In reply to Trangia:
You are correct Trangia, at the Up and Under Group we have a lot of experience of working in this type of structure, a deep confined space, and low oxygen is just one of the potentially fatal hazards that may be present.
If the well owner is really interested in finding out what is down his well, it might be a good idea to contact a company or group with the relavent experience.
I fully understand the desire to know though
(sadly from experience it's usually water, mud, rocks and possibly the bones of lost animals).
Cheers