I imagine that there will be some fairly major technical issues to overcome, hence the seemingly long time period to complete the rescue bore. The drill cuttings have to be removed to surface (that's a large volume from a 2 ft hole over 2000 ft)and the rotating bit will need to be cooled and lubricated, similar to the principals involved in oil and gas well driling. That involves setting up a lot of heavy duty equipment. I doubt the drill bits will be 'off the shelf' so may have to be produced. Drilling through granite won't be quick and the drill string will probably need to be pulled regularly to replace the bit. The deeper you go the longer this takes each time it's done.

I wish the guys the very best of luck and look forward to them being rescued as soon as possible, it would seem that every available resource is being thrown at this. One of the most important factors in maintaining their mental wellbeing will be providing them regular information on the drilling progress.

Chris