Sub-Sea Well Heads

A sub-sea gas- or oil-well comprises a hole lined with casings in which casings below sea-bed level there is a valve arranged to close to prevent leakage and contamination of the ocean. On top of these casings there is a connector mounting a so-called christmas tree. In the christmas tree there is a back-up or master valve. It has been proposed to enclose the entire well-head in a capsule. However in this proposal, if there is a fault between the two valves, the contents of the well-head between the two valves whilst insufficient seriously to pollute the ocean will probably escape into the confined space of the capsule and seriously impede operations on the christmas tree. Moreover if the first valve fails, there will be an increase of pressure and additional strains on the seals in the well-head when the master valve is closed tending to increase the risk of escape into the capsule. Since repair of the first valve would involve plugging the well by means introduced into the well through a lock-through arrangement associated with the christmas tree, it is desired to minimise contamination of the capsule by any leakage.

According to the present invention there is provided a well-head comprising a connector and a christmas tree having a capsule enclosing the christmas tree and a master valve within the christmas tree characterised in that the master valve is contained within a member forming the foot of the christmas tree, the member penetrating and being sealed into the bottom of the capsule and supporting the capsule, and in that the master valve is contained within a part of the member within the capsule.

An embodiment of the invention will now be described, by way of example, with reference to the accompanying drawing which is a vertical section through a capsule enclosing a christmas tree and showing a connector of a well-head.

In the FIGURE, from a portion of the sea-bed 11 project well-head casings 12 on which is mounted a christmas tree 14 enclosed in a sealed capsule 15. Pipes 16 are brought through suitable penetrations 17 in the wall of the capsule to connect up to the christmas tree. The well-head casings terminate in a connector 110 on which the christmas tree is mounted. The seals between the casings and the connector are outside the capsule so any leakage is outside the capsule. A member 111 forming the foot of the christmas tree is a solid block(in that it comprises a one-piece housing) and penetrates the bottom of the capsule and is sealed thereto by seals 115 as shown, the capsule is supported on a flange 111a of member 111 and is retained in place on the flange by a suitable securing ring 116, such as a split ring. The member 111 member contains in the part of the member within the capsule a master valve 112 operable by a handwheel 113 or by a hydraulic motor 114 controlled remotely by hydraulic means. The operating means are within the capsule. This member is of course sealed to the connector which is immediately below it but the seals are outside the capsule.

It will be appreciated that with this construction, any leakage into the capsule must be from the master valve member which can be designed to obviate any possibility of leakage; thus the capsule is not subject to contamination by leakage from the well-head.