Thermal Tests

Over the years, various approaches to releasing the heavy, viscous bitumen from the oil sands have been tried. Common to many has been the use of heat to liquefy the oil and increase its ability to flow. Key to the ongoing innovations in enhanced oil recovery was the support of Alberta Oil Sands Technology and Research Authority (AOSTRA), which sponsored testing of a number of different thermal (heat-based) oil recovery processes at in situ pilot projects on all of Alberta’s oil sands deposits. These included cyclic steam stimulation (CSS), steam flooding, forward combustion, reverse combustion, and combined forward combustion and water injection.

CSS—also called steam soak or huff ‘n puff—is a three-stage method of thermal bitumen recovery. The first stage is injection, during which a slug of steam is introduced into the oil sand reservoir underground. The second stage, or soak phase, requires that the well be shut in for several days to allow heat to distribute uniformly throughout to thin the oil. Finally, the third stage consists of the thinned oil being brought to surface through the well. The cycle is repeated as long as oil production is profitable.

Another approach to thermal recovery, steam flood—also called continuous steam injection or steam drive—injects steam into the reservoir through specially distributed injection wells. When steam enters the reservoir, it heats up the oil and reduces its viscosity. The heat also distills light components of the oil, which condense in the underground deposit ahead of the steam spray, further reducing the oil viscosity. The hot water that condenses from the steam and the steam itself generate an artificial drive that sweeps oil toward producing wells.

In forward combustion—also known as fire flood—a flame is generated in the reservoir by igniting a fire at the sand face of an injection well. The flame is maintained by the continuous injection of air or another gas mixture with high oxygen content. The fire moves through the reservoir production wells. Heat from the fire reduces oil viscosity and helps turn reservoir water to steam. The steam, hot water, combustion gas and distilled solvent all act to drive oil in front of the fire toward production wells.

In reverse combustion, the burning front moves in an opposite direction to the injection well. Initially, air is injected into a production well and the fire ignited. After the burning front has advanced some distance from the production well, air is supplied only near the injection well. The burning front advances through the oil sands deposit, liquefying the oil and causing it to move toward the production well.

Combined forward combustion and water injection is a technique in which water is injected simultaneously or alternately with air into a formation. Wet combustion actually refers to wet forward combustion and was developed to use the great

amount of heat that would otherwise be lost in the formation. The injected water recovers the heat from behind the burning front and transfers it to the oil deposit ahead. Because of this additional energy, oil displacement is more efficient and requires less air.

In the years since Jacob Absher first experimented with hot steam- and combustion-based techniques, enhanced oil recovery using thermal methods has been greatly refined. Thermal in situ techniques have now unlocked the valuable energy resource from Alberta’s oil sands, making them the third largest (after Saudi Arabia and Venezuela) proven oil reserve in the world.