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FIELD OF THE INVENTION  
       [0001]     The present invention relates to sub-sea control and monitoring, and is concerned particularly with an apparatus and a method for controlling and/or monitoring sub-sea equipment such as is used in a well.  
       BACKGROUND  
       [0002]     Connecting to down-hole installed equipment, such as a pressure sensor and/or a temperature sensor or else to a pump, via a cable such as an electrical cable is now common in the oil business. The use of electric submersible-pump power cables and the attachment of instrumentation cables to down-hole devices have been known for many years, especially on land and in shallow water.  
         [0003]     The sub-sea environment (operations where the oil well is effectively constructed with its datum and attached pipe-work at seafloor level) presents special challenges for engineers. A sub-sea operation that could straightforwardly be undertaken on dry land has to be undertaken with specialist equipment that has failsafe modes and appropriate margins for failure of equipment. Even with the use of divers and ROVs (remotely operated vehicles), certain operations cannot be undertaken at sea floor level.  
         [0004]     During well construction, water depth usually precludes the use of fixed work platforms secured to the seabed. Instead, semi-floating work platforms (semi-submersible rigs) are floated out to the work area and either secured by chains or kept on station by satellite co-ordinated thrusters (i.e. the platforms are dynamically positioned).  
         [0005]     Since the well equipment is located on the seabed, whilst being suspended from the semi-floating platform, it is difficult to attach cables to the equipment. There is also a risk that any electrical cable or delicate equipment could easily be damaged during the installation procedure.  
         [0006]     Over the years the number of pockets of known hydrocarbon deposits that are accessible by land has diminished, and even those deposits that are accessible within shallow water are becoming scarce. Consequently, operators are moving into ever greater water depths to access oil reserves. This has led to a requirement for more complex, time consuming and costly operations to access and produce oil in deep water. At the same time, the necessary technology to monitor down-hole conditions has become more freely available. What was originally all mechanical equipment is now frequently being replaced by a combination of mechanical and sophisticated electronic monitoring equipment to optimise and monitor well conditions. Whilst the technology to develop electronic sensors and equipment robust enough to work in the harsh sub-sea environment is now available, the methods of connecting and switching the signals are still under development.  
         [0007]     As outlined above, there is a drive towards drilling in deeper, more remote waters and to monitor well conditions and performance in order to optimise return on investment. This has led to a review of operations previously considered as routine in order to save the significant increased costs of these operations or the cost of their failure in the deepwater environment. For example, the operation of installing tubular production strings (conduits for the oil) and connecting a permanent monitoring cable to a down-hole device might now take much longer on deep sub-sea wells. Previously, if the equipment was installed without cable or sensor monitoring and it was found to have failed, the equipment would be pulled back out (a so-called “work over”) and the damaged item repaired. However, in the deepwater environment, these work over (repair) costs are becoming prohibitively high.  
         [0008]     One method for monitoring and therefore controlling the well after installation requires the use of a down-hole pressure and temperature transducer (DHPTT). This is a package that is located on the lowermost end of the production tubing (string) to give a continuous read-out of well pressure and temperature. Through the acquisition of temperature and pressure information from multiple wells, an operator can control a number of wells located in the same reservoir.  FIG. 1  shows a typical sub sea layout with multiple well/drill centres.  
         [0009]     The following is a description of a typical prior art “running” (i.e. installation) procedure.  
         [0010]      FIGS. 2   a  to  2   e  show, schematically, the various stages of running culminating in a completed installation in which the well is being permanently monitored according to a previously considered method.  
         [0011]     In  FIG. 2   a  the well has been constructed with the wellhead  10  prominent above the seabed  12 . It has been installed with a mechanical actuator  14 , attached on the side of the wellhead  10 , which will subsequently be used to make an electrical connection to a down-hole cable (not shown) inside the well head by penetrating through the wellhead to accommodate an electrical “wet mate” connector in a radial direction through the side of the well head. This procedure is described in detail in U.S. Pat. No. 5,558,532 (Hopper). A signal cable  16  leads from the mechanical actuator  14  to a dynamically positioned floating semi-submersible platform  18  on the surface for eventual monitoring of a down-hole device after installation.  
         [0012]     In  FIG. 2   b , which depicts the next stage of the process, a tubular string  20  is lowered through the floating semi-submersible platform in short screwed-together sections. Any electronic sensors or devices are conveyed to the seabed well on this tubular string. A down-hole monitoring cable (not shown in the figure) is attached to the devices and is located within the tubular string as the assembly is lowered to the seabed. Once the calculated length of tubes is installed to fit the well depth, a ‘tubing hanger’  22  is attached to the tubes to allow the installation to hang from a profile  26  in the sea bed known in the industry, on account of its shape, as a “Christmas tree” (a steel housing that remains at the well head and allows tubes to hang and valves to be attached). The tubing hanger  22  and tubing  20  are conveyed to the “tree” at sea floor by a releasable latch known as a tubing hanger running tool  24 . This is attached to a profile in the tubing hanger  22  and the entire assembly (string) is then conveyed to the sea floor by adding lengths of screwed tubing until the tubing hanger reaches and engages the tree. This is a standard procedure.  
         [0013]      FIG. 2   c  shows the running tool after it has just been disconnected. The running tubes can now be retrieved to the surface.  
         [0014]      FIG. 2   d  depicts a remote-operated vehicle (ROV)  28  mechanically turning the actuator  14  that pushes forward the wet mate horizontal connector to make a permanent connection to the down-hole devices via the down-hole cable.  
         [0015]      FIG. 2   e  shows the final configuration when the well is complete and the permanent monitoring cable  16  is commissioned to a final vessel or semi-floating work platform.  
         [0016]     In view of the high costs of repair work in the deep sea environment, as outlined earlier, there is a strong incentive to monitor equipment to check that it is functioning during installation, in order to avoid the need for a costly work over. Thus, a device that is developed as part of the installed sub sea well head that allows electrical signals to be switched from monitoring whilst running (i.e. whilst installing) to permanent monitoring (i.e. after installation) is desirable, especially in the arduous sub sea environment.  
         [0017]     One disadvantage of the prior system, as outlined above with reference to  FIG. 2 , is that the process does not permit monitoring of the down-hole device during installation (running).  
       SUMMARY  
       [0018]     The present invention is defined in the attached independent claims, to which reference should now be made. Further, preferred features may be found in the sub-claims appended thereto.  
         [0019]     In one aspect, the invention provides a system for monitoring and/or controlling at least one device mounted on a tubing string of a well, the system comprising: a down-well cable for conveying a signal to and/or from at least one device mounted on a tubing string of a well; a temporary surface cable for conveying a signal between the at least one device and a first monitor/control station prior to and/or during installation of a tubing string in a well; a permanent surface cable for conveying a signal between the at least one device and a second monitor/control station after installation of the tubing string in a well; and switch means configurable between a first configuration, in which the down-well cable and the temporary cable are connected, and a second configuration, in which the down-well cable and the permanent cable are connectable.  
         [0020]     The invention also provides switch means for use in switching a signal from at least one device mounted on a tubing string of a well, the switch means being configurable between a first configuration, in which a down-well cable, for conveying a signal from/to at least one device mounted on a tubing string of a well, and a temporary surface cable for conveying a signal between the at least one device and a first monitor/control station prior to and/or during installation of a tubing string in a well are connected, a nd a second configuration, in which the down-well cable and a permanent surface cable for conveying a signal between the at least one device and a second monitor/control station after installation of the tubing string in a well are connectable.  
         [0021]     The invention also provides a method of monitoring and/or controlling at least one device mounted on a tubing string of a well, the method comprising: monitoring and/or controlling said device via a temporary surface cable connected to a down-well cable and arranged to convey a signal between the at least one device and a first monitor/control station prior to and/or during installation of the tubing string in the well, in a first configuration; monitoring and/or controlling said device via a permanent surface cable connected to the down-well cable and arranged to convey a signal between the at least one device and a second monitor/control station after installation of the tubing string in a well, in a second configuration; and switching between the first and second configurations.  
         [0022]     The invention also provides a system for monitoring and/or controlling at least one device mounted on a tubing string of a well, the system comprising: a down-well cable for conveying a signal to and/or from at least one device mounted on a tubing string of a well; a temporary surface cable for conveying a signal between the at least one device and a first monitor/control station prior to and/or during installation of a tubing string in a well; and switch means configurable between a first configuration, in which the down-well cable and the temporary cable are connected, and a second configuration, in which the down-well cable and the temporary cable are not connected.  
         [0023]     The invention also includes any combination of the features or limitations referred to herein, except combinations of such features as are mutually exclusive.  
       BRIEF DESCRIPTION OF THE DRAWINGS  
       [0024]      FIG. 1  shows schematically a modern sub-sea oilfield comprising a number of wells with monitoring cables connected to a floating station,  
         [0025]      FIGS. 2   a  to  2   e  show schematically a series of steps for installing a tubing string in a sub-sea well and monitoring signals from sensors on the string, according to a prior art method,  
         [0026]      FIGS. 3   a  to  3   e  show schematically a series of steps for installing a tubing string in a sub-sea well and monitoring signals from sensors on the string, according to a preferred embodiment of the present invention,  
         [0027]      FIG. 4   a  shows schematically switching means in a first configuration, according to a first embodiment of the present invention,  
         [0028]      FIG. 4   b  shows schematically the switching means of  FIG. 4   a  in a second configuration,  
         [0029]      FIG. 5   a  shows schematically switching means in a first configuration, according to a second embodiment of the present invention,  
         [0030]      FIG. 5   b  shows schematically the switching means of  FIG. 5   a  in a second configuration,  
         [0031]      FIG. 6   a  shows schematically switching means in a first configuration according to a third embodiment of the present invention,  
         [0032]      FIG. 6   b  shows schematically the switching means of  FIG. 6   a  in a second configuration, and  
         [0033]      FIGS. 7   a  and  7   b  show one example of the construction of a switching means suitable for use in the above-described embodiments. 
     
    
     DETAILED DESCRIPTION  
       [0034]     Turning now to  FIGS. 3   a  to  3   e , these show schematically the various stages of running culminating in a completed installation in which the well is being permanently monitored in accordance with a preferred embodiment of the present invention. Where possible, features common with the prior art example of  FIGS. 2   a  to  2   e  have been given the same reference numbers.  
         [0035]     In  FIG. 3   a , as before, the well has been constructed with the wellhead  10  prominent above the seabed  12 . It has been installed with a mechanical actuator  14 , attached on the side of the wellhead  10 , which will subsequently be used to make an electrical connection to a down-hole cable (not shown) inside the well head by penetrating through the wellhead to accommodate an electrical “wet mate” connector in a radial direction through the side of the well head. A permanent cable  16  leads from the mechanical actuator  14  to a dynamically positioned floating semi-submersible platform  18  on the surface for use in monitoring a down-well device permanently after installation. The permanent cable  16  is a surface cable in that it is above the well. It could, of course, lead to a monitoring station below the surface of the sea.  
         [0036]     In  FIG. 3   b , which depicts the next stage of the process, a tubular string  20  is lowered through the floating semi-submersible platform in short screwed-together sections. Any electronic sensors or devices are conveyed to the seabed well on this tubular string. A down-hole monitoring cable (not shown in the figure) is attached to the devices and is located within the tubular string as the assembly is lowered to the seabed. Once the calculated length of tubes is installed to fit the well depth, a tubing hanger  22  is attached to the tubes to allow the installation to hang from a tree profile  26  in the sea. The tubing hanger  22  and tubing  20  are conveyed to the “tree” at sea floor by a releasable latch known as a tubing hanger running tool  24 . This is attached to a profile in the tubing hanger  22  and the entire assembly (string) is then conveyed to the sea floor by adding lengths of screwed tubing until the tubing hanger reaches and engages the tree.  
         [0037]     In contrast with the prior art, the present invention makes possible the monitoring of the equipment during running. To achieve this, the tubing hanger contains through bores that accommodate a vertical electrical connector that is connected to a temporary monitoring cable  34  for monitoring the down-well device during (installation) running. The monitoring cable  34  is attached via clamps (not shown) adjacent to the running tool tubing all the way to the surface.  
         [0038]      FIG. 3   c  shows the running tool after it has just been disconnected. The running tubes and temporary monitoring cable  34  can now be retrieved to surface.  
         [0039]     By use of switch means described in detail with reference to FIGS.  4  to  7 , the connection between the temporary monitoring cable  34  and the down-well cable (not shown) has been opened, whilst a new connection between the down-well cable and the permanent monitoring cable  16  has been prepared, awaiting only actuation of the wet-mate connector by the actuator  14 .  
         [0040]      FIG. 3   d  depicts a remote-operated vehicle (ROV)  28  mechanically turning the actuator that pushes forward the wet mate horizontal connector to make a permanent connection to the down-hole devices via the down-hole cable.  
         [0041]      FIG. 3   e  shows the final configuration when the well is complete and the permanent monitoring cable  16  is commissioned to a final vessel or semi-floating work platform.  
         [0042]     FIGS.  4  to  7  will now be referred to as embodiments of the invention are described in more detail.  
         [0043]     Referring now to  FIG. 4   a , this shows generally a well head  32  during installation of a tubing hanger  22 . The tubing hanger  22  is still attached to the tubing hanger running tool  24  and has engaged the tree  26 . A temporary monitoring cable  34  extends upwards through the tubing hanger running tool  24  to monitoring apparatus located at the surface (not shown). A down-well monitoring cable  36  extends downwards inside the tubing hanger  22  through the tubing string (not shown) to down-well sensor equipment. The temporary cable  34  and the down well cable  36  are connected by a spring-loaded switch  38 . To the side of the tree  26  is a wet mate connector  40  having a mechanical actuator  14 . Inside the tubing hanger  22  and connected to an unused contact of the switch  38  is a short cable portion  42  shown in broken lines. The short cable portion leads from the switch to a horizontal wet mate pin  44  which is arranged in use to engage and make electrical contact with a female wet mate connector portion  46  upon actuation by the mechanical actuator  14 .  
         [0044]     The switch  38  comprises a first contact position in which the down-well monitoring cable  36  is in electrical contact with the temporary monitoring cable  34 , and a second contact position in which the down-well monitoring cable is in electrical contact with the short cable portion  42 . A compression spring  38   a  is located within the switch between the first and second contact positions. In the configuration shown in  FIG. 3   a  the presence of the tubing hanger running tool  24  in engagement with the tubing hanger  22  biases the switch  38  in the position shown by means of a switch pin  48  (shown more clearly in  FIG. 4   b ) compressing the switch spring  38   a .  
         [0045]      FIG. 4   b  shows the well head immediately after the tubing hanger running tool  24  has disengaged from the tubing hanger  22 . Upon withdrawal of the switch pin  48  the compression spring  38   a  biases the switch  38  in the second configuration (shown) in which the down-well monitoring cable  36  is no longer connected to the temporary monitoring cable but is now connected to the short cable portion  42 . In this figure the mechanical actuator  14  has also been operated to cause the female wet mate connector  46  to make electrical contact with the horizontal wet mate pin  44 , thereby allowing monitoring signals from the down-well cable  36  to be taken out of a permanent monitoring connection  50 , which is connected via a permanent monitoring cable (not shown) to a permanent monitoring station on the surface or on land.  
         [0046]     If the tubing hanger running tool  24  is reconnected to the tubing hanger  22 , the switch pin  48  will cause the switch  38  to become biased in the first configuration, with the down-well monitoring cable becoming reconnected to the temporary monitoring cable  34  in the tubing hanger running tool. The process can be repeated as often as necessary and each time the reversible connections will be made reliably and cleanly.  
         [0047]      FIGS. 5   a  and  5   b  correspond to  FIGS. 4   a  and  4   b  respectively, but in this case the biasing spring  38   a  is at a location spaced from the switching contacts.  
         [0048]     Similarly,  FIGS. 6   a  and  6   b  correspond to  FIGS. 4   a  and  4   b , but in the embodiment shown in  FIGS. 6   a  and  6   b  there is a second spring-loaded switch  52  which is moveable between the position shown in  FIG. 5   a , in which the wet mate connector has not yet been actuated and the switch  52  is biased by a compression spring  52   a  to connect the down-well monitoring cable via the short cable portion  42  to the temporary monitoring cable, and a second position shown in  FIG. 5   b  in which the wet mate connector has been actuated and the switch  52  connects the down-well monitoring cable to the permanent monitoring cable  50 .  
         [0049]     In a further embodiment, which may utilize the switch means of any of FIGS.  4  to  6 , the switch pin  48  is retractable into the tubing hanger running tool  24 . Thus, in this embodiment, when the tubing hanger running tool  24  is connected to the tubing hanger  22 , the switch pin  48  will normally cause the switch  38  to become biased in the first configuration, with the down-well monitoring cable  36  being connected to the temporary monitoring cable  34  in the tubing hanger running tool. When the switch pin  48  is retracted inside the tubing hanger running tool  24 , however, the compression spring  38   a  biases the switch  38  in the second configuration (shown) in which the down-well monitoring cable  36  is no longer connected to the temporary monitoring cable. In this way, switching between the first and second configurations can be performed without needing to disengage the tubing hanger running tool from the tubing hanger. Advantageously, this enables the temporary monitoring cable  34  to be disconnected from the down-well monitoring cable  36  before the tubing hanger has engaged with the tree  26 . Then, by electrically isolating the retracted switch pin, electrical testing can be performed on the temporary monitoring cable. In this way, if a fault develops before the tubing hanger has reached the sea bed, testing can be performed to determine if the fault is in the temporary monitoring cable or in the permanently installed equipment.  
         [0050]      FIGS. 7   a  and  7   b  show one example of the construction of a switching means suitable for use in the above described embodiments.  
         [0051]     The switching means comprises the spring-loaded switch  38  having a housing  90  in which is contained a contact ring  100 , the compression spring  38   a  and a shuttle body  110  having two parts  110   a  and  110   b , each connected to one end of the compression spring. The down-hole monitoring cable  36  is permanently connected to the contact ring  100 . In  FIG. 7   a , the switch is in the first contact position, in which the switch pin  48  provided at the end of the temporary monitoring cable  34  is in contact with the contact ring  100 . In this first configuration, the compression spring is biased in a compressed state.  
         [0052]     In  FIG. 7   b , the tubing hangar running tool has been disengaged from the tubing hangar, or the switch pin has been retracted into the tubing hanger running tool, such that the switch pin  48  of the temporary monitoring cable  34  has become disconnected from the contact ring  100 . The compression spring  38   a  now biases the switch  38  in the second configuration, in which the shuttle body  110   a  makes contact with the contact ring  100 . This completes the circuit across the switch  38 , through the shuttle body part  110   a , the spring  38   a  and the shuttle body part  110   b , such that the down-hole monitoring cable  36  is now electrically connected to the short cable portion  42  leading to the permanent monitoring connection  50 .  
         [0053]     There are various other means (not shown) of switching in this environment and location. It is possible to use a diode to isolate each line electronically without using a mechanical device. However, due to the electrical properties of a diode in the reverse direction, the current that passes through the diode in the reverse direction may be too great for satisfactory performance and integrity testing when the current and voltage are low (instrumentation level installation). The switching could be achieved by the use of a solenoid. Alternatively, the switching could be achieved via a contact-less method where no horizontal actuator was needed through the use of magnetic induction or other matching sensors that line up and transfer the current.  
         [0054]     An ROV (remotely operated vehicle) or a diver can rotate the mechanical actuator so as to extend the female wet mate connector horizontally to connect to the horizontal male wet mate connector. This connects the electrical signal to the permanently installed monitoring line.  
         [0055]     One advantage of the system outlined above with reference to FIGS.  3  to  7  is that the process is reversible i.e. even after the temporary monitoring cable  34  on the tubing hanger running tool has been disconnected from the down-hole cable in the tubing hanger it remains possible to re-connect it. Re-connection might be desirable if, for example, a fault were to be detected during permanent—i.e. post-installation—monitoring. In such a case, being able to lower the tubing hanger running tool and re-connect the temporary monitoring cable to the down-well cable might allow an operative to determine whether the fault is with the down-well sensors or else with the wet-mate connector, or even with the permanent monitoring cable itself. During installation (“running”) it is not uncommon for the tubing hanger running tool to be disconnected and reconnected several times if problems are encountered in engaging the tubing hanger with the tree or if unsatisfactory or puzzling readings are detected. In such cases the ability to disconnect and reconnect the temporary monitoring cable provides an advantage.  
         [0056]     Furthermore, switching may be performed by retracting the switch pin into the tubing hanger running tool, without needing to disconnect the tubing hanger running tool from the tubing hanger. In this way, testing can be performed before the tubing hanger has engaged with the tree.  
         [0057]     Reversible switching of an electrical signal in the complex, permanently installed well head hanger has previously not been undertaken and has the potential to save sub sea well operators significant amounts of time by avoiding remedial work. The integrity of the cables and the functioning of the down-hole devices can now be monitored throughout installation and thereafter with immediate feedback, and the operator has the option of reconnecting to a temporary monitoring cable by reconnecting the tubing hanger running tool.  
         [0058]     Whereas the specification speaks mainly of using electrical cables and electrical switch means to monitor and/or control down-well devices, it will be understood that the invention is equally applicable to the use of optical cables and electrical switches.  
         [0059]     Also, whilst the embodiments described are concerned with sub sea oil wells, it will be understood that the invention is equally applicable to other kinds of wells such a gas wells.  
         [0060]     Although the invention has been described with respect to specific embodiments for a complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying suitable modifications and equivalents that may occur to one skilled in the art and which fairly fall within the basic teaching herein set forth.

Summary:
A system for monitoring and/or controlling at least one device mounted on a tubing string of a well, the system comprising: a down-well cable for conveying a signal to and/or from at least one device mounted on a tubing string of a well; a temporary surface cable for conveying a signal between the at least one device and a first monitor/control station prior to and/or during installation of a tubing string in a well; a permanent surface cable for conveying a signal between the at least one device and a second monitor/control station after installation of the tubing string in a well; and switch means configurable between a first configuration, in which the down-well cable and the temporary cable are connected, and a second configuration, in which the down-well cable and the permanent cable are connected.