| 主权项 |
1. A device for control of return flow from a borehole, wherein drilling fluid is supplied from a drilling platform through a drill string disposed in a borehole, the device comprising:
an annulus formed between a pipe and the drill string, the annulus being in fluid communication with or forming part of a return path for the drill fluid, the pipe extending from the borehole to the drilling platform; a choke positioned in the annulus, the choke comprising a cylinder disposed between two spaced apart bodies in an interior of the pipe, the spaced apart bodies disposed in an annular space between an interior of the pipe and an exterior of the cylinder, the choke comprising an annular space between an interior of the cylinder and an exterior of the drill string; and an automatically operated annular seal element disposed in the pipe above the drill fluid return path, the automatically operated annular seal element being open to fluid flow in the annular space between the interior of the cylinder and the exterior of the drill string when fluid flow rate in the pipe and differential pressure across the choke are below respective selected amounts, the annular seal element disposed in a housing adjacent to a piston movable along an exterior of the cylinder at one longitudinal end of the cylinder, the housing sealingly engaged with an interior of the pipe, the annular seal eminent configured to close the annular space between the interior of the pipe and the exterior of the drill string to fluid communication when at least one of a selected fluid flow rate in the pipe and a selected pressure differential across the choke is reached. |
