Temperature Mapping of Select Devonian Strata in Alberta

This report presents the results and findings of a subsurface temperature mapping project conducted by the Alberta Geological Survey. Alberta’s long history of petroleum exploration has resulted in a wealth of temperature data, from various sources and of varied quality. Temperature measurements from drillstem tests and annual pool pressure surveys are considered higher quality, whereas temperature measurements recorded from wireline logs as bottomhole temperatures (BHT) are considered lower quality. The BHTs often reflect the temperature of drilling mud in the wellbore, which has not equilibrated with the formation temperature, and the temperatures need to be corrected to be representative of in situ conditions. To maximize the amount of BHT data available for this project, a temperature correction method based on a derivation of the Harrison correction was developed. The resulting Alberta-calibrated Harrison equation was applied to previously unused BHT data to estimate more accurate formation temperatures. These corrected BHTs were then merged with a pre-existing temperature dataset to provide an updated subsurface temperature database for the Alberta Basin. A three-dimensional subsurface temperature model was generated using the new database, and two-dimensional temperature maps were produced for some of Alberta’s deeper sedimentary formations which may be targeted for future geothermal exploration and development. Units mapped for this project are, in descending stratigraphic order, the Wabamun Group, the Winterburn Group, the Leduc Formation, the contiguous Swan Hills and Slave Point formations, the Watt Mountain Formation, the Sulphur Point Formation, and the Keg River Formation. In addition, the temperature at the top of the Precambrian crystalline basement (base of the sedimentary succession) was also mapped. An updated thermal gradient map of the Alberta Basin was produced, which provides an estimate of the average temperature increase with depth from the surface to the top of the Precambrian.