DEVICE AND METHOD FOR CONTROLLING RETURN FLOW FROM A BORE HOLE

摘要

There is provided a device and method for control of return flow from a borehole (18) where drill fluid is supplied from a surface rig (16) via a multi section drill string (4) to a bottom hole assembly (18), the drill pipe sections (6) having tool joints (8) that include an enlarged outer diameter portion (9), and where an annulus (12) is formed between a pipe (2) and the drill string (4), and where the annulus (12) is in fluid communication with or forms part of a return path (40) for the drill fluid, and where a choke (1) is positioned in the annulus (12), and where the length (L) of the choke (1) exceeds the distance (M) between the enlarged outer diameter portion (9) of two adjacent tool joints (8).