drilling rig vs oil rig

drilling rig and oil rig both are nouns.

Word	Noun	Adjective	Verb	Adverb
drilling rig	Yes	No	No	No
oil rig	Yes	No	No	No

As nouns, drilling rig and oil rig are synonyms defined as:

Other synonyms of drilling rig include drill rig, oilrig.

drilling rig (noun)	oil rig (noun)
rig used in drilling for oil or gas	rig used in drilling for oil or gas