As part of the experimental program to assess the viability of fireflooding as an in situ recovery process for the Wabasca Oil Sands, an ignition test was conducted to determine whether combustion can be initiated at the bottom water/oil sands interface. Following a brief introduction on the state-of-theart of combustion studies in the Alberta Oil Sands, experimental procedures and data analysis for the subject test are documented. The general conclusion of the work is that in a preheated reservoir it is possible to successfully initiate combustion at the water/oil interface and propagate the combustion front towards the production well. Also very useful engineering and scientific knowledge has obtained from the test which has proved useful in design and operation of a fireflood pilot.
The Alberta Oil Sands are unique not only in their tremendous reserves, but also in their extremely high viscosity which has prevented any significant primary production of oil. The total reserves for the well known deposits Athabasca, Cold Lake, Peace River and Wabasca have been recently estimated at 980 × 109 STB. The reservoirs consist of sands of fluvial, deltaic and marine origin and the complex sedimentary nature has resulted in high variability of reservoir parameters.
The sands are unconsolidated with high porosities (20 to 35 °) and are commonly associated with shale, clay and calcareous material. In general, the bitumen has a gravity of less than 10–12 ° API and its viscosity at normal reservoir condition is generally in the range 6 × 104 cp to 6 × 106 cp.
Laboratory tests have been generally used to determine fuel and air requirements for the combustion process. However, considerable care must be taken when applying the results from laboratory tests to a field situation. For example, in linear tubes there is usually some initial mobility in the oil sand pack (obtained, for example, by preheating the combustion tube) prior to ignition and combustion. On the other hand in the field some tar may be heated in the vicinity of the combustion front, but the mobile oil cannot displace the immobile oil ahead of it. Either the whole reservoir must be preheated or a path must be provided to remove the mobile oil.
One of the common methods of creating this communication is by fracturing the formation with fluids such as steam, oil water or air. A second method would be to choose a tar sands formation where the pay section overlies a relatively thin permeable water zone.
Generally horizontal fractures are the best fracture geometry and they should be created near the base of the oil sands for maximum volumetric sweep efficiency and best CDOR. However the direction of the fractures are mainly determined by the geology of the formation and it is possible that the fracture may be inclined or vertical.