Produced Water: What USGS Research Shows About Oil and Gas Wastewater

Oil (top) and produced water (bottom) separating after collection from a well in the Permian Basin, Texas. Francisco Reyes, USGS.

Produced water is the water that comes up with oil, gas and coalbed methane. It is managed by recycling, treatment and discharge, spreading on roads, evaporation or infiltration, and above all deep well injection. USGS scientists in its Energy and Minerals and Environmental Health mission areas study it and publish the data.

Terms

What it is, and how much

In conventional wells, produced water is mostly natural brine plus water injected to push oil toward wells (waterflooding). In shale and tight reservoirs, fluid and sand (proppant) are pumped in under very high pressure to fracture the rock, and what comes back mixes that fluid with formation brine. Salinity ranges from that of drinking water to several times seawater, and the water can carry salts, petroleum and other organic compounds, solids, trace elements, bacteria, naturally occurring radioactive material, and anything injected.

• Volume: U.S. production generated about 57.4 million barrels of water a day in 2007 (a barrel is 42 gallons), and much more since.
• Pennsylvania: gas output rose from 0.20 to 2.26 trillion cubic feet from 2006 to 2012, mostly from the Marcellus Shale; produced water rose from 6.6 to 24.4 million barrels a year.
• Bakken: in the Williston Basin, oil production and well numbers have climbed steeply.

Bakken oil production and producing wells. Data: North Dakota Industrial Commission, Department of Mineral Resources. USGS.

Fast growth in places with little history of drilling can overwhelm local infrastructure for storing, treating, moving and disposing of this water.

Where it goes

More than 95% is injected — into dedicated Class II disposal wells or back into oil wells to boost recovery or hold pressure. The rest is treated and discharged, reused, or recycled for fracturing. Fresher water, often after treatment, can serve irrigation, livestock, habitat, aquaculture, dust control and deicing, firefighting, drilling mud and cooling. The industry has valued the salts in brine for more than 100 years, and some still pay: iodide from Oklahoma produced water is the largest U.S. source of iodine.

Risks

• Spills and leaks from storage and pipelines.
• Old wells, badly plugged or cemented, can let deep fluids reach shallow fresh water.
• Evaporation pits, mostly historical, can affect shallow groundwater.
• Deep injection can cause earthquakes.

The first USGS multidisciplinary study, 2001–2006 at Skiatook Lake on the Osage Reservation in Oklahoma, traced where produced water went and what it did near the surface, helping officials, landowners and companies plan cleanups.

Tracing it

• Geophysics: borehole, ground and airborne electromagnetic surveys map salty water underground, since conductivity rises with dissolved solids. At the East Poplar oil field in Montana, they helped model a hidden saline plume several miles across from a failed injection well.
• Chemical fingerprints: ratios of sodium and chloride to bromine reveal where salinity came from (used for Marcellus water); strontium-87/86 and radium-228/226 ratios tell apart otherwise similar waters from different reservoirs.

What's in it

The USGS Produced Waters Geochemical Database holds analyses of more than 160,000 samples. Three examples, in milligrams per liter:

The USGS keeps sampling where data are thin — the Appalachian, Permian and Williston Basins.

Hydrogen sulfide–producing bacteria cultured from shale gas produced water; the black is iron sulfide, a sign of sulfide production. The clear bottle is an uninoculated control. Darren Dunlap, USGS.

Microbes matter too: sulfide-producing bacteria can sour wells and corrode equipment, while others might boost gas output or break down contaminants. USGS scientists have studied them in shale gas water from northern Pennsylvania.

Research for decisions

• Drip irrigation, Powder River Basin: coalbed methane water there is fairly fresh but high in sodium, a threat to soil. With the Department of Energy's National Energy Technology Laboratory and an industry partner, USGS tracked treated water injected about 3 feet underground to grow forage crops. Calcium from slowly dissolving gypsum kept sodium from building up to harmful levels — so operators need to track soil gypsum.
• Road spreading, Northeast: Michigan, Ohio, Pennsylvania and New York have spread salty produced water on roads for decades for dust and ice. Its main salts are fairly benign, but radium in Pennsylvania and New York water is unusually high and clings to clays. Soil sampling beside treated roads has so far found limited evidence of radium buildup.

USGS scientists inspect a sediment core taken beside a road spread with produced water, Crawford County, Pennsylvania. Mark Engle, USGS.

As shale gas and tight oil have grown, the USGS has shifted its research to their produced water, working with the Bureau of Reclamation, the Department of Energy, state water and oil and gas agencies, and industry.

Sources

Based on Engle MA, Cozzarelli IM, Smith BD, "USGS investigations of water produced during hydrocarbon reservoir development," U.S. Geological Survey Fact Sheet 2014–3104; a work of the United States government in the public domain. The imported text stopped mid-sentence; its table, figures, road-spreading passage and closing section were recovered from the fact sheet's PDF. A photograph credited to a USGS volunteer is not reproduced.