Abstract

Alberta’s huge oil sand deposits situated at shallow depths can be successfully exploited using the steam assisted gravity drainage (SAGD) process, as demonstrated at the underground test facility (UTF) located in the Athabasca area in northeastern Alberta. The SAGD process is based on using pairs of horizontal wells to inject steam at high temperature and pressure, decreasing the bitumen viscosity several orders of magnitude, and to produce a mixture of oil, condensate, and formation water. One potential environmental issue related to the application of this process is the possible contamination of shallow groundwater aquifers used for water supply, in the case that produced fluids escape from the pay zone and migrate upward. The hydrogeological analysis of the sedimentary strata above the pay zone at the UTF site shows that shallow groundwater contamination by produced fluids is extremely improbable because (1) the temperature in the pay zone around the injection-production wells decreases rapidly, such that no steam remains in the vapor state; (2) the pay zone is overlain by a thick succession of aquitards which impedes upward fluid flow; and (3) the site is a recharge area for local groundwater flow systems and a strong downward-driving hydraulic gradient would have to be overcome by any fluids attempting to migrate upward. The analysts shows that it is very important to know the general geology, hydrostratigraphy, and flow of meteoric and formation waters at prospective bitumen extraction sites, because these may be controlling factors for either positive or adverse environmental effects.