What's new in production
No, the marriage is fine. Today, we’re revisiting a subject more germane to your interests: produced water. This is arguably the industry’s longest-running, unsolved problem, and we’re taking a look at a new way to separate oil from it.
First, a sketch of the problem, as reported by the National Science Foundation (NSF). Each year, the U.S., alone, generates more than 21 Bbbl (approximately 900 billion gal) of produced water from oil and gas extraction, including hydraulic fracturing. To treat this water before disposal or reuse, the industry depends on filtration and separation technologies.
Typically, dispersed particles or droplets are removed from a host liquid using a series of complex techniques. These techniques are energy-intensive and may require the addition of chemicals to work. They also have proven to be inefficient at removing the tiniest oil droplets and contaminants.
Operators manage the problem, with varying degrees of effectiveness, but a solution, in a permanent, universal sense, remains elusive. That may change, if a technology described in a recent report from the NSF achieves commercial-scale success.
With funding from the NSF, FloDesign Sonics, based in Wilbraham, Mass., has developed a new separation technology that can help clean produced water. The company’s design uses acoustic waves to continuously capture and separate substances from water or other liquids without using filters or chemicals. The company demonstrated their separation technology at a White House Water Summit earlier this year.
Sound separation. The basis of the technology is a method called acoustophoresis, in which droplets or particles within a liquid can be manipulated with a special acoustic wave pattern. The new system uses a pattern of ultrasonic waves in the megahertz range. The wave pattern exerts acoustic forces that bind substances dispersed in the liquid into clusters. Depending on their relative density compared to the liquid, these larger clusters either settle to the bottom or rise to the surface, where they can be separated easily.
“Acoustophoresis has been used primarily in microfluidics and other microscale systems,” explained Jason Dionne, senior engineer and co-founder of the company. “When the U.S. Army was looking for a technology for rapid detection of anthrax spores in large bodies of water, we got the idea to develop an acoustic separation technology that works at the macroscale.”
The company’s patented system, called Acoustic Wave Separation (AWS), was designed to treat produced water from hydraulic fracturing operations. The company notes that the amount of produced water generated [from a well] changes over the lifetime of the well and depends on the geologic formation, but can reach 100,000 gal/day.
“It’s challenging for current technologies to remove particles smaller than 20 microns without the addition of chemicals,” Dionne said. “AWS separates particulates, oil droplets, sand and bacteria as small as 1 micron.”
AWS in detail. A more detailed description of the concept can be found in “Acoustics in microfluidics and for particle separation I: Standing waves, streaming, and radiation forces” (Dionne et. al., 2013). “Ultrasonic standing waves are used to trap, i.e., hold stationary, the secondary phase particles in a fluid stream. This is achieved when the acoustic radiation force exerted on the particles is stronger than the combined effect of fluid drag and buoyancy force. The action of the acoustic forces on the trapped particles results in concentration, agglomeration and/or coalescence of particles and droplets. Heavier-than-water particles are separated through enhanced gravitational settling, and lighter particles through enhanced buoyancy.
A combination of experiment results and computer modeling is used to investigate the fundamental interaction between the piezo-electric transducer and the acoustic field, with the goal of maximizing the acoustic trapping potential. The novel acoustophoretic separation technology provides for a cheaper and lower cost-of-energy separation of multi-component phase mixtures, especially for micron-sized particles.”
Produced water treated with the AWS system meets or exceeds the U.S. Environmental Protection Agency’s standards for safe discharge. “With NSF funding, we have scaled up our technology to an industrially relevant scale,” Dionne said. “We now have a 7,000-gal/day prototype that we are ready to pilot with a partner. The ultimate goal for our technology within the oil and gas industry is to build a system capable of processing 100,000 gal/day. Compared to current methods for treating produced water, the AWS system would reduce energy and chemical usage by up to 75%.”
A solution to the problem? Is this a solution to the problem or another tool for managing it? In your meditations, consider its potential, which was summed up nicely in the NSF’s Small Business Innovation Research (SBIR) Phase II project abstract: “The broader impact/commercial potential of this project is that the novel acoustophoretic separation technology provides for a cheaper and lower cost-of-energy separation of multi-component phase mixtures. It can function as a drop-in replacement for conventional separation technology, such as hydrocyclones and other methods. The societal impact is the development of separation technologies that are sustainable and environmentally benign, since they do not generate any waste or use consumables. Enhanced extraction of micron-sized oil droplets from water offer opportunities for EOR and oil-spill cleanup, and reduce the emission of micron-sized oil droplets into the environment. This project increases the science and technology behind the use of acoustic radiation force on large volume flowrate.”
To borrow from Nobel laureate Bob Dylan, “Oh, Mama, can this really be the end…” to a huge and heretofore intractable industry problem? 
