The major challenge is to deal with unexpected events downhole without downhole sensors. On surface high sensible acoustic sensors listen what happens downhole. Data is combined with water pressure, rate of penetration and load. In a split second the data is compared with historical data. The analysis helps the operator to make the right decisions which result in higher success rate and shorter operation.
For a traditional oil well this approach is nice to have but for deep geothermal applications this is the only way to control tools. High reservoir temperatures, low injection temperature, deviated wells, no core samples, sometimes hard limestone reservoirs makes life sometimes very tough. The penetration speed can go down form 2 meter per minute (typical sandstone) to 2 meter per hour (typical limestone of a dry well). The penetration speed can be so low in combination with a deviated well no progress can be seen. Better understanding what is happening result in longer tool life and more progress. In wells of 4000 meter tool changes can be reduced which result in a dramatic increase in progress per day.
Better data results also in a better choice for the different tools. Beside the traditional jetting tools also microdrills has recently added to the toolbox.
Those critical applications can be handled. Operating time may be more extended. (From 10 to 30 days).