Yes, Texas, you missed something.
The OP needs to run a ground wire between the panels. This wire would be a "EGC," or EQUIPMENT grounding conductor.
The OP suggests that he instead run a separate wire to his well. This would be a "GEC," or grounding ELECTRODE conductor. Different wire, different purpose.
The OP's idea fails, as 'grounding' the panel to the well will do nothing to help fault current return to the PoCo transformer. He is confusing the electrical 'ground' with the earth under his feet.
A word to the OP: There are sizing issues here as well. You probably ought to have a chat with an electrician. We're out of DIY territory.
