Produced water
- Also known as
- formation water, oilfield brine, produced brine
Produced water is the water that comes to the surface along with oil and gas from a well. It includes water naturally present in the reservoir, injected water and returning fracturing fluid, and it is usually salty, with dissolved minerals, traces of oil and production chemicals.
What is produced water?
Oil and gas reservoirs almost always contain water as well as hydrocarbons. When a well produces, that water comes up too, along with any water injected for waterflooding and, in newly fractured wells, flowback of fracturing fluid. Together these are produced water. By volume it is the largest waste stream of the oil and gas industry: many U.S. wells produce several barrels of water for every barrel of oil, and the share rises as fields mature.
What produced water contains
- Dissolved salts, often at levels far above seawater; see total dissolved solids.
- Dissolved and dispersed hydrocarbons, including oil droplets and BTEX.
- Metals and scale-forming ions, such as calcium, barium, strontium and iron.
- Naturally occurring radioactive material in some formations.
- Residual production and fracturing chemicals.
- Suspended solids and bacteria.
Composition varies widely between formations, and within a field over time.
How produced water is managed
- Injection for disposal into deep formations through saltwater disposal wells, regulated as Class II injection wells.
- Injection for enhanced recovery, reusing the water to maintain reservoir pressure.
- Reuse in hydraulic fracturing, after treatment.
- Treatment and discharge or beneficial reuse, which is limited by the cost of treating very salty water and by regulation, but is an active area of development.
Challenges
Handling produced water is a major part of lease operating expense. Before injection or reuse, oil and solids must be removed, and water from different sources must be checked for compatibility to avoid mineral scale. Poor water quality plugs disposal wells and reduces their injectivity.
Frequently asked questions
Flowback is the fluid returning soon after hydraulic fracturing, mostly the injected fracturing fluid. Produced water is water from the formation, produced throughout the well’s life. Over the first weeks after fracturing, flowback gradually becomes produced water.
Yes. Most is reinjected, either for disposal or to maintain reservoir pressure, and a growing share is treated and reused for hydraulic fracturing. Wider reuse outside the oilfield is limited by treatment cost and regulation.
Sources
- Produced water, U.S. Geological Survey
- Produced water in oil and gas extraction, U.S. Environmental Protection Agency
- produced water, SLB Energy Glossary