Terrestrial heat flow evaluation from thermal response tests combined with temperature profiling

Abstract

The terrestrial heat flux density, an essential information to evaluate the deep geothermal resource potential, is rarely defined over urban areas where energy needs are important. In an effort to fill this gap, the subsurface thermal conductivity estimated during two thermal response tests was coupled with undisturbed temperature profile measurements conducted in the same boreholes to infer terrestrial heat flow near the surface. The undisturbed temperature profiles were reproduced with an inverse numerical model of conductive heat transfer, where the optimization of the model bottom boundary condition allows determining the near-surface heat flow. The inverse numerical simulation approach was previously validated by optimizing a steady-state and synthetic temperature profile calculated with Fourier's Law. Data from two thermal response tests in ground heat exchangers of one hundred meters depth were analyzed with inverse numerical simulations provided as examples for the town of Québec City, Canada, and Orléans, France. The temperature profiles measured at the sites and corrected according to the paleoclimate effects of the quaternary glaciations were reproduced with the model. The approach presented offers an alternative to assess heat flow in the preliminary exploration of deep geothermal resources of urban areas, where thermal response tests may be common while deep wells sparsely distributed over the area to assess heat flow.

Estimation of In-Situ Heat Capacity and Thermal Diffusivity from Undisturbed Ground Temperature Profile Measured in Ground Heat Exchangers.

“…For example, several field measurements were performed with different equipment to accurately assess TUGT [4,10;16] and several types of TRT were carried out in different seasons (fall, winter, summer) to infer TC and borehole thermal resistance [4,10,11,16,33]. Recently, other work of interest was made to evaluate heat flux density [19], subsurface thermostratigraphic log and groundwater flow [16], as well as in-situ HC evaluation [11].…”

“…Applying the heat balance concept, it is assumed that Zdd and C1 are integrated parameters of the thermocline zone (Figures 1-2) and the interpolated undisturbed ground temperature at the depth of zero temperature amplitude, when considering one-dimension heat conduction, respectively [19][20][21][22][23][24]27,28,[32][33][34]. Therefore, an equation can be used as upper boundary condition to describe the surface temperature variations transferred to the subsurface by oscillatory heat diffusion [28,33,[43][44][45][46].…”

“…Moreover, ground temperature profiles measured in the BHE before the TRT have also commonly been used to evaluate the undisturbed ground temperature [10,[15][16][17]. Such equilibrium temperature profiles can be reproduced numerically to extend the conventional in-situ TC assessment of a TRT and to infer the terrestrial heat flow [18,19]. Ground temperature profiles measured in observed wells are also used to evaluate other thermal properties such as in-situ TD [20][21][22][23][24].…”

Uncertainty and Risk Evaluation of Deep Geothermal Energy Source for Heat Production and Electricity Generation in Remote Northern Regions

“…The lower boundary condition is the basal heat flux. A numerical approach has been developed by Marquez et al [88] and improved by Miranda et al [89] to simulate climate events and find the basal heat flux that best matches a measured temperature log. The results of the latter were used in this work.…”

“…Deep temperature profiles will enable to ascertain more accurately the heat flux and, subsequently, the subsurface temperature and more complex geostatistical tools can then be applied for the uncertainty quantification [74,131,132]. Nevertheless, the adopted methodology developed by Marquez et al [88] and improved by Miranda et al [89] to infer heat flux from shallow temperature logs (80 m), together with the thermophysical properties of the surficial rock samples, is a valuable tool to carry out a first-order assessment of the deep geothermal potential in remote northern communities.…”