ROCK DRILLING IN GREAT DEPTHS BY THERMAL FRAGMENTATION USING HIGHLY EXOTHERMIC REACTIONS EVOLVING IN THE ENVIRONMENT OF A WATER-BASED DRILLING FLUID

摘要

A method and a device to thermally fragment rock for excavation of vertical and directional boreholes in rock formations, preferentially hard rock, using highly exothermic reactions are suggested. Exothermic reactions are initiated directly in the pressurized, aqueous environment of a water-based drilling fluid preferably above the critical pressure of water (221 bar). After reaction onset temperatures within the reaction zone exceed the critical temperature for water (374°C) providing supercritical conditions, which favor the stabilization of the reaction, e.g. a supercritical hydrothermal flame. Since reactions can be run directly in a water- based drilling fluid, the method proposed here allows high density drilling action as in conventional rotary drilling. Apart from that the hot reaction zone of the proposed reaction can be brought directly to the rock surface in case of hard polycrystalline rock, where high temperatures are required. Additionally, alternating cooling (drilling fluid) and heating (reaction) is suggested to further increase drilling performance by enhancing thermal gradients within the rock surface layer. The method and device proposed here aim at uniting advantages of rotary and thermal spallation drilling techniques and allow for combinations thereof.