Why Beneficial Use?
Large volumes of produced water are pumped to the surface during production of oil and gas, including coalbed methane (CBM), throughout the United States. U.S. CBM basins are shown in the image on the right. Water must be pumped out of the coal layers (referred to as dewatering) in order to reduce the hydrostatic head (i.e., reservoir pressure) and allow the release of methane. The produced water generated during these operations is by far the largest byproduct or waste stream associated with gas production. The quantity of water produced during the life of a well is typically from 1 to 3 barrels (bbl) of water per thousand cubic feet (bbl/mcf) of gas. Water production is greatest in the early stages of well production, and it diminishes over time.
Produced water is an inextricable part of the natural gas recovery process. If an operator cannot reduce water production rates or sufficiently minimize water management costs, CBM fields cannot be efficiently developed, and a valuable energy resource may be lost or diminished.
The costs of produced water management vary extensively depending on the location, disposal method, the type of waste (quality and quantity), and the extent of competition in the local or regional area. Direct discharge and impoundment/evaporation are the least expensive management options, while commercial hauling of water or brine disposal are the most expensive options for management of produced water.
Today, freshwater resources in the Western United States are fully allocated. Population forecasts suggest that the majority of U.S. population growth by 2020 will occur in western states, representing regions already lacking sufficient and adequate water resources (See the image to the right). Increasing water demands associated with energy production and use exacerbate the situation in the West. While this scenario represents enormous challenges, it also provides opportunities for beneficial use of new water resources such as produced water. There are clear needs and strong economic drivers to develop integrative approaches to improve treatment, handling, disposal, and beneficial use of water brought to the surface during production of CBM and other unconventional gas resources.
References:
- Energy Information Administration. Available at: <http://www.eia.doe.gov/oil_gas/rpd/cbmusa2.pdf [PDF]>
- J. Hoffman, S. Forbes and T. Feeley. 2004. Freshwater needs to meet 2025 electricity generating capacity forecasts. Department of Energy/National Energy Technology Laboratory, Washington, D.C.