I am planing on drilling 12 wells for a ground source heat pump myself this summer.
The current plan is to drill each well 60 feet down and insert a smaller tube inside to make a closed loop. There would be a cap at the bottom along with a one time use drill paddle bit.
I've also looked into directional drilling using a star configuration. In this method you start in a pit drilling downward and curving upwards. Once the bit pops up someplace in the distance a backreemer bit and a swivel is attached. A plastic pipe is then folded in half and the resulting pair is pulled back to towards the pit until the far end is pulled below the frost line.