Enhancing the Drilling Process for Geothermal Resources by Combining Conventional Drilling and the Spallation Technology

Abstract

In order to enhance the integration of geothermal energy in the energy mix, the drilling costs have to be significantly reduced, as they account for up to 70% of the total investment for a geothermal power plant. A possible solution to intensify the conventional drilling process is to improve the energy transport from the surface to the drill head (currently performed by the drill string) by pumping combustible reactants to the front face of the bit. If these reactants are ignited, localized heat is transferred to the rock surface to spall or thermally weaken the rock structure. Spalling of rocks is based on the effect that certain crystalline rocks locally disintegrate into small disc-like fragments. Thermal rock weakening describes the significant reduction of the rock strength due to thermal crack formation. Besides the improved energy transport, thermally enhanced drilling decreases the wear-rate and increases of the rate of penetration in all rock formations, which significantly reduces the drilling costs for a geothermal project. In this report the working principles of such a combined hybrid-technology are reported, together with implementation possibilities, which aim to minimize the required adaptions of the currently used conventional drilling equipment. Additionally, the characteristic response of representative sandstones and granites to a thermal treatment was analyzed showing the feasibility of such a combined drilling process.