A method for lifting oil from the bottom of a well comprises, (1) injecting a fluid of less specific gravity into the well with a fluid flow control valve, and (2) equalizing the fluid pressure on all sides thereof for making the fluid flow control valve balanced and frictionless as the fluid of less...http://www.google.de/patents/US4251191?utm_source=gb-gplus-sharePatent US4251191 - Method for lifting oil in a well
