An Advanced Geothermal Drilling System

Abstract

The historical developments of drilling technology for geothermal resources worldwide have followed similar trends. Local expertise and drilling equipment have been adapted from existing drill rigs used for mining, civil, and water well projects. In ihose areas with hydrocarbon resources, petroleum drilling hardware has been adapted; and in other countries, these units have been imported. This ad hoc approach has provided adequate exploration and production wells. However, the costs of drilling a prospect are high and often are 40 to 60 percent of project resources. Evaluations in the USA indicate that major cost factors are due to lost circulation problems, and to low penetration rates and bit life. In contrast to the incremental improvements in conventional drilling system components, this paper proposes a purpose-developed concept that would solve the above major problems by design. Performance goals of 4 depth, and penetration rates greater than 8 m/h were selected. This advanced geothermal drilling system features: a percussion-hammer drill, a dual-wall or multi-flow path reverse-circulation drillstring, and a versatile drilling fluid subsystem. Results of a preliminary design study are presented.