Probably /is/ a screwback. It might've been closed too tight before and/or the threads weren't lubricated so it might not be possible to open it by a hand-held wrench.
Where are you located? People might be able to help you.

 

Thanks Vicc......I think I will try again to spin it off with my opener. And I am Eastern Shore of Maryland.

 

When you have one that defies your strength and lug wrench look for a full service watch maker with a press type case back opener. They can twist off the tightest back. If you are doing this yourself be sure to use a decent wrench not one of the 4.99 wonders.

I had a second look at your original post. That is not a 'pop off case back, some can be quite tight.

 

See if a quick blast of hot air from a hair dryer will loosen it.

 

Thanks Ard......might need to a take it to a shop since I can't budge it.

 

Hmmm......I wil grab a hair dryer and give it a try tomorrow. Thanks!!

 

You could also try a small sticky ball or a tight ball of duct tape.

 

Plus a few hot air as opposed to gas.

 

Give John’s hot air method a go an if there’s no joy it looks like a trip to the shops is called for.

 

You can give the Ball a try. I've had some success with it. The key is proper inflation. You will need a football needle and pump.

 

Ha, I read this thread thinking it was an Oris watch, not Orvis. I <3 me some Orvis products.