SAGD short stories: The Game Changer?
“SAGD short stories” is a blog series about SAGD and process operations.
A new technology being developed in Canada could be the game changer for SAGD development of the oil sands.
Direct Contact Steam Generation (DCSG) research and development teams are working to reduce the environmental footprint of steam generation through increased efficiency and lower emissions.
The DCSG process is possible because of the development of oxy-fuel boilers and the quest for lowering emissions from burning hydrocarbons. It has incredible potential in regard to Carbon Capture and Storage (CCS) because it can be designed to use coal, oil or natural gas as the fuel.
With oxy-firing, pure oxygen mixed with recycled flue gas (RFG) is burned along with a fuel to produce heat. The flue gas is mainly carbon dioxide and H2O. This is significantly different than air-fired flue gas, which typically contains more than 70% nitrogen (air is 78% N2).
Because there is such a significant reduction in total emission volume with oxy-firing compared to air firing (with no N2 involved), the concentration of CO2 in oxy-fire flue gas can be well over 50%. From the carbon capture point of view, the high concentration allows for efficient CO2 separation and storage using existing, established technology (such as a cryogenic separation process).
To apply oxy-fire boilers to DCSG service, an additional function is added to spray water directly at the oxy-fire flame. The flame instantly vaporizes the water to steam to produce a flue gas with high steam content. The operating pressure can be set using standard pressure control methods to vent the steam/flue gas.
In SAGD applications, natural gas is almost always available, pure oxygen can be supplied from a local Air Separation Unit, and produced water can be used as feed water. What? Oh, did I forget to mention oily water could be used for steam generation with DCSG? Yeah, direct contact means no tubes!
Imagine a skid mounted DCSG unit and 3 phase emulsion separator at a Well Pad. The separator outputs produced gas, produced water and emulsion. Some of the gas and most of the produced water are sent to the DCSG unit to produce flue gas with around 80-90% steam content, with the remaining flue gas being mostly carbon dioxide. This effectively means the stream is high-pressure steam with some flue gas. There are no exhaust emissions to the atmosphere as the entire volume is directed into the reservoir.
No HP Steam supply pipeline. Much less produced gas going to the CPF; possibly no produced water! Theoretically, a closed water loop could be nearly self-sustaining.
Here are some of the main improvements over traditional
Once Through Steam Generators (OTSG) or Drum Boilers
proving to be possible.
- Instead of burning a fuel-air mixture for SAGD operations,
DCSG burns a fuel-oxygen mixture (oxy-fired).
By eliminating the nitrogen component of air (air contains 78% nitrogen), more heat energy is applied to steam generation.
- Instead of exchanging heat energy from air-fired flue gases to Boiler Feed Water (BFW) through boiler tubes,
DCSG exchanges heat energy through direct contact between the oxy-fire flame/flue gases and oily Produced Water.
This eliminates the need for completely de-oiling and treating the produced water for re-use as BFW. Minimal preparation of feedwater is required, and even tailing water could conceivably be used.
- Instead of exhausting OTSG/Boiler flue gases directly to the atmosphere,
DCSG generates a mixed flue gas of steam and carbon dioxide (CO2) that is then injected directly into the reservoir through the SAGD Injector Wells.
This provides a Carbon Capture and Storage (CCS) solution, as most of the CO2 should remain underground and most of the steam/water is recovered along with bitumen through the Producer Wells.
- Instead of large, complex OTSG/Boiler houses at a Central Processing Facility,
DCSG units can be small enough to be mobile.
This has the potential to allow moving units to meet changing demands for steam generation. Once proven, DCSG could eliminate the need for centralized high-pressure steam generation and processing facilities, as well as steam pipelines and their condensate-handling systems.
To find out more about how SAGD works in the Canadian Oil Sands
you can viewContendo’s SAGD Oil Sands Online Training Courses.
Kevin Fox is a senior technical writer at Contendo.
He is a power engineer who has written process education programs for industrial clients since 2009.