Jasmin Raymond

A review of thermal response test analysis using pumping test concepts.

The design of ground-coupled heat pump systems requires knowledge of the thermal properties of the subsurface and boreholes. These properties can be measured with in situ thermal response tests (TRT), where a heat transfer fluid flowing in a ground heat exchanger is heated with an electric element and the resulting temperature perturbation is monitored. These tests are analogous to standard pumping tests conducted in hydrogeology, because a system that is initially assumed at equilibrium is perturbed and the response is monitored in time, to assess the systems properties with inverse modeling. Although pumping test analysis is a mature topic in hydrogeology, the current analysis of temperature measurements in the context of TRTs is comparatively a new topic and it could benefit from the application of concepts related to pumping tests. The purpose of this work is to review the methodology of TRTs and improve their analysis using pumping test concepts, such as the well function, the superposition principle, and the radius of influence. The improvements are demonstrated with three TRTs. The first test was conducted in unsaturated waste rock at an active mine and the other two tests aimed at evaluating the performance of thermally enhanced pipe installed in a fully saturated sedimentary rock formation. The concepts borrowed from pumping tests allowed the planning of the duration of the TRTs and the analysis of variable heat injection rate tests accounting for external heat transfer and temperature recovery, which reduces the uncertainty in the estimation of thermal properties.

Evaluating the geothermal heat pump potential from a thermostratigraphic assessment of rock samples in the St. Lawrence Lowlands, Canada.

The installation cost and the performance of geothermal heat pump systems are influenced by the thermal state and properties of the subsurface. The ground ability to transfer heat described by thermal conductivity is a dominant factor affecting the favorability of closed-loop ground heat exchangers installed in vertical boreholes. A study that aimed at evaluating the geothermal heat pump potential by mapping the thermal conductivity of rock sequences was, therefore, performed for the St. Lawrence Lowlands sedimentary basin in Canada. Thermal conductivity was measured in the laboratory on rock samples collected in outcrops and used to complete design calculations of a geothermal system with a single borehole. Results allowed the definition of thermostratigraphic units that can be linked to depositional environments. Basal quartz-rich sandstones formed in a rift environment show a high geothermal potential. Overlying dolomites, argillaceous limestones and shales deposited in a passive margin evolving to a foreland basin exhibit a transition toward the top from high to low geothermal potential. Upper turbidites and molasses have a moderate geothermal potential. The thermal conductivity of the thermostratigraphic units is dominantly influenced by the mineralogy of the sedimentary rocks. Understanding their origin is a key to improve geothermal resource assessment and system design to anticipate new installations in the area.

Public Perception Regarding Deep Geothermal Energy and Social Acceptability in the Province of Québec, Canada

Deep geothermal energy is unknown to a large proportion of Canadians and even less well known in the province of Quebec. Public outreach and acceptance associated with this “new” energy is a key factor for its development. In the fall of 2013, an Internet-based public awareness and opinion survey of Quebec province residents was conducted to investigate their opinion about energy with a focus on their knowledge and opinion about deep geothermal energy. Quebec’s population recognized the challenge of developing renewable energies. However, geothermal energy was more or less known. Only 17% knew the difference between shallow and deep geothermal energy. After reading a text describing deep geothermal energy exploitation, 67% of the respondents supported its use to produce electricity in the province, and 64% would be in favour of a pilot project in their region. When hydraulic fracturing was introduced as a technique sometimes used in deep geothermal energy, the level of support decrease to 56% for the use of deep geothermal energy to produce electricity in the province and to 52% for a pilot project in their region. The main concerns of Quebec’s population on deep geothermal energy are related to groundwater pollution and soil contamination.

Underground thermal energy storage in subarctic climates: a feasibility study conducted in Kuujjuaq (QC, Canada)

Underground thermal energy storage can provide space and water heating and has been used in temperate climates so far. A step forward is to evaluate the efficiency and viability in arctic to subarctic environments, where rather low ground and air temperatures can make the design of such systems difficult. The present contribution describes the design of an underground storage system in Kuujjuaq (Québec, Canada) to heat the drinking water distributed in the town. The system was designed and modeled with TRNSYS and a parametric study was carried out to improve its efficiency based on 5-year simulations. The 20% of the 425 MWh annual demand can be satisfied by a solar collector area of 500 m coupled to a 10,000 m underground storage through two short term tanks. Further improvements could be adopted to reach the target of 50% energy from the underground store.

Numerical simulation of geothermal energy transfer beneath exothermic waste rock piles

The installation of a ground coupled heat pump system can be expensive because it requires the drilling of boreholes to install ground heat exchangers. The cost of a system can be reduced by decreasing the total heat exchanger length or the number of boreholes, which depends, among other factors, on the ambient subsurface temperature. Systems designed according to heating loads therefore require fewer heat exchangers for higher subsurface temperatures. At open pit mines, where waste rock is accumulated in piles, exothermic oxidation of sulfide minerals within the piles can increase subsurface temperatures. To investigate the potential reduction in borehole length resulting from increased subsurface temperatures, heat transfer associated to a vertical ground heat exchanger installed beneath a waste pile was simulated with a numerical model. The physical characteristics of the pile are based on those of the South Dump waste rock pile of the Doyon Mine in Abitibi, Québec, Canada. Optimization of the heating loads assigned to the exchanger shows that the borehole length required for a given building can be reduced by 15% to 46%, depending on the location of the system relative to the waste rock pile.