There has been a drift in the last generation towards employing as well as as a coordinating conjunction equivalent to and; but this use still raises eyebrows in formal registers. It will annoy many readers, so until we're all dead (or at least retired from positions where we exercise influence over your audience) I recommend you reserve as well as for marking supplemental (parenthetical) clauses.
But even with and I would avoid this sort of conjunction:
I have completed this project
and been working on another one.
This is technically "grammatical"; but the coordination of a simple and a progressive perfect is jarring—it makes the reader shuttle backward to sort out the syntax. As a courtesy to your reader, use the long form instead:
I have completed this project
and have been working on another one.