Heat flow (Q) determined from bottom-hole temperatures measured in oil and gas wells in Alberta show a large scatter with values ranging from 40 to 90 mW m -2 . Only two precise measurements of heat flow were previously reported in Alberta, and were made more than half a century ago. These were made in wells located near Edmonton, Alberta, and penetrated the upper kilometre of clastic sedimentary rocks yielding heat flows values of 61 and 67 mW m -2 (Garland & Lennox). Here, we report a new precise heat flow determination from a 2363-m deep well drilled into basement granite rocks just west of Fort McMurray, Alberta (the Hunt Well). Temperature logs acquired in 2010-2011 show a significant increase in the thermal gradient in the granite due to palaeoclimatic effects. In the case of the Hunt Well, heat flow at depths >2200 m is beyond the influence of the glacial-interglacial surface temperatures. Thermal conductivity and temperature measurements in the Hunt Well have shown that the heat flow below 2.2 km is 51 mW m -2 (±3 mW m -2 ), thermal conductivity measured by the divided bar method under bottom of the well in situ like condition is 2.5 W m -1 K -1 , and 2.7 W m -1 K -1 in ambient conditions), and the geothermal gradient was measured as 20.4 mK m -1 . The palaeoclimatic effect causes an underestimate of heat flow derived from measurements collected at depths shallower than 2200 m, meaning other heat flow estimates calculated from basin measurements have likely been underestimated. Heat production (A) was calculated from spectral gamma recorded in the Hunt Well granites to a depth of 1880 m and give an average A of 3.4 and 2.9 µW m -3 for the whole depth range of granites down to 2263 m, based on both gamma and spectral logs. This high A explains the relatively high heat flow measured within the Precambrian basement intersected by the Hunt Well; the Taltson Magmatic Zone. Heat flow and related heat generation from the Hunt Well fits the heat flowheat generation relationship determined for other provinces of the Canadian Shield. However, this relationship could not be established for Q estimates from industrial temperatures data for the study area that includes the Taltson Magmatic Zone and neighbouring Buffalo High and Buffalo Utikuma domains to the west. It appears that the spatial wavelength of heat generation change is much smaller than that of heat flow. Thermal modelling of heat flow and heat generation data from the Hunt Well, using mantle heat flow contributions of 15 ± 5 mW m -2 results in lithosphere-asthenosphere boundary depth estimates of near 200 km. This mantle heat flow value is consistent with the range for the stable continental areas, 15 (±3) mW m -2 .
Abstract:Heat flow and geothermal gradient of the sedimentary succession of the Western Canada Sedimentary Basin (WCSB) are mapped based on a large thermal database. Heat flow in the deep part of the basin varies from 30 mW/m 2 in the south to high 100 mW/m 2 in the north. As permeable strata are required for a successful geothermal application, the most important aquifers are discussed and evaluated. Regional temperature distribution within different aquifers is mapped for the first time, enabling a delineation of the most promising areas based on thermal field and aquifer properties. Results of previous regional studies on the geothermal potential of the WCSB are newly evaluated and discussed. In parts of the WCSB temperatures as high as 100-210 °C exist at depths of 3-5 km. Fluids from deep aquifers in these "hot" regions of the WCSB could be used in geothermal power plants to produce electricity. The geothermal resources of the shallower parts of the WCSB (>2 km) could be used for warm water provision (>50 °C) or district heating (>70 °C) in urban areas.
This study explores the distribution of Paleozoic formations in the Central Alberta Basin and investigates rock properties with regard to their usability as geothermal reservoirs. The study area of this regional-scale investigation is about 160 km × 200 km in size and located around Edmonton where the basin depth ranges between 1.8 and 3.5 km. A three-dimensional (3D) geological model was developed based on stratigraphic tops from about 7000 wells from the database of the Alberta Geological Survey (AGS). Spatial distribution and thickness of deep formations were established in the 3D geological model. Porosity and permeability of four Devonian carbonate formations — Cooking Lake, Leduc, and Nisku formations, and Wabamun Group — were investigated using data from more than 50 000 core analyses. Average porosity of the Devonian strata in the study area ranges from 4.5% (Nisku) to 8.7% (Wabamun), average permeability is between 3.5 × 10−15 m2 (Wabamun) and 26 × 10−15 m2 (Leduc). The distribution of both parameters was analyzed using geostatistical methods. Based on an average geothermal gradient and the geometry of formations from the 3D modeling study, an estimation of formation temperatures for the Paleozoic formations is presented. Temperature in the Cambrian Basal Sandstone Unit ranges from 62 °C in the shallower northeast (1.8 km) to 122 °C in the deeper southwest (3.5 km); temperature in the Devonian strata ranges from 22 to 87 °C. With these new results, potential geothermal reservoirs can be delineated in the Alberta Basin around Edmonton, enabling future detailed exploration and field development.
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