H.L. Lam

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.

Terrestrial heat flow and geothermal gradients in relation to hydrodynamics in the Alberta basin, Canada

Abstract Geothermal gradients in the Alberta part of the Western Canadian sedimentary basin have been studied on the basis of 55,244 bottom-hole temperature values from 28,260 petroleum exploration wells. Gradient estimates for different depth and stratigraphic intervals together with a study of the heat conductivity distribution indicate both regional heat flow variations and variations with depth. The regional hydrodynamics of the basin strongl influences both grad ifT gradient and heat flow increase with depth in water recharge areas to the west and decrease with depth in discharge areas to the north and east. The results indicate that heat flow in the central part of the basin should be approximately equal to the deep crustal heat flow.

The variation of heat flow density with depth in the prairies basin of western Canada

Bottom-hole temperature values from approximately 36,000 wells in Alberta. Saskatchewan and Manitoba, Canada, have been used to study thermal gradients and heat flow density there. It is found that variations of heat flow density with depth occur throughout the Prairies basin. Differences in heat flow density exist between the Mesozoic + Cenozoic and Paleozoic sediments and are related to the hydrodynamics which is controlled by the topography. The heat flow density through the Mesozoic + Cenozoic of the upper part of the section is less than that in the Paleozoic formations of the lower part of the section in recharge areas, but greater in discharge areas. A zone in which heat flow is approximately constant with depth extends down the central part of the basin between the recharge and discharge areas. Heat flowdensity in this zone lies between 60 mW m−2 and 80 mW m−2 and is thought to be representative of the deep crustal heat flow density. It is suggested that temperature variations on the Precambrian basement that are not depth related may be associated with anomalous heat flow regimes in the lower crust.

A statistical analysis of bottom-hole temperature data in southern Alberta

When bottom‐hole temperatures (BHT) are plotted as functions of depth for different areas, the plots exhibit differences in the spread of the data. The regional variations in spread in southern Alberta were mapped in detail on the basis of 33 653 BHT data from 18 711 wells. There are local areas with anomalously high spread values, and the spread generally increases westward toward the Disturbed Belt. Also, the spread values for data below the Paleozoic erosional surface are greater than those above. Greater spread in the data appears to be associated with the occurrence of faults, steeply dipping strata of different thermal conductivity, and rough topography. The increased spread associated with faults and steeply dipping strata is probably due to water movement. This suggests that bottom‐hole temperatures may provide information about subsurface structure and phenomena as well as information on temperature.

Geothermal gradients in the steen river area of Northwestern Alberta

Abstract A total of 6540 bottom-hole temperature values from 1879 petroleum exploration wells in northwestern Alberta in the region 57°N–60°N and 114°W–120°W have been used to estimate temperature gradients there. A thermal gradient contour map constructed for the region shows a number of local high geothermal gradient areas. Comparison with available aeromagnetic and gravity maps indicates that a high geothermal gradient near Steen River is probably associated with an igneous intrusion and that nearby high geothermal gradient areas may be due to the transport of heat away from the basement by upward and lateral water motion. Also, it is noted that, in this region of Alberta, oil field locations appear to coincide with areas of low geothermal gradient, whereas gas fields appear to coincide with high geothermal gradients.

Topography and the subsurface temperature regime in the western canadian sedimentary basin: implications for low-enthalpy geothermal energy recovery

Abstract Bottom-hole temperature data have been used to investigate the relationship between topographic relief and the sub-surface temperature regime in the Alberta part of the western Canadian sedimentary basin. Five sections through the basin have been considered, and temperature gradients from both above and below the Paleozoic erosional surface have been correlated with surface topography. The results indicate that for regions of higher surface elevation the temperature gradients above the Paleozoic surface are less than those in regions of low elevation. Below the Paleozoic surface, the relationship between temperature gradient and surface topography is much less certain, but it appears that there is a general increase of gradient associated with high relief. These results are consistent with those expected to be associated with gravity imposed water motion related to recharge and discharge areas. Cross-sections showing temperature as a function of depth and distance indicate that the effect of regional changes in surface topography is felt to great depth, and perturbations to the thermal regime are caused by both local and regional water flow patterns. As a consequence, the influence of topography on the hydrodynamics and the temperature regime greatly affects the geothermal energy potential of the area.

An investigation of the potential for geothermal energy recovery in the Calgary area in southern Alberta, Canada, using petroleum exploration data

The geothermal gradient in the Calgary area of southern Alberta is about 24 °C/km. Although this is only an average geothermal gradient, the city lies on the flank of a deep portion of the western Canadian basin with sediment thickness of over 4 km so that a wide temperature range exists in the sediments. This factor, and the substantial population of the city and surrounding area, satisfy two prerequisites for successful recovery and use of low‐grade geothermal energy. The Calgary area is, therefore, a suitable candidate for an investigation of its geothermal energy potential. The results of a study of petroleum exploration data show that good aquifers exist in the carbonate rocks of the Elkton formation of the Mississippian and the Wabamun formation of the Upper Devonian. The water temperatures range from 60 °C to 90 °C with salinities of 70 000 to 100 000 mg/l, which is two to three times that of average sea water. High water flow rates up to 700m3/hr from the Elkton formation at moderate depths may be...

HEAT FLOW AND GEOTHERMAL GRADIENT STUDIES IN THE ALBERTA BASIN AN ESSENTIAL PART OF GEOTHERMAL POTENTIAL EVALUATION

ABSTRACT Geothermal gradients in the Alberta part of the prairies basin in Canada have been studied on the basis of 55,246 bottom-hole temperature values from 28,260 petroleum exploration wells. Gradient estimates for different depth and stratigraphic intervals together with the study of the heat conductivity distribution have provided knowledge of both regional heat flow variations and heat flow variations with depth. It is found from the study that both regional and depth variations of grad T and heat flow are influenced by the regional hydrodynamics of the basin. The geothermal gradient and heat flow tend to increase with depth in the meteoric water recharge areas in the high relief parts of Alberta (foothills and western Alberta plains), and tend to decrease with depth in the water discharge shallower part of the basin in northern and eastern Alberta. Heat flow in the central part of the basin, between recharge and discharge areas, seems to be close to the deep crustal heat flow. The regional thermal regime brings the isotherms nearer the ground surface in the shallower part of the basin and causes them to be farther from the surface in the deep part of the basin close to the eastern limit of the disturbed belt. The search for high temperature areas suitable for geothermal energy production must therefore be a compromise in that the basin must be sufficiently deep so that temperatures above 60°C are obtained, but at the same time the isotherms should be close to the surface such as in the region where the heat flow decreases with depth.