The present invention generally provides apparatus and methods for reducing the pressure of a circulating fluid in a wellbore. In one aspect of the invention an ECD (equivalent circulation density) reduction tool provides a means for drilling extended reach deep (ERD) wells with heavyweight drilling...http://www.google.com.au/patents/US7395877?utm_source=gb-gplus-sharePatent US7395877 - Apparatus and method to reduce fluid pressure in a wellbore
