Abstract
Borehole creation involve complex thermal phenomena such as the injection of a fluid to cool the cutting tool and carry debris to the surface, generation of heat caused by the cutting tool, and the thermal interactions between the flowing fluid and the stationary rock. These phenomena alter the temperature of the rock from its undisturbed state. An accurate characterization of the temperatures within the rock prior to the drilling operation is necessary for resource extraction, geothermal heat conduction calculations, and for paleoclimate studies. Disturbances in the rock temperature can lead to uncertainties in these calculated quantities and in the application of the inverse method. Presently, methods are available which treat the flowing fluid in a simplified manner, often as a stationary medium, and allow estimation of the temperature disturbances in the rock wall. Nevertheless, to the best knowledge of the authors, there are no published studies which fully include the fluid flow in the borehole during the drilling operation and its direct impact on temperatures. Additionally, the impact of the heat generation at the drill head on the temperatures in the fluid and the surrounding rock have not fully been studied. A method is proposed for determining temperatures within boreholes and the surrounding rock both during and after the drilling operation. The method encompasses all the issues listed above. It was discovered that the coolant temperature is dependent upon location within the borehole, and the relaxation time of rock temperatures to their equilibrium values varies with depth in the borehole. Abstract Copyright (2014) Elsevier, B.V.