Underbalanced drilling method and apparatus

摘要

A method of drilling well bore ( 20 ) through and below permeable formation ( 22 ) bearing such fluids as gas, oil, water wherein drill cuttings may be evacuated by formation fluid ( 23 ) being produced through the drill string ( 26 ) either by decreasing well head back pressure or by gas lift. Production rate is kept substantially stable by operating choke valves ( 140 ) and ( 142 ) placed after separator ( 52 ). Formation fluid being produced while drilling may be pumped into well bore ( 20 ) through annulus ( 31 ) or utilized. The unique injector included in the drill string provides for possibility to pump simultaneously into annulus ( 31 ) lifting gas and produced liquid and may be operated from the surface. A method and system ( 90 ) comprising a plurality of special 3-way valves included in drill string ( 26 ), are provided for making connections without interrupting flushing the well bore.