SYSTEM AND METHOD FOR REPLACING AN INSERT UNIT INCLUDED IN AN ASSEMBLY LOCATED AT A REMOTE LOWERED LOCATION

Abstract: System and method for replacing an insert unit included in an assembly located at a remote distance below a location from where the assembly can be serviced and controlled by manpower, for example an insert valve assembly (22) belonging to a subsea production system for oil and gas. In carrying out the method with said system at a subsea production site, a manipulator (1) is brought by means of a sheave (2), a hoisting cable (3), and guide wires (4, 5) down to a predetermined location on the bottom of the sea. The manipulator comprises a telescopic arm (15, 16) which is then moved towards and fixed by means of a hook (20) and a lug (21) to a valve tree (17) which supports a valve (22), the insert unit 26, of which is to be unscrewed from the respective valve housing and be replaced. A carriage (18) located in the manipulator and comprising retrac tion, aligning and fixing devices (32, 33, 34) is brought with the aid of the telescopic arm and a rail (19), located on the top side of the carriage, towards the valve tree and is fixed to retraction cones (35, 36, 37) mounted on the valve tree. This allows a moment producing tool (31), mounted in the carriage, to grapple a castellated nut (24) which fixes the insert unit to the valve housing of the valve. Thereafter, a releasing moment is applied on the castellated nut, whereby the castellated nut with the insert unit is unscrewed from the valve housing and the valve tree. The carriage with the insert unit is separated from the valve tree and is brought back via the telescopic arm to the manipulator. The insert unit of the valve is replaced by a new insert unit, either by a new insert unit stored in the manipulator and with the aid of gripping arms present in the manipulator, or by raising the manipulator to the surface where the replacement is carried out, whereafter the manipulator is again lowered and the carriage is again moved towards and fixed to the valve tree. This also allows the moment producing tool to move the new insert unit with its castellated nut towards the valve housing, whereupon a tightening moment can be applied.

Description: This invention relates to a system for replacing an insert unit included in an assembly located at a remote lowered location according to the precharacterising part of Claim 1. The invention also relates to a method to operate the system. The insert unit assembly to which the invention relates is preferably an insert unit assembly for a subsea production system for gas and oil. Such a production system is often called an SPS system, which is an abbreviation of Submerged Production System. Other areas for application of the invention are, for example, deep sea mining and shaft mining. In order to describe the invention in its proper context, a short description of the preferred technical field to which the invention belongs will first be given. This technical field is described, inter alia, in STU-Information No. 118-1979, Offshore, by J Palmer and L Edström (issued by the National Swedish Board for Technical Development). The hole which is drilled into the bottom of the sea for oil and gas extraction is built up of a number of casing pipes, which are cast to the different sediments with a predetermined distance and with decreasing hole dimensions from the surface of the sea bottom down towards the largest depth. On the bottom of the sea and around the opening of the casing pipe a so-called wellhead is attached, which forms the foundation of the bottom-based part of the subsea production system. Inside the casing pipes are placed the production pipes, which are to lead the normally multi-phase fluids up to the surface. These fluids may consist of solid particles, oil, water, and gases. On the foundation and around the production pipes there is mounted a substantially tubular structure which, among other things, supports valves connected to the production pipes. These valves are intended for flow control of the different fluids. This structure is designated valve tree (or "Christmas tree"), the reason being that the tubular structure may be conceived as the stem of a tree with the projecting valves as the branches. On the foundation and around the valve tree there is placed the remaining underwater based production equipment, which together form the under-water production site. It consists, among other things, of guide posts with guide wires for guiding and positioning peripheral equipment of various kinds. The peripheral equipment comprises operating, control and auxiliary equipment for valves, safety systems of different kinds, etc. Proper functioning of the valves which are used for controlling the various production flows is very important. However, the valves operate under difficult conditions, both as far as the actual fluids are concerned and as far as the surroundings are concerned. To ensure satisfactory operation, the valves have to be capable of being repaired, and, possibly, non-operating parts of the valves have to be capable of being replaced. Normally, therefore, the valves are designed so as to have their vital parts built into a replaceable insert unit. Upon replacement, the existing non- operating insert unit must first be removed from its valve housing, whereafter a new insert unit van be mounted into the valve housing. To ensure satisfactory sealing between the valve housing and the insert unit, relatively high tightening moments are applied to the nut - normally a castellated nut - which fixes the insert unit to the valve housing. When detaching the insert unit, a releasing moment of at least the same magnitude as the tightening moment is normally required. Since a valve tree comprises a plurality of valves whose insert units may need to be replaced, the tool that is to bring about the releasing and the tightening, respectively, of the castellated nut must be capable of being positioned against the valve in question. It is also desirable for this part of the replacement process to be carried out by means of remote control. An example of a device for positioning a tool for replacement of insert units is given in the above-mentioned STU publication. The oil company Exxon has in its SPS system a manipulator which is capable of being moved on a rail system secured to the surrounding steel structure of the wellhead. The movement around in the production tree and the associated pipe system takes place by means of a rack. The positioning is remote-controlled and takes place, among other things, by means of TV and video cameras. Secured to and built into the manipulator are on the one hand moment producing devices intended for releasing and tightening, respectively, the castellated nut which fixes the insert unit of the valve to the valve housing, and on the other hand moment producing tools for threading in and out the insert unit. The reason for having different moment producing devices for effecting the releasing and tightening moment, respectively, and for effecting the moment for threading the nut in and out is due to the considerable difference in magnitude between the two required moments. The high releasing and tightening moment in the Exxon design, which is generated in the above-mentioned manipulator, is brought about by allowing two hydraulically operated piston rods to act against two projections on a rotatable ring which is in engagement with and surrounds the castellated nut. In the Exxon manipulator, the moment for threading the nut in and out is brought about with the aid of a worm gear which engages external splines on the rotatable ring mentioned. The problems with the Exxon design and similar designs are manifold. The manipulator including the moment producing devices as well as devices for positioning consist of large and clumsy structures which may have a weight of some twenty or thirty tons or more. The high weight necessitates that the manipulator is bottom-based and that transportation must take place on some form of rail system. Also the associated rack structure for transportation will therefore require large dimensions, the power requirement for the positioning operation being correspondingly high. The moment producing devices for releasing and tightening, respectively, of the castellated valve nut also have a limited range of rotary motions. The fact that two different moment producing devices are needed to release the insert unit also is a disadvantage of this solution. Therefore, for a long time there has been a need of light and easily manageable constructions, improved moment producing devices, etc., to facilitate the process when replacing an insert unit in valves used in SPS systems for oil and gas production. The invention aims at a system and a method for replacing an insert unit included in an assembly located at a remote low ered location which do away with the afore-mentioned shortcomings of the previous systems and methods. To achieve this aim the invention suggests a system according to the introductory part of Claim 1, which is characterized by the features of the characterizing part of Claim 1. A method for operating the system according to the invention is characterized by the features of Claim 2. Further developments of the method are characterized by the features of the additional claims 3 and 4. The method, which will be described in detail below, comprises a sequence of operations which presupposes that certain mechanical devices are available. Some of these are part and parcel of the general store of mechanical constructions. The invention is based on the use of a modified version of a manipulator produced by Deep Ocean Technology Inc., USA, disclosed, inter alia, in its pamphlet "BANDIT", revised October 1984, and in ASEA's pamphlet "The Bandit - a Working Mac hine for Drilling Support". This is a lightweight manipulator that need not be stationed on the bottom of the sea. By means of a hoisting cable tethered to the manipulator, the manipulator can be lowered to the bottom of the sea and be lifted up to the surface. By means of guide wires secured to the bottom, which serve as guidelines, the manipulator is guided with the aid of guide frames, mounted on the manipulator, towards a pre-determined location on the wellhead when the manipulator is lowered down. At this pre-determined location at least two guide posts are to be arranged, which are either especially intended for the manipulator ore are otherwise included in the production tree. For a method according to the invention, the manipulator is to be mounted on the beam which, at either end, has guide slots to accommodate said guide posts towards which said beam is moved by the guide wires. Built into the manipulator is a carriage which, among other things, supports the tool - a nut tightener - which is used for releasing and tightening the castellated valve nut. The manipulator with carriage, tool, etc. is now to be positioned, on the basis of the guide posts used, in such a way that the tool - both laterally and vertically - is positioned approximately straight in front of and opposite to the valve that is to be replaced. This can be done by a suitable lateral mounting of the manipulator on the above-mentioned beam, and by placing spacing sleeves on the guide posts so as to obtain an approximately correct height above the wellhead. The manipulator also has mounted on it a remotely operable telescopic arm. After the manipulator has been approximately correctly placed according to the method described, the telescopic arm is moved against and fixed by means of a hook on the arm to a lug on the valve tree. This causes the telescopic arm to become loadable. The above-mentioned carriage with the tool for applying a moment on the castellated valve nut is now moved on the telescopic arm towards the valve in question. In order for the tool to be able to grapple the castellated valve, an accurate position of the tool is required. In addition to the moment producing tool, the carriage also contains two or more devices for exact positioning, alignment, and fixing of the tool. A suitable device for carrying out these operations is disclosed in SE-A-8604505-1. A device according to the above may consist of a mechanism with two or more symmetrical fingers with hook-shaped ends, which mechanism is attached to a sleeve which is urged by a motor-driven screw, the hooks of the fingers being guided towards an inner and an outer funnel. Upon movement of the fingers towards the valve tree, the fingers open so as to create a sufficient gap to close around a retraction cone mounted on the valve tree. By reversing the finger movement away from the valve tree, first a substantially radial movement of the fingers for closing around the retraction cone is obtained by the mechanism. Thereafter, a substantially axial movement is obtained, whereby the inner funnel is drawn towards the cone, which, after additional movement, is urged towards the innermost part of the funnel. This results in a precise positioning and fixing of the alignment devices and of the moment producing tool fixed to these devices. Since the tool for applying a moment on the castellated valve nut is now correctly positioned, this part of the replacement procedure can now commence. A suitable tool for carrying out the replacement procedure may consist of a ring rotatable in a bearing housing, the ring having internal splines for engaging the splines of the castellated nut and having external splines for engaging diametrically positioned drive devices for the rotary motion. Since this tool is fixed to the valve tree by means of the alignment device, the telescopic arm will not be loaded with any mechanical stresses in connection with the release or tightening of the castella ted nut. After the insert unit with the castellated nut has been detached from the valve housing, the alignment devices are opened, and the carriage with the tool, the alignment devices and the detached insert unit is guided on the telescopic arm, resting on the lug, out to the manipulator. The further replacement procedure may comprise lifting the manipulator towards the surface for removing the defect insert unit and attaching a new insert unit in the tool. Alternatively, an operational insert unit may be stored in the manipulator and be placed in the tool with the aid of gripping arms included in the manipulator. The method for mounting the new insert unit in position comprises the same steps as have already been described with reference to the telescopic arm, the movement of the carriage, the alignment and fixing of the tool, the development of moments, etc. The method and device according to the invention will now be described in detail with reference to the accompanying drawing, the single figure of which shows a valve tree 17 of the above-mentioned kind having mounted thereon two insert valve assemblies 22 and 23 with respective castellated nuts 24 and 25, as well as insert units 26 and 27. The figure further shows a manipulator 1 with a telescopic arm 15, 16, a carriage with retraction, aligning and fixing devices 32, 33 and 34, as well as a moment producing tool 31. The fundamental construction of the manipulator 1 consists of a parallelepipedic frame structure which can be lifted and lowered by means of a surface-based sheave 2 and a hoisting cable 3, attached to the upper part of the manipulator 1. Via guide wires 4 and 5, acting as guidelines running in respective guide frames 6 and 7 attached to the manipulator 1, the manipulator 1 is guided, depending on which valve is to be repaired, towards a pre-determined position on the wellhead. The manipulator 1 is fixedly mounted on a beam 8 having guide slots 9 and 10 for receiving the guide posts 11 and 12. The manipulator 1 can be positioned vertically by means of spacing sleeves 13 and 14 on the guide posts 11 and 12 and laterally by lateral displacement prior to being fixed on the beam 8. The manipulator 1 comprises a remotely operated telescopic arm 15 and 16 capable of being steered towards a valve tree 17. Displaceably mounted on the telescopic arm 15, 16 is a carriage 18 which, in order to provide a clearer view, is shown detached from the arm. The suspension and guiding device of the carriage 18 in the telescopic arm 15, 16 consists of the rail 19 placed on the top side of the carriage 18. As mentioned above, the telescopic arm 15, 16, with the carriage 18 still mounted in the manipulator 1, is brought towards the valve tree 17. The position of the manipulator 1 at the pre-determined location, in relation to the valve in question, now allows a hook 20 at the tip of the telescopic arm 15, 16 to be brought into engagement with a lug 21 on the valve tree 17. In the example shown in the figure, the valve tree 17 supports at least two valves 22 and 23 with castellated nuts 24 and 25 and replaceable insert units 26 and 27. The valve tree 17 is fixedly mounted on the wellhead by means of four guide posts belonging to the SPS system, three of which (28, 29 and 30) are shown in the figure. These guide posts may replace the guide posts 11 and 12. When the hook 20 of the telescopic arm 15, 16 has been brought into engagement with the lug 21 on the valve tree 17, the carriage 18 may be brought, via slots in the arm and the rail on the upper side of the carriage, from the manipulator 1 and towards the valve tree 17. As will also be clear from the above disclosure of the principle of the invention, the carriage 18 includes devices for aligning, retraction and fixing the carriage 18 as well as a tool 31 for releasing and tightening, respectively, and for threading in and out, respectively, the castellated nut of the valve. As will be clear from the above, the positioning devices are formed so as to have a retracting and a fixing function. In the example shown in the figure, the carriage 18 includes three such devices, shown at 32, 33 and 34. Corresponding retraction cones 35, 36 and 37 are positioned on the valve tree 17. The location of the lug 21 and these cones in relation to the valve 22 is such that when the telescopic arm 15, 16 and the carriage 18 with their respective opposite attachment devices have been mounted into engagement, the moment-producing tool 31 mounted in the carriage 18 has the correct position to enable it to grapple the castellated valve nut. Once the cones 35, 36 and 37 have firmly engaged, the load on the telescopic arm 15, 16 via the hook 20 and lug 21 ceases. Corresponding lugs and guide cones (not shown for valve 23) exist for all the valves on the valve tree. By remote control, the moment-producing tool is then brought into engagement with the castellated valve nut, whereupon a remote-controlled moment for releasing and threading out the nut is applied. This enables the insert unit of the valve to be unscrewed and be replaced in a corresponding manner.

Claims: 1. A system for replacing an insert unit (26) included in an assembly located at a remote distance below a location from where the assembly can be serviced and controlled by manpower, for example an insert valve assembly (22) belonging to a subsea production system for oil and gas, with a manipulator (1) characterized in that there area hoisting cable (3), adapted to raise and lower the manipulator to the desired depth,guide wires (4, 5), acting as guidelines passing through guide frames (6, 7) fixed to the manipulator, and adapted to be positioned at the desired location on the floor carrying the assembly, for example the ocean floor,a beam (8), on which the manipulator is mounted, the beam having guide slots (9,10) intended to receive guide posts (11, 12), which are placed on the floor carrying the assembly, for example the ocean floor, and which are provided with spacing sleeves (13, 14) to obtain the proper height for the manipulator above said floor,a remotely operable telescopic arm (15, 16), being built in the manipulator and provided with a hook (20) at the end of the arm,a built-in carriage (18) movable on the telescopic arm, said carriage comprising a moment producing tool (31) as well as aligning, retraction and fixing devices (32, 33, 34) for said carriage and said tool,that the assembly (22) with its insert unit (26) is mounted on a support unit, for example a valve tree (17), which has a lug (21) for receiving the hook of the telescopic arm, andguide cones (35, 36, 37) for aligning, retraction and fixing devices mounted on the carriage,that there is a nut (24) by which the insert unit can be screwed to and unscrewed from, respectively, the rest of the insert unit assembly,and that the moment producing tool is formed so as to engage and grapple said nut of the insert unit. 2. Method to operate a system according to Claim 1, characterized by the following sequential steps:- by means of the hoisting cable and guide wires, the manipulator is lowered down from its upper position towards the floor carrying the assembly, for example the ocean floor, and is positioned via the beam, the guide slots, the guide posts and the spacing sleeves so that the tool carried by the carriage arrives in front of the insert unit assembly whose insert unit is to be replaced,- the telescopic arm of the manipulator is brought towards a support unit, for example a valve tree, supporting said insert unit assembly, so that the hook of the arm is secured to the lug on the support unit,- the carriage is moved towards the support unit,- the aligning, retraction and fixing devices in the carriage are manoeuvred into en gagement with the respective retraction cones on the support unit, - the moment producing tool is guided towards the insert unit assembly so as to engage and grapple the nut of the insert unit,- via the moment producing tool, a releasing moment is applied on the nut of the insert unit,- via the moment producing tool, a moment is applied for threading the insert unit out of the rest of the insert unit assembly,- the aligning, retraction and fixing devices in the carriage are detached from their respective retraction cones on the support unit,- the carriage with the insert unit is moved back to the manipulator,- the disengaged insert unit is replaced by a new insert unit,- the carriage with the new insert unit is again moved towards the support unit,- the aligning, retraction and fixing devices in the carriage are manoeuvred into engagement with the respective retraction cones on the support unit,- the moment producing tool is manoeuvred towards the remaining part of the insert unit assembly, the new insert unit being inserted into said part,- via the moment producing tool, a moment is applied on the nut of the insert unit for threading in the insert unit,- via the moment producing tool, a fastening moment is applied on the nut of the insert unit,- the moment producing tool is withdrawn from the nut of the insert unit, - the aligning, retraction and fixing devices in the carriage are detached from their respective retraction cones on the support unit,- the carriage is moved back to the manipulator,- the hook on the telescopic arm is disengaged from the lug on the support unit,- the telescopic arm is moved back to the manipulator, and- the manipulator is raised back to its initial upper position, for example the surface of the sea, by means of the hoisting cable and the guide wires. 3. Method according to Claim 2, characterized in that after the retraction of the carriage carrying the disengaged insert unit to the manipulator the replacement of the disengaged insert unit by a new insert unit is continued by the following steps- raising the manipulator to its initial upper position, for example the surface of the sea, by means of the hoisting cable and the guide wires,- replacing the disengaged insert unit by a new insert unit, and- lowering the manipulator with the aid of the hoisting cable and the guide wires towards the floor carrying the assembly, for example the ocean floor, and positioning it in front of the insert unit assembly to be replaced. 4. Method according to claim 2 or 3 with a manipulator being provided with manoeuvrable gripping arms and at least one operational insert unit, characterized in that the replacement of the disengaged insert unit by a new insert unit is carried out with the aid of the gripping arm as follows: - the disengaged insert unit is detached from the moment producing tool, and- a new insert unit is inserted into the moment producing tool.

Inventors: ANDERSSON, ROLF JACK, HOEGLUND, KJELL, HOYLAND, SIGBJORN, HUSEBYE, RAGNAR, LINDLAND, HANS, MONG, TORE, NESSE, ERLING, NILSSON, TORE, PAJES, CHAJKIEL, Höglund, Kjell
Applicants: AB ASEA-ATOM, STATOIL
Application year: 1987
Main classification: E21B41
IPC codes: B63C11, E21B41