OVERVIEW OF THE ENVIRONMENTAL ASSESSMENT OF THE IMPACT ON SHALLOW AND DEEP GROUNDWATER SYSTEMS BY BITUMEN EXTRACTION USING THE STEAM ASSISTED GRAVITY DRAINAGE PROCESS AT THE UNDERGROUND TEST FACILITY, ATHABASCA OIL SAND DEPOSIT, CANADA

摘要

Huge oil sands deposits in the Alberta basin, Canada, are situated at various depths due to the westward dipping of the strata which host these deposits. Depending on their depth, these deposits are exploited by open-pit mining, or by various thermal in situ processes. Lately, the steam assisted gravity drainage (SAGD) process has proven to be extremely successful in recovering bitumen from shallow depths amenable to horizontal well drilling. The SAGD process is based on using pairs of horizontal wells to inject steam at high temperature and pressure, decreasing the bitumen viscosity by several orders of magnitude, and to produce a mixture of oil, condensate and formation water. This mixture is separated and treated at the surface, and the resulting residual water is disposed of by injection into deep formations. At the same time, the process requires large quantities of water for steam production, obtained from shallow groundwater aquifers. The SAGD process was successfully experimented at the Underground Test Facility (UTF) in northeastern Alberta, which is now being developed into a full scale commercial facility.In using the SAGD process for bitumen extraction, environmental issues arise from the need to protect the aquifers used for water supply and other water resources which may be contaminated in the long run either by improper disposal of residual water or by fluids which may escape from the pay zone and migrate upward. An approach using hydrogeological and geochemical analysis was applied to assess the possible environmental impact of SAGD operations at the UTF site.