The system improves the efficiency of treating and safely reusing water used for hydraulic fracturing at drill sites, researchers say. The filter can produce up to 50 percent more water for reuse compared with other filtration systems, greatly reducing demand for fresh water.
In addition to producing a higher volume of purified water, the new filter system also operates at lower pressure than traditional systems, meaning significant energy savings.
The technology could help reduce the environmental impact and financial costs of fracking, which has seen intense growth during the past decade because of advances in horizontal drilling. As production continues to increase, the National Petroleum Council estimates that 80 percent of wells drilled during the next decade will require fracking.
“Recycling flowback water on-site offers a cost-effective solution that conserves water and energy, saves roads from wear and tear, and keeps production costs down,” says Dan Miller, a researcher working with Benny Freeman, professor of chemical engineering at the University of Austin at Austin. “Everyone who uses water and natural gas can benefit from this technology.”
As reported in the Journal of Membrane Science, the team’s pilot study tested a system of specially coated membranes, which are pliable sheet-like structures made out of plastic that act as a barrier, to filter contaminated water that returns to the surface after it is pumped down a well during fracking.
The process of hydraulic fracturing pumps millions of gallons of water mixed with sand and chemicals down a well at high pressure to break, or fracture, shale rock to extract natural gas and oil trapped deep underground. Each well can use up to 6 million gallons of water during the hydraulic fracturing phase of production, which can last a week—the equivalent of nine Olympic-size pools.
The advantage of the team’s approach is a patented coating that makes membranes more resistant to damage caused by contaminants, also known as fouling. Mixtures of salt, oils, and other particles often clog membranes and cause significant, irreversible deterioration that shortens their lifespan.
The coating, which helps membranes last longer, is a water-based solution that can be easily applied to membrane surfaces by simply rinsing it through the recycling system.
“Our students developed the concept of using polydopamine as an adhesive coating that attracts a layer of tightly bound water molecules to protect membranes from direct contact with contaminants,” Freeman says. “This makes membranes more durable, easier to clean, and more energy efficient, which could reduce operational costs by half.”
Other membrane coating approaches must be applied before production is finalized and require new manufacturing methods or harsh chemicals that can cause deterioration.
More efficient membranes enabled the team to build a more compact system that is easier to move from drill site to drill site. These improvements make recycling at the drilling site a competitive alternative to conventional practices of either disposing of flowback water in wastewater wells or trucking it to treatment facilities.
“Disposal costs run $1.50 to $2 a barrel and transportation costs to disposal sites can add up to $4 a barrel,” Freeman says. “Recycling flowback water at the drill site can address both of these costs and make reuse a viable economic option.”
The team’s water recycling system is licensed by the University of Texas at Austin to Advanced Hydro Inc., which was founded by Freeman in 2009.
Source: University of Texas at Austin