Thermal Performance, Design, and Sustainability of Borehole Heat Exchangers within Challenging Hydrogeological Environments

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The overall objectives are to advance the use and performance of low temperature geothermal energy (borehole heat exchangers [BHEs]) in challenging hydrogeologic environments. Two environments are considered: systems accessing deep medium-temperature anomalies, and shallow systems in discontinuous permafrost. In essence, these represent two `end-member' problematic zones for geoexchange systems. In-situ oil sands thermal recovery schemes inject a tremendous amount of energy into bitumen reservoirs 100's of metres underground, raising the temperatures from 7 - 11°C to as high as 200°C at the steam chamber edge, and 50°C along the reservoir edge. In essence, these operations have unintentionally acted as underground thermal energy storage systems. This project will design efficient and sustainable closed loop BHEs that work within the reservoirs and perform comprehensive energy and carbon balance assessments. Economic analysis will support the business and regulatory case for considering the recycled energy to be a negative carbon (i.e. CO2) component of the bitumen extraction operations. A greenhouse industry is proposed as the model case for consumption of the extracted heat. Low temperature geothermal applications are normally limited to areas whose average ground temperatures are 5 to 10°C or warmer. However, the potential exists to use BHEs to extract heat in zones of discontinuous permafrost. Heat extraction can effectively reverse permafrost degradation and stabilize foundations. While it would not normally be economical to use BHEs for space heating needs in cold climates, the benefits of moving away from diesel fuel sources in remote areas, while stabilizing permafrost are mitigating factors. FEFLOW's BHE simulation ability will be used but now with the new piFreeze plug-in to simulate freezing ground conditions. Ground source geothermal systems are drawing increased attention due to concern about greenhouse gas emissions, sustainability, and high energy prices. However, design considerations and the regulatory framework have not advanced at the same pace. Challenging environments receive little industry attention because the research base is not there to support the `practice'. Oil sands reservoirs are currently one of Canada's largest energy assets. However, concerns about greenhouse gas based emissions required to produce the reservoirs remain. A novel idea is to recover the heat remaining in the reservoir at the end of production. By utilizing this energy to support a greenhouse industry, post closure, existing infrastructure will be utilized and employment opportunities will be maintained for the local population. Using BHEs as a source of building heat in regions of discontinuous permafrost could stabilize foundations and allow for a clean energy source to replace diesel.