There’s potential for significant environmental benefits coming from the Suncor-led development of Direct Contact Steam Generation (DCSG) technology – an evolving technique that could become the standard for the in-situ method of steam-heating bitumen and pumping it to the surface.
The method, used in steam assisted gravity drainage (SAGD), uses direct contact between water and hot combustion products to produce a steam and CO2 mixture that is then pumped underground.
“This is a process that could eliminate or drastically reduce the need for water treatment in SAGD plants,” explains Suncor’s Todd Pugsley, who led the earlier stages of the project.
“Among other benefits, DCSG could also reduce the footprint of steam generation, increase thermal efficiency of steam generation by capturing water of combustion and sensible heat of flue gas while requiring little or no waste disposal, and eliminate direct carbon dioxide (CO2) emissions from steam generation.”
In current SAGD operations, a well is drilled and steam produced from large Once Through Steam Generators (OTSG’s) is injected down the well to heat the bitumen until it becomes warm enough to flow.
The bitumen and steam – now cooled and turned back into water – are brought to the surface through a second well and then separated so the water can be used again.
CO2 from combustion is conventionally released from the OTSG’s exhaust stacks.
The DCSG method replaces conventional boiler technology using a direct combustion process which generates a flue gas stream containing both steam and CO2.
DCSG could reduce the footprint of steam generation, increase its thermal efficiency and eliminate direct CO2 emissions from steam generation.
The resulting mixture is then pumped underground to aid in bitumen extraction. The concept is that CO2 is sequestered underground in a reservoir, which would be like creating instant carbon capture and storage, while the bitumen and condensed steam is pumped back to the surface.
“So far, we’ve learned that the gas produced from the DCSG process is 90 per cent steam and 10 per cent CO2,” explains Kostis Katsimihas of Suncor, who is helping to lead the research phase to the next step.
“By sequestering CO2 underground, we would have complete control over the CO2 emissions.”
Meanwhile, the system recycles 90 per cent of the water it uses, requiring just 10 per cent of additional water to replenish it.
The recovered water can be recycled with minimal treatment since DCSG can operate with lower water quality requirements. There’s also the potential that tailings water could be used.
“The DCSG units would also be much smaller than conventional boilers” Kostis adds. One unit would fit in a typical office meeting room.
“That means potentially smaller water handling facilities, and the option of transporting the units to other locations where we need to generate steam.”
Recovered water can be recycled with minimal treatmentsince DCSG can operate with lower water quality requirements.
COSIA’s involvement in this DCSG began several years back.
“NRCan researchers brought the project and its early pilots to COSIA and its member companies,” explains John Brogly, COSIA Director, Tailings.
“With their involvement and COSIA’s initial support, the testing of DCSG technology using actual SAGD-produced water is now well underway.”
To be used to its full potential, the mixture of oxygen, fuel and water to produce steam needs to run in highly pressurized environments such as 100 bar (1450 psi) with dissolved hydrocarbons and solids in the water.
So far, no technological hurdles to steam-generator performance have been identified. Short-duration tests at lab-pilot scale have been successful, while CO2 co-injection field trials at Suncor’s MacKay River facility have been ongoing.
“The technology requires continuous testing in the field to prove its operability and reliability in an oil sands operation, including injections at various reservoirs to explore what happens underground with CO2 movement,” Todd explains. “Among the ongoing research will include testing the separation of CO2 from the steam, and producing the CO2 at steam pressure.”
Development of DSCG technology continues and is supported by research being done in Canadian government and university labs such as CanmetENERGY.
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