Alan M. Jessop

Heat flow and heat generation in the superior province of the canadian shield

Abstract Nine new heat flow determinations and several measurements of radioactive heat generation are presented for the Superior Province. The average value of twenty-one heat flows now published for the Superior, corrected for Pleistocene glaciation, is 40 ± 8 mW / m 2 . Heat generation values are low generally less than 3 μWW / m 3 . Although individual values of the ratio of thorium to uranium vary considerably, the geometrical average of four is lower than results from other Archean rocks. A linear relation between the heat flow and radioactive heat generation may exist. The reduced heat flow, 21 mW / m 2 , and the characteristic depth, 14 km, from this relation are quite different from other heat flow provinces. Since large thicknesses of the crust have been eroded away and since the original heat generation was much larger than the values measured now, a linear relation equivalent to those found in younger heat flow provinces is not expected. To account for the large differences in heat flow and heat generation observed in different Archean shields an Archean crustal model is proposed which includes thin (2–4 km) radioactive surface veneers over some areas. The thermal parameters of a young crust may well determine whether or not it will survive. Since Archean times the heat flow of each newly stabilized region has been a constant, and since the time of formation or last orogeny the heat flow in each province has steadily decreased. The geothermal gradients in Archean crust have decreased the most, causing significant underplating, and increasing the strength of the crust.

Ground temperature histories in eastern and central Canada from geothermal measurements: evidence of climatic change

Abstract Inverse and direct methods have been used to analyze a large number of borehole temperature logs in order to infer past climatic changes. Results indicate a warming of 1–2°C in eastern and central Canada during the past 150 years. A period of cooling between 500 and 200 years before present, corresponding to the time of the “Little Ice Age”, has also been identified in the same areas. A regional ground temperature history is estimated for eastern and central Canada from the simultaneous inversion of several temperature logs. The inferred temperature changes appear correlated with the concentration of atmospheric carbon dioxide as reported from a Greenland ice core, and agree with existing meteorological and dendrochronological records for the area.

Terrestrial Heat Flow in Canada

Abstract Heat flow has been measured at 214 separate sites in Canada and on the surrounding continental shelves. Most geological provinces show average heat flow that conforms approximately to world averages for areas of similar tectonic age, but the northern Prairies show an anomalously high heat flow that is probably controlled by deep water movement, and the coastal zone of southern British Columbia shows a low heat flow that is believed to be associated with recent subduction of small ocean plates.

The detection of groundwater flow by precise temperature measurements in boreholes

The flow of water is a very effective means for the transfer of heat, and one method of detecting such flow is to make precise temperature measurements at closely spaced intervals in a borehole that intersects a flow zone. Water can flow through permeable formations; within a borehole it can flow between two aquifers or fracture systems; it can flow into a fracture system during the drilling of a borehole; and it can flow up or down narrow, dipping fracture zones. Each of these phenomena produces a characteristic thermal signature on a borehole temperature log that can be modelled mathematically. Analysis of such thermal anomalies permits, therefore, a quantitative estimate to be made of the amount and rate of fluid flow. In principle, very small flow rates can be detected from their thermal effects, but in practice other factors, such as thermal conductivity variations, can cause variations in thermal gradients that limit the detectability. Anomalies that persist over large depth ranges compared with the diameter of the borehole can generally be interpreted unambiguously. Examples of each type of flow are given.

The variability of heat flow both regional and with depth in southern Alberta, Canada: Effect of groundwater flow?☆

Abstract Detailed studies of terrestrial heat flow in southern and central Alberta estimated on the basis of an order of magnitude larger data base than ever used before (33653 bottom-hole temperature data from 18711 wells) and thermal conductivity values based on detailed rock studies and measured rock conductivities show significant regional and local variations and variations with depth. Heat flow values were estimated for each 3 × 3 township/range area (28.8 × 28.8 km). A difference in heat flow exists between Paleozoic and Mesozoic strata. Generally lower heat flow values are observed in the strata above the Paleozoic erosional surface (20–75 mW m−2). Much higher values are estimated for the Younger Paleozoic formations, with large local and regional variations between 40 and 100 mW m−2. Average heat flow values based on heat flow determinations below and above the Paleozoic surface that agree within 20% show an increase from values less than 40 mW m−2 in southern and southwestern Alberta to values as high as 70 mW m−2 in central Alberta. The predominance of regional downward groundwater flows in Mesozoic strata seem to be responsible for the generally observed heat flow increase with depth. The results show that the basin heat flow pattern is influenced by water movement and even careful detailed heat flow measurements will not give correct values of background steady-state heat flow within the sedimentary strata.

Heat flow, heat generation and crustal temperature in the kapuskasing area of the Canadian Shield☆

Abstract Combined heat flow and heat production measurements in three boreholes in the Superior Province of the Canadian Shield were made to test the geothermal consequences of the Kapuskasing fault zone. The evidence of gravity and geomagnetic investigation suggests that this zone is a deeply eroded remnant of a crustal rift. A linear relation between heat flow (q) and surface heat production (P), q = qo + bP, where qo and b are empirical constants, has been found by F. Birch, R. Roy and A. Lachenbruch for different heat-flow provinces over the North American continent. The results from the Kapuskasing zone clearly confirmed this relation, giving qo = 0.63 μcal. · cm−2 · sec−1 and b = 13.5 km. The significance of these parameters for the crustal structure study and the probable temperature-depth distribution are discussed in the paper. The influence of different surface temperature during the past on the underground temperature is mentioned. The consistent elimination of the climatic effect on measured heat flow is necessary when a geothermal model is to be constructed.

Climatic changes in central and eastern Canada inferred from deep borehole temperature data

Abstract We analyzed data from 23 boreholes at 19 sites in central and eastern Canada, for the purpose of estimating ground surface temperature (GST) histories. These boreholes were logged down to at least 550 m depth with thermistor probes. Thermal conductivity measurements had been previously made at small depth intervals for the entire depth ranges of most of the boreholes. The temperature profiles of these boreholes do not indicate water disturbance. We estimated terrain effects for each borehole using a time dependent solid-angle method. The thermal perturbations caused by lakes or deforestation near the borehole sites are insignificant in most cases. However, four of the holes were found to be severely influenced by terrain effects. GSTs estimated from the borehole data less influenced by the terraineffects form two groups. The first group, which are generally from data of better quality, show a cold period near the end of the last century before the recent warming trend; the second show it 80–100 years earlier. We consider the former typical of the climate of the Boreal climatic region of Canada. The difference between the two groups may reflect the spacial variability of the climate. Four GST estimates do not belong to either type, and the reasons are discussed.

Present Heat Flow Along a Profile Across the Western Canada Sedimentary Basin: The Extent of Hydrodynamic Influence

Compilation of bottom-hole temperature (BHT) data (3,466 readings) and their correction along the 680-km profile from the Rocky Mountain Foothills to the western edge of the Canadian Shield has allowed detailed analysis of the 2D temperature distribution, calculation of the thermal gradient, and estimate of heat flow. Temperature data are available typically from only a section of the depth interval making 2D contouring of the temperature field difficult. Surface temperature values were used in calculations of the thermal gradient. The quality of the BHT data deteriorates towards the shallow part of the basin where larger errors of heat-flow estimates of the profile are calculated. Estimated heat flow increases from the southwest towards the northeast. Anomalously high values between 300 km – 500 km of the profile are questionable.

Clean Energy from Abandoned Mines at Springhill, Nova Scotia

Flooded former coal mines of Springhill, Nova Scotia, contain about 4,000,000 m3 of water which circulates by convection and may be recovered at the surface at a temperature of about 18°C. The heat in the water is derived from the normal heat of the rocks and the contribution from chemical heating is negligible. Water is pumped from the mines to act as the primary input to heat pumps for heating and cooling industrial buildings. Annual heat exchange with the mine by the largest user puts more heat into the mine in summer than is taken out in winter. Buildings without heavy machinery, such as office buildings, drain little heat from the mine, so that many heat exchange systems could operate indefinitely, without significant depletion of the heat source. Initial costs of heat pump installation are higher than the costs of conventional oil furnaces, but the operating costs are substantially lower. In the Springhill systems, heat pumps provide summer cooling as well as winter heating and total costs of geothe...

Geothermal measurements in a deep well at Regina, Saskatchewan

Abstract The University of Regina Geothermal Project was designed to demonstrate the use of moderate-temperature geothermal resources from sedimentary aquifers in heating large buildings. The first well was drilled on the campus of the University of Regina in the winter of 1979. Hydraulic potentials show that individual aquifers of the Basal Clastic Unit are not in direct hydraulic connection, and temperature measurements show that flow is occurring in the open hole. Apparent terrestrial heat flow varies vertically in the Upper Clastic Unit, showing either cross-formational water flow or errors in the measurement of thermal conductivity of shales. A reasonably uniform heat flow of 51 mW/m 2 in the Carbonate-Evaporite Unit may represent the terrestrial heat flow from the basement, but this cannot be demonstrated with certainty.