Construction and dismantling drill pipe arrangement in pressurized borehole, using movable safety valve connected to fixed safety valve via telescopic casing

摘要

A movable safety valve (11) connected to a fixed safety valve (10) via a telescopic casing (9) is mounted in a closed position around the drill pipe arrangement (20), the fixed valve is then opened and the movable valve is moved downwards to retract the casing while the drill pipe arrangement is held by this valve and then the fixed valve is closed and the movable valve is opened and moved upwards to extend the casing while the drill pipe arrangement is held by the fixed valve. Constructing a drill pipe arrangement which is located in a pressurized borehole and movable by a safety valve having a fixed position relative to the borehole comprises: (a) mounting a safety valve which is movable relative to the borehole in a closed position around the drill pipe arrangement and at a distance above the fixed valve, using a telescopic casing around the arrangement to connect the two valves; (b) opening the fixed valve; (c) moving the movable valve in a downwards direction so that the telescopic casing becomes retracted while the drill pipe arrangement is held by this valve; (d) closing the fixed valve; (e) opening the movable valve; and (f) moving the movable valve in an upwards direction so that the telescopic casing becomes extended while the drill pipe arrangement is held by the fixed valve. Independent claims are also included for the following: (a) dismantling the same drill pipe arrangement, comprising the same steps as above except that in step (c) the movable valve is moved in an upwards direction so that the casing becomes extended while the drill pipe arrangement is fixed to the movable valve and in step (f) the movable valve is moved in a downwards direction so that the casing becomes retracted whilst the drill pipe arrangement is held by the fixed valve; and (b) an apparatus (1) for carrying out both of these methods, in which the casing is in sealed contact with the fixed valve.