Produced water

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 oil and natural gas,^[1] or used as a medium for heat extraction.^[2][3][4][5] Water that is produced along with the hydrocarbons is generally brackish and saline water in nature.^[6] 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 plays, 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.^[2] Oil wells sometimes produce large volumes of water with the oil, while gas wells tend to produce water in smaller proportions.

A shale gas well being drilled by a drilling rig in Pennsylvania

As an oilfield becomes old, its natural drive to produce hydrocarbons decreases leading to the decline in the 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 the offshore areas, sea water is used. In the onshore installations the injected water is obtained from river, treated produced water or from the 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 proportion ("cut") of the total production increases.

Water quality

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. In oil fields, almost all produced water contains oil and suspended solids.^{[citation needed]} 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.^[7][8] Metals found in produced water include zinc, lead, manganese, iron, and barium.^[9] In geothermal fields, produced waters are classified into 3 chemical types: HCO3-Ca⋅Mg, HCO3-Na and SO4⋅Cl-Na.^[2] The U.S. Environmental Protection Agency (EPA) in 1987 and 1999 indicates that during drilling and operations, additives may be used to reduce solid deposition on equipment and casings. Water produced from underground formations for geothermal electric power generation often exceeds primary and secondary drinking water standards for total dissolved solids, fluoride, chloride, and sulfate.

Water management

 

Diagram of an injection well for disposal of produced water

Water is required for both traditional geothermal systems and EGS throughout the life cycle of a power plant. For traditional projects, the water available at the resource is typically used for energy generation during plant operations.^[10]

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 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^[11][12] and discharges to surface waters.^[13] 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.^{[citation needed]}

Gravity separators, hydrocyclones, plate coalescers, dissolved gas flotation, and nut shell filters are some of the technologies used in treating wastes from produced water.^[14]

Radioactivity

The use of produced water for road deicing has been criticized as unsafe.^[15]

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.^[16]

See also

• Industrial waste water treatment
• Oil–water separator

References

1. Klemz, Ana Caroline; Weschenfelder, Silvio Edegar; Lima de Carvalho Neto, Sálvio; Pascoal Damas, Mayra Stéphanie; Toledo Viviani, Juliano Cesar; Mazur, Luciana Prazeres; Marinho, Belisa Alcantara; Pereira, Leonardo dos Santos; da Silva, Adriano; Borges Valle, José Alexandre; de Souza, Antônio Augusto U.; Guelli U. de Souza, Selene M. A. (2021-04-01). "Oilfield produced water treatment by liquid-liquid extraction: A review". Journal of Petroleum Science and Engineering. 199: 108282. doi:10.1016/j.petrol.2020.108282. ISSN 0920-4105. S2CID 233073324.
2. Su, Shujuan; Li, Ying; Chen, Zhi; Chen, Qifeng; Liu, Zhaofei; Lu, Chang; Hu, Le (2022-06-01). "Geochemistry of geothermal fluids in the Zhangjiakou-Penglai Fault Zone, North China: Implications for structural segmentation". Journal of Asian Earth Sciences. 230: 105218. Bibcode:2022JAESc.23005218S. doi:10.1016/j.jseaes.2022.105218. ISSN 1367-9120. S2CID 248019293.
3. Song, Guofeng; Song, Xianzhi; Ji, Jiayan; Wu, Xiaoguang; Li, Gensheng; Xu, Fuqiang; Shi, Yu; Wang, Gaosheng (2022-03-01). "Evolution of fracture aperture and thermal productivity influenced by chemical reaction in enhanced geothermal system". Renewable Energy. 186: 126–142. doi:10.1016/j.renene.2021.12.133. ISSN 0960-1481. S2CID 245682408.
4. Tao, Jian; Yang, Xing-Guo; Ding, Pei-Pei; Li, Xi-Long; Zhou, Jia-Wen; Lu, Gong-Da (2022-06-05). "A fully coupled thermo-hydro-mechanical-chemical model for cemented backfill application in geothermal conditions". Engineering Geology. 302: 106643. doi:10.1016/j.enggeo.2022.106643. ISSN 0013-7952. S2CID 247848365.
5. Li, S.; Wang, S.; Tang, H. (2022-03-01). "Stimulation mechanism and design of enhanced geothermal systems: A comprehensive review". Renewable and Sustainable Energy Reviews. 155: 111914. doi:10.1016/j.rser.2021.111914. ISSN 1364-0321. S2CID 244823147.
6. D. Atoufi, Hossein; Lampert, David J. (2020). "Impacts of Oil and Gas Production on Contaminant Levels in Sediments". Current Pollution Reports. 6 (2): 43–53. doi:10.1007/s40726-020-00137-5. ISSN 2198-6592. S2CID 211080984 – via Springer Nature.
7. "About Produced Water". Advanced Water Technology Center. Golden, CO: Colorado School of Mines. Retrieved 2016-05-14.
8. Igunnu, Ebenezer T.; Chen, George Z. (September 2014). "Produced water treatment technologies". International Journal of Low-Carbon Technologies. 9 (3): 157–177. doi:10.1093/ijlct/cts049.
9. Veil, John A.; Puder, Markus G.; Elcock, Deborah; Redweik, Robert J. (2004). A white paper describing produced water from production of crude oil, natural gas, and coal bed methane (PDF) (Report). Argonne, IL: US Argonne National Laboratory. ANL/EA/RP-112631.
10. Clark, C. E.; Harto, C. B.; Sullivan, J. L.; Wang, M. Q. (2010-09-17). "Water use in the development and operation of geothermal power plants". doi:10.2172/1013997. OSTI 1013997. {{cite journal}}: Cite journal requires |journal= (help)
11. "Underground Injection Control Regulations and Safe Drinking Water Act Provisions". Washington, DC: U.S. Environmental Protection Agency (EPA). 2016-10-17.
12. "General Information About Injection Wells". EPA. 2016-09-06.
13. "Oil and Gas Extraction Effluent Guidelines". EPA. 2019-05-15.
14. Development Document for Final Effluent Limitations Guidelines and New Source Performance Standards for the Offshore Subcategory of the Oil and Gas Extraction Point Source Category (Report). EPA. 1993. pp. IX-15–IX-19. EPA-821-R-93-003.
15. Bain, Daniel J; Cantlay, Tetiana; Garman, Brittany; Stolz, John F (1 November 2021). "Oil and gas wastewater as road treatment: radioactive material exposure implications at the residential lot and block scale". Environmental Research Communications. 3 (11): 115008. doi:10.1088/2515-7620/ac35be.
16. Nobel, Justin (21 January 2020). "America's Radioactive Secret". Rolling Stone.