Lori A. Cook

B. Sc. Honours Thesis

Pre-Feasibility Study for Underground Thermal EnergyStorage (UTES) at Dalhousie University, Halifax, Nova Scotia

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A study to determine whether geological conditions at Dalhousie University are suitable for Underground Thermal Energy Storage (UTES) was carried out over the campus area. Parameters studied include lithology, mineral content of bedrock, occurrence of groundwater, surficial cover thickness, and bedrock thermal conductivity. Geological parameters constrained for the campus were used to model a store with 1500MWh capacity. Depending on a number of assumptions, several preliminary optimal storage design parameters are recommended for the Dalhousie campus site.

Halifax Group slates and siltstones underlying the campus contain variable amounts of sulphides (0-10%) and indicate insignificant lithological porosity or permeability. Four main fracture sets occur throughout the study area. Water content in the rocks is mainly in bedding - parallel (63/60) and conjugate bedding - parallel (243/59) fracture sets. AC and conjugate AC fractures are closed to soil- filled. High-density fracture zones also display water seepage. Fracture opening and water content decreases with depth in bedrock. Cleavage is highly annealed due to contact metamorphism of the rocks in the study area.

Surficial cover is composed of slate-dominated, muddy till facies (Beaver River Till, Stony Till Plain). Depth to bedrock determined using refraction seismics and indicated by outcrop exposures ranges from 0 to 4.2 m.

Thermal conductivity (l) of the slates and siltstones, determined using the hot-wire method, is an average of 3.06 W/mK. Volumetric heat capacity of the bedrock is extrapolated to be 0.60 kWh/m3K from similar rock types.

Surficial cover composition and thickness is insufficient for aquifer thermal energy storage (ATES) and duct thermal energy storage (DTES). Bedrock stability, high sulphide and iron content, cover thickness for thermal insulation, and thermal conductivity are sufficient to recommend a combined duct-borehole storage system at this stage.

SmartStore modeling results for a generic 1500 MWh borehole thermal energy store (BTES) on campus indicate that a hexagonal or cubic storage geometry (50 m X 50 m) containing 80 to 90 wells with diameters of 0.115m, spacings of 5.0 to 5.3m and depths of 150 to 160m, would provide minimal heat losses from the store (maximum storage efficiency).

Keywords: Dalhousie University, UTES, Halifax Group, slates, siltstones, sulphides, iron, porosity, permeability, fracture sets, water seepage, Beaver River Till, depth to bedrock, refraction seismics, thermal conductivity, hot-wire method, volumetric heat capacity, ATES, DTES, BTES, SmartStore, storage geometry, modeling
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Supervisors: Gunter Muecke