Steam assisted gravity drainage (SAGD) is a common method of extracting heavy oil buried deep underground. A well is drilled and steam, produced from large boilers, is injected down the well to heat bitumen until it becomes warm enough to flow. The bitumen is then pumped to the surface through a second well drilled horizontally underneath the first well. The bitumen and steam, which has since cooled and turned back into water, are pumped to the surface and then separated. Carbon dioxide is released through the boiler exhaust stacks vented above ground.
To help reduce the environmental footprint of extraction, researchers are piloting a technique called direct contact steam generation, or DCSG. In this process, wastewater is in direct contact with the products of oxygen-fuel combustion. This creates a mixture of steam and carbon dioxide which replaces steam generated using conventional boiler technology.
Natural Resources Canada (NRCan) researchers developed a novel concept whereby a direct combustion process would generate a flue gas stream containing both steam and carbon dioxide. The resultant mixture would then be pumped underground to aid in bitumen extraction, with a portion of the carbon dioxide remaining underground.
The concept is a topic of a patent application filed in 2008. However, research was required to prove its feasibility. Additionally, the cost of implementing DCSG at commercial scale was a question for the new technology. An economic feasibility study showed the technology would be competitive with existing steam generation technologies, but with additional associated environmental benefits.
Researchers needed to determine whether direct steam generation was indeed possible in a pressurized environment. Using a mixture of oxygen, fuel, and water, they were able to produce steam in an environment of 15 bar pressure, or 15 times the typical atmospheric pressure at sea level. However, to be used to its full potential the technology needs to run in highly pressurized environments of 100 bar or higher with dissolved hydrocarbons and solids in the water.
The NRCan researchers brought the project, with its economic feasibility study and early pilots to the member companies of COSIA. With COSIA member company involvement, the testing of DCSG technology with actual SAGD -produced water will now get underway.
In early 2014, the Suncor-led project completed testing under pressurized conditions, and in the spring of 2014 COSIA companies received the results on steam generator performance. The results indicated no significant technical hurdles and identified the further development work that will be needed to scale-up the technology. Suncor is currently working with CanmetENERGY (Government of Canada) to design the pilot for the next development phase.
Suncor is progressing two areas of DCSG technology development. A six-12 month pilot project at MacKay River is currently co-injecting CO2 with steam into one well pair to assess the potential impacts to reservoir performance, determine if production is maintained, achieve a lower steam-to-oil ratio and confirm CO2 sequestration potential. The field pilot began in the fourth quarter of 2016 and is scheduled to last until the middle of 2017. The results are expected be available in late 2017.
The system recycles 90 percent of the water it uses, and requires just 10 percent of additional water to replenish the system. If taken from existing tailings water, tailings pond water could be consumed with this technology.
This new technology has the potential to reduce greenhouse gas emissions because a significant portion of the carbon dioxide may be sequestered underground in the SAGD reservoir. Alternatively a capture-ready carbon dioxide steam could be separated from the steam for use in enhanced oil recovery (EOR) or sequestration in other geological formations outside of the oil sands.
Tailings water removal will accelerate land reclamation.
COSIA member companies involved in the DCSG pilot project are Suncor, Devon and Canadian Natural.