Brackish water, in the petroleum industry, is the subsurface or produced water that exhibits a moderate salinity level lying between that of fresh water and seawater or high-salinity brine. This classification has long been applied to formation waters encountered during oil and gas exploration and production, as well as to water sourced from aquifers for operational purposes such as injection or steam generation. The industry define brackish water specifically as containing 1,000 to 10,000 ppm NaCl, distinguishing it from fresh water (0 to 1,000 ppm NaCl), salty water (10,000 to 100,000 ppm NaCl), and brine (over 100,000 ppm NaCl).
Such water commonly appears in oilfield operations as co-produced fluid alongside hydrocarbons, originating from connate or formation sources that have interacted with reservoir rocks over geologic time, resulting in dissolved salts primarily from chloride, sodium, and other ions. In practice, brackish water serves as a practical alternative source for waterflooding, hydraulic fracturing, or thermal enhanced recovery processes when fresh water supplies are limited.
