St. Lawrence Lowlands Bottom-Hole Temperature: Various Correction Methods

Abstract

The Cambro-Ordovician sedimentary basin of the St. Lawrence Lowlands (SLL) in the province of Québec located in eastern Canada is actually under exploration for its low-temperature geothermal resources. The goal of this actual work is to better correct BHT data in order to evaluate the undisturbed subsurface temperature with more certainty and then improve the quality of the resource assessment. Very few subsurface temperature data collected in thermal equilibrium exist in the SLL basin. We realised new corrections in order to reduce uncertainty of the estimated rock formation temperature. BHTs were initially corrected following Harrison method. The maximum and minimum gradients enclosing the data corrected by Harrison method are approximately 14-37 °C/km and 14-34 °C/km for the caprocks and the reservoir rocks respectively. Horner corrections were additionally performed for temperature measurement series collected in wells where sufficient information was available. The maximum gradients deduced for BHTs corrected with Horner method are 23.0 and 24.0 °C/km for the caprocks and the reservoir rocks, respectively. The comparison of BHT data corrections for the St. Lawrence Lowlands (SLL) sedimentary basin show that the Horner method is yielding a narrower range of temperature and is potentially generating less uncertainty compared to Harrison method. Analysis of the results, with the help of a 3D model of the basin, indicate that the Cairnside and the Covey Hill formations, at depths of more than 3 km, are targets for low-temperature geothermal systems, since temperatures in these units can potentially be above 80 °C.