Feasibility Analysis of Drilling with Liquid Nitrogen in High Temperature Geothermal Wells

Abstract

 The main costs of developing geothermal processes are concentrated in the project of drilling, accounting for more than 70% of the total budget. Inspired by thermal stimulation technology，a new concept of drilling with liquid nitrogen was presented in this paper. The main objective of this paper is to investigate the effect of rapid cooling on bit-rock interaction and the feasibility of drilling with liquid nitrogen. Through the hardness test experiment results, it showed that the thermal stress caused by rapid cooling can reduce the resistance of indenter invades the rock. Then the micro-bit drilling experiment results indicated that liquid nitrogen can eliminate the thermal damage and enhance the wear resistance, which is the main factor affected the life and footage per bit in geothermal drilling. The negative effect is that liquid nitrogen increase the rock failure resistance slightly and need about 8% more mechanical specific energy compared with drilling with air, but the increase about 8% in mechanical specific energy is affordable to drilling engineers. All these results showed that drilling with liquid nitrogen is beneficial to improve the life and footage per bit, reduce non-production time and reduce drilling costs, it is a promising technology in geothermal engineering.