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Produced water is a term used in the oil industry to describe water that is produced as a byproduct along with the oil and gas. Oil and gas reservoirs often have water as well as hydrocarbons, sometimes in a zone that lies under the hydrocarbons, and sometimes in the same zone with the oil and gas.
Oil wells sometimes produce large volumes of water with the oil, while gas wells tend to produce water in smaller proportion.
To achieve maximum oil recovery, waterflooding is often implemented, in which water is injected into the reservoirs to help force the oil to the production wells. The injected water eventually reaches the production wells, and so in the later stages of waterflooding, the produced water proportion ("cut") of the total production increases.
The water composition ranges widely from well to well and even over the life of the same well. Much produced water is brine, and most formations result in total dissolved solids too high for beneficial reuse. All produced water contains oil and suspended solids. Some produced water contains heavy metals and traces of naturally occurring radioactive material (NORM), which over time deposits radioactive scale in the piping at the well. Metals found in produced water include zinc, lead, manganese, iron, and barium.:8
Historically, produced water was disposed of in large evaporation ponds. However, this has become an increasingly unacceptable disposal method from both environmental and social perspectives. Produced water is considered an industrial waste.
The broad management options for re-use are direct injection, environmentally acceptable direct-use of untreated water, or treatment to a government-issued standard before disposal or supply to users. Treatment requirements vary throughout the world. In the United States these standards are issued by the U.S. Environmental Protection Agency (EPA) for underground injection and discharges to surface waters. Although beneficial reuse for drinking water and agriculture have been researched, the industry has not adopted these measures due to cost, water availability, and social acceptance.