I agree with FishinRod, but I think I would still like to dig around the old wellhead and take a look at the cap. The production casing may not have been pulled so it could have multiple welded caps/wraps. If all casing strings are welded up tight, then very low chance for anything to ever leak. If everything is healthy and green around the well and old tank battery, than more than likely you'll be fine. Plus once you uncover the well you'll have a nice sump to fill with water to check for any gas leaks.

Was this well plugged while you owned the property? I'd say modern P&A jobs were much more sanitary than older ones.

If you post your email address I can contact you directly and help you find the old well record too if needed.

When we dug our 9 acre pond I didnt research well records because I knew they were so old and OKLA doesnt have that great of a database prior to 1970. Luckily we didnt uncover anything.