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Produced water is a term used in the oil industry or geothermal industry to describe water that is produced as a byproduct during the extraction of Petroleum and natural gas, or used as a medium for heat extraction. Water that is produced along with the hydrocarbons is generally Brackish water and saline water in nature. 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. In geothermal plants, the produced water is usually hot. It contains steam with dissolved solutes and gases, providing important information on the geological, chemical, and hydrological characteristics of geothermal systems. Oil wells sometimes produce large volumes of water with the oil, while gas wells tend to produce water in smaller proportions.
As an oilfield becomes old, its natural drive to produce hydrocarbons decreases leading to decline in production. 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. In offshore areas, sea water is used. In onshore installations, the injected water is obtained from rivers, treated produced water, or underground. Injected water is treated with many chemicals to make it suitable for injection. The injected water eventually reaches the production wells, and so in the later stages of water flooding, the produced water's proportion ("cut") of the total production increases.
Historically, produced water was disposed of in large . However, this has become an increasingly unacceptable disposal method from both environmental and human health perspectives. Produced water is considered 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 . Although beneficial reuse for drinking water and agriculture have been researched, the industry has not adopted these measures due to cost, water availability, and public health concerns.
Gravity separators, , plate coalescers, dissolved gas flotation, and nut shell filters are some of the technologies used in treating wastes from produced water.
In January 2020, Rolling Stone magazine published an extensive report about radioactivity content in produced water and its effects on workers and communities across the United States. It was reported that brine sampled from a plant in Ohio was tested in a University of Pittsburgh laboratory and registered radium levels above 3,500 pCi/L. The Nuclear Regulatory Commission requires industrial discharges to remain below 60 pCi/L for each of the most common isotopes of radium, radium-226 and radium-228.
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