Capturing natural gas from the Barnett Shale in northern Texas requires at least 4 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 since 2005 has been recycling much of the water used in this process. It costs more than traditional disposal methods, but Devon believes the extra expense 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 upon Devon its 2008 Chairman’s Stewardship Award — its highest honor for environmental care.
Through its recycling partner, Fountain Quail Water Management, Devon installed its first mobile recycling unit near Decatur, Texas, in 2005. Also that year, the Texas Railroad Commission approved the process, which involves boiling flow-back water to create steam and separate the salty concentrate.
Each recycling unit operates 24 hours per day. Devon has recovered more than 500 million gallons — enough water to complete more than 100 wells.
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.
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.