The Japanese government-funded geothermal exploration Well WD-1A reached 3729 m at total depth, where the bottomhole static temperature is more than 500°C. A trajectory correction run was carried out with a positive displacement motor and measurement while drilling tool where the formation temperature is greater than 350°C. The combination of large surface mud containers and sufficient mud cooling equipment were used to cool return mud from the well. A top drive system was used to cool the bottomhole assembly while running each drillpipe stand in the hole. A borehole dynamic temperature experiment and drill bit tests were carried out in this well.

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