Cecil,
You are correct, but lifting the well water uses a lot of energy ($$$). In my neck of the woods a well is 200-600 feet deep, so lifting 12gallons/min = 61,200 ft/lb/min = 1383 watts. Then you lose 30% efficiency in your pump motor, so it takes 1975 watts (about a 2HP pump) to lift the water, assuming a 600' well. A closed loop has no lifting load, only circulation, so we typically run a 1/15HP pump.
Also, how long can you pump 12g/min before your well gets low? Then what? Around here if you use a well for geothermal, you have to return the water into a seperate well.
I know a good bit about geothermal systems and how they work in warmer climates. Lakes around here will always be (relatively) cool on the bottom in summer and warm in winter. I suspect this is the same up north. If your pond is deep enough to not freeze solid.
Engineering would be fun if it weren't for all the technical stuff.
