Laser Supported, Thermal Rock Weakening and Drilling for Hard Rock and Geothermal Applications

Abstract

There has been a substantial increase of interest in recent years for widespread exploitation of geothermal energy, however, the progress still hinges on finding cost-effective solutions to drill into hard crystalline rocks. Conventional drilling almost solely relies on mechanical abrasion and has effectively been used by the oil and gas industry for over 100 years also by incremental modification and optimization of the drilling process. But problems in conventionally drilling of geothermal reservoirs mainly include very low rate of penetration with very high bit wear. Therefore, multiple attempts are underway worldwide to develop a novel drilling method to overcome the latter problems and facilitates deep drilling process a more economic and safer operation. Thermal drilling techniques such as Laser supported Drilling, could potentially be such fundamental change and thus, significantly improve drilling into deep geothermal reservoirs. International Geothermal Centre in Bochum is investigating such innovative thermal drilling technologies, especially mechanically assisted LaserJet drilling. It employs a laser-water-jet (LWJ) to deliver additional thermal energy to the rock surface. The beam induces thermal stresses by a sudden increase in temperature, which consequently does result in rock’s mechanical strength reduction and thermal spallation. The now softened hard rock may easily be drilled out with the optimized mechanical drill bit. This paper will discuss the results obtained from fundamental investigation of rock breaking via thermal spallation and thermal rock softening and the requirements for putting LaserJet drilling into a full-scale drilling setup.