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.de/patents/US6837313?utm_source=gb-gplus-sharePatent US6837313 - Apparatus and method to reduce fluid pressure in a wellbore
