Canada, as is well known, has massive untapped heavy oil and bitumen resources, much of it located in Western Canadian Sedimentary Basin. Heavy oil and natural bitumen are oils set apart by their high viscosity (resistance to flow) and high density (low API gravity), notes the US Geological Survey. (These attributes reflect the presence of up to 50 wt% asphaltenes—very high molecular weight hydrocarbon molecules incorporating many heteroatoms—atoms other than carbon or hydrogen, e.g., sulfur—in their lattices.)

Location of the Western Canadian Sedimentary Basin. Map: USGS. Click to enlarge.

A number of in-situ thermal methods, such as steam flooding, cyclic steam stimulation (CSS) (earlier post) and steam-assisted gravity drainage (SAGD), have been used to attempt to reduce the heavy hydrocarbon viscosity to enable production.

However, the researchers note, for the reservoir with thin net-pay—i.e., the thickness of the zone in which the oil or bitumen resides—in presence of bottom water zone and/or with high water saturation in the pay zone, the thermal methods tend to be neither effective nor economical due to significant heat loss and large heating and water source requirement.

In this proposed CPCSI process, a vaporized solvent near its dew point is continuously injected into the reservoir to maintain reservoir pressure and also to supply extra gas drive to flush the diluted oil out through an injector that is located on the top of the reservoir; while a producer, which is located at the bottom of the reservoir, is operated in a shut-in/open cyclic way.

Experiments found that in comparison with continuous injection process, such as vapor extraction (VAPEX), and cyclic injection process, such as cyclic solvent injection (CSI), CPCSI offers free gas driving, and the reservoir pressure is maintained during the producer opening period so that the diluted oil viscosity is kept low.

Based on their results, the team suggests that CPCSI could be an alternative optimization production scenario for applying solvent-based in situ EHOR techniques for heavy oil reservoirs in Western Canada.

Resources

• Tao Jiang, Fanhua Zeng, Xinfeng Jia, Yongan Gu (2013) A new solvent-based enhanced heavy oil recovery method: Cyclic production with continuous solvent injection. Fuel, Volume 115, 426-433 doi: 10.1016/j.fuel.2013.07.043

• Meyer, R.F., Attanasi, E.D., and Freeman, P.A. (2007) Heavy oil and natural bitumen resources in geological basins of the world: U.S. Geological Survey Open-File Report 2007-1084, available online