Laser-rock interactions, is drilling rocks possible with a laser?

The application of laser technology for drilling rocks has drawn the attention of scientists and engineers for decades (Xu et al., 2003; Buckstegge et al., 2016; Jamali et al., 2019; El Neiri et al., 2023), promising a revolution in well-drilling operations of the oil and gas industry and geothermal energy sector. High-power lasers can penetrate hard rock formations with greater rate and precision, without physical contact with the rock which eliminates wear on drill bits and subsequently reduces significantly drilling time and well completion costs. This work is a part of the DeepU Project that addresses problems of conventional drilling in search of cheaper and environmentally friendly drilling technique for the exploitation of geothermal energy. A series of laboratory-scale experiments were performed with the Ytterbium fiber laser with a wavelength of 1070±10nm, operating in continuous mode within a power range of 170-30000W. The temperature of the lasing process and IR imaging were recorded by thermo-camera FLIR GF77a with HSM mode allowing for gas visualization. The craters in laser-affected rocks were further investigated by photogrammetry and electron microscopy while ejected particles were collected and characterized. This comprehensive study has revealed the nature of petro-thermo-mechanical phenomena occurring during laser irradiation of rocks. The three observable processes are: thermal spallation, melting and vaporization. They are controlled mainly by power density (delivered to the rock surface), irradiation time and lithology (texture, mineral and chemical composition). The photogrammetric analysis of laser-affected rocks has shown the efficiency of the laser drilling process, expressed by the rate of penetration and specific energy i.e., the amount of energy necessary to remove a unit of volume. The microscopic study of lased surfaces has revealed the impact of the laser on the rock samples. Depending on the drilling regime the result was: 1) smoothly cut craters with shallow fractures generated by thermal spallation at lower power or 2) a rugged glass layer of vitrified molten rock formed by melting and vaporization at higher power. The power-dependent transition between the processes, thus drilling regime was defined for granite, sandstone and limestone. These results allowed to design and apply a DeepU thermal spallation laser system to successfully drill larger diameter boreholes (<10cm), and bring closer to the successful application of laser technologies in the geothermal field.

This research is funded by the European Union (G.A. 101046937). However, the views and opinions expressed are those of the author(s) only and do not necessarily reflect those of the European Union or EISMEA. Neither the European Union nor the granting authority can be held responsible for them.

References

Buckstegge F., Michel T., Zimmermann M., Roth S., Schmidt M., 2016, PP, v. 83, p. 336–343, doi:10.1016/j.phpro.2016.08.035.

El Neiri M.H., Dahab A.S.A.H., Abdulaziz A.M., Abdelghany K.M., 2023, JEAS, v. 70, p. 98, doi:10.1186/s44147-023-00260-2.

Jamali S., Wittig V., Börner J., Bracke R., Ostendorf A., 2019, GEE, v. 20, p. 100112, doi:10.1016/j.gete.2019.01.001.

Xu Z., Reed C.B., Leong K.H., Parker R.A., Graves R.M., 2003, ICALEO, Laser Institute of America, p. P531, doi:10.2351/1.5060167.