Co-injection of Solvent
The recovery model at Clearwater is SAGD complemented by co-injected diluent. The diluent acts as a solvent and mixes with the bitumen in the reservoir, “thinning” or reducing the viscosity of the bitumen, which is too thick to flow at ambient reservoir temperature.
Adding a solvent is designed to achieve a range of technical, economic and environmental benefits, principally by reducing the amount of steam needed to produce a given amount of bitumen, known as the steam-to-oil ratio (SOR). The type of solvent chosen for use at Clearwater is diluent, also known as condensate, a very light crude oil that is produced in numerous natural gas fields in western Canada. Diluent is commonly used to thin produced bitumen for trucking and/or transportation via pipeline to upgraders and/or refineries.
AOS has developed a two-fold use for the diluent that it will need for transporting its produced bitumen. A fractionator at the SAGD facility will extract the diluent’s lighter components, creating a light injection fluid. This will be mixed with steam at the wellhead and the steam-diluent mixture will be co-injected via the SAGD injection wells. The mixture will heat and thin the extra-heavy bitumen to an expected viscosity of 10° API at a temperature of about 180° C, which will then drain into the producing well and be pumped to surface. The lighter diluent will remain in the produced bitumen, while the previously removed heavier portions of the diluent will be added to the mixture at surface, and the resulting product will be trucked to a pipeline terminal for sale.
Supplementing SAGD with solvents is an increasingly common method to improve the efficiency of SAGD bitumen recovery. Established oil sands operators have commenced field testing of solvent-assisted SAGD, seeking higher well productivity and a significantly reduced SOR. Some of these operators use propane or other light hydrocarbons as the solvent injectant.
The AOS approach uses an established liquid hydrocarbon, condensate, in a new way. Technical research by Alberta Innovation suggests that a heavier solvent such as condensate can be more effective in SAGD than lighter, gaseous hydrocarbons. Please click here for more information. AOS is therefore incrementally advancing the industry’s approach to the use of solvents in SAGD. In addition, the Clearwater SAGD Project design includes much more sophisticated surface and subsurface measurement of results than is standard in SAGD projects, which will facilitate fine-tuning of the recovery model.
Recovering the maximum possible amount of co-injected diluent will be an important objective. Diluent left in the reservoir after bitumen depletion represents an added cost. AOS will employ two main approaches to minimizing diluent loss: a “wind-down” phase as each well nears the end of its operating life, and basement well production, which will help to recover diluent together with additional bitumen that drained by gravity to the bottom of the reservoir.