Preliminary experimental validation of the improved ROP using hammer and High Pressure Water Jet
Résumé
Increasing drilling speeds to reduce drastically the costs is the main challenge to promote deep geothermal systems. Traditional rotary techniques show limitations in drilling speed on very hard deep crystalline rocks with low ROP and/or high wear level. This is the challenge pursued by ORCHYD, using the combination of high-pressure water jetting (HPWJ) and percussion to break the rock. For this, the stress release effect is exploited by combining these two techniques of rock breakage. A peripheral groove is created by the rotating jet at the bit, reducing the stress concentration at the center, reducing the energy required to crush the rock in the center by the hammer action. Two test experimental devices have been adapted to emulate the realistic down-hole pressure conditions on a hard rock sample. A high pressure cell to analyze at the nozzle or insert level where we can use the percussion or the jet to cut the rock. A vertical drilling test rig to analyze drilling behavior using a combination of high pressure water jet slotting and percussion action at drill bit scale and under realistic drilling conditions. The hammer is fluid driven and thus, appropriate hydrostatic and confining pressures are applied during the operation. Parameters investigated include chamber (bottom hole) pressure, nozzle orifice diameter, stand-off distance, rotation rate as well as in-situ stress and pore pressure conditions. Experimental results are analyzed in terms of rock breakage mechanisms, depth and shape of the groove and rate of penetration with and without jetting, in order to assess the efficiency of the combined tool.
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