Low-Temperature Geothermal Waste Heat Utilization from In-Situ Bitumen Recovery Operations

In-situ thermal methods for bitumen recovery introduce a tremendous amount of energy into the reservoirs, raising ambient temperatures of 13°C to as high as 200°C at the steam chamber edge and 50°C along the reservoir edge. A majority of this heat is lost to the surroundings. In essence these operations have unintentionally acted as aquifer storage and recovery systems. The subsurface waste heat from in-situ thermal bitumen recovery activities can be utilized using closed loop geothermal systems to support ongoing production activities and industrial facilities. In addition they act as thermal remediation systems returning reservoirs, and more importantly overlying aquifers, more quickly to baseline temperatures.

Three numerical models were developed using FEFLOW^® 6: 3D regional groundwater flow model of the Cold Lake (Alberta, Canada) region (85 x 88 x 0.616 km), local-scale groundwater and heat transport model of Imperial Oil’s in-situ production site (6 x 4 x 0.60 km) and a borehole heat exchanger (BHE) model to investigate the feasibility of closed loop geothermal systems (0.5 x 0.5 x 0.6 km).  The in-situ production site model was able to fairly accurately reproduce the disturbed subsurface temperature field.  While injection stage temperatures were closely matched, it was more difficult to match the production stage due to FEFLOW’s inability to account for steam (gas) phase injection and latent heat of vaporization (condensation).  Single U-tube, double U-tube, and coaxial BHEs were tested and analyzed by comparing the inlet and outlet temperature and heat extraction rates.  However, unlike typical ASR systems, the bitumen reservoirs at Cold Lake are 410 m to 470 m below ground surface.  Thus grout thermal conductivity and BHE type were found to play an important role in heat recovery.  A greater potential likely exists in the Athabasca area where bitumen deposits are much shallower (65 to 115 m deep).