System for Manipulating Subsea Equipment and Controlling a Subsea Barrier System

Abstract

-a subsea pump (30) arranged in fluid connection with the well interior (38, 39) providing a closed system suitable for pressure and flow regulation and establishing a temporary fluid flow between the subsea pump and the well interior, -a fluid source (31) supplying fluid to the subsea pump, wherein the subsea pump has a mode of operation for regulation of the flow and/or pressure between the pump and the well interior to operate equipment arranged in the well, -a safety control system for controlling shut down of a valve arrangement in a subsea position, which safety control system is also arranged in a subsea position and comprises a control unit (60) and an actuation unit (70) for local control and operation of the valve arrangement, - the valve arrangement is operated by the control unit into a valve configuration providing a barrier system between a reservoir in fluid communication with the well interior and the surroundings, -a plurality of sensors (100, 51, 52) arranged for measuring fluid parameters transmitted as signals to the control unit, which also receives other signals from subsea and or topside locations, where the control unit is configured such that when at least one transmitted signal deviates from allowable value the control unit activates the actuation unit for the closing of the valve arrangement. The invention also concerns a method.

Claims

1: A system for manipulating equipment in a subsea well and controlling a barrier system for the well, the system comprising: a subsea pump which is connected to the well through a temporary fluid connection to thereby define a closed system suitable for pressure and flow regulation; a fluid source for supplying a fluid to the subsea pump; wherein in one mode of operation the subsea pump regulates at least one of a flow and a pressure of the fluid to operate the equipment; a safety control system for controlling shut down of a valve arrangement for the well, the valve arrangement being located subsea, and the safety control system being located subsea and comprising a control unit and an actuation unit for local control and operation of the valve arrangement; wherein the control unit operates the actuation unit to close the valve arrangement and thereby provide a barrier system between an environment external to the well; and a plurality of sensors which are configured to measure a number of parameters of the fluid and to transmit signals representative of the parameters to the control unit, wherein the control unit is configured such that when at least one parameter deviates from an allowable value, the control unit activates the actuation unit to close the valve arrangement.

2: The system in accordance with claim 1, wherein the control unit is provided on a skid positioned on the top of a X-mas tree which is connected to the well.

3: The system in accordance with claim 1, wherein the control unit is provided on a skid which is located proximate the well but positioned away from a X-mas tree which is connected to the well.

4: The system in accordance with claim 1, wherein the control unit is provided on a skid which is positioned at a manifold that is fluidly connected to the well.

5: The system in accordance in accordance with claim 1, wherein the actuation unit is located in a X-mas tree control module and is in communication with the control unit.

6: The system in accordance with claim 1, wherein the actuation unit comprises a quick dump valve unit for dumping a control fluid from an actuator of at least one valve of the valve arrangement, thereby causing the valve to go to a fail safe close position.

7: The system in accordance with one of claims 2-4, wherein the skid comprises a subsea tool.

8: The system in accordance with claim 1, wherein the valve arrangement comprises a barrier valve for a X-mas tree which is connected to the well, and wherein control and operation of the barrier valve is carried out by the control unit and the actuation unit.

9: The system in accordance with claim 1, wherein at least one valve of the valve arrangement is located on a subsea tool which is temporarily connected to the well.

10: The system in accordance with claim 1, wherein the control unit is configured to receive operation signals from a topside location, through one of an umbilical or a wireless system.

11: The system in accordance with claim 10, wherein the control unit is configured to receive the signals through a communication system of an ROV which is connected to the control unit during operation.

12: The system in accordance with claim 1, wherein the pump is located on an ROV and the fluid connection is provided by fluid lines extending between the ROV and the well.

13: The system in accordance with claim 1, wherein the control unit is located on an ROV.

14: A method for manipulating equipment in a subsea well and controlling a barrier system for the well, the method comprising: providing a pump subsea proximate to the well and a fluid source for supplying fluid to the pump; establishing a fluid connection for fluid flow between the pump and the well as a closed system which is suitable for pressure and flow regulation; operating the pump to regulate at least one of a flow and a pressure of the fluid in the well to thereby control the operation of equipment in the well; providing a temporary safety control system at a subsea location, the safety control system comprising a control unit and an actuation unit for locally controlling and operating a valve arrangement which is positioned subsea; wherein the control unit operates the actuation unit to close the valve arrangement and thereby provide a barrier system between the well and an environment external to the well; providing the control unit with signals representing measured parameters of the fluid, and when at least one parameter deviates from an allowable value, operating the actuation unit to close the valve arrangement.

15: The method in accordance with claim 14, wherein the equipment in the well comprises a barrier assembly; and wherein in one mode of operation the pump generates a pressure in the well which is necessary to open the barrier assembly.

16: The system in accordance with claim 7, wherein the subsea tool comprises a running tool for a X-mas tree.

Description

DETAILED DESCRIPTION

[0095] In the following, embodiments of the invention will be described in detail with reference to the enclosed drawings, where:

[0096] FIG. 1 shows an example of an overall view of one embodiment of the invention.

[0097] FIG. 2 shows an example of a subsea tool and a X-mas Tree installed on a well head.

[0098] FIG. 3 shows a schematic layout of a subsea tool.

[0099] FIG. 4 shows an example of a well control unit to be included in a subsea tool.

[0100] FIG. 5 shows an example of a well control unit connected to a X-mas tree installed on a well head, no pumping of fluid shown.

[0101] FIG. 6 illustrates the pumping of fluid into the well interior.

[0102] FIG. 7 illustrates the return of fluid from the well interior.

[0103] FIG. 8 shows an overall view of the subsea tool connected to the X-mas tree installed on the well head and communication between the subsea tool and top site facility and subsea tool and well interior .

[0104] FIG. 9 shows a principle sketch of a well control unit providing a safety control system for a well.

[0105] FIG. 10 shows an example of a subsea well opening system where the well control unit is included and positioned on the Xmas Tree

[0106] FIG. 11 shows an example of a subsea well opening system including the well control unit and being positioned at the manifold.

[0107] FIG. 12 shows the well opening system including the well control unit and located proximate to the well, and with the pump of the well control unit located on an ROV

[0108] FIGS. 10 through 12 shows typical configurations of the well opening system. Other configurations are possible.

[0109] FIG. 1 shows a vessel 1 lowering a subsea tool 2 here shown as a running tool arranged with a X-mas tree 3 to be positioned at a subsea installation location for installing the X-mas tree 3 on a subsea wellhead assembly. The subsea tool 2 is lowered from the vessel 1 by a deployment line 4 such as a wire line. A remotely operated vehicle (ROV) 5 is provided for supplying power and control lines for the operation of the subsea tool during use. An umbilical 6 transmitting power, electrical and or optical signals are connected to the vessel 1 and the ROV 5 and transfers power, communication and or video images between the ROV and the vessel and thereby to the tool . An overall operation module 7 such as hand carried operator console controls the entire operation from a remote location, possibly from a top side location on the vessel 1 1, but it could also be at a remote location at land or in a ROV control cabin at the vessel. The ROV is therefore a carrier, carrying signal and or power between the operator and the running tool.

[0110] Equipment such as down hole equipment for instance a barrier assembly, here shown as an upper tubing hanger plug 8 and a lower set plug 9, is arranged in a well 10 and forms the barriers in the well before the installation of the X-mas tree or when the X-mas tree is removed to be maintained or replaced. The plugs 8 and 9 may be provided as disappearing plugs or alternatively one may have valves as barrier elements that are arranged to open and close for fluid flow in response to an activation mechanism operated by a pressure or flow sequence or levels in the fluid in well.

[0111] When the down hole equipment is a barrier assembly, the removal or opening of the barrier assembly is typically carried out by pressure build up or pressure variation generated by a pump arranged in fluid connection with the interior of the well 10.

[0112] The pump is to be provided subsea preferably proximate to the well or at least at a set distance compatible with providing an efficient fluid connection between the pump and well interior. The pump may favorably be positioned on the subsea tool arranged to be connected to a X-mas tree or on the ROV. A fluid source supplies fluid to the pump.

[0113] The pump 30 and the fluid source 31 may be arranged on the subsea tool 2 as illustrated on FIG. 3-5. Alternatively the pump may be arranged at a subsea location for instance at a manifold 16, see FIG. 2, or on the ROV. Further, the fluid source may be located at a subsea location and may be contained in a vessel and positioned on the manifold or the ROV. The fluid source may also be provided by a subsea service line, whereto the subsea tool may be connected for instance by a fluid line. Another possibility is to use a fluid source positioned at a topside location with a fluid line down to the tool.

[0114] The subsea tool 2 as shown in the figures is also capable of carrying the X-mas tree from the vessel during installation and have the provisions for setting, installing and testing the X-mas tree on the wellhead. Such provisions for setting, installing and testing the X-mas tree may be found in prior art and there are several publications describing different manners of doing such a procedure. The tool according to the invention may comprise one such system.

[0115] When the X-mas tree is installed on the wellhead, which may be done by the subsea tool according to the invention or the X-mas tree may be already installed and the subsea tool according to the invention is provided in the vicinity or at the X-mas tree, the next step is to open the well for production, by removing or opening the barrier assembly in the well, below the X-mas tree. When this can be done in one procedure this gives additional time and cost savings. However having the tool provide for opening of the barrier as such, provides cost savings and a more controlled operation.

[0116] When later retrieving the X-mas tree installed on the wellhead, down hole equipment such as a barrier assembly must be closed before removing the X-mas tree from the wellhead. The retrieval of the subsea tool requires that the valve arrangement such as barrier valves for the well, as for instance in the X-mas tree are closed before the retrieval is carried out. These precautionary measures for well safety ensure that a double barrier is established between the reservoir and the surroundings, before well related equipment such as a X-mas tree and a subsea tool is removed from the installation site.

[0117] When manipulating equipment in a well such as removing or opening the barrier assembly, the first step is to establish a temporary fluid connection for fluid flow between the subsea pump and the well interior providing a closed system suitable for pressure and or flow regulation. The subsea pump has a mode of operation for regulation of the flow and/or pressure of the pumping fluid at the outlet of the pump and to forward this flow and/or pressure regulation to the fluid of well interior through the fluid connection to operate the down hole equipment in the well interior during the temporary fluid connection between the pump and the well interior. When the down hole equipment is a barrier assembly the pump may be operated at intervals generating pressure build up in the pumped fluid flowing into the well interior through the fluid connection to produce pressure build up in the fluid of the well interior until opening the barrier assembly. The operation of the barrier assembly could be activated by an activation mechanism requiring a sequence of pressure build up, a number of pressure build up, a given threshold pressure for a given time period or pressure variations for activation. This arrangement is to prevent accidental activation of the equipment. After carrying out the activation or opening or closing of the down hole equipment the fluid connection between the pump and the well interior is then closed, establishing a barrier system around the reservoir upstream of the fluid connection between the pump and the well interior for a production well, terminating the temporary fluid flow between the pump and the well interior.

[0118] FIG. 2 illustrates the subsea tool 2 and the X-mas tree 3 installed on the well head assembly 8. A simplified concept of the main functions and the technical features of the X-mas tree 3 are illustrated in the FIG. 2 as concept modules. A main module 19 illustrates the actual X-mas tree, module 18 illustrates the subsea control of the X-mas tree 3. Module 14 is a flow module 14 arranged with a fluid line assembly 15 to a manifold 16. The manifold 16 is connected to a set of pipelines 17 for distribution of fluid to production facilities as illustrated by arrow A. A module 20 illustrates a permanent guide base comprising a conductor housing for receiving the well head. A further module 8 illustrates well head, tubing hanger and downhole equipment. Module 21 describes functions and technical features of the subsea tool 2.

[0119] The subsea tool 2 as shown in FIGS. 1 and 2 is provided for the installation of the X-mas tree 3, and as mentioned above the pump and possibly also the fluid source may be provided on the subsea tool 2. However, it is also possible in accordance with the invention to install the x-mas tree using a subsea tool 2 as shown in the figures and then to lower the pump along for instance arranged on a ROV which attached and connects to the subsea tool or without the fluid source as this may be taken from a service line subsea, or from an fluid line to the topside either attached to the subsea tool or to the ROV.

[0120] A schematic outlay 20 of a subsea tool is shown schematic in FIG. 3. The schematic outlay 20 is suitable for the subsea tool 2 used for the installation of a X-mas tree as illustrated in FIG. 1, but is also applicable for a subsea tool to be connected to an installed X-mas tree and for carrying out operations in the well interior in addition to the function and barrier testing of the X-mas tree.

[0121] The subsea tool has a ROV connector interface 21 for power and communication transmittal with or through the ROV and a shaft receptacle 22 for driving of a valve controlling pump provided for controlling flow and pressure of a control fluid for operating a valve arrangement such as barrier valves positioned on the running tool. The shaft receptacle 22 may alternatively be fluid connections or power connections depending on the type of valve controlling pump on the running tool. This valve controlling pump and the other pump as described in the following for regulating the flow and/or pressure of the fluid in the well interior may be a hydraulically and or electrically driven pumps. In the case where the valve controlling pump is positioned on the subsea tool there may be a power transmission to this pump but the fluid pump for the well interior fluid may receive a power transmission or fluid transmission if it is positioned on the subsea tool depending on how this is driven. If this pump for the fluid for the well interior is arranged in the ROV, there may be fluid line connections from the ROV to the tool

[0122] Further an X-mas tree connector face 123 is provided for testing of the X-mas tree functionality and correct installment and a potentially replaceable adapter 24 for the X-mas tree comprising a valve pack 25 for the X-mas tree and a fluid reservoir 26 for operation or the installment and testing of the X-mas tree. The subsea tool according to the invention has a reservoir 27 for hydraulic fluids, a valve tool pack 28 for operating for instance barriers valve arranged on the tool and or at the X-mas tree, a well shut down unit 60 and a quick dump unit 70 for controlling the barrier valve arrangements such as illustrated in FIG. 4, the barrier valves being arranged at the subsea tool or the X-mas tree. This form part of a well control unit 23 for operating barrier valves in a manner for manipulating equipment in a well with the subsea tool and still keep full control of the well when opening downhole barrier assembly. The further details of the well control unit 23 is shown schematically in FIG. 4.

[0123] FIG. 4 shows an example of the subsea tool in fluid connection with the well interior through fluid connection between flow passages of the X-mas tree and the well control unit 23. The well control unit 23 of the subsea tool comprises a system comprising a number of fluid lines arranged and a number of valves of the valve arrangement arranged in these fluid lines which may be in an open or closed position to provide a flow passage and a return passage directing the fluid flow to and from the well interior.

[0124] The well control unit 23 comprises a pump 30 which extracts fluid from a fluid source 31 such as a MEG reservoir through a fluid source line 32 including a suction filter 33. The fluid source 31 has a fluid filling point 34. The pump 30 may also be arranged to draw fluid from different fluid sources with different parts of the pump, as indicated in the figure. The pump is operated to deliver pumped fluid to the well interior to regulate the flow and/or pressure of the fluid in the well interior for controlling the opening and closing of down hole equipment of the well.

[0125] The pumped fluid is discharged from the pump 30 and passed through a pump outlet fluid line 35 arranged with an isolation valve 36 and a pump barrier valve 37. A flow meter 52 is included in the pump outlet fluid line 35 for measuring of the characteristic of the pumped fluid flow. The pump barrier valve 37 is arranged in an open position to direct the pumped fluid flow to the well interior. The pumped fluid may enter the well interior following at least two different flow paths. The different flow paths are provided by opening and closing of the valve arrangement as shown in the well control unit 23.

[0126] In accordance with a first flow path for pumping fluid to the well interior and thereafter returning the fluid, the pumped fluid is allowed into a X-mas tree main bore fluid line 38 and the fluid returns through the same X-mas tree main bore fluid line 38. The fluid may be routed in a different manner in the return path in the tool. The X-mas tree main bore fluid line 38 leads the fluid to the main bore 138 of the X-mas tree 3, as illustrated by the connection of X-mas tree main bore fluid line 38 and the main bore 138 of the X-mas tree 3 as shown in FIG. 5, and from there into the interior of the well 10.

[0127] In accordance with a second flow path the pumped fluid is allowed into the X-mas tree annulus bore fluid line 39, see illustration in FIGS. 4 and 6, and returns the fluid through the same X-mas tree annulus bore fluid line 39, see illustration in FIGS. 4 and 7. The X-mas tree annulus bore fluid line 39 leads the fluid to the annulus bore 139 of the X-mas tree 3, as shown in FIG. 6, where the pumped fluid is directed to the X-mas tree main bore 138 by the arrangement of a X-mas tree cross over valve arrangement 170, and further into the interior of the well 10.

[0128] When following the first flow path the pumped fluid flows though the X-mas tree main bore fluid line 38 to the well interior. A X-mas tree main bore barrier valve 40 arranged in the pump outlet fluid line 35 is then arranged in an open position. This configuration allows for fluid flow from the pump 30 to the X-mas tree main bore 138 and into the interior of well 10. The pressure and flow of pumped fluid is thereby forwarded to the fluid of the well interior for controlling the opening and closing of down hole equipment such as a barrier arrangement arranged in the well.

[0129] A fluid branch 41 diverts from the pump outlet fluid line 35 and is divided into a fluid return line 42 and into a cross over fluid line 43. The fluid return line 42 is arranged with a return barrier valve 44 which is in a closed position as the pumped fluid passes from the pump outlet fluid line 35 through the X-mas tree main bore barrier valve 40 and into the X-mas tree main bore fluid line 38.

[0130] The cross over fluid line 43 is arranged with a cross over barrier valve 45 which also is in a closed position as the pumped fluid passes from the pump outlet fluid line 35 to the X-mas tree main bore fluid line 38.

[0131] When returning the fluid from the well bore interior after opening or closing the down hole equipment arranged in the well, the X-mas tree main bore barrier valve 40 is in open position. The pump barrier valve 37 and the cross over barrier valve 45 are each in a closed position whereas the return barrier valve 44 is in an open position, thereby allowing the return fluid into the fluid return line 42.

[0132] The fluid return line 42 is divided into a fluid source return line 48 and an additional fluid return 46 in fluid connection with a hydrocarbon collector 149 for collection of potential excess hydrocarbon from the well. The additional fluid return line 46 is arranged with flush valve 47 controlling the flushing of the system after completing operations in the well.

[0133] The fluid source return line 48 is arranged with a choke valve 49 for controlled reduction of pressure in the return fluid passing in the return line 48 before directing the return fluid to the fluid source 31. An isolation valve 50 is arranged in the fluid source return line 48 providing a possibility for isolation of the fluid source 31. A flow meter 52 is included in the pump outlet fluid line 35 for measuring the characteristic of the pumped fluid.

[0134] An excess pressure fluid line 102 arranged with a safety valve 53 connects the pump outlet fluid line 35 and the fluid source return line 48. If the pressure of the pumped fluid exceeds a predetermined value the overpressure is vented to the fluid source through the excess pressure fluid line 102.

[0135] When following the second flow path as illustrated in FIG. 6, the pumped fluid is allowed into the X-mas tree annulus bore fluid line 39 by directing the pumped fluid through the fluid branch 41. The pump barrier valve 37 is then in an open position and the X-mas tree main bore barrier valve 40 is in a closed position. From the fluid branch 41 the pumped fluid is diverted into the cross over fluid line 43 by opening the cross over barrier valve 45 and closing the return barrier valve 44. The fluid line 43 splits into a X-mas tree annulus bore connecting line 150 and second connecting line 151 arranged with a second annulus bore barrier valve 74 for fluid connection with a fluid source filling line 55. The X-mas tree annulus bore connecting line 150 is arranged with a first annulus bore barrier valve 54 which is in an open position to let the pumped fluid enter the X-mas tree annulus bore fluid line 39 and into the annulus bore 139 of the X-mas tree 3 (FIG. 6). The second annulus bore barrier valve 74 is closed when the pumped fluid enters the X-mas tree annulus bore fluid line 39.

[0136] As explained above the pumped fluid is directed from the X-mas tree annulus bore fluid line 39 to the X-mas tree main bore 138 by the arrangement of a X-mas tree cross over 170, and into the well interior. The pressure and flow of the pumped fluid is thereby forwarded to the fluid of the well interior to open and/or close the down hole equipment for instance a barrier arrangement arranged in the well, the barrier arrangement is shown as tubing hanger plug 8 and a lower set tubing plug 9 in FIG. 6.

[0137] When returning the fluid from the well bore interior through X-mas tree main bore 138 via the X-mas tree cross over 170 and into the X-mas tree annulus bore fluid line 39, see FIG. 7. The first annulus bore barrier valve 54 and the cross over barrier valve 45 are both in an open position and the second annulus bore barrier valve 74 is closed, thereby allowing the fluid to return to in the cross over fluid line 43. Further the pump barrier valve 37 and the main bore barrier valve 40 are each in a closed position whereas the return barrier valve 44 is in an open position thereby directing the returning fluid through the fluid return line 42 and into the fluid source return line 48. If excess of hydrocarbon from the well this flows through the additional fluid return line to the hydrocarbon collector 149.

[0138] It is also possible to direct the pumped fluid into the X-mas tree main bore fluid line 38 and to return the fluid in the X-mas tree annulus bore fluid line 39. Alternatively to direct the pumped fluid into the X-mas tree annulus bore fluid line 39 and to return the fluid in the X-mas tree main bore fluid line 38.

[0139] The fluid source 31 in the example shown in FIG. 4 is shown with connection to the fluid filling point 34, where for instance a fluid line extending from a top side facility is to be attached for filling the fluid source 31. The filling of the fluid source may also be carried out by supplying fluid from the sea floor, for instance from a service line. The first annulus bore barrier valve 54 and the second annulus bore barrier valve 74 are then in open position, whereas the cross over barrier valve 45 is closed. Fluid is withdrawn from the service line (not shown) through the X-mas tree annulus bore fluid line 39 and into the fluid source filling line 55 which is connected to the fluid source return line 48, thereby directing the fluid from the service line to fluid source 31.

[0140] The well control unit 23 has a safety control system for shutting down the well including a control unit such as a well shutdown unit 60 and an actuation unit/pressure relief unit, such as quick dump unit 70 which include a quick dump manifold 72 and a control valve 71 (Quick Dump Valve). A control fluid for instance a hydraulic fluid is used to control the opening and closing of the barrier valve in a normal flow mode, wherein the barrier valves are provided as fail safe valves and each is operated by a spring unit 65, 66, 67, 68, 69, 270 71. The flow of control fluid between the manifold 72 of the quick dump unit 70 and the barrier valves is illustrated by fluid lines 1, 2, 3, 4, 5, 6 on the manifold and with fluid lines 1, 2, 3, 4, 5, 6,7 which each belong to a specific barrier valve 37, 40, 44, 45, 50, 54, 74. The barrier valves have an initial mode which also is a fail safe mode, where the barrier valves are closed. The control fluid is distributed to the actuation chamber/spring chamber of the barrier valve in order to open the barrier valves. When the control fluid in the manifold and the spring chamber exerts a pressure force which exceeds the spring force of the barrier valve, this barrier valve is brought to an open position. If the force provided by the pressure of the control fluid does not exceed the spring force, then the barrier valve remains in a closed position, ie when there is no pressure in the control fluids the valve will be closed, a fail safe closed valve.

[0141] Several pressure transducers and or sensors 100 measures the pressure of the fluid in the various fluid lines as shown in FIG. 4. The pressure transducers may also be located elsewhere in the flow path than the shown locations, for examples also in the X-mas tree. The parameter measured by the transducers, for instance pressure, is communicated as input signals 101 to a communication unit 110, which may also be called a safety unit. There are also other sensors in the system providing input signals to the communication unit 110, as for instance flow measurements, of flow into and out of the well and comparing these. If the measured parameters are within a predetermined value or value range, the input signal 101 does not deviate from a signal threshold or a signal range and an output signal QD is transmitted from the communication unit 110 to the control valve 71, which remains in a position where the dumping outlet 75 is closed as illustrated by the no flow symbol 76 on the control valve 71. The fluid flow in the system then follow normal flow mode as described above. It is then possible to keep the barrier valves in an open position, thereby returning fluid to the fluid source 31 following normal flow mode as described above.

[0142] If one of the measured parameters deviates, for instance exceeds, from predetermined value or value range the signal input 101 representing the measured parameter deviates from the allowable signal threshold or signal range. No signal QD is then transmitted from the communication unit 110 to the control valve 71, and the safety control system enters a shut down mode. In that case the control valve 71 is brought into a position as shown in FIG. 4 where flow is allowed through the dumping outlet 75. The control fluid is then drained from spring chamber of the spring units belonging to the barrier valves and to the quick dump manifold 72. Fluid dumping from the barrier valve are indicated by arrows on the lines 1, 2, 3, 4, 5, 6 and 7 illustrated on the quick dump manifold 72. The dumping of control fluid from the control unit of the barrier valves causes the barrier valves to close. The barrier valves will then go to a fail state close position containing the well with two barriers in the system both on X-mas tree and the running tool.

[0143] As shown the well shut down unit 60 also receives an input signal RC from the ROV. If the ROV communication fails such as when the well shut down unit 60 receives no signal from the ROV, this also initiates no output signal QD being transmitted to the control valve 71, which also initiates the dumping procedure and the barrier valves to go to a fail shut down mode, closing the well as described above. As the skilled person will realize also other parameters than the ones exemplified here, may be used for indicating the status of the system, in which case the absence of signals causes the shut down mode and the presence of signals indicates normal flow mode.

[0144] Further the well shut down unit 60 includes a flow comparator 111 where the measurements from the pump flow meter 52 are compared with the measurements from the return flow meter 51. The deviation of measured pump flow and the measured return flow may provides the bases for causing the system to shut down or not. If the measurement of the return flow meter 51 is significantly larger or smaller than the measurement of the pump flow meter 52, when they are supposed to be similar, the input signal 102 is outside the signal threshold or allowable value or value range and no output signal QD is transmitted to the control valve 71. The control fluid keeping the barrier valves in an open position is dumped through the quick dump unit 72 and the barrier valves goes to a fail state closed position closing the well with a double barrier system.

[0145] The operator at the topside facility may also initiate this procedure of dumping the control fluid from the spring unit of the barrier valve and thereby operate the well barrier valve to a fail safe close position.

[0146] It is within the scope of the invention to have the well shut down unit to communicate with barrier valve in the X-mas tree, to initiate a well shut down and provide a two barrier functionality in the system of X-mas tree and running tool.

[0147] It is also within the scope of the invention to have the well shut down unit communicating with barrier valves that are electrically operated or semi-electrically operated, to be kept in an open position, or in a different manner kept in an open position, which when such a signal is lost have the functionality of closing the valve to a fail safe close position to form the barrier for the well on X-mas tree and running tool.

[0148] FIG. 8 is a schematic illustration of the interaction between the various components of the overall system and also shows the line of communication between these components. The subsea tool 20 has an outlay similar to the outlay shown in FIG. 3. The flow pattern through the X-mas tree 3 is similar to the flow pattern shown in FIG. 6. FIG. 8 shows the subsea tool 20 connected to the X-mas tree 3 by a tool connector 80 and the X-mas tree 3 connected to the well head by a well head connector 90. Pressure cycles 110 are illustrated provided from the pump on the running tool, see FIG. 4, for operation of the to down hole equipment such as plugs 8, 9 and pressure responsive valve 111. When mentioning components shown in the FIG. 8 that have been discussed earlier the same reference numbers are applied. The X-mas tree 3 has a SCM unit for controlling the valve arrangement of the X-mas tree 3 based on signals from the signal line 93. Line 94 transmits electric power from the subsea tool to the SCM unit of the X-mas tree 3. Fluid line 92 supplies hydraulic power to the X-mas tree 3. The ROV 5 is illustrated with an electric power line 95 and a communication line 96. The lines 95, 96 are included in the ROV umbilical 6 and illustrate the communication between the surface control unit 100 of the vessel 1 and the ROV 5. Additional electric power line 98 and communication line 99 provides a connection from the ROV 5 to the subsea tool 20 and thereby provides the communication between the control unit 100 of the vessel 1 and the subsea tool 20. A fluid line 101 is connected between the ROV and the subsea tool 20. A supply fluid line 102 is also shown illustrating the possibility of filling the fluid source 3 through the fluid filling point 34, as described above when discussing FIG. 4.

[0149] FIG. 9 is a schematic illustration of a well control unit 24 provided as a generalized version of the well control unit 23 of FIG. 4. The well control unit 23 of FIG. 4 is shown included in a subsea tool, whereas the well shut down unit 60 and the actuation unit shown as Quick Dump Valve 70 of the well control unit 24 as shown in FIG. 9, may be positioned at various locations. FIGS. 10, 11 and 12 show examples of various locations for positioning the well shut down unit 60 and the Quick Dump Valve 70.

[0150] The working principles of the well control unit 24 in FIG. 9 in principle follows the working principle of the well control unit 23 in FIG. 4, and a summarized explanation of the well control unit 24 using the same numbers when referring to components already explained with reference to FIG. 4 follows: The pump 30 draws pumping fluid from the fluid source 31 which may be provided as a well fluid reservoir and forwards the pumped fluid to the X-mas tree (not shown) and from the X-mas tree to the well interior for manipulation of equipment in the well. The pumped fluid entering the X-mas tree is illustrated by arrow W. The pump and the fluid source may be arranged at various locations and the pump and the fluid source may be provided in various ways as described previously in this document.

[0151] A safety valve 53 and a arrangement of return fluid lines ensures the ventilation of the pressure of the pumped fluid to the fluid source, should the pumped fluid exceed a predetermined value.

[0152] The return fluid from the well interior flows in the direction opposite to that of arrow W and into the return fluid lines directing the return fluid back to the fluid source. A choke valve 49 is provided for controlled reduction of pressure in the return fluid before directing the return fluid to the fluid source 31. Usually an isolation valve (not shown) for isolation of the fluid source 31 and a flow meter (not shown) are also included in these return lines. The isolation valve and the flow meter are shown in FIG. 4.

[0153] A hydrocarbon collector 149 is arranged in return fluid lines and in the cases of the excess hydrocarbon from the well, the potential excess hydrocarbon is to be deposited in the hydrocarbon collector 149.

[0154] In addition an arrangement for flushing after completing operations in the well is provided.

[0155] A service hub provides a fluid filling point 34 for the fluid source 31 and also access for well services such as as injectivity testing, acid stimulations and hydrate remediation.

[0156] The signal input 101 from various sensors and the communication signals is illustrated by arrow 93 between the well shutdown unit 60 and the quick dump unit (QDU) 70 for controlling the shut down of a valve arrangement in a subsea position.

[0157] As explained above the and the quick dump unit (QDU) 70 is arranged to dump a control fluid from a spring unit (or other pressure source units or mechanisms controlling the opening and closing of the valve) of a valve, thereby causing the valve to go to a fail safe close position.

[0158] FIG. 10 shows a skid provided as the subsea tool 20 arranged with the well control unit 24 on the top of the X-mas tree. The subsea tool 20 is connected to the X-mas tree 3 by the tool connector 80. The quick dump unit (QDU) 70 is also shown arranged on the subsea tool 20. In the example in FIG. 10, the subsea tool 20 is provided with barrier valves 130, 131 enabling access to the main bore 132. The barrier valves and the fluid lines may be provided in various ways. The barrier valves 130, 131 are provided as fail safe valves. The well shutdown unit 60 controls the operation of the quick dump unit in (QDU) 70 as illustrated by signal line 93 and thus control the closing of the barrier valves 130, 131 into a fail safe close position to form the barrier for the well in X-mas tree.

[0159] Further a quick dump unit (QDU) 70 is shown arranged on the X-mas tree 3. The Quick Dump Unit (QDU) 70a on the X-mas tree 3 may be provided by the Quick Dump Unit (QDV) 70a of the X-mas tree control module 120. The Quick Dump Unit (QDU) 70, 70a arranged X-mas tree 3 may control barrier valves (not shown in FIG. 10) of the on the X-mas tree 3 into fail safe close position to form barrier for the well.

[0160] In FIGS. 10, 11 and 12 the Quick Dump Unit 70, 70a is shown on the subsea tool 20 and on the X-mas tree 3 for the purpose of illustrating various positions for the Quick Dump Unit 70, 70a. This of course does not indicate that the plural Quick Dump Units 70, 70a as illustrated in the figures need to be present at the same time for the working of the well control unit.

[0161] FIG. 11 shows the well control unit 24 arranged on a skid 500. The skid 500 is located away from the X-mas tree 3 but proximate to the well and is shown positioned at a manifold 50. The well shutdown unit 60 is arranged on the skid 500, whereas the quick dump unit (QDU) 70 is arranged on the X-mas tree for operating barrier valves 230, 231 of the X-mas tree. The Quick Dump Valve (QDU) 70 on the X-mas tree 3 may be provided by the Quick Dump Valve (QDV) 70a of the X-mas tree control module 120.

[0162] The quick dump unit s (QDU) 70a of the X-mas tree 3 is provided to operate barrier valves 230, 231 of the X-mas tree into fail safe position.

[0163] The barrier valves 230, 231 are shown controlling the fluid flow through annulus bore 140 and enables access to the main bore 130, possibly via a cross over line. A well fluid line 97 is arranged between the subsea tool 20 and the X-mas tree 3.

[0164] FIG. 12 shows the well control unit 24 arranged on the skid 500. The skid 500 is located away from the X-mas tree 3 but proximate to the well. The position of the skid 500 as shown in FIG. 12 is meant to illustrate that the skid may be located at other positions than at the manifold 50 as illustrated in FIG. 11. In this embodiment the pump 30 is arranged on the ROV 5. The fluid connection between the pump 30 and the well interior is provided by the fluid lines 250, 251 arranged between the ROV and the subsea tool 20 in combination with the fluid line 97 between the skid 500 and the X-mas tree 3. Alternatively the fluid connection between the pump and the well interior may be provided by fluid lines arranged between the ROV 5 and the X-mas tree 3. The positions of the well shut down unit 60 and the quick dump units 70, 70a are the same as in FIGS. 10 and 11.

[0165] For the embodiments shown in FIGS. 10, 11 and 12 the well shut down unit 60 may also be arranged to control a combination of barrier valves in the X-mas tree and barrier valves of the subsea tool.

[0166] In the preceding description, various aspects of the apparatus according to the invention have been described with reference to the illustrative embodiment. For purposes of explanation, specific numbers, systems and configurations were set forth in order to provide a thorough understanding of the apparatus and its workings. However, this description is not intended to be construed in a limiting sense. Various modifications and variations of the illustrative embodiment, as well as other embodiments of the apparatus, which are apparent to persons skilled in the art to which the disclosed subject matter pertains, are deemed to lie within the scope of the present invention.