OPT EAD is NOT a travel document.  It is an employment authorization document that allows you to work in the US after completing your studies.  If you need to or want to travel internationally while in OPT status, you can do so only if you have a valid F-1 visa, which is your underlying status while in OPT.  If you do not have a valid visa, you may not travel internationally with a hope of returning to the US.