Abstract

The steam-assisted gravity drainage (SAGD) process is the only commercially proven in-situ recovery method for Athabasca oil sands but it is challenged by high capital and operating costs and project economics are very sensitive to oil price fluctuations. The SAGD process also uses large quantities of water and produces significant greenhouse gas emissions during steam generation. It has become important to develop lower cost and more environmentally sustainable in-situ recovery technology for Athabasca oil sands.

In-situ reflux (ISR) is a new and lower cost alternative to SAGD that uses long electrical resistance heaters in horizontal wells to vaporize connate water to produce a rising steam chamber above the heater well. In ISR a relatively small amount of water or solvent may be injected to enhance heat transfer into the formation and assist in reducing bitumen viscosity. Steam condensate formed by the cooling of steam migrates downward along with heated bitumen but as these fluids approach the heater well and production conduit, the water is re-vaporized or refluxed while the oil continues its downward travel and is produced. SAGD-like horizontal well pairs are contemplated for ISR although it may be possible to operate single wells. Capital costs for ISR are much reduced compared to SAGD since there are no steam generators, only a small water treatment plant is needed and the required capacity of the production separation train is significantly reduced. Operating costs for ISR are also reduced compared to SAGD through elimination of surface and wellbore heat losses during energy transmission to the producing formation. Greater energy efficiency in ISR leads to lower carbon dioxide production and water requirements compared to SAGD. This paper presents a description of the ISR process, a comparison of the SAGD and ISR processes and the steps taken to assess the viability of ISR. The many possible applications of the ISR recovery process are also discussed.

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