CRNG wrote, on Wed, 02 Jul 2014 06:59:30 -0500:

My *guess* is that to drill deeper via an existing well, the "deeper"
part will have to be a smaller diameter than the pre-existing well

That makes sense.

I know I have two wells, where the new well is a few hundred feet
from the old well.

So, in my case, they certainly drilled a separate well (but both
are producing water, albeit slowly).