Heirs and Assigns omitted from deed

I live in PA. Like the title says, if a deed makes use of the phrase "heirs and assigns" for the grantee twice in the deed, yet leaves it out when it reserves oil and gas rights, would that reservation simply become a life estate reservation? I have been told by my real estate attorney it would be, but he is not exclusive to oil/gas law.

The reservation simply says, "grantor reserves oil/gas rights." Any thoughts? thanks.