What Is Produced Water?
Produced water is water trapped in underground formations that is brought to the surface along with oil or gas. Because the water has been in contact with the hydrocarbon-bearing formation for centuries, it contains some of the chemical characteristics of the formation and the hydrocarbon itself. It may include water from the reservoir, water injected into the formation, and any chemicals added during the production and treatment processes. Produced water is also called “brine” and “formation water.” The major constituents of concern in produced water are:
- Salt content (salinity, total dissolved solids, electrical conductivity)
- Oil and grease (this is a measure of the organic chemical compounds)
- Various natural inorganic and organic compounds or chemical additives used in drilling and operating the well
- Naturally occurring radioactive material (NORM)
Produced water is not a single commodity. The physical and chemical properties of produced water vary considerably depending on the geographic location of the field, the geological host formation, and the type of hydrocarbon product being produced. Produced water properties and volume can even vary throughout the lifetime of a reservoir.
How Much Produced Water Is Generated?
Produced water is by far the largest volume byproduct or waste stream associated with oil and gas exploration and production.
- Approximately 21 billion bbl (barrels; 1 bbl = 42 U.S. gallons) of produced water are generated each year in the United States from nearly a million wells. This represents about 57 million bbl/day, 2.4 billion gallons/day, or 913,000 m3/day (Clark and Veil 2009).
- More than 50 billion bbl of produced water are generated each year at thousands of wells in other countries.
Early in the life of an oil well, the oil production is high and water production is low. Over time the oil production decreases and the water production increases. Another way of looking at this is to examine the ratio of water-to-oil:
- Worldwide estimate – 2:1 to 3:1
- U.S. estimate – 5.1 to 8:1, because many U.S. fields are mature and past their peak production (Clark and Veil 2009), although the ratio may be even higher.
- Many older U.S. wells have ratios > 50:1
At some point the cost of managing the produced water exceeds the profit from selling the oil. When this point is reached, the well is shut in.
In contrast, a coal bed methane well initially produces a large volume of water, which declines over time. The methane production starts low, builds to a peak, and then decreases.
This information and much of the background material used throughout the PWMIS site is based on Argonne’s produced water white paper [external site].
Clark, C.E., and J.A. Veil, 2009, Produced Water Volumes and Management Practices in the United States [external site], ANL/EVS/R-09/1, prepared by the Environmental Science Division, Argonne National Laboratory for the U.S. Department of Energy, Office of Fossil Energy, National Energy Technology Laboratory
Veil, J.A., M.G. Puder, D. Elcock, and R.J. Redweik, Jr., 2004, “A White Paper Describing Produced Water from Production of Crude Oil, Natural Gas, and Coal Bed Methane,” prepared by Argonne National Laboratory for the U.S. Department of Energy, National Energy Technology Laboratory.