US Patent 7886849 System for drilling under-balanced wells

A system and method for drilling a well bore with an under-balanced hydrostatic pressure. The system used in the method includes a tubular member containing a first port, a compression member disposed about the outer portion of the tubular member and having an internal sliding mandrel extending therefrom with a second port, an external sliding sleeve having a third port and being in contact with the internal sliding mandrel and operatively associated with the internal sliding mandrel, and a compressible seal disposed about the external sliding mandrel that is responsive to a longitudinal weight transferred to the compression member. In a closed position the first, second and third port are misaligned and in an open position the first, second and third ports are aligned.