PETROLEUM INDUSTRY

Produced Waters

Water is a significant byproduct of oil and gas production: more than 7m3 of water is produced for every cubic meter of oil or gas equivalent (10 bbl water/bbl oil) obtained from gas and oil wells in the continental U.S. (American Petroleum Institute, 1987). This water is known as produced water, formation water, or brine (because of its typically high chloride level), and its components typically include residual hydrocarbons, heavy metals, radionuclides, numerous inorganic species, suspended solids, and chemicals used in treatment and hydrocarbon extraction. Apart from nonhazardous industrial wastes, produced water from oil and gas wells represents, by some estimates, the single largest source of waste generated in the U.S.

In the U.S., produced waters may not be discharged to onshore navigable waters unless they are being used for agriculture or wildlife propagation, in which case the maximum daily effluent limitation for oil and grease is 35 mg/L.

Subsurface injection is the primary method for disposal of produced water for land-based oil and gas operations and is not currently regulated. Produced water may be reinjected to the same reservoir from which it came to aid in enhanced oil recovery (EOR) processes, reinjected to sallower saltwater formations, or reinjected to older, depleted producing formations. However, high oil and suspended solids concentrations may damage injection equipment or clog the reinjection formation. Thus, treatment of produced waters before disposal may be desirable based on both cost and environmental criteria.