Fouling Resistant Membrane for Produced Water Desalination
* Can produced water from oil and gas wells be treated economically to provide a new source of water?
Need and Benefit
Produced water is the remnant water left from the extraction of oil or gas from deep beneath the surface of the earth. This water contains residual hydrocarbons, heavy metals, radionuclides, numerous inorganic species, suspended solids, and chemicals used in treatment and hydrocarbon extraction. The amount of water pumped up with the gas or oil increases as the oil deposit becomes exhausted. On average in the United States, seven times more water than oil and gas is produced in the extraction and cleaning process.
This water is either injected back into the formation to wash out more oil or discharged to the surface where it causes environmental problems. Treating for beneficial use is complicated. The water may actually belong to the people with water rights to aquifers in area. When the water right is settled, there is still the problem of contamination. In some areas, the water cannot be re-injected as is, because of the high scaling potential. Pumping the water back into the formation after it has been equilibrated with the atmosphere can plug the formation with sulfates or carbonates. This type of water must be stabilized or discharged to the surface, which salts out the local soils and/or increases the salt loading in downstream rivers.
A short description of the extraction process, compliments of Emerson Process Management, will help set the stage for this proposal. Oil and water are pumped up from the formation into a tank and allowed to separate naturally. The oil is decanted off the top and the remaining water is treated with emulsion breaking chemicals to clean more oil from the mixture. Water effluent is allowed to settle and then discharged. Dissolved air floatation and media filtration are used in larger facilities to remove more of the oil residue. Final effluent still has dissolved hydrocarbons, heavy metals and salts. This water eventually ends up in water sources managed by Reclamation. Oil and gas development has escalated in Wyoming, Montana, Colorado, Texas, Oklahoma, and New Mexico. Eventually, most all of the produced water that cannot be re-injected ends up on land, or in water in Reclamation territory.
Remaining emulsified oil and dissolved hydrocarbons in the final stream make it difficult to use a membrane process for desalting. Current commercial membranes become fouled by oil very quickly. This proposal will test a variation on new fouling resistant membrane coatings developed for the Navy for use in shipboard treatment of blackwater for their ability to handle produced water.
Produced water can provide a new source of water for communities and industry near the wells. Currently in the state of Texas alone 400 million gallons per day of produced water must be reinjected or disposed offsite. The cost is $10 per thousand gallons (kgal) for reinjection or $30- $50/kgal for offsite disposal depending on the distance. (David Burnette, Texas A&M Global Petroleum Research Institute.)
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This information was last updated on April 19, 2014
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