Learn English – Is a comma necessary before “for which”

According to some authorities, such as Purdue OWL, yes, a comma should be used before "and" in that sentence:

Use commas to separate independent clauses when they are joined by any of these seven coordinating conjunctions: and, but, for, or, nor, so, yet.

It's a compound sentence, as you identified, and should therefore have a comma.

That being said, a more reasonable guideline, as given at Grammartips.homestead.com, governing comma use is that they, like all punctuation, should be used to reduce or eliminate ambiguity. You can often eliminate the comma

if both independent clauses are quite short, especially if the two clauses are very closely related, and even more so if the subject of both clauses is the same, or

if only the first clause is quite short, especially if the two clauses are very closely related, and even more so if the subject of both clauses is the same.

Here is an example involving two short clauses conjoined with 'but':

John went to the store but he didn't buy anything.

In this context, "as well as" is a coordinate conjunction, combining two clauses into one sentence. A good rule of thumb here is to substitute another coordinate conjunction you're more familiar with, such as "and"; if you were to use "and" in place of this phrase (for instance, "We have carried out works for private individuals and property developers and carried out our own projects") it would not take a comma.

That said, Mustafa is also right; the second clause of the sentence can't stand alone without a verb. Throwing a verb in there as suggested should make everything okay.