ANALYSIS OF PETROPHYSICAL PROPERTIES OF ROCKS AFFECTED BY NEW LASER DRILLING TECHNIQUE

Geothermal energy is pivotal for sustainable energy strategies, yet its advancement is hindered by high drilling costs and challenges in hard rock formations. In particular, the DeepU EU Project, in which this work participates, is developing a deep closed-loop system with the application of laser drilling technology. Laser drilling techniques offer a promising solution by enhancing efficiency and reducing environmental impact of drilling operations. This study investigates the effects of laser drilling on the petrophysical properties of granite, limestone, and sandstone which are common rock types encountered in geothermal reservoirs. Samples of unaffected granite, sandstone, and limestone were initially selected and characterized in detail. Thermo-physical properties such as thermal conductivity, thermal diffusivity, P-wave velocity, S-wave velocity, Young’s modulus, Poisson’s ratio and water absorption were measured. The samples of analogue rocks were used in several DeepU laser drilling experiments. The drilling process was recognized as thermal spallation. The spallation process is defined as detachment of the near-surface portion of the rock due to thermal stress induced by rapid heating. Representative cores were acquired from the vicinity of the laser-drilled craters for the investigation. Subsequently, their thermo-physical properties were measured with respect to the distance of the crater, in order to evaluate changes induced by laser irradiation. The changes in properties of thermally spalled samples were cross compared with changes induced by mechanical drilling reported in the literature. This investigation revealed that laser-drilled rocks maintain natural integrity and have significantly less spatial damage than rocks drilled with classical techniques. These results contribute to the development of laser drilling technology by shedding more light on laser-rock interactions and their effect on the rocks. This work contributes to the future application of laser drilling in the geothermal sector that aims to enable unlimited and clean energy of deep geothermal reservoirs.