CFD Simulation to Optimize Depressurization of Thermal-Shock Enhanced Drill Bit

Abstract

For decades, utilization of the high-enthalpy supercritical geothermal resources has been pursued to improve the efficiency and capacity of geothermal power generation. However, to develop the supercritical geothermal systems, technologies that efficiently and safely drill into the hard ductile formations where the temperature exceeds 400°C are crucial. The author proposed the concept of an innovative drilling tool, named the thermal-shock enhanced drill bit in the previous study. The thermal-shock enhanced drill bit combines a Venturi mechanism with a PDC bit. There are two drilling modes; drilling mode which uses a conventional PDC bit drilling mechanism and depressurizing mode which locally reduces the pressure of drilling fluid just below the bit by the Venturi mechanism. If the depressurization is large enough to vaporize and cool the drilling fluid because of the latent heat, the rock is fractured or weakened by the thermal shock or thermal stress. The drillability of hard rocks encountered in ductile and supercritical geothermal formations might be improved. In this paper, optimization of Venturi nozzle and flow lines design to maximize the depressurization beneath the bit and feasibility of the thermal-shock enhanced drill bit are discussed on the basis of the computational fluid dynamics (CFD) simulations.