A wellbore drilling system has an umbilical that carries a drill bit in a wellbore. Drilling fluid pumped into the umbilical discharges at the drill bit bottom and returns through an annulus between the umbilical and the wellbore carrying entrained drill cuttings. An active differential pressure device...http://www.google.com.au/patents/US7114581?utm_source=gb-gplus-sharePatent US7114581 - Active controlled bottomhole pressure system & method
