The Collaborator - Detail
A COSIA Newsletter
Issue 11 - November 2017
A geotechnical time machine: cutting-edge beam centrifuge research reduces a 100-year study timeframe down to days
Think of it as a kind of geotechnical time machine. By utilizing the University of Alberta’s cutting-edge beam centrifuge research facility, tailings reclamation specialists are able to spin tailings samples at more than four times a second (260 revolutions per minute). As a result, they expect to predict, in a matter of days, the tailings consolidation pattern that would take 100 years to study in real time.
That, in essence, is the process at work in an ongoing COSIA-led investigation seeking to answer a question that has vexed tailings researchers for years, namely: to what degree, if any, does the residual bitumen in fluid fine tailings (FFT) slow down the consolidation of tailings, thus inhibiting the ultimate transformation of tailings ponds into reclaimed land surfaces or end-pit lakes?
During the bitumen extraction process, over 90% of the bitumen in the ore is recovered. However, typically five-to-10% of the bitumen remains present in FFT in the tailings pond. It has long been an open question as to whether or not the presence of bitumen impacts the consolidation process—and, if so, by how much.
The question is a pressing one, both from an environmental and business perspective. Implementing measures to further reduce residual bitumen in FFT would be a long and costly process. If the environmental payoff was big enough, then that might be a sound business decision. But first it’s important to know to what degree residual bitumen in FFT is a problem.
Adedeji Dunmola, a Tailings Technology Geotechnical Associate with Syncrude, is the technical leader for this COSIA Tailings Environmental Priority Area-led study. As Adedeji explains, until recently, there were only two possible ways to determine the impact of residual bitumen on FFT consolidation.
“The first,” he says, “was to wait 100 years to see how the tailings pond performs in real time—which is obviously not a feasible option for us. The second way we’ve tried to tackle this is doing lab-based consolidation tests on tailings samples and plugging the resulting data into numerical models to generate a prediction. But even that process takes up to two years to complete and the predictions can be inaccurate because of factors such as human and analytical error.”
Since becoming operational in 2014, the University of Alberta’s beam centrifuge—the only one in Western Canada—has opened up a third option. By rapidly accelerating tailings samples in the beam centrifuge using a 2.2-metre-long steel arm, it’s possible to physically model the consolidation process as it would take place in nature, but in a fraction of the time.
Adedeji collected FFT samples from one of Syncrude’s tailings ponds last fall and sent them to the U of A for testing, with results expected by the end of 2017.
The samples were identical in every regard but one—they had been manipulated to vary in the amount of residual bitumen each one contained.
“That’s the variable we want to study for,” explains Adedeji. “For example, is a one percent bitumen content better than a six percent content when it comes to the pace of consolidation?”
This is just one of the ways the beam centrifuge, a key part of the U of A’s Geomechanical Reservoir Experimental Facility (GeoREF), is advancing research into a range of hydrocarbon recovery solutions.
Overseeing the GeoREF is Rick Chalaturnyk, Professor of Geotechnical Engineering and Foundation CMG Research Chair in Reservoir Geomechanics for Unconventional Resources.
One of the main areas of research to date is using the beam centrifuge to study the integrity of cap rock formations—layers of tightly-packed, almost impermeable clay that lie beneath the Earth’s surface and oil sands buried deep underground.
The goal of these studies, says Rick, is to find ways to better predict conditions under which the caprock might fail during SAGD extraction, thereby preventing a repeat of some serious incidents in the past where caprock failure posed safety risks and resulted in significant environmental damage.
“As someone who used to work in the tailings field, I find this area of study very exciting,” says, Rick Chalaturynk. “It’s cool to see how relatively simple tests are able to generate results that have the potential to really change our way of thinking and will help companies make sound decisions going forward.”
The great advantage of the centrifuge beam, he adds, is that it can spin core or rock samples fast enough to simulate stress conditions deep underground of 100 G (one hundred times the gravitational force). The results from these tests are then used to help validate separate and sophisticated modelling studies into caprock failure.
Rick notes that the centrifuge beam is also being increasingly employed by tailings researchers to quickly simulate how various treatments and interventions, over a long period of time, might accelerate the reclamation process.
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