My parents built a energy efficient home in 1985. Part of the design included a geothermal "heat-pump." Since the well provides plenty of water their system is configured as an "open-loop" design. However, I have seen systems that skip the coolant-to-water heat transfer and circulate the coolant itself in copper ground loops.
My idea years ago (I live in Florida) was to bury a matrix of 12" PVC pipes in the ground, deep enough to be below the water table (about 4' or deeper during dry season here) The temperature of the water is always about 68°F year round. A circulation fan would direct air through the pipes and back into the house duct system with appropriate dust and critter filters.......