There are two reasons to ground things: First, for protection of your gear and the electrical distribution systems. There should be a ground that is bonded to your breaker panel in your home. If lightning strikes, you NEED that ground to be bonded to whatever else is in your station. You will want to ride that ground reference as the local ground potential goes up and down.
The other reason is to act as a counterpoise for your antenna system. This is a situation where you may not want to use the household ground system because it may be too far away electrically. If the ground wire is a significant portion of a wavelength it may not be a good ground reference anyway.
If you set up a tower, you really should bond it to a system of ground rods right next to the tower with heavy ground wires (#8 AWG or larger) to the ground rods in as nearly a vertical straight line as possible.Your coaxial cable should leave the tower at a right angle and it is preferable to bond the shield of the coax to the tower right where it makes that bend (assuming you have a balun at the top). I have seen tower systems with similar grounds and antennas and they survive direct lightning strikes without a hiccup.
If you're setting up a ground mounted vertical antenna, a ground system isn't quite as important. What IS important is that you have radials. LOTS of radials. Medium Wave (AM) Broadcast stations use about 120 radials for their antenna system. You could easily do well with less, but you do need to have some form of radial system.
Nevertheless, you should isolate your coaxial feed line from the antenna system so that it doesn't radiate in the building or pick up common electrical fields from inside your home. The further the antenna system is away from everything, the better off you'll be.
That's a very quick overview of grounding issues. People write extensive books about this subject. For a very complete technical reference, I recommend Antennas by Krause. However, this is a book that few will understand without a significant education or experience in RF Engineering. The ARRL antenna book is better, though their explanations are sometimes oversimplified and therefore somewhat cryptic or confusing. Another great book is from Jerry Sevick, on baluns. There are some very good explanations of what a Balun is and how to isolate antenna systems from the home. There is also a nice appendix on short (compared to a quarter wave) vertical antennas.
That said, the well casing is probably a good ground, provided that you get a clean, high conductance bond to it. Exothermic welding is often the preferred method, but I have seen decent results with a bug clamp too, provided it is protected with electricians putty from the elements. If the well casing is close to your home foundation, you may want to add it to your electrical ground system. If you erect antennas above that well casing, that ground could be used to dissipate lightning strikes. Note that if there are higher structures around your antenna, it is unlikely it will be hit directly. That said, if anything in the vicinity of your antenna IS hit, you will see the ground voltage potential rise up thousands of volts. Unless you are carefully bonded to your home electrical system or carefully isolated from it, you will see significant damage.
Read your local electrical codes and consult with a master electrician before doing any of this. The rules and codes differ from place to place. Unless you're experienced in this sort of thing, this technology can seem arcane and bizarre.
