A typical well-head assembly comprises a large number of fluid-actuated valves together with associated electrical, pressure and temperature transducers which are controlled and monitored by a control module which is coupled to a remote operating station to enable control of the well-head assembly, and the monitoring of its performance, from a remote position. Such an arrangement can be used with land-based oil fields, but is particularly useful with underwater oil fields.

With an underwater oil field, the well-head assembly is usually permanently attached to the well-head and is provided with a mounting base for supporting a detachable control module which is connected to a general operating station on the surface. Typically the surface operating station would be located on an oil rig, or vessel, which is connected to one or more underwater stations, each comprising one or more well-heads, by respective umbilical cords providing the means for conveying electrical and/or fluid energy, together with the transmission of electrical and/or optical signals for controlling and monitoring oil extraction.

With some underwater oil fields the operating station could be shore-based.

It will therefore be appreciated that the surface operating station provides remote control of a

substantial number of valves which are supported from the sea bed by the well-head assemblies. Such valves typically comprise a valve actuator, such a piston, which is connected to a supply of pressurised fluid via the control module that is detachably secured to the mounting base on the well-head assembly. The control module therefore includes control valves for regulating the flow of pressurised fluid to each of the fluid-actuated valves in the well-head assembly. Thus the control module is essential for connecting the fluid actuated valves to the supply of pressurised fluid and for controlling their operation. The control module is also essential for monitoring the operation of the well-head assembly.

Typically a subsea control module is lowered on a line from a work barge, or service vessel, using guide wires and remotely operated tooling to ensure both a soft landing on the mounting base and correct alignment. The engagement of the control module with the mounting base essentially requires the correct alignment and joining of a plurality of connectors to provide the necessary fluid, electrical and/or optical transfer between the control module and the well-head assembly. Hitherto, these connectors have been arranged between the bottom surface of the control module and an upwardly facing surface of the well-head assembly. Due to the very substantial separation forces in the fluid-pressure connectors, the subsea control module is typically heavy and requires a strong mechanism for releasably connecting it to the well-head assembly. The weight of a typical control unit is at least one tonne as it requires substantial framing to withstand the clamping force of the mechanism, and also to support counter weights to balance the loads on the well-head apparatus. A typical connecting mechanism comprises a base plate having individual connectors mounted on it for connection of electrical and/or hydraulic power, and also for connection with electrical and/or optical control lines.

Where a large number of connections are required to monitor and control a well-head

assembly, the base plate may typically have a diameter of 900mm. The base plate is also required to be of sufficient thickness to resist bending due to the axial separation forces exerted by the pressurised fluid in the individual connectors. Typically the thickness of the base plate would be 75mm and its weight would be 300Kg. To secure the control module to the well-head assembly, it is essential to use a high tensile latching mechanism to withstand the separation forces. A typical latching mechanism would provide a tensile force of SMN and would typically weigh 150 Kg.

Due to the above factors, the mounting plate and the latching mechanism contribute both directly, and indirectly, to the size and weight of the subsea control module, typically 50% of the overall weight.

The subsea control module needs to be securely mounted to the well-head assembly for very long periods, for instance up to 20 years, before removal for servicing. This requires the latching mechanism to be of a specification and design which will provide reliable detachment despite the accretion of marine growths and the inevitable corrosion.

Therefore, it is known for an oil field apparatus to comprise a well-head assembly arranged to monitor and/or control flow to or from a well, a mounting base carried by the well-head assembly, a control module moveable along an axis between an operative position in which it engages the mounting base and an inoperative position in which it is separated from the mounting base, a plurality of connectors each comprising a first connector portion carried by the mounting base and a second connector portion carried by the control module, each connector being arranged such that its first and second portions intercommunicate whenever the control module is in its operative position but are disconnected whenever the control module is in its inoperative position, and the first and second connector portions defining mutual sealing surfaces which when engaged lie in a plane parallel to the axis The present invention is concerned with providing an interface between a control module and 5 a well-head assembly which can eliminate the requirement for any high tensile latching mechanism and can significantly reduce the size, weight and cost of the overall apparatus.

According to the invention the control module defines a spigot and the first potions are arranged about the spigot in a circular configuration, the mounting base defines a co-operating socket the second connector potions are arranged about the socket in a corresponding circular 10 configuration and their mutual sealing surfaces are located in a radial gap between the spigot and the socket. In this manner connectors for the fluid pressure lines are arranged transversent to the axis of engagement of the control module with the mounting base so that the line of action of the separation forces is always at right angles to the direction in which the control module can move. This arrangement eliminates the requirement for a high tensile latching 15 mechanism as the control module can be held securely in position by its own weight. The elimination of the previously required high tensile latching mechanism also eliminates the need for a substantial base plate and substantially reduces the overall size and weight of the control module. Connectors for electrical and optical lines can conveniently be arranged in the same manner as the connectors for the fluid pressure lines.

20 The first and second connector portions of each connector are relatively moveable between an engaged position and a disengaged position and are spring biased towards the disengaged position and movement of the control module into its operative position is arranged to engage the sealing surfaces with a shearing action. In this manner, whenever the control module is moved into its operative position, the sealing surfaces will be wiped across each other thereby removing any particulate contamination.

5 Each pair of first and second connector portions includes a piston which is connectable to a pressurised fluid whenever the control module is in its operative position, and the piston is arranged to force their mutual sealing surfaces together. In this manner, whenever the well- head assembly is operatively connected to the control module, the sealing surfaces of the connectors will be pressed together to prevent leakage, in the case of a fluid pressure 10 connector, and to ensure the best possible connection of electrical and optical lines.

If desired, the mounting base may define the spigot and the control module could define the co-operating socket.

The spigot and socket are preferably of cylindrical configuration but could, instead, be multi- faceted. With a cylindrical configuration the connectors are preferably arranged in a circular 15 configuration around the radial gap between the spigot and the socket. Furthermore, the connectors may be arranged in a plurality of circular arrays around the radial gap. In this manner a large number of connectors can be arranged in a small area.

The connectors are arranged so that their respective separation forces are substantially balanced.

A housing ring maybe mounted for axial movement within the mounting base socket between a first axial position in which it covers the first connector portions and a second axial position in which the first connector portions are uncovered. Another housing ring may be mounted for axial movement along the control module spigot between a first axial position in 5 which it covers the second connector portions and a second axial position in which the second connector portions are uncovered. The, or each, housing ring preferably includes a sealing means to seal its connector portions whenever it is in the first axial position. The, or each housing ring is moved, from its first axial position to its second axial position by movement of the control module to its operative position. Similarly, the, or each, housing ring is moved 10 from its second axial position to its first axial position by movement of the control module to its inoperative position.

The invention will now be described, by way of example only, with reference to the accompanying drawings, in which:- Figure 1 is a plan view of a subsea well-head assembly with associated mounting base and 15 control module; Figure 2 is a side elevation of Figure 1; Figure 3 is an enlarged view of the control module and mounting base illustrated in Figure 1, the control module being shown in elevation at an inoperative position whilst the mounting base is shown partly in section;

Figure 4 is an enlarged cross-section, taken along the line 4-4 in Figure 3, through the control module and the mounting base whilst they are in their operative position; Figure 5 is a vertical section, taken along the line 5-5 in Figure 4, illustrating the control module in an inoperative position, during insertion into the mounting base; Figure 6 is the vertical section, similar to Figure 5, but illustrating the control module and mounting base in their operative position ; With reference to Figures 1 and 2 a subsea well-head assembly 20 is supported by four legs 21 from the seabed 22 and is connected to well-head 23 in a conventional manner. The well- head assembly 20, or"Christmas Tree", comprises a variety of control devices, some of which have been generally indicated by reference 24, and is designed to meet the particular requirements of the oil or gas field in which it is to be used. The specific arrangement and the design of the well-head assembly 20 does not form part of the present invention apart from its interface with a control module 25 and the associated mounting base 26.

The subsea control module 25 is designed to control and monitor the specific design of the associated well-head assembly 20. The subsea control module 25 is provided with a lifting attachment 27 which is secured to a lifting line 28 whereby the control module 25 can be lowered from the surface into the mounting base 26, and can subsequently be retrieved in the same manner. Thus, whilst the well-head assembly 20 would normally remain secured to the well-head 23, the subsea control module 25 can readily be released from the mounting base 26, moved to the surface for servicing or replacement, and subsequently returned to its

position within the mounting base 26. This process is conventionally achieved, in one manner, by remotely operated tooling operated from a surface vessel using guide wires to ensure gentle engagement of the control module 25 with the mounting base 26 and also their correct alignment.

With reference to Figure 3, it will be seen that the subsea control module 25 defines a spigot 29 of which an upper portion is shrouded by a housing ring 30 the function of which will be described later with reference to Figures 5 and 6. The control module 25 is also provided with a protective cover 31 which is guided vertically downwards into a frusto-conical mouth 32 at the top of a tubular locator 33 forming part of the mounting base 26. Inside the tubular locator 33 is a connecting ring 34 which defines a socket 35 for receiving the spigot 29. The tubular locator 33 and the connecting ring 34 are mounted from a structure 36 which is permanently connected to the well-head assembly, various fluid, electrical and optical lines 37 being permanently connected between connecting ring 34 and the well-head assembly. As the control module 25 is lowered into the mounting base 26, the frusto-conical mouth 32 guides the protective cover 31 into near concentricity within the tubular locator 33. The spigot 29 is provided with a chamfered edge 38 which engages the mouth of the socket 35 and guides spigot 29 into the socket 35 to leave a narrow radial gap 39 as shown in Figure 4.

With particular reference to Figure 4 it will be seen that the spigot 29 has been positioned, in the manner just described, radially within the socket 35 defined by the connecting ring 34. It is also necessary to provide both axial and rotational alignment between the spigot 29 and the socket 35 as will be described later with reference to Figures 5 and 6. However, it should be noted that, with the correct axial and circumferential alignment, sixteen connectors 40 are

simultaneously aligned to connect respective lines 41 in the spigot 29 with corresponding lines 42 in the connecting ring 34. As shown these lines are for pressurised fluid but they could equally well be electrical or optical lines.

The axial alignment of the connectors 40 will now be described with reference to Figures 5 and 6. It should be noted that each connector 40 comprises a pair of shoes 43,44, the shoes 43 being located in the spigot 29, whilst the shoes 44 are located in the connecting ring 34.

As shown in Figure 5, the shoes 43 and 44 are not in alignment as the spigot 29 is only partially inserted into the socket 35 defined by the connecting ring 34. As shown in Figure 5, the shoes 43 are covered by the housing ring 30 which is provided with a pair of circular seals 45 to inhibit the ingress of water during mounting of the spigot 29 within the socket 35. The housing ring 30 is held in the position as shown in Figure 5 by a spring detent 46 but has a surface 47 which will engage a flange 48 within the socket 35 as the spigot 29 is moved annually downwards. This engagement between the surface 47 and flange 48 causes the detent 46 to ride over the co-acting surface on the inside of the housing ring 30, thereby progressively stripping the housing ring 30 offthe shoes 43. At the same time, the lower surface of the spigot 29 forces a piston 49 axially downwards within the socket 35 so that sealing shoes 50 are progressively stripped downwards off the shoes 44. Continued downward movement of the control module 25 eventually causes the shoes 43 and 44 to aline as shown in Figure 6, to provide communication between the lines 41 and 42.

With particular reference to Figure 6, it should be noted that the lines 41 and 42 are connected together, the axial position of the spigot 29 being precisely controlled by the engagement of the bottom surface of the spigot with the top surface of the piston 49 of which the downward

movement is limited by the top surface of a plug 51 which is annually located within the connecting ring 34. It will also be noted that the sealing shoes 50 are isolated from the surrounding water by seals 52 carried by the piston 49.

A second spring detent 53 is located in the plug 51 for use when the spigot 29 is withdrawn from the connecting ring 34. Upward movement of the spigot 29 is transmitted to the piston 49 by a magnet 54 so that the piston 49 will be withdrawn upwards until further movement is stopped by the spring detent 53, at which position the sealing shoes 50 have sealingly covered the shoes 44 in the connecting ring 34. A second magnet 55 is similarly used to draw the housing ring 30 downwards to sealingly cover lines 41 in the spigot 29. Once the housing ring 30 and the piston 49 have been moved to these positions, further upward movement of the spigot 29 causes decoupling of the magnets 54,55 thereby allowing the control module 25 to be progressively withdrawn. A circumferential alignment between the spigot 29 and the connecting ring 34 can be achieved in any convenient manner, for instance by using one or more keys engaging axial grooves in the connecting ring 34. It will be noted from Figures 5 and 6 that there are three separate bays of connectors 40 which are spaced axially of the spigot 29 but are each arranged in the cylindrical configuration illustration in Figure 4. By appropriately positioning the connectors 40, it is possible to substantially counter balance the forces of separation which are therefore all contained within the connecting ring 34.

Whilst various forms of connector 40 can be used, provided they have neutral sealing surfaces which when engaged lie in a plane parallel to the axis of the spigot 29, we prefer to use the form of connectors 40 which are described in our co-pending British Applications 9621770.8 A and 9621769.0 A the whole contents of each being incorporated herein by reference.