A 60m borehole is not a source of energy, it is a store of energy. It only makes sense if you can sink enough heat into it in the summer, to use that energy in the winter. Or vice versa in warmer climates.
We have a ground source heat pump and one summer we were away and did not use out air conditioning that year much at all. Mid winter our return loop temperatures (the glycol being brought in to our heat pump after circulating in the ground) was at one point 3 degrees C cooler than it had been any other year. Quite a noticeable difference. For reference, our loops are 8 vertical at 250ft.
Wait, do you need eight 250ft wells?
Yeah for a family home that seems about right. 250ft is not very deep at all, and you need to store a lot of energy to past a whole winter/summer.
For a closed loop system, yes. I think that would be the minimum (6000 sq ft house) at 250ft depths.