overrun vs well over

overrun is a noun but well over is not a noun.

Word	Noun	Adjective	Verb	Adverb
overrun	Yes	No	Yes	No
well over	No	No	Yes	No

As verbs, overrun and well over are synonyms defined as:

Other synonyms of overrun include brim over, overflow, run over.

overrun (noun)	well over (noun)
too much production or more than expected

overrun (verb)	well over (verb)
run beyond or past	flow or run over (a limit or brim)
seize the position of and defeat
flow or run over (a limit or brim)
invade in great numbers
occupy in large numbers or live on a host