Feasibility of Spallation Drilling in a High Pressure, High-Density, Aqueous Environment: Characterization of Heat Transfer from an H2-O2 Flame Jet

Abstract

Due to the high costs associated with drilling deep wells with conventional rotary drilling, novel drilling technologies could be a key to implementing engineered geothermal technologies on a global scale. One such technology, flame jet thermal spallation drilling, uses high heat fluxes to rapidly heat the surface of rock, inducing thermal stresses that cause rock fragments, or “spalls,” to be ejected from the rock surface. To date, all field and laboratory tests investigating jet flame drilling have been performed in air-filled holes at near ambient pressures. In order to drill deep wells in practice with this technique, stable flames will need to be created in aqueous media over a range of pressures. As a first step, we have experimentally investigated a hydrogen-oxygen flame jet in water at a pressure of 100 bar (1500 psi) in a lab-scale apparatus that replicates conditions that would be found in a fluid filled borehole at a depth of about 1 km (3300 ft.). The heat flux from the jet flame to a brass block was determined by measuring the steady state temperature profile within the brass block. Estimated maximum heat fluxes on the order of 0.5 MW/m2 (44 BTU/ft2-s) were observed, which should be high enough to induce thermal rock spallation.