High Temperatures Predicted in the Granitic Basement of Northwest Alberta - an Assessment of the Egs Energy Potential

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PROCEEDINGS, Thirty-Ninth Workshop on Geothermal Reservoir Engineering Stanford University, Stanford, California, February 24-26, 2014 SGP-TR-202

HIGH TEMPERATURES PREDICTED IN THE GRANITIC BASEMENT OF NORTHWEST ALBERTA - AN ASSESSMENT OF THE EGS ENERGY POTENTIAL

Jacek Majorowicz1*, Greg Nieuwenhuis1, Martyn Unsworth1, Jordan Phillips1 and Rebecca Verveda1

1University of Alberta Department of Physics, Canada *email: [email protected] Keywords: Heat flow, EGS, Alberta, Canada

ABSTRACT Northwest Alberta is characterized by high subsurface temperatures that may represent a significant geothermal resource. In this paper we present new data that allows us to make predictions of the temperatures that might be found within the crystalline basement rocks. In this region the Western Canada Sedimentary Basin (WCSB) is composed of up to 3 km of Phanerozoic sedimentary rocks with low thermal conductivity, which act as a thermal blanket. Commercial well-logging data was cleaned of erroneous data and corrected for paleoclimatic effects to give an average geothermal gradient of 35 K per km, and maximum geothermal gradients reaching 50K per km. These gradients, along with a thermal conductivity model of sedimentary rocks, were then used to estimate heat flow across the unconformity at the base of the WCSB. The calculations assumed a heat generation of 0.5 µW/m3 within the sedimentary rocks. Estimation of temperatures within the crystalline basement rocks requires knowledge of the thermal conductivity (TC) and heat generation (HG) of these rocks. These are mainly granitic Precambrian rocks. Thermal conductivity (TC) and heat generation (HG) of the basement rocks were measured on samples recovered from hundreds of wells that sampled the Pre-Cambrian basement rocks. TC values were corrected for pressure and temperature variation. Using these data, we have developed a temperature model of Northern Alberta which predicts temperatures in the 3-6 km depth range. Analysis of the temperature variations in NW Alberta has resulted in the discovery of the Rainbow Lake high temperature anomaly. The heat flow below the sedimentary cover (> 2 km) at this location represents the highest heat flow in Alberta. This is the hottest spot found in Alberta at these depths. The temperature model predicts high temperatures (>170°C at 4 km depth, 200°C at 5 km depth, and as high as 230oC at 6 km) within the Precambrian basement rocks in part of Northwest Alberta under 2.5-3km thermal blanket of sedimentary rocks. Since this temperature anomaly is located within crystalline basement rocks, an Engineered Geothermal System (EGS) would be required to utilize this heat. The development of an EGS in this location could be facilitated by the presence of naturally occurring fractures within the Great Slave Lake Shear Zone.

1. INTRODUCTION The goal of this study is the assessment of the EGS potential in Northwest Alberta, which has been known for its high heat flow. NPHFA - Northern Plains Heat Flow Anomaly (see: Majorowicz, 1996) extends from north-eastern British Columbia and Northwestern Alberta to the southern Northwestern Territories between the Precambrian shield (Slave Province) and the Cordillera (Mackenzie Fold Belt) as seen in this more recent heat flow data compilation shown in Fig. 1 from Majorowicz and Weides, (2013).

Figure 1: Regional heat flow map in WCSB and location of the study area (modified from Majorowicz and Weides 2013).

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We focus on two goals: 1) determining the spatial and depth variations of temperature within the Precambrian basement rocks that underlie Northern Alberta, and 2) determining how much geothermal energy is available and whether electrical production could be economic.

In order to calculate how temperature changes with depth beyond the depths where measurements are available in boreholes, we need to know (a) the properties of the rocks such as thermal conductivity (TC) and heat generation (A), and (b) the heat flow (Q) through the subsurface. Since we have access to many temperature measurements made by oil companies in wells drilled into the overlying sedimentary rocks, we are able to calculate the heat flow. Assuming that the heat flow is one dimensional, and estimating the amount of heat generation that occurs within the sedimentary basin, it is possible to calculate the heat flow at the top of the Precambrian basement rocks. To calculate temperatures within the Precambrian basement rocks we must know the heat generation and thermal conductivity of these rocks. In summary, to calculate the temperature change with depth below the top of the Precambrian basement, we need accurate estimates of three values, all of which change across Alberta: 1) heat flow at the surface, 2) heat generation of the sedimentary rocks in the basin and underlying Precambrian basement rocks, and 3) thermal conductivity of the basement rocks.

2. RELIABILITY OF THE INDUSTRIAL TEMPERATURE DATA IN THE BASIN The temperature data used in this study to predict the deep geothermal field within the sedimentary basin are: Annual Pool Pressure surveys (APP), Drill Stem Tests (DST) and Bottom Hole Temperatures (BHT), (Gray et al., 2012), as well as a small number of precise equilibrium logs (Garland and Lennox, 1962, Majorowicz et al., 2012). Measurement and systematic errors inherent to the APP, DST, and BHT data are significant (Hackbarth, 1978; Majorowicz et al., 1999; Gray et al., 2012) and can result in large data noise (Lam et al., 1985; Majorowicz et al., 2012, 2013a, Gray et al., 2012). To this end these data were initially cleaned to remove erroneous data as described by Gray et al., 2012 (e.g. a significant overestimation of Alberta industrial well logs from shallow depths was removed <1000m). Where possible Gray et al., (2012) also applied the standard corrections (Horner, Harrison, SMU etc..., Lachenbuch and Brewer, 1959; Harisson et al, 1983; Blackwell and Richards, 2004, respectively).

The surface heat flow has previously been calculated by the geothermal group at the University of Alberta using industrial temperature data collected in the basin, as described by Gray et al, (2012), and Majorowicz et al, (2012a,2013b). A paleoclimatic correction was also applied based on a correction factor derived from the Hunt Well temperature data by Majorowicz et al., (2012, 2013b). See Gosnold et al., (2011) and Majorowicz and Wybraniec, (2010) for a description of the correction methodology.

Prior to using these heat flow values, we used computer software developed at Southern Methodist University to determine which heat flow estimates can be considered reliable. This has resulted in a confirmation of our previous results, which showed that heat flow calculated from shallow boreholes in the basin are not reliable. To further constrain the heat flow in Northern Alberta we applied an algorithm which is being developed as part of the Geothermal Atlas of Alberta (Nieuwenhuis et al., 2014). This algorithm uses robust statistics to remove data which is not reliable, and resulted in the removal of approximately 25% of the measured temperature data. Here we show the newest edition of the heat flow map of the Northern area after paleoclimatic correction has been applied.

Figure 2: Heat flow map of the study area. The heat flow data (Q) are based on approximately 30,000 data points from bottom hole temperatures, drill stem test temperatures, temperature measured annually in shut in wells and a small number of shallow (few hundred meters) precise logs in equilibrium. The thermal conductivity model of sediments is from 2 Majorowicz et al. measured sedimentary rock conductivity averages for common rock types (Beach et al., 1987) and abundances of the 13 main sedimentary rocks. The paleoclimatic correction developed for North Alberta has been applied (Majorowicz et al., 2012a; 2013a).

3. HEAT FLOW AT THE SURFACE VS. HEAT FLOW AT PRECAMBRIAN TOP As discussed above, in order to determine heat flow at the Precambrian surface, the heat generation in the sedimentary basin must be known. We have estimated heat generation of the sedimentary cover above the Precambrian crystalline basement from gamma logs. We have used the empirical relationship between GR (API units) and A (W/m3), equation (1), developed by Bucker and Rybach (1996):

A=0.0158(GR [API]-0.8) (1)

Four well logs which were measured through the entire depth of the basin at four different locations (Peace River, High Level Hinton-Edson and Edmonton vicinity were analyzed (Figure 3). The resulting estimates of A for the sedimentary basin show that the contribution in heat flow from the heat generation of the sedimentary basin is less than the error in the heat flow, confirming our previous results from the Hunt Well (Majorowicz et al., 2013a). This means that spatial and depth variations in the heat generation throughout the sedimentary basin are not significant, and an average value (0.6W/m3) has been used throughout Northern Alberta.

Figure 3: Heat generation estimated in four wells in the sedimentary rocks of Northern Alberta, resulting in an average of 0.6 W/m3.

The cleaned and corrected temperature database described above was used to calculate the heat flow at the surface. Heat flow at the surface reduced by the sedimentary heat generation contribution gives the heat flow at the Precambrian surface, which in the study area varies in depth from a few hundred meters down to 3500 meters. Heat flow contribution from sedimentary rocks is low and will not be higher than 3.5mW/m2, which is less than the error of heat flow determination from thermal data in sediments (15%). This heat flow was used for further calculation of temperature in the Precambrian basement.

4. THERMAL CONDUCTIVITY OF THE PRECAMBRIAN BASEMENT In 1986 a divided bar set up was used in the University of Alberta Physics Department geothermal lab, supervised by Prof. Walter Jones. It was used to measure the thermal conductivity of rocks sampled by 32 wells in North Western Alberta (mainly granites; Tempest Geophysical, 1986/GSC Open File).

Over the past three years we have measured the thermal conductivity of many more rocks in partnership with the Alberta Geological Survey (AGS), who own a thermal conductivity measurement instrument that uses the heat impulse principle (Mathis Tci 1; see Fig. 4). This has resulted in 185 thermal conductivity measurements being made on core samples from Northern Alberta Precambrian basement (a set of typical samples are shown in Fig 5). Measurements have been made on wet polished surfaces, and since the contact area for the measurement device is relatively small, 6 measurements were made per sample, and the contact has been moved over the sample at random for each measurement with noticed variability within 0.2 W/m K.

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Figure 4: Measuring thermal conductivity of Alberta basement rocks with heat impulse method in the AGS lab in the spring 2011.

In 2012, the thermal conductivity of Precambrian basement drill core samples from 30 wells in the vicinity of Fort McMurray (mainly from the Precambrian Taltson domain of the Western Canadian Shield) were measured using the heat impulse method with an instrument provided by the Alberta Geological Survey. The average thermal conductivity was found to be 2.9±0.8 W/m K. The thermal conductivity of the crystalline basement rocks, mainly of granitic composition, varies over a wide range.

In 2013 we have extended this study by measuring the thermal conductivity of a much larger number of crystalline basement rocks from subsurface locations to the West of those measured in 2012. The thermal conductivity of 124 samples has a mean value of 3.3±0.7 W/m K. These values are located in Northwestern Alberta, and are higher than those from the Ft. McMurray area measured in 2012 (2.7 W/m K).

Figure 5: Some of the cores collected from University of Alberta, Professor Ron Burwash rock collection museum and used to measure thermal conductivity of the Precambrian basement rocks of Northwest Alberta.

Additionally, In 2011/2012, the thermal conductivity of granite core from a deep well near Fort McMurray was measured (Hunt well; see Majorowicz et al, 2013a,b, 2014 for description of these results). We have compared our heat impulse method 4 Majorowicz et al. measurements with measurements on the same set of rock samples in other labs, using other instruments. The Hunt well samples were sent to Dr. William Gosnold at the University of North Dakota (UND) where they measured the thermal conductivity using the divided bar. They were also sent to Dr. Andrea Forster at the Geoforshung Zentrum GFZ lab in Potsdam Germany where thermal conductivity was measured using an optical scanner. We have found that measurement in wet conditions (i.e. saturated rocks) agree within measurements error (+/-0.1 W/m K). Figure 6a shows a comparison of the results measured by the heat impulse method (AGS TC) and the optical scanner method (GFZ TC), and Figure 6b shows the results of the heat impulse method compared to the divided bar method. This comparison shows that all methods have given us very similar results for the Hunt well samples, and have given us confidence in using the heat impulse device from the AGS for further measurements on crystalline rocks from other wells

4 y = x

2 CORE PLUGS

AGS AGS TC W/mK Linear (TC AGS=TC GFZ 1 reference line)

0 0 1 2 3 4 GFZ TC W/ mK

4 y = x

Heat impulse TC vs. 2 Divided bar TC in saturated conditions Linear (TC AGS=TC UND 1 reference line)

HEAT HEAT IMPULSE DEVICE MEASURED TC W/m K 0 1 2 3 4 DIVIDED BAR MEASURED TC W/ m K

Figure 6: Comparison of measured thermal conductivity of the Precambrian basement rocks in Hunt well using two methods; a), (AGS heat impulse vs. GFZ optical scanner in wet conditions) and b) (AGS heat impulse vs. UND divided bar in wet conditions). Note: The spread is comparable with error by the heat impulse method 0.2 W/m K.

The observed range of measured thermal conductivities in the Hunt Well (i.e., 2-4 W/m K) results in large variations in the prediction of temperature below where temperature measurements are available. To give an example, using a heat flow value of 60 mW/m2, and a measured temperature at 2 km of 60oC, temperature predictions at 5 km depth range from 105-150oC with thermal conductivity values of 4 and 2 W/m K, respectively. This significantly large range in temperature predictions highlights the uncertainty in estimating temperature at depths below where direct measurements are available.

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With this new set of thermal conductivity measurements available from across northern Alberta, we have shown that the thermal conductivity generally increases to the West across Northern Alberta (see Figure 7). The westward thermal conductivity increase is likely controlled by variations in the quartz abundance. The thermal conductivity of quartz is 7.3 W/m K and is approximately 2.5 times higher than the conductivity of other minerals such as the feldspars which make up the most common WCSB Precambrian basement rocks we have studied i.e. granites, granodiorites, etc.), (Jessop, 1990). Samples came from the Precambrian basement, sampled by oil and gas wells a few meters below the unconformity surface at the base of the sedimentary basin. This surface varies in depth from a couple hundred meters near the shield to 5000 meters in the deep basement in the study area.

In order to account for the dependence of thermal conductivity on pressure and temperature, we have used a pressure – temperature correction developed by Chapman and Furlong (1992). We have considered granite below the sedimentary rocks of the Alberta Basin. The correction of thermal conductivity TC as a function of depth z and temperature T was considered in the form

TC (z, T) = TCo (1 + c z) / (1 + b (T-293)) (2)

where TCo is thermal conductivity at a temperature of 293K and atmospheric pressure. Typical values of coefficients c and b for the granitic upper crust are c = 1.5 * 10-6 m-1, b = 1.5 * 10-3 K-1 (Chapman and Furlong, 1992), which were used for this study.

The Alberta basement granites from a depth of 1820 m in the Hunt well were measured at ambient conditions on the stationary divided bar at minimal pressure, at room temperature at the University of North Dakota under the direction of Prof. William Gosnold. We have also investigated the dependence of TC on pressure and temperature up to the conditions observed at the base of the Hunt well (Majorowicz et al., 2014). This involved thermal conductivity measurements on the stationary divided bar at about 50⁰C, and pressurized to 5 520 Newtons / cm2 (8k psi, pound per square inch), represent the in situ conditions and sufficient to close micro-cracks. Approximately 20% of the samples did not survive the pressure long enough to get the final measurement because the samples shattered. Unless a sample had a very high porosity the uniaxial pressure along the Z axis when measuring thermal conductivity along the Z axis is an adequate replication of the in-situ conditions. Micro-cracks in the X / Y directions should close with the Z axis pressure. Micro-cracks in the Z direction should not affect conductivity in the Z direction, so there was no need for confining (3D) pressure. Since our samples all had very low porosity (<1%) using uniaxial pressure along the measurement axis was a close approximation of the conditions at depth, with respect to vertical heat flow. This measured data fit the correction predicted by eq. [2].

Figure 7: Spatial variation of the thermal conductivity (W/m K), mapped along with the Precambrian basement units (these are named and boundaries shown in black lines from Pilkington et al., 2000). Measurements mapped here are from the present study (2011-2013) using the AGS heat impulse method as well as measurements made by the divided bar instrument at the University of Alberta geothermal lab in the 1980s.

5. HEAT PRODUCTION OF THE PRECAMBRIAN BASEMENT CRYSTALLINE ROCKS

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Heat generation of the Precambrian crystalline rocks is a parameter that must be measured in order to estimate the heat flow distribution with depth and to predict subsurface temperatures. Heat flow Q (z) will decrease with depth z as heat generation A (z):

Q (z) = Qo - ∫Adz (3) where Qo is the heat flow at the Precambrian basement surface.

The study of Burwash and Cumming (1976) has provided data on the uranium and thorium concentrations for 182 samples from the Precambrian basement of the western Laurentia in Alberta and Saskatchewan and the Superior province in eastern Saskatchewan and Manitoba. The measurements were made by the delayed neutron activation method. Jones and Majorowicz (1987) included additional data from the Peace River area (total of 229 samples analyzed in a nuclear reactor facility at the University of McMaster. First analysis and mapping of the heat generation trends across the WCSB was reported by Jones and Majorowicz (1987) who delineated 3 major high heat generation trends across the basement underlying the basin and concluded that these do not correlate with heat flow for the same study area (based on their heat flow data). Bachu and Burwash (1991) also did further analysis and mapping for Alberta and the WCSB, respectively based on previously reported measurements (Burwash and Burwash, 1989)

Heat generation for all the wells drilled into the Precambrian basement rocks in northern Alberta (Fig. 8), A=2.2 W/m3 and average heat flow (average from N=29100 determinations in Northern Alberta Q=53+/-9 mW/m2 ) is higher than in the exposed Precambrian rocks of the Canadian Shield to the East A=1+/0.6 W/m3 and Q=40 mW/m2 (Jessop, 1992), While across Canada heat flow-heat generation averages correlate statistically , spatial correlation is difficult to find in more local scale of Northern Alberta itself (Majorowicz et al., 2014).

Figure 8: Pattern of A (in W/m3) based on data compiled by Burwash and Burwash (1989) and Jones and Majorowicz (1987).

The lack of correlation of Q with A patterns is visible from comparing the map of Q in Fig. 2 and the map of A in Fig. 8. This lack of spatial correlation was previously noted for all of Alberta by Jones and Majorowicz (1987) and Majorowicz and Jessop (1993).

The relationship between pairs of Q and A for large Precambrian domains of Northern Alberta has been recently investigated (Majorowicz et al., 2014, Geoph.J.Int. - in press). Correlation could not be established between Q estimates and A from the basement rocks in Northern Alberta.

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6. TEMPERATURE OF DEEP GRANITES-PREDICTION

Using the estimates of heat flow, heat generation, and thermal conductivity described above, we have calculated (examples shown in Fig.9) for two communities in Northwest Alberta, Rainbow Lake and High Level in vicinity of high temperature anomaly (Fig.2).

Figure 9: Temperature model at 0-10 km depth constrained by measured temperature in sedimentary succession and at the depth to the Precambrian basement for two Northwest Alberta communities, High Level and Rainbow Lake in the high temperature zone broadly related to the Great Slave Lake Shear Zone (marked on the map in Fig. 10 as GSLSZ).

Temperature changes with depth across Northern Alberta. Based on this temperature model we have shown that the temperature at Fort McMurray is ~ 180°C at a depth of 10 km, and ~ 250°C at the same depth beneath Peace River. This westward increase in temperature has been interpreted as resulting from the thickening of the basin to the west and Northwestward increase of heat flow (Fig.2). Since the basin acts as a low thermal conductivity thermal blanket, temperature below thicker portions of the basin tends to be higher as shown before along the 50 km wide cross-section oriented East-West across northern Alberta (Majorowicz et al., 2013a). Here, we show the predicted temperature at a reasonable drilling depth of 5 km (Fig.10). We have based temperature prediction on heat flow and the new temperature database described above. A high heat flow zone in Fig. 2 coincides with the high temperature (see Fig 10 for 5km depth slice) discovered in Northwest Alberta, which we find to be broadly associated with the Great Slave Lake Shear Zone (GSLSZ). This anomaly is associated with temperatures close to 200°C at a depth of 5 km, giving a similar thermal environment to the EGS geothermal projects at EGS Soultz Geothermal Project (France) or Landau in Germany.

This temperature model constructed for northern Alberta has been used as a constraint for reservoir modeling of an EGS system in similar geological environment of fractured granites, however, much colder Precambrian granitic rocks in north eastern Alberta for heating processed oilsands as described in Majorowicz, et al., 2013a,b.

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Figure 10: Temperature model at 5 km depth. Contour lines show the depth to the Precambrian basement, showing that the high temperatures in NW Alberta are located within the crystalline basement rocks that underlie the sedimentary basin. The ‘anomalous” high temperature zone in the northwest is broadly related to the Great Slave Lake Shear Zone (marked on the map as GSLSZ).

7. PREDICTION OF NET EGS

The second focus has been in determining the feasibility of electric power production in Northern Alberta using an EGS. Using the temperature model developed above and a 50 litres per second flow rate, based on Soultz and Landau experiments (Tester et al., 2006, MIT Report online), the spatial and depth variation in electrical power generation potential has been calculated. In order to produce net positive electrical power, an EGS would need to mine heat from depths within the Precambrian basement rocks. Since these rocks tend to be quite impermeable, we expect that such a system would have to artificially create a network of fractures in order to build a heat exchanger at depth. Another possibility is to find regions where a thermal anomaly exists within a zone of natural permeability and porosity, possibly within a large scale shear zone such as the GSLSZ.

EGS have already been proven to be practical in other crystalline rocks, such as within the Cooper basin (Australia), Soultz (France) and in sedimentary rocks of the Renishe Graben in Landau (Germany) to name few (Tester et al., 2006).

Net electrical power generations from Engineered Geothermal Systems (EGS) at a depth of 5 km are shown in Figure 11. These assume a 50 liter per second flow rate, and a two well system similar to the installation in Landau, Germany. Based on this figure, electrical energy production is not economically feasible in Fort McMurray, though heat production is, as shown by Majorowicz and Weides (2012). In contrast, NW Alberta shows significant potential, where an ORC cycle running at 11% efficiency could give a net 2.5 MW electrical output from an EGS system at a depth of 5 km when 50oC drop off temperature, 50l.s flow rate and 1.1MW for the injection and production pump system power draw assumed. At 6 km we estimate net electrical energy production of 3.5 MW. The main uncertainty is our lack of knowledge of possible fracture systems in the area due to a lack of deep drill holes going to such depths into the granites. The assumed flow rate of 50 liters per second is close to the peak production designed for the Soulz, France EGS ongoing experiment and feasible for other EGS systems (Tester et al., 2006). However, half of that number may be more realistic, which would lower the output by half and increase the cost competiveness. Also, thermal conductivity estimates can significantly affect temperature estimates. In case part of the high heat flow in sediments or fractures of the SLSZ is due to hydrodynamic component our estimated of deep temperatures based on the assumption of conductive heat transport only can be affected. However, the hydrodynamic component in the basin has been assessed as minimal to limited due to low Darcy velocities in known aquifers (mm-cm/year) by Bachu and Burwash, (1991) and Majorowicz et al., (1989). However, our knowledge of heat transport and fractures in deep granitic basement of the GSLSZ is not known and drilling geothermal exploration well is needed to confirm our prediction.

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Figure 11. Net electrical power in MW that could be produced from an EGS system at a depth of 5 km, using a doublet (2 wells) system. Calculations include the electrical power needed to run both surface and underground pumps.

We estimate the cost of drilling and fracturing the subsurface reservoir, plus the cost of building the surface installations, would be around $21 million per system. If we assume a maximum production of 3 MW electrical, there is an upfront (initial) investment cost of $7 million per MW. This is to be amortized over the lifetime of the system (15-30 years), which is a large range, and therefore the estimates of cost per kWh is theoretical at best. Regardless, if we assume a 15 year lifetime for the system, with the ideal theoretically assumed system running continuously throughout, we would expect an overall cost of $0.06/kWh, making it competitive with other energy sources available in Alberta. Even if we assume something more realistic 10% down time for maintenance the cost increase to 0.07 kWh be competitive if compared to CO2 emitting power plants in case carbon tax taken into account.

8. CONCLUSION

Temperature model predicts high temperatures near 200°C at 5 km depth, and >200oC at 6km, within the Precambrian basement rocks in part of the area of Northwest Alberta. Since this temperature anomaly is located within crystalline basement rocks under some 2.5km of sedimentary rocks, an Engineered Geothermal System (EGS) would be required to utilize this heat. The development of an EGS in this location would made more economical if it could use naturally occurring fractures in geological features such as the Great Slave Lake Shear Zone.

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ACKNOWLEDGEMENTS We would like to thank to Dr. Matt Grobe and Gordon Jean ((Alberta Geological Survey),), Dr. Andrea Foerster (Geoforshung Zentrum), Prof. Will Gosnold, Dr. Rob Klenner, James Crowell (Dpt Geol. Geol. Eng., University of North Dakota), Dr. Jan Safanda and Dr. Peter Dedecek (Czech Academy of Science) for help with thermal conductivity tests. Dr. Alan Jessop (Geological Survey of Canada) is thanked for allowing us use of older thermal conductivity data measured by divided bar at University of Alberta geothermal lab and acquired by Geological Survey of Canada in the 80th. We thank Dr. Maria Richards (Southern Methodist University, Geothermal Lab for allowing us to use her code for the reliability check of the heat flow data. We acknowledge research funding from the Helmholtz-Alberta Initiative. The research has been conducted under Helmholtz- Alberta Initiative Theme 4 (Prof. Martyn Unsworth, Leader)

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