Energy Recovery from Oil Sands Reservoirs
Date
2021-01-04
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Abstract
Alberta's oil sands are the third largest proven crude oil reserve in the world, after Saudi Arabia and Venezuela. The proven reserve is ~165.4 billion barrels. At original reservoir conditions, for in-situ methods, the bitumen is too viscous to extract directly with viscosities of the order of hundreds of thousands to millions of centipoise. To extract bitumen via in-situ recovery processes, the bitumen's viscosity must be lowered to less than 20 cP. In all current commercial oil sands recovery processes, this is done by injected high pressure and temperature saturated steam into the reservoir. One such process, Steam-Assisted Gravity Drainage (SAGD), has been proven to produce bitumen, but due to steam generation has high emissions intensity with large energy requirements. The research presented here studied the SAGD process from multiple angles. The first study is focused on the edge of steam chamber where both SAGD and Steam and Gas Push (SAGP) processes were compared to understand the impact of non-condensable gas on heat transport at the edge of the chamber. The second approach uses a detailed compositional model to exam the time scales for steam and bitumen flow within the depletion chamber. The approach used for multiple steam and multiple bitumen components is novel. The third study examined the instantaneous steam-to-oil ratio behavior when the steam chamber was exposed to different reservoir features. The last study explored the recovery of heat energy from post-SAGD chambers. The analysis reveals the following results. 1. non-condensable gas does improve the thermal efficiency of SAGD, but it changes the behaviour of the edge of the chamber by creating a more extensive depletion zone at the edge of the chamber. 2. the time scales for steam flow and bitumen mobilization, drainage, and production can be weeks to months to years depending on the stage of the process. This speaks to the 'thermal momentum' that is established in the reservoir during the process. 3. The SOR, in particular, the instantaneous SOR provides a signal that can be used to identify reservoir features. This could be used with multiple SAGD well pairs to determine reservoir features across pads. 4. A large fraction of the injected heat energy in the reservoir remains in the reservoir rock (sand grains) and the overburden and understrata. However, it is possible to extract a significant fraction of the energy remaining in the reservoir after SAGD operations have finished. This should be explored in the field since this provides a means to raise the overall energy efficiency of SAGD.
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Keywords
steam-assisted gravity drainage (SAGD), non-condensable gas (NCG), steam and gas push (SAGP), oil sands, time scales, steam-to-oil ratio, process efficiency, thermal efficiency, thermal energy recovery, heat recovery, energy efficiency, instantaneous SOR (iSOR), finger print
Citation
Wang, J. (2021). Energy Recovery from Oil Sands Reservoirs (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.