from the separator and from the wastewater storage tank on the pad had suspended solids dominated by ferrihydrite and quartz. Partitioning of strontium, barium, mercury, and lead from the aqueous to solid phases increased with increasing pH. Lead-210 (210Pb, half-life 22.2 years) and radium-226 (226Ra, half-life 1600 years) were the principal radioactive constituents, with 210Pb predominantly associated with the solids and 226Ra predominantly associated with the aqueous phase. Potential impacts of releases of OG wastewater were examined in a creek near Williston, North Dakota, United States, after discovery of a wastewater spill from a leaking pipeline. The wastewater had a total dissolved salt concentration of 300 g/L (ionic strength 8.1) with elevated concentrations of ammonium, strontium, barium, and radium. Wastewater-derived ammonium likely contributed to fish mortality observed during in-stream incubations conducted at a site 7.2 kilometer downstream of the spill. Wastewater-derived constituents, including 226Ra, were observed in stream-water, groundwater, stream-sediments, and seep-sediments at sites up to 7.2 km downstream of the spill site up to 2.5 years after the spill was discovered. Chemical extractions of sediments showed that barium, which is a surrogate for radium, was present predominantly as one or more solids while strontium was predominantly sorbed. These investigations provide guidance on assessing potential impacts of releases of OG wastewater.
Free admission ~ Reception to follow in DC 1301
Douglas B. Kent
Scientist Emeritus
Earth Systems Process Division U.S. Geological Survey
Doug Kent is a scientist emeritus at the United States Geological Survey. He holds a bachelor of Arts degree in chemistry from the University of Caliornia, San Diego and a Ph.D. in oceanography from Scripps Institution of Oceanography in La Jolla, California. After a stint in the Civil Engineering Department at Stanford University, he joined the United States Geological Survey (USGS), where he has conducted research focused on understanding water-quality impacts on the availability of water to sustain humans and aquatic ecosystems.