Writer: Emily C. Kelley
A team of researchers in New Mexico State University’s Department of Civil Engineering, led by Assistant Professor Pei Xu, is working to develop solutions to the problems related to produced water. Fracking flow-back water and produced water are the waste streams generated in oil and gas exploration and production.
“Oil and gas are buried underground and are mixed with water for extraction,” Xu said. “When we get oil and gas out of the ground, we also have the produced water that is the by-product. The quantity of the oil and gas produced water is significant in the United States.”
Produced water management is a significant challenge for the oil and gas industry. Based on a survey conducted by Argonne National Laboratory, approximately 98 percent of produced water generated from onshore production is deep well injected, which is costly for producers and is a waste of water resources, especially since much of the nation’s oil and gas exploration is in arid or semi-arid areas like Texas, New Mexico, Colorado and Wyoming.
Xu’s goal is to find safe, beneficial uses for the produced water. This first requires examining the characteristics of produced water – its varying levels of salinity and both organic and inorganic contaminants – and how to treat the water to remove those contaminants.
“After we have a very good understanding of the water’s characteristics, then our focus shifts to develop the treatment technologies to treat this water,” Xu said.
Her research team consists of several graduate and Ph.D. students, all studying varying aspects of produced water and water reuse. They currently are doing research with produced water from Permian Basin production operations, though produced water from other areas likely will have different characteristics.
Xu also collaborates with the oil and gas industry, Lea County, Lea Soil and Water Conservation District, and colleagues Nagamany Nirmalakhandan in civil engineering, and Kenneth Carroll, Oman Holguin and Tanner Schaub from the College of Agricultural, Consumer and Environmental Sciences.
Xu and her team are using several technologies to treat the water in the lab, including reverse osmosis membrane systems that remove salt from the water, leaving a freshwater stream and a concentrate stream after treatment. The concentrate stream still requires disposal. They also use another membrane system, an electrodialysis system, which uses electrical potential to separate the salt ions from the produced water. The products are fresh, purified, desalted water, but also a concentrate that needs to be disposed of, as with the reverse osmosis system.
“Even though the desalination technologies are very important to remove the salt so we can use the water, these membranes can be fouled quickly by the produced water because of the particulate, inorganic and organic matter in the water,” Xu said. “In order to protect the membranes, we have to remove these substances from the water so the membranes can be operated for a longer time and more cost effectively.”
In order to reduce the membrane fouling and scaling, the team is trying to develop these pretreatment technologies.
“What we do right now is use biological treatment to remove organic contaminants from the water. For example, we use biofilters,” Xu said. “We use activated carbon as the attachment materials for microbes to grow on. The activated carbon can not only support their growth, but also can help biodegrade the organics in produced water by providing longer retention time so that the bacteria can continue to degrade the organics that absorb on the activated carbon.”
Zach Stoll, civil engineering Ph.D. student in Xu’s lab, and Josue Magana, civil engineering graduate student, are both working on produced water treatment using biological processes.
“We’re trying to extract the energy from produced water – instead of just using energy to treat it, if we can get energy out and treat it at the same time, then that’s a win-win,” Stoll said. “There’s a big problem with produced water though, because it has organics in it, and it also has high salt. If you try to use some of the conventional processes right now for desalinating the produced water, you kind of clog everything up with the organics. The big challenge for biological treatment is that because the salt is so high, that if you try to treat it biologically, you kill the microbes hat are not used to a highly saline environment. Specialized microbes do exist in nature that can tolerate these high salinities but aren’t normally found in produced water. Our work focuses on trying to acclimate the microbes to highly saline produced water so they remove the organics.”
Magana is experimenting with microbiological approaches to treat the flow-back water containing the viscous guar gums used as a gelling agent for hydraulic fracking.
“There are different types of guar gums used in the hydraulic fracturing process. What it essentially does is carry the pumping into the hydraulic fractures to maintain the structure of the fracture to extract the oil, petroleum, gases,” Magana said.
This guar gum-treated water is extremely viscous, so the water becomes more like a semi-solid or gel, which maintains the structure of the fracture. Pumping viscous water, however, is very expensive.
“We’re looking at treating it at the plants to use it as a source of food, so the microbes can maintain their metabolism and degrade all the other organics (in the produced water) that are toxic to humans, and the environment,” Magana said.
The lab has only been fully operational since January, but Xu and her students’ work is already drawing attention.
“If we can beneficially use this water, then this will reduce the cost to producers and this will also augment regional water supplies, which is why produced water research is so important,” Xu said.
“There are billions of gallons of water used in the hydraulic fracturing process and if we can reclaim or reuse some of this water, using different processes like granulated activated carbon and microbes, we should essentially be able to save some of this water and reuse it, potentially, saving energy and water, which we’re in need of here in the Southwest and in the world,” Magana said.