Patent ID: 7281593

Claim:
A method for the circulation of gas when drilling or working a well, the method comprising: (i) pressurizing at least two chambers of a multi-chambered accumulator with inert gas, said chambers of said multi-chambered accumulator operatively connected to one another and individually or in combination isolatable from each other; (ii) isolating at least one chamber of said accumulator that has been pressurized with inert gas such that during drilling or working the well said isolated chamber remains pressurized with gas that has not been mixed with well gas returns; (iii) extracting pressurized gas from one or more of the non-isolated chambers of said accumulator and injecting said pressurized gas into the well; and, (iv) collecting and compressing at least a portion of the gas returns from the well and delivering said pressurized returns to at least one of the non-isolated chambers of said multi-chamber accumulator.