Capturing natural gas from the Barnett Shale in northern Texas requires roughly 3.5 million gallons of water per well. The water, injected with high pressure, cracks open, or “fractures” the shale, creating the porosity necessary for the gas to flow.
Through a novel approach, Devon now is recycling much of the water used in this process. It costs about 40 percent more than traditional disposal methods, but Devon believes the extra cost benefits both the environment and the company.
So does the city of Fort Worth, which has endorsed the recycling program and indicated its hopes that other Barnett Shale producers follow suit.
Devon’s program prompted the Interstate Oil and Gas Compact Commission to bestow its 2008 Chairman’s Stewardship Award -- its highest honor for environmental care – on the company.
Through its recycling partner, Fountain Quail Water Management, Devon recycles 600,000 gallons a day. Fountain Quail installed its first mobile recycling unit near Decatur, Texas, in 2005. Also that year, the Texas Railroad Commission approved the process, which involves boiling flowback water to create steam and separate the salty concentrate.
The partnership now operates nine such units in rural areas near Fort Worth. Volume has grown steadily since then, to a projected total of 133.5 million gallons of recycled water in 2008.
The result: Distilled water that is suitable for drinking, but instead is transported to other nearby Devon well sites, where it is used again. This reduces the need for obtaining water from farm ponds, streams or municipalities.
Nine mobile recycling units at four sites operate 24 hours a day. Devon has recycled enough water since inception to fracture shale at 80 wells.
Recycled water now accounts for nearly 15 percent of what Devon uses to cause “fracs” in the Barnett Shale. Because the fracturing process requires fresh water, Devon is exploring ways to make this process more cost-effective and incorporating it beyond the Barnett Shale. One idea involves sharing the cost of each recycling unit among multiple gas producers.
Fountain Quail wants to expand the technology further by developing a pipeline network to use treated sewage in the fracturing process to further reduce demand on community water resources.
How the recycling process works
This photo shows water samples from each of the four stages involved in the recycling process.
Step 1: Once wastewater is removed during the fracturing of shale, a flocculant is added to make the fine waste particles congeal. The congealed matter settles at the bottom, making it easier to separate suspended solids from the remaining water.
Step 2: Those suspended solids, including polymers and a coagulating agent, are removed and disposed in a landfill.
Step 3: Salt is separated through a boiling, vaporizing and distillation process. The salty concentrate that remains can be used as “kill fluid” to aid in another well completion.
Step 4: The distilled water (about 80 percent of the original captured water) is returned to use in the field. Between 10 and 15 percent of the water used in Devon’s shale fracturing process comes from this recycled water.