Heavy-oil processing technology making gains in Canada

Canada’s Petrobank recently passed a milestone with its patented Toe-to-Heel Air Injection (THAI) process for oil-sands production. The technology received independent validation that it works as designed : to extract significantly more oil from a reservoir compared to conventional methods, and in a cost-effective and sustainable manner.

The THAI process is an in-situ combustion process for heavy-oil production that was developed earlier this decade at the University of Bath in the UK and was patented by Petrobank. It combines a horizontal production well with a vertical air-injection well located at the toe of the producer. For a period of approximately 2–3 months, steam is injected down the vertical well to condition the reservoir around it and to heat the horizontal well. After this period, air is then pumped down the vertical well, initiating combustion in the reservoir and raising the temperature to 400–600°C (750–1100°F), which is the temperature regime in which thermal cracking and coking of the heavy oil begin.

As air is continuously injected into the formation through the vertical well, it creates a combustion front that moves along the horizontal well from its toe to its heel. The thermal cracking along the horizontal well results in partial upgrading of the heavy oil by as much as 6–8°API, according to the company. This upgraded oil has a low enough viscosity that it can flow into the horizontal well—along with vaporized water from the reservoir and gases like CO2 that form during combustion—and be produced to the surface. Once at surface, the oil is sent through a processing plant for treatment prior to shipping to market.

Petrobank states that a series of laboratory tests and numerical simulations conducted over the past several years have demonstrated that the process can recover 60–80% of the heavy oil in a reservoir, compared to the 20–50% that can be recovered by other in-situ methods such as steam-assisted gravity drainage (SAGD). The company also states that because THAI only requires one horizontal well (vs. the two required for SAGD), it is applicable to thinner reservoirs without concerns of the presence of top or bottom water that act as heat thief zones. During THAI, approximately 10% of the oil is consumed in the coking reaction.

spe.org