Jacek Majorowicz

Geothermics of the Williston Basin in Canada in relation to hydrodynamics and hydrocarbon occurrences

Over 8 400 bottom‐hole temperature (BHT) values from the Canadian part of the Williston Basin were analyzed and a temperature high was discovered in the Weyburn area of southeastern Saskatchewan. Geothermal gradients, thermal conductivities, and heat flow have been investigated for most of the Mesozoic‐Cenozoic clastic unit as well as the Upper Paleozoic carbonate‐evaporite unit. Regional heat flow variations with depth occur which are closely related to the hydrodynamics governed by the topography and geology. The blanketing effect of low‐conductivity shaly formations may cause a temperature anomaly in the south where the thickest Phanerozoic cover exists. However, the Weyburn high can be explained only partially in this way. Hydrodynamics has also contributed to formation of the temperature anomaly there. The process of forming the anomaly by the blanketing effect and hydrodynamics also contributed to oil deposition. There is a correlation between Mississippian oil occurrences in the southeastern part o...

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.

Geothermal conditions for gas hydrate stability in the Beaufort-Mackenzie area: the global change aspect ☆

Abstract Gases locked in hydrates or trapped beneath a gas hydrate cap within the earth are potential contributors to the greenhouse effect, and therefore both thermal conditions of and occurrences of the methane hydrates should be considered in the study of past climate change and of future global warming. The decomposition of methane hydrates triggered by an increase in near surface temperatures and the subsequent upward migration of released gases is occurring at present in the Beauffort-Mackenzie area of northern Canada. In addition to surface warming, the warming effect of the upward flow of the deep fluids, recharged in high elevation areas bordering the Alaska and Yukon coastal plain, may also be a factor in the release of methane directly from deeper buried hydrates in the fluid discharge zones. Any assessment of the total methane contribution to the atmosphere and the rate of the release requires a knowledge of the distribution, spatially and with depth, the temperature and composition of the gas hydrates. In this study the zones of methane hydrate stability are predicted by a thermal method and compared with the distribution of hydrates detected on well logs. An extensive hydrate prone layer extending to as deep as 1400±200 m over an area of 50,000 km2 is predicted by the thermal data and hydrate stability field. Comparison of the predicted maximum depths of methane hydrate stability with the maximum depths of hydrate occurrences in 52 wells shows general agreement in the areas of thick offshore and onshore permafrost. Differences in several areas of up to 400 m between the thermally predicted hydrate base and the deepest detected hydrates (detected hydrates are deeper than the predicted ones) can be explained by changes in gas composition. Otherwise low near-surface thermal gradients of approximately 15 mK/m to 20 mK/m (in comparison with observed deep thermal gradients of 25–40 mK/m) would be needed to explain the existence of deep hydrates in the area of the southern Mackenzie Delta trough and offshore north of 71° N latitude. Unfortunately there is no reliable industrial temperature observation from wells to support the latter. Such regional studies of the distribution of gas hydrates, including the stability of those deposits, form a crucial component of an assessment of the influence of gas hydrate formation and decomposition on the proportion of methane present in the earths atmosphere. Current estimates suggest that between 10.E18 and 10.E21 tonnes of methane may be presently locked in gas hydrate deposits. To fully assess the total amount and the potential contribution to global warming, similar regional assessments are needed for each of the major areas of occurrence, especially in the circumpolar regions which are subject to the greatest increase in temperature conditions.

Heat flow and heat generation estimates for the churchill basement of the western canadian basin in Alberta, Canada

Abstract Heat flow through the sediments and temperatures of the Churchill province basement under the sedimentary cover are determined for 24 locations in the central part of the Prairies basin in Alberta where the vertical heat flux is approximately constant from the base of the sediments to the surface. The contribution to heat flow from heat generation in the sediments is also considered. The average heat flow through the sediments is found to be 71 mWm −2 ± 12 mWm −2 which is about 30 mWm −2 higher than in the neighbouring shield area of the Churchill province, and the contribution from heat generation in the sediments to the surface heat flow is only approximately 2.5 mWm −2 . The relationship between basement heat generation and heat flow is investigated, and it is found that the platform heat flow/heat generation values are in general higher than those from the Churchill province of the shield found by Drury 1985. Although for the platform and shield data, the reduced heat flow is about 40 mWm −2 and the slope is about 8 km, it is apparent that the platform data alone are not good enough to establish a precise relationship.

Potential causes of differences between ground and surface air temperature warming across different ecozones in Alberta, Canada

Abstract Analysis and modelling of temperature anomalies from 25 selected deep wells in Alberta show that the differences between GST (ground surface temperature) warming for the northern Boreal Forest ecozone and the combined Prairie Grassland ecozone and Aspen Parkland transition region to the south occur during the latter half of this century. This corresponds with recent changes in surface albedo resulting from permanent land development in the northern areas and also to increases in natural forest fires in the past 20 years. Differences between GST and SAT (surface air temperature) warming are much higher in the Boreal Forest ecozone than in the Prairie Grassland ecozone and Aspen Parkland transition region. Various hypotheses which could account for the existing differences between the GST and SAT warming in the different ecozones of Alberta, and western Canada in general, are tested. Analysis of existing data on soil temperature, hydrological piezometric surfaces, snowfall and moisture patterns, and land clearing and forest fires, indicate that large areas of Alberta, characterised by anomalous GST warming, have experienced widespread changes to the surface landscape in this century. It is postulated that this has resulted in a lower surface albedo with a subsequent increase in the absorption of solar energy. Heat flow modelling shows that, after climatic SAT warming, permanent clearing of the land is the most effective and likely cause of the observed changes in the GST warming. The greater GST warming in the Boreal Forest ecozone in the latter half of this century is related to landscape change due to land development and increasing forest fire activity. It appears to account for a portion of the observed SAT warming in this region through a positive feedback loop with the overlying air. The anthropogenic effect on regional climatic warming through 20th century land clearing and landscape alteration requires further study. In future, more accurate quantification of these various forcings will be necessary in order to distinguish between, and to detect, the variety of natural and anthropogenic influences and on climate.

Gas hydrate distribution and volume in Canada

Gas hydrate, a solid form of natural gas and water, is inferred to widely occur in Canadian polar and continental shelf regions and in sediment of outer continental margins. Although direct indications of hydrate are few and widely separated, conditions potentially favorable for gas hydrate formation and stability, especially low to moderate temperatures under permafrost or the deep sea, combined with favorable geological conditions for gas generation and storage, cover vast areas and indicate an immense potential for natural hydrocarbon gas in the upper 2 km of many Canadian sedimentary basins. We have analyzed the potential of gas hydrates for the vast continental shelves and Arctic permafrost regions of Canada (Mackenzie delta-Beaufort Sea and Arctic Archipelago in the north and Davis Strait, the Labrador Shelf, Scotian Shelf, and Grand Banks of Newfoundland along the Canadian Atlantic margin and Canadian Pacific margin). Our conservative calculation suggests 1010-1012 m3 of gas hydrates in these regions has an associated methane gas potential estimated to be in the range of 1012-1014 m3. The volume of methane in hydrates in Canada are geographically distributed in the following regions: 0.24-8.7 x 1013 m3 in the Mackenzie delta-Beaufort Sea, 0.19-6.2 x 1014 m3 in the Arctic Archipelago, 1.9-7.8 x 1013 m3 on the Atlantic margin, and 0.32-2.4 x 1013 m3 on the Pacific margin. The total in-situ amount of methane in hydrates of Canada is estimated to be 0.44-8.1 x 1014 m3, as compared to a conventional Canadian in-situ hydrocarbon gas potential of approximately 0.27 x 1014 m3. This comparison suggests that gas hydrates represent a possible future assurance of North American energy supply if the gas can be recovered and separated from the hydrate form.

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.

Large ground surface temperature changes of the last three centuries inferred from borehole temperatures in the Southern Canadian Prairies, Saskatchewan

Abstract New temperature logs in wells located in the grassland ecozone in the Southern Canadian Prairies in Saskatchewan, where surface disturbance is considered minor, show a large curvature in the upper 100 m. The character of this curvature is consistent with ground surface temperature (GST) warming in the 20th century. Repetition of precise temperature logs in southern Saskatchewan (years 1986 and 1997) shows the conductive nature of warming of the subsurface sediments. The magnitude of surface temperature change during that time (11 years) is high (0.3–0.4°C). To assess the conductive nature of temperature variations at the grassland surface interface, several precise air and soil temperature time series in the southern Canadian Prairies (1965–1995) were analyzed. The combined anomalies correlated at 0.85. Application of the functional space inversion (FSI) technique with the borehole temperature logs and site-specific lithology indicates a warming to date of approximately 2.5°C since a minimum in the late 18th century to mid 19th century. This warming represents an approximate increase from 4°C around 1850 to 6.5°C today. The significance of this record is that it suggests almost half of the warming occurred prior to 1900, before dramatic build up of atmospheric green house gases. This result correlates well with the proxy record of climatic change further to the north, beyond the Arctic Circle [Overpeck, J., Hughen, K., Hardy, D., Bradley, R., Case, R., Douglas, M., Finney, B., Gajewski, K., Jacoby, G., Jennings, A., Lamourex, S., Lasca, A., MacDonald, G., Moore, J., Retelle, M., Smith, S., Wolfe, A., Zielinski, G., 1997. Arctic environmental change of the last four centuries, Science 278, 1251–1256.].

Investigation of the geothermal state of sedimentary basins using oil industry thermal data: Case study from Northern Alberta exhibiting the need to systematically remove biased data

Subsurface temperature data from industrial sources may contain significant biases that greatly reduce their overall quality. However, if these biases can be identified and removed, the data can provide a good preliminary source of information for further studies. In this paper, industrial thermal data from three sources: bottom hole temperatures, annual pool pressure tests and drill stem tests are evaluated to provide an updated view of the subsurface temperatures below the oil sand regions of Northern Alberta. The study highlights some of the potentially large systematic biases inherent in industrial temperature data which affect estimates of geothermal gradient and regional mapping of the geothermal field.