Note:
I'm no expert.. But, I have read up on open loop systems a bit.
I wanted to know about freeze prevention etc. My 'knowledge' is pretty general..
A 2 inch, 100 foot pipe does not hold a lot of water. Under 10 gallons, I think.
Dipping a closed loop of copper down into the well isn't likely to be a good transfer source.
Unless the well walls are very porous to some moving ground water,
this looks like an open-loop app.
So, you need to find out what kind of flow you can get out of the well, during sustained pumping.
If you could get a lot of water out of the well without problem,
and, had another 'well' some distance away, to dump the water back into..
You might be able to harvest a usable amount of heat..
The 'Dump' well needs to be a fair distance away from the source well,
so the water that's recycled, has a change to regain the ground water temperature.
I guess it all depends on the ground water level, and it's movement.
If it's stagnate / the ground isn't real porous..?.
Maybe a pump-out test will tell. It would be interesting to see if you could
learn about underground flow, by lowering a temperature sensor into the well.
If the water temp is higher than expected, that might mean the 'two rivers'
are influencing your well.. Which would a good thing!!
(If/when water temp of the rivers is actually higher than ground water).
Keep us posted.. I have high ground water and have been thinking about
all that 60deg F water sitting down there, a few feet under my basement.
It sure seems a waste not to tap it..
Cheers,
Rich