WELLS

Abstract: A workover control system (10) has a hydraulic power unit (30) and an electrical signal control unit located on a vessel and a control module (36) located proximate to a subsea well (14). An electrohydraulic umbilical (32) transmits electrical and hydraulic power and signals from the vessel to the control module (36). During workover of the well, workover devices (12) are operated by hydraulic signals provided by an electrohydraulic switch in the control module. The hydraulic signals are produced in response to electrical signals from the vessel.

Description: WELLS This invention relates to workover of wells. It is particularly, but not exclusively, related to installation of and intervention into subsea wells, for example subsea production wells. An oil or gas well, hereinafter referred to as a well, is constructed by drilling a borehole and then lining it with a steel casing. The upper end of the well, that is the part of the well accessible at the surface, for example on land or on the seabed, is referred to as the wellhead. In the following, the terms run and retrieve have specific meanings. When used in relation to equipment, run means to install the equipment in a well (even if only temporarily) and retrieve means to bring the equipment out of the well and up to the surface. For a subsea well, surface means the subsea wellhead. A conduit for carrying extracted fluids from a lower region of the well to the surface, referred to as a completion, is inserted into the casing and extends from the surface to the lower region where extraction occurs. The completion is also referred to as production tubing or a tubing string. The completion is supported from an upper end by a tubing hanger which rests on, and is locked into place on, the wellhead. The process of placing the tubing hanger on the wellhead, inserting the completion into the casing and fitting a flow control device referred to as a Christmas tree to the wellhead so that the well is ready for production is a workover process referred to as installation. This process may also include testing seals and joints between the wellhead and the tubing hanger, the tubing hanger and the completion and between the Christmas tree and the wellhead. The Christmas tree is locked into place on the wellhead and controls operation of the well. In a so-called "conventional" Christmas tree the completion is placed in the wellhead before the Christmas tree is locked into place on the wellhead. Another type of Christmas tree, referred to as a "horizontal" Christmas tree (or a spool or lateral tree), is locked into place on the wellhead before the completion is installed in the well. The completion is run into the production casing and thus into the well through the Christmas tree. An advantage of a horizontal Christmas tree is that a part of the completion can be changed without moving the Christmas tree. Since a Christmas tree can weigh more than twenty tonnes moving it is undesirable. Once the well is on-stream (that is in production), it may be necessary for another workover process referred to as intervention to take place. This requires production of the well to cease and a tool or a device to be run downhole, typically down the completion. This includes running sensing apparatus to monitor well temperature and pressure or to monitor downhole formations, retrieving and re-installing sensing apparatus, operating a zone control valve, running remote viewing apparatus such as a TV camera to view tubing damage or investigate other matters, locating and retrieving objects dropped down the well and running downhole gas lift assemblies. According to a first aspect of the invention there is provided a workover control system comprising a hydraulic power unit an electrical control unit an electrohydraulic umbilical and a workover assembly comprising a plurality of workover devices characterised in that electrohydraulic switch means is also provided which switches hydraulic power to operate at least one of the workover devices in response to receiving signals from the electrical control unit. Preferably a plurality of workover devices are controlled by the electrohydraulic switch. In this embodiment the electrohydraulic switch supplies hydraulic power to one or more of the workover devices as a consequence of being instructed to do so by one or more electrical switch signals. Preferably there is a single umbilical. Most preferably the same umbilical is used to control at least one workover device during an installation operation and an intervention operation. Whilst it is convenient for the electrohydraulic umbilical to be a single umbilical, it may comprise a plurality of umbilicals bundled together or otherwise. For example, hydraulic power and electrical signals may pass down separate umbilicals. Preferably the electrical signal control unit receives a control instruction from control means instructing the or each workover device to be operated. This may include switching the workover device on or off, operating valves or ports to open or close or causing it to lock onto or unlock from another device. Preferably the or each workover device provides a function which enables workover to occur. The or each workover device is selected from a retainer valve, a subsea test tree, a tubing hanger running tool, a tubing hanger, and a lower marine riser package. According to a second aspect of the invention there is provided electrohydraulic switch means for switching hydraulic power to at least one workover device in a plurality of workover devices. Preferably an electrical signal produced by the electrical signal control unit and conveyed to the electrohydraulic switch by the electrohydraulic umbilical controls at least one valve to provide hydraulic power to the or each workover device. Preferably in the switch hydraulic power is switched through individual directional control valves. Preferably the switch receives hydraulic power through a single hydraulic supply line. Most preferably it receives hydraulic power through two hydraulic supply lines. One supply line may supply hydraulic fluid at low pressure and the other line may supply hydraulic fluid at high pressure. Preferably the system is used to workover a horizontal Christmas tree. Alternatively it is used to workover a conventional Christmas tree. Preferably the system is used to workover wells which have subsea wellheads. Preferably the electrohydraulic switch contains an electrical module. Preferably the electrical module receives an electrical control signal to operate a particular workover device and activates one or more electrical actuators to operate a particular valve or group of valves to route hydraulic power to operate one or more workover devices. An embodiment of the invention will now be described by way of example only with reference to the accompanying drawings in which: Figure 1 shows a workover control system; Figure 2 shows a completion being installed in a well; Figure 3 shows a well intervention; Figure 4 shows detail of a Christmas tree during well intervention; Figure 5 shows an exploded view of a riser control module; Figure 6 shows a perspective view of the module of Figure 5; Figure 7 shows a hydraulic schematic of the module of Figures 5 and 6; Figure 8 show an electronic schematic of the module of Figures 5 and 6; and Figure 9 shows an alternative electronic schematic of the module of Figures 5 and 6. Figure 1 shows a workover control system 10 being used in the installation of a completion 12 into a well 14. The workover control system 10 is used to control operation of a Christmas tree during workover, that is installation of a completion or intervention into the well. The well 14 has a wellhead 16 on which is located a horizontal Christmas tree (XT) 18. Located on the XT 18 is a blow-out preventer system (BOP) 20 which supports a lower marine riser package (LMRP) 22. The LMRP 22 is disposed at a lower end of a BOP riser 24 down which the completion 12 is lowered. It is introduced into the well through the LMRP 22, BOP 20 and XT 18. The BOP riser 24 extends from a vessel, such as a ship or an oil rig, (not shown) to provide a conduit through which the completion 12 travels from the vessel to the well 14. As the completion is lowered into the well, it is supported by an installation assembly 25 at the end of a completion riser 26 such as a monobore riser. The completion riser 26 is used as a landing string for running the completion 12 into the wellhead 16. It also provides a vertical pressure retaining point of entry from the surface into the XT 18 during installation of the completion. The combination of the completion 12, the installation assembly 25 and the completion riser 26 is called a completion string. The installation assembly 25 comprises a plurality of individual workover devices, or packages, which are discussed below. By workover devices is meant devices which operate during workover to assist in installation of the completion and intervention into the well. The devices are controlled by a workover control station 28 and a hydraulic power unit (HPU) 30 which are both located on the vessel. In addition to hydraulic power generation means, and means to generate hydraulic control signals, the HPU 30 also comprises an electrical power unit and a control system. Control of the workover devices is via an umbilical 32 extending from a reel 34 on the vessel. It should be noted that the workover devices of the installation assembly 25 are each provided with a bore so that, once connected together, the installation assembly 25 has a continuous bore through which fluid can pass, from the completion 12 to the completion riser 26 and thence to a surface test tree. It is usual to perform a well test after installation to make sure that the well is operating properly. It should also be noted that the completion 12, installation assembly 25 and the completion riser 26 form a long continuous conduit. The installation assembly 25 has a completion riser control module (RCM) 36, a retainer valve (RV) 38, a subsea test tree (SSTT) 40, a tubing hanger running tool (THRT) 42 and a tubing hanger (TH) 44. These workover devices are discrete and separate units which have been assembled and joined together to form the installation assembly 25. The RCM 36 is connected to the completion riser 26 by a threaded connection. The RV 38 is a safety valve which retains pressure and fluid within the completion riser 26 in the event that the connection between the RV 38 and the SSTT 40 is broken. This may occur if the vessel moves off-station. This can occur during any workover operation. The SSTT 40 is used to contain pressure in the completion in the event that the completion riser 26, RV 38 and RCM 36 are retrieved. Installation occurs as follows. The XT 18 is carried down into place on the wellhead 16 by a tree running tool (TRT) (not shown). A hydraulic command from the HPU 30 on the vessel causes the XT 18 to lock to the wellhead 16. The connection and seal between the XT 18 and wellhead 16 are tested. The TRT then returns to the vessel. The BOP riser 24 (incorporating the BOP 20 and LMRP 22) is placed on the XT 18 and then the completion string (comprising the completion 12, the installation assembly 25 and the completion riser 26) is lowered so as to run the completion 12 through the BOP riser 24 and then the XT 18 and then into the well 14. Operation of the XT 18 is controlled by a workover subsea control module (SCM) 66. The TH 44 is locked onto the THRT 42 and carried by it into the wellhead 16. When the TΗ 44 is located and locked into place in the wellhead 16, the THRT 42 is unlocked from the TH 44. When in place, the TH 44 supports the completion 12 in the well 14. It also allows for access by wireline services into the completion 12. The umbilical 32 provides a hydraulic supply 70 and an electrical supply 72 to the RCM 36. The RCM 36 provides hydraulic supplies 70a, 70b and 70c to the RV 38, SSTT 40 and THRT 42 respectively. It provides an electrical control signal 72a which passes through the THRT 42 and is used to interrogate downhole pressure and temperature sensors. Data provided by such sensors is in the form of an electrical communication signal 74 which passes through the THRT 42 directly to the vessel or is relayed by the RCM 36. The RCM 36 also sends an electronic signal to the surface which indicates whether the hydraulic supply has reached the required pressure to operate completion tools. Hydraulic and electrical supplies 70d and 72b travel from the TH 44 downhole to control and are used to monitor a surface controlled sub-surface safety valve (SCSSV) and downhole pressure and temperature sensors. Located in the vessel at the top of the completion string is a lubrication valve (LV). This is not shown in Figure 1. Its purpose is to permit the passage of wireline services into the well 14. A surface test tree (not shown) is located on the vessel, above the LV. When the completion 12 is correctiy located in the well 14, the well is tested to make sure that hydrocarbons in the well are under sufficient pressure to flow from the well. Valves are opened in the LV, RV 38 and SSTT 40 to allow the hydrocarbons to flow up the completion 12 and through a surface test tree present on the vessel. Once testing has been satisfactorily completed, the valves in the LV, RV 38 and SSTT 40 are closed, the THRT 42 is disconnected from the TH 44 and the completion riser 26 is retrieved together with the majority of the installation assembly 25. The TH 44 is left in place in the wellhead 16. The TH 44 is then sealed with a crown plug and internal tree cap to prevent hydrocarbons from flowing out of the well. Also shown in Figure 1 are emergency shut down panels 120. These are provided on the vessel at suitable locations such as the driller's station and the surface test tree operating station to enable shut-down of the well in the event of an emergency such as leakage of hydrocarbon (oil or gas) on the vessel. Figure 2 is another illustration of installation of a completion 12 into a horizontal well. Features which are common to Figures 1 and 2 have been given corresponding reference numerals. The lubrication valve (LV) mentioned above is shown designated by reference numeral 48. The LV 48 is controlled via an umbilical 54 supplied by a reel 56. During workover, signals from the HPU 30 pass down an umbilical 50 and are used to operate the workover SCM 66. The umbilical 50 is supplied by a reel 52. Commands from the workover control station 28 are supplied down electrohydraulic umbilical 32 to the RCM which then operates appropriate workover devices to enable installation to occur. Following installation, when the BOP 20 and LMRP 22 are retrieved, the umbilical 50 is also removed and replaced by a production jumper. This operates a production subsea control module (SCM) 46 (shown in Figure 4) which controls the XT 18 during production. Once installation workover is complete the well is ready to be brought on-stream for production to begin. Figure 3 shows an intervention into the well after production has been occurring. The SCSSV (not shown) is closed. This stops production, by preventing hydrocarbons flowing into the XT 18. The completion riser 26 is used to lower an intervention assembly 58 onto the XT 18. The intervention assembly 58 comprises, in order from top to bottom, the RCM 36, the RV 38, a stress joint 60, the LMRP 22 and the SSTT 40. The stress joint 60 is simply a joint provided to accommodate relative movement between the completion riser 26 and the XT 18. An LV 48 is located at the top of the completion string. The intervention assembly 58 is analogous to the installation assembly 25 as shown in Figure 1. They are both located at the end of the completion riser 26 and their functions are respectively to provide control of the completion during intervention and installation. The installation assembly 25 additionally has the function of supporting the completion during installation. Intervention equipment, such as wireline tools and services, is passed down the completion riser 26 and passes through open valves in the LV 48, the RV 38, the stress joint 60, the LMRP 22 and the SSTT 40 and then enters the well. It should be noted that the same umbilical, umbilical 32, can be used both in installation and intervention. The foregoing describes the invention applied to workover of a horizontal Christmas tree. It can also be used in the workover of conventional Christmas trees. This is described in relation to Figure 4. This shows a topside control system similar to that of Figure 1 located on a vessel being used in workover of a conventional Christmas tree. Installation is shown as Figure 4a in which the umbilical 32 from the reel 34 is attached to the installation assembly 25. Intervention is shown in Figure 4b in which the umbilical 32 from the reel 34 is attached instead to the XT 18 via workover equipment. Referring to Figure 4a installation is generally similar to the installation procedure described above in relation to horizontal wells and so will not be described here. Of course the major difference is that a completion is installed in the well using controls transmitted along the umbilical 32 and then the XT 18 is locked onto the wellhead, again following a command which is transmitted along the umbilical 32. Referring to Figure 4b, intervention into a conventional well will now be described. Located on the XT 18 is the LMRP 22. Located on the LMRP 22 is an emergency disconnect package (EDP) 63. The completion riser 26 terminates into the EDP 63. The RCM 36 is not used in this configuration. The umbilical is connected direcdy to the EDP 63. The umbilical 32 from the reel 34 is universal and is used both in installation, as shown in Figure 4a, and intervention, as shown in Figure 4b. Therefore, a single umbilical is used in these two operations. According to the invention a single umbilical is used in these two operations in horizontal Christmas trees. The HPU 30 receives pneumatic and electrical supplies from the workover vessel and converts them into hydraulic and electrical power supplies and electrical control signals. The power and control signals are combined into an umbilical jumper 64 which runs to the reel 34. The hydraulic supplies and electrical signals then travel along the umbilical 32 to the workover SCM 66 where they are switched to provide hydraulic control signals to operate various hydraulically actuated latches and valves on the EDP 63, LMRP 22, XT 18 and downhole SCSSV. The system also enables testing of various seals at connections between workover devices and enables signals from pressure and temperature transmitters mounted on the XT 18 and downhole to be connected to a monitoring system in the HPU 30 on the vessel. The reel 34 is powered and is used to deploy and retrieve the workover umbilical 32 and the tubing hanger running tool umbilical, as required, in a controlled and safe manner without damage. The reel 34 receives pneumatic power from an external source via the umbilical jumper 64. An electrical control circuit controlled by a THRT control unit 62 monitors the status of control valves in the RCM 36 to check that they are supplying and not supplying hydraulic fluid as commanded. For conventional Christmas trees the EDP 63 and LMRP 22 are located below the completion riser. Control of the EDP 63 and the LMRP 22 during a light workover operation, for example wireline downhole intervention, is shared between two subsea control modules, one being the production SCM 46 on the XT 18 which controls all of the functions normally under control during production and the other being the workover SCM 66 which controls additional functions associated with the EDP 63 and LMRP 22 such as connections between the XT 18 and the wellhead and the EDP 63 and the XT 18. It is used to lock and unlock these connections and to test their integrity when they are locked. Electrical flying leads 68 installed by a remotely operated vehicle (ROV) connect the LMRP 22 both to the production SCM 46 and the workover SCM 66. They are used to monitor tree and downhole instrumentation. The XT 18 can be controlled by a hydraulic supply from the production SCM 46 or a hydraulic supply from the workover umbilical 32. A three-way, two-position isolation valve located on the XT 18 switches between each of these hydraulic supplies. The valve is switched by an ROV. The RCM 36 is shown in Figure 5 in exploded view. It is a discrete section of the installation assembly 25, adjacent to the RV 38. It is an electrohydraulic package, supplied from the vessel at the surface with hydraulic and electrical supplies. Two low pressure (LP) hydraulic supplies are connected to connectors 80 in a manifold block 88 where they are consolidated together by means of a shuttle valve. Two high pressure (HP) hydraulic supplies are connected to connectors 82 in the manifold block 88 where they are consolidated together also by means of a shuttle valve. The hydraulic connectors 80 and 82 are l A" female JIC fittings. They are located at the top of the RCM 36. Two pairs of electrical control wires and two pairs of electrical power wires are connected to electrical connectors 84 and 86 respectively. Electrical conduits run from the electrical connectors 84 and 86 and into the manifold block 88. The electrical connectors 84 and 86 are manually mateable bulkhead mounted underwater electrical connectors. It should be noted that the duplication of the LP and HP supplies, and electrical power and control wires (that is the provision of pairs of all of these features), is for dual redundancy. Therefore in the event of failure of a main supply, a spare is provided. The RCM 36 has a steel casing comprising a pair of steel covers 90 and a baseplate 92. The covers 90 and the baseplate 92 are bolted onto the manifold block 88 to protect various hydraulic fittings. The manifold block 88 itself provides a support on which to locate the covers 90 and the baseplate 92. The covers 90 and the baseplate 92 are provided with ring seals at their joints to provide a leakproof seal to prevent escape of a dielectric oil which is enclosed within the casing. A pressure and temperature compensator is fitted within the casing to accommodate any changes in fluid volume due to changes in temperature and hydrostatic pressure. The pressure and temperature compensator is a rubber bladder located and covering a port in the casing. The rubber bladder is a barrier between the dielectric oil on the inside of the casing and production fluid on the outside of the casing, for example brine located in the BOP riser 24. As the RCM passes down the BOP riser 24 static pressure in the production fluid increases. This acts on the dielectric fluid through the bladder and thus pressure is equalised. A pressure valve is installed in the casing at its lower end to vent dielectric fluid in the event of malfunction of the pressure and temperature compensator or in the event of leakage of hydraulic fluid. Suitable inlet and outlet ports for the dielectric fluid are provided in the casing. Cathodic protection in the form of sacrificial anodes is provided within the casing to protect the interior of the RCM 36 against any production fluid which penetrates into it. Telemetry readbacks from downhole pressure, temperature and choke position sensors are made through two telemetry electrical connectors (not shown) which are located at the bottom of the manifold block 88. Threaded connections at the top of the RCM 36 provide attachment to the completion riser 26 and at the baseplate 92 to an adjacent workover device. The baseplate 92 is deep enough to provide protection for eighteen V " female JIC hydraulic fittings 91 and the two telemetry electrical connectors. Of the JIC fittings, sixteen are for LP hydraulic supply lines and two are for HP hydraulic supply lines. The manifold block 88 comprises a machined gallery carrying eighteen directional control valves (DCVs) 95, sixteen of which are LP function and two of which are HP function. The RCM 36 also contains an electrical or electronics module which is described further below with reference to Figures 8 and 9. The assembled RCM 36 is shown in Figure 6. It is generally cylindrical in shape having a single axial bore running through it from an upper end to a lower end. It should be noted that the single bore is appropriate for use with a monobore completion riser. Two bores would be provided if a dual bore completion riser was used. The purpose of the bore is discussed above. As mentioned above, the RCM 36 is provided with pairs of LP and HP hydraulic supplies. These are shown on Figure 7 as two LP hydraulic supplies from the connectors 80 and two HP hydraulic supplies from the connectors 82. Pressure transducers 93 are used to measure the pressures of the pairs of hydraulic supplies before they are each consolidated. The pressure transducers 93 can be seen in Figure 5. In an alternative embodiment a pressure transducer can be provided for each line controlled by a DCV. The signals from the pressure transducers 93 are multiplexed in the electrical module of the RCM and returned to the workover control unit 28 by means of, for example, twisted pair wires. Each hydraulic supply is filtered by its own supply line filter 94 each of which is a 20 micron assembly. These filter the supplies before they are consolidated. The filters are all contained in a filter manifold which is a sub-assembly bolted to the manifold block 88. This filter manifold is integral with the internal structure of the manifold block 88 of the RCM 36. The filters 94 are part of a valve sub-assembly comprising check valves to prevent reverse flow through the filter and allow reverse flow around the filter. A forward check flow valve is provided to allow forward flow in the event of the filter becoming clogged. In this embodiment these check valves work at a differential pressure across the filter of 1.2 to 3.0 bar. Each pair of the LP and HP hydraulic supplies (from connectors 80 and 82) is consolidated into a single hydraulic supply through shuttle valves 96 which are fitted to the lower end of the manifold block 88. The filtered and consolidated hydraulic supplies are then connected to distribution galleries within the hydraulic manifold block 88. Referring specifically to Figure 7, this shows a schematic of the hydraulic system of an RCM 36. It should be noted that its functionality is dependent on its particular purpose. For example sixteen rather than eighteen DCVs may be present. The system is of an open loop design with returned hydraulic fluid being vented to the annulus or to the sea depending on operating mode via O-ring check valves 100 and 102 mounted in the baseplate 92. Separate vent circuits are provided for each of the HP and the LP hydraulic supplies venting through the check valves 100 and 102 respectively. HP hydraulic supply is provided to two HP DCVs 104 and 106 which control the operation of the SCSSV. LP hydraulic supply provides LP pilot pressure to all of the DCVs 95 and function line pressure to the sixteen LP DCVs 108. The function line outputs from all of the DCVs 95 have flow controllers 110 which enable valve profiling to take place. DCV outputs pass through the hydraulic connectors in the baseplate 92 to operate workover devices. For example, the DCV outputs may open and close the RV 38, open and close valves on the SSTT 40, latch or unlatch the SSTT 40 to and from another workover device, lock and unlock the TH 44 onto the wellhead 16 or the XT 18 and latch and unlatch it onto the THRT 42. Figure 8 illustrates schematically part of the electronics module of the RCM 36. This module receives incoming electrical control signals by means of, for example, modem 121. Microprocessor 122 translates the serial messages from the modem as simple shut or open commands for the DCVs 95. The microprocessor 122 directs these commands to the appropriate solenoid driver boards, such as board 123 (only one solenoid driver board is shown in this diagram for clarity), in order to control the required DCV, or group of DCVs. The DCVs 95 are solenoid operated three-way, two-position valves. Energising the solenoid directs hydraulic fluid to the function line and thence to the associated workover device. For example, the output of DCV 95 is arranged to activate an actuator 126 to operate a valve 127, in order to route hydraulic power to a workover device. Sensors 124 may be provided to monitor the DCV 95 and/or the associated workover device. Sensor signals are sent to the microprocessor 122 via a 4-20 milliamp board 125. Signals from the sensors are then transmitted, by means of the modem, for example to the vessel. Figure 9 illustrates an alternative electronic configuration to that shown in Figure 8. In this embodiment, the microprocessor 122 is arranged merely to process signals from the sensors 124. In order to translate the incoming messages to the modem 121 into commands for the DCVs, a programmable logic array (PLA) 128 and associated circuitry is provided. The PLA 128 decodes the modem output commands and routes them to the appropriate DCVs 95 via their respective solenoid drivers 123. The PLA is an array of hard wired logic devices, typically low cost. This arrangement removes total dependence on the correct operation of the microprocessor 122 to effect control of the DCVs 95, and hence improves reliability. The PLA 128, and any interface circuitry required, could be mounted on the microprocessor board in order to share its packaging and power supply interfaces. A solenoid must be continuously energised to maintain the hydraulic supply to its respective workover device. Loss of the electrical signal causes the function line to de- pressurise. Purely hydraulic actuators which require a first hydraulic signal to open followed by a second hydraulic signal to close, for example the actuators to lock and unlock the tubing hanger running tool, remain "as is" on loss of hydraulic power. Actuators which are provided with return springs, for example the SSTT valves, close on loss of electrical or hydraulic power. Monitoring functions and test lines from the THRT control unit 62 pass straight through the RCM 36 and go to the appropriate workover device. Therefore they either terminate at upper and lower riser interface/connection flanges between adjacent workover devices or go directly into the appropriate workover device. The RCM 36 connects and disconnects connections between workover devices. It also enables downhole mounted sensors to be monitored. It operates control and safety valves downhole. The use of the RCM, which uses a single low pressure supply and a single high pressure supply, duplicated for redundancy of course, to switch hydraulic fluid to all of the workover devices provides a workover system which is particularly suitable for operating in deep water, such as 1000 to 4000m. Effectively the RCM 36 is a demultiplexer of control signals which operates various of the workover devices. By decoding appropriate address information, whether electrically or hydraulically addressed, the RCM 36 operates the appropriate workover device.

Claims: CLAIMS 1. A workover control system comprising a hydraulic power unit an electrical control unit an electrohydraulic umbilical and a workover assembly comprising a plurality of workover devices characterised in that electrohydraulic switch means is also provided which switches hydraulic power to operate at least one of the workover devices in response to receiving signals from the electrical control unit. 2. A workover control system according to claim 1 characterised in that the workover assembly is connected to the end of a completion riser to form a completion string. 3. A workover control system according to claim 1 or claim 2 characterised in that the electrohydraulic switch means is part of the workover assembly. 4. A workover control system according to any preceding claim characterised in that the workover assembly is an installation assembly. 5. A workover control system according to any of claims 1 to 3 characterised in that the workover assembly is an intervention assembly. 6. A workover control system according to any preceding claim characterised in that the electrohydraulic switch means is an in-line unit in the workover assembly. 7. A workover control system according to any preceding claim characterised in that the workover assembly and the electrohydraulic switch means are connected together to form a common conduit through which fluid can flow. 8. A workover control system according to any preceding claim characterised in that the electrohydraulic switch means comprises a cental node which receives all of the hydraulic supplies used in operating the workover devices. 9. A workover control system according to any preceding claim characterised in that the electrical signals produced by the electrical signal control unit and conveyed to the electrohydraulic switch means by the electrohydraulic umbilical controls at least one valve to provide hydraulic power to the or each workover device. 10. A workover control system according to any preceding claim characterised in that the same umbilical is used to control at least one workover device during an installation operation and an intervention operation. 11. A workover control system according to any preceding claim characterised in that the or each workover device is operated to carry out an action selected from a group consisting of switching the workover device on or off, operating valves or ports associated with it to open or close and causing it to lock or unlock from another device. 12. A workover control system according to any preceding claim characterised in that in the electrohydraulic switch means hydraulic power is switched through individual directional control valves. 13. A workover control system according to any preceding claim characterised in that the electrohydraulic switch means receives hydraulic power through two hydraulic supply lines one supplying hydrauUc fluid at low pressure and the other supplying hydraulic fluid at high pressure. 14. A workover control system according to any preceding claim characterised in that the system is used to workover a horizontal Christmas tree. 15. A workover control system according to any of claims 1 to 13 characterised in that the system is used to workover a conventional Christmas tree. 16. A workover control system according to any preceding claim characterised in that the system is used to workover wells which have subsea wellheads. 17. A workover control system according to any preceding claim characterised in that the electrohydraulic switch comprises an electrical module which receives the electrical control signals to operate a particular workover device and activates one or more electrical actuators to operate a particular valve or group of valves to route hydraulic power to operate one or more workover devices. 18. A workover control system according to claim 17 characterised in that the electrical module includes a microprocessor arranged to activate one or more electrical actuators in dependence on the received electrical control signals. 19. A workover control system according to claim 17 characterised in that the electrical module includes an arry of logic devices arranged to activate one or more electrical actuators in dependence on the received electrical control signals. 20. A workover control system substantially as described herein with reference to Figures 1 to 7 of the accompanying drawings. 21. Electrohydraulic switch means for switching hydraulic power to at least one workover device in a plurality of workover devices. 22. Electrohydraulic switch means according to claim 20 characterised in that it is adapted to be incorporated into a workover assembly comprising the plurality of workover devices. 23. Electrohydraulic switch means according to claim 20 characterised in that the workover assembly comprises a common conduit through which fluid can flow. 24. Electrohydraulic switch means for switching hydraulic power to at least one workover device substantially as described herein with reference to Figures 1 to 9 of the accompanying drawings.

Inventors: JONES DAVID JOHN, STEWART DAVID HENRY, WINCHESTER JOHN NIGEL, JONES, DAVID, JOHN, STEWART, DAVID, HENRY, WINCHESTER, JOHN, NIGEL
Applicants: ABB OFFSHORE SYSTEMS LTD, JONES DAVID JOHN, STEWART DAVID HENRY, WINCHESTER JOHN NIGEL, ABB OFFSHORE SYSTEMS LIMITED, JONES, DAVID, JOHN, STEWART, DAVID, HENRY, WINCHESTER, JOHN, NIGEL
Application year: 1999
Main classification: E21B
IPC codes: E21B33, E21B41