Specific cutting energy reduction of granite using plasma treatment: A feasibility study for future geothermal drilling

Abstract

Geothermal Energy is one of the most consistent and viable sources of renewable energy. However, harnessing this energy has proved to be a challenge mainly due to the difficulty in drilling hard igneous rock formations that occur in and around geothermal wells. Therefore, an energy efficient method that can drill hard rocks needs to be developed. In this paper, the effect of micro-scale energy delivery, in the form of plasma, to weaken rock by inducing micro-cracks is studied. Two different types of granite (igneous rock) were sampled and used in this study, out of which the one control group was treated with five, 40kV, 80J pulses of plasma while the other was left uncracked. The effect of the cracks is quantified by conducting facing tests on the plasma cracked and uncracked samples and measuring a reduction in the specific cutting energy. Two different methods were used to estimate the specific cutting energy, where the first method considered the entire cutting process and the second method considered only the stable cutting region. The plasma treatment showed a maximum of 65% and a minimum of 15% reduction in specific cutting energy and was regarded as being dependent on mainly the hardness and size of the samples. All results in this study are validated using statistical analysis.