Large Scale Geothermal High in the Westernmost North American Covered Craton – Can Heat Flow Vs. Basement Heat Production Be a Reliable Tool in Predicting Deep EGS Geothermal Resource?

Abstract

High heat production A in the ‘granitic’ basement of covered cratons is in many cases an indication of high heat flow q and good EGS geothermal potential. The Australian Cooper basin is the best example of such a geothermal system. However, in other circumstances, it will be difficult and sometimes misleading to predict high heat flow solely on measurements of radiogenic heat production A from the basement rocks. Here we report the case of the westernmost North American Craton (about 2 billion years old) located between the Cordillera and the Canadian Shield. Here q reaches 90 mW/m2, which is quite unexpected for modest A of its granitic rocks. Heat flow between 49oN and 62oN shows a northward increase of q along the forefront of the disturbed belt. This northern q anomaly presents very good potential for future EGS installations with recorded temperatures T in vicinity of 200oC for some 4.5 km depth in the hottest places. Based on A data from mostly granitic basement rocks of the crystalline crust, that a heat flow vs. heat generation statistical relationship is non – existent. A correlation of heat flow patterns with other potential fields cannot be identified. The average A is basically constant from south to north, while heat flow changes by a factor of 2. To account for this observation we would need to assume that high A layer of the upper-mid crust varies in thickness as much as factor of two or more.