OK--so, I guess, that your parcel was part of the lease signed in 1973, it was all unitized, and thus you are HBP by this older well which is now owned by Chesapeake. Sounds like that's the end of the story.
On a side issue--your OP asked how neighbors could sign new leases, on pieces of what was your grandfather's farm. It's pretty common for a lease to be written and even recorded when, later, it is found to be invalid. Almost always this is discovered before any actual site work begins.