Abstract: A method for managed pressure drilling comprising: extending a drilling riser with a drill string from a floating installation to a subsea blow-out preventer stack; providing a first fluid in the drilling riser annulus and a second fluid in a fluid conduit extending from the floating installation, where the first fluid has a higher density than the second fluid; circulating the second fluid through a control valve which is fluidly connected to the fluid conduit and operating the control valve to apply a surface back-pressure so as to obtain a pre-determined, desired combined hydrostatic and frictional circulation pressure below the subsea blow-out preventer stack.

Abstract: A protection system for a drilling riser. The drilling riser includes a main drilling riser bore and a drilling riser annulus and extends from a floating installation to a location on a seafloor and is fluidly connected to a subsea BOP. The system includes a fluid conduit which extends from the floating installation to a lower region of the drilling riser. The fluid conduit is fluidly connected with the drilling riser annulus in the drilling riser. The fluid conduit provides at least one of a rapid pressure relief and a fluid bypass for the main drilling riser bore to prevent the drilling riser from an uncontrolled pressure build-up due to an inadvertent plugging or a restriction resulting in a maximum allowable working pressure (MAWP) of the drilling riser being exceeded, if a restriction, a plug or a blockage exists in the drilling riser annulus or in riser outlets.

Abstract: A method for managed pressure drilling comprising: extending a drilling riser (2) with a drill string (20) from a floating installation (52) to a subsea blow-out preventer stack (1); providing a first fluid in the drilling riser annulus (12) and a second fluid in a fluid conduit (6,7) extending from the floating installation (52), where the first fluid has a higher density than the second fluid; circulating the second fluid through a control valve (31) which is fluidly connected to the fluid conduit (6,7) and operating the control valve (31) to apply a surface back-pressure so as to obtain a pre-determined, desired combined hydrostatic and frictional circulation pressure below the subsea blow-out preventer stack (1).