The research center’s focus on membrane technology could result in new management approaches and uses for both low- and high-salinity produced water.
As ConocoPhillips’ Global Water Sustainability Center (GWSC) celebrates its 10-year anniversary, it continues to partner with top universities around the world to innovate produced water management practices and technologies. The Qatar-based center is at the forefront of research dedicated to transforming the industry’s wastewater into a resource while cutting costs for operators and meeting environmental objectives.
In separate studies published in 2020, GWSC focused on using membranes to treat high- and low-salinity produced water, low-salinity industrial process water, and seawater desalination brine. By implementing the principles of pressure-retarded osmosis (PRO) – wherein osmosis causes water from a lower-salinity stream to move against a hydrostatic pressure gradient and through a semipermeable membrane into a higher-salinity stream – and osmotic concentration – a type of forward osmosis (FO) that does not employ a draw solution – GWSC director Samer Adham believes that these water streams can be better managed while optimizing certain oil & gas operations.
PRO meets produced water
Researchers at GWSC and Texas A&M University at Qatar jointly analyzed the potential benefits of PRO for waterflooding activities. The study contemplated using a hypersaline produced water draw solution (28% total dissolved solids [TDS]) and seawater feed stream (3.5% TDS). The resulting permeate would increase the amount of water available for waterflooding by an estimated 67%. Under the study’s main assumptions, this additional water would translate into an extra 13 bbl/d of oil production per module, or an economic benefit of $71,700/module-year.
“Not only would we be injecting more water to extract additional oil, we would also be injecting water of even better quality than is used now,” Adham told WiO, referring to the expectation that the salinity of the water used for waterflooding would be 40% lower than the produced water currently injected. He explained that the use of lower-salinity water for waterflooding has been shown to result in higher oil recovery, especially if divalent ions such as calcium and magnesium are removed. PRO IN ACTION
Though research in this area is set to end in 2021, several hurdles must be overcome before operators can take advantage of PRO for waterflooding. Adham’s team hopes to follow up the presentation of their findings soon with a larger-scale field demonstration that will help prove out the technology and garner buy-in from reservoir engineers.
Additionally, produced water pretreatment will have to be optimized with cost-efficiency in mind. The researchers are now comparing various options to filter out suspended solids and de-oil the water to prevent membrane fouling. Adham said that GWSC has already begun to pinpoint promising pretreatment strategies by adapting conventional technologies targeting solids and organics removal.
High-salinity produced water has an osmotic pressure of around 200 bar, representing significant osmotic energy that can be harnessed to supplement pressure pumps used in waterflooding or even drive electricity-generating turbines. Maximizing osmotic energy recovery would require membranes more durable than the commercially available membranes researchers used for the waterflooding study.
“We’re trying to enhance membrane material with nanotechnology to allow them to withstand higher hydrostatic pressures. We’re looking into graphene-based enhancement and other options,” Adham said. He added that GWSC is working with Texas A&M University at Qatar and the University of Technology Sydney in this endeavor.
Qatar’s status as the world’s fourth-largest natural gas producer means that in addition to managing produced water, the country’s operators must also handle the large volumes of water generated at its numerous gas-processing plants. The predominant method for addressing this challenge has been to inject the water into disposal wells, a practice which the local industry is trying to minimize due to increasing costs, well capacity limitations and environmental concerns.
In response, Qatargas has installed membrane bioreactors (MBR) and reverse osmosis (RO) systems to treat process water at several facilities. The RO concentrate is disposed and the permeate is recycled at the plants as boiler feedwater. Adham told WiO that while this approach has gone a long way towards reducing gas-processing plant disposal volumes, a more cost-efficient solution is needed.
GWSC, in collaboration with Qatar University, recently published a study comparing the use of three different hollow-fiber FO membranes in osmotic concentration to reduce disposal volumes from gas processing plants. The study on process water was a follow-up to previous research conducted with Nanyang Technological University Singapore on the feasibility of using osmotic concentration to reduce gasfield produced water, which typically has a salinity below 5,000 mg/L, compared to the gas plant process water, which has a salinity range of 2,000-5,000 mg/L.
According to Adham, osmotic concentration could shrink feed streams by as much as 75% when placing seawater desalination brine on the other side of the membrane. The resulting concentrate could be sent to disposal wells and the diluted brine discharged to sea.
“I think we’ve proven the process in bench-scale testing. Next, we need to design a system and pilot it at a plant,” Adham said, noting that the 2020 pandemic has created obstacles to moving this research forward. “We are awaiting the right opportunity.”
TWO WASTES, ONE SOLUTION