Effective hole cleaning and maintenance of an appropriate equivalent circulating density (ECD) is much more difficult to implement in long extended-reach geothermal wells than in oil and gas wells. We conducted a number of cuttings transport experiments, using a large-scale flow-loop apparatus and field measurements of annular pressure, using PWD (pressure while drilling) in a geothermal directional well recently drilled in Japan. Numerical simulation for the targeted long extended-reach geothermal well with a total depth 3,000 m, horizontal departure of 2,500 m, and maximum hole inclination angle of 70° was performed using a transient hydraulics simulator we developed and modified in this study on the basis of these experiments and field data. In addition, the optimum hydraulics conditions for effective hole cleaning and appropriate ECD management in long extended-reach geothermal drilling are discussed in this study.
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