Abstract:
Apparatus for recovery of sections of tubing and inter alia, the tubing hanger, from a subsea well to enable the abandonment of a subsea well to be accomplished from a mono-hull vessel includes a dual gripper assembly ( 1 ) adapted for onshore or offshore deployment is configured to handle oilfield tubulars and associated completion equipment and configured for attachment to a wellhead structure and subsequent reciprocation cycles whereby oilfield tubulars can be run-in hole or pulled to surface without requiring a riser. A cutter mechanism ( 22 ) is disclosed for severing sections of tubular to form a clean cut end for attachment of a connection mandrel. The individually controllable gripping devices ( 19, 20 ) are operated such that during a reciprocation cycle at least one of the gripping devices is engaged around the tubular body for supporting same, and the other is spaced from the tubular body sufficiently for said other gripping device to slide over the tubular body to be selectively re-positioned to take up a fresh gripping position on the same or a further tubular body. The respective gripping devices can be used to bring together tubulars to be connected using a connection mandrel ( 28 ) or to manipulate a running and recovery tool ( 26 ), and to make up or break standard tool joints of wellbore tubulars. A method for pulling or running a completion is disclosed.

Description:
[0001]    The technical field of the invention is concerned with operations associated with exploitation of oil and gas reservoirs. In particular, but not exclusively, the invention provides the means for carrying out a subsea operation such as recovery of wellhead equipment, and pulling of the completion especially providing means for extracting pipe or tubing (oilfield tubulars) from a wellbore. The invention to be more particularly described hereinafter enables recovery of sections of tubing and inter alia, the tubing hanger, from a subsea well to enable the abandonment of a subsea well to be accomplished from a mono-hull vessel. 
       BACKGROUND OF THE INVENTION 
       [0002]    Generally, after a well has been completed, and production has begun, it may be necessary at some stage to suspend the production and make some form of well intervention to overcome an unforeseen problem, or to conduct remedial maintenance to realise satisfactory production from the well. Such an operation generally falls within the industry term “workover”. Most workovers, require only limited repair of an underwater oil, or gas well, and do not require a floating drilling rig. Running wireline or coiled tubing into the subsea well completion for data acquisition or remediation of the well can be currently be conducted from a relatively small, dynamically positioned, monohull vessel. However removal of the production tubing requires a full size subsea blow-out preventer (BOP) stack and large bore riser to surface to remove the tubing hanger and pull the completion. 
         [0003]    It would be advantageous to improve the procedure and provide a system and operational method that did not depend on the use of a large bore riser. 
       SUMMARY OF THE INVENTION 
       [0004]    The present invention offers improvements in subsea operations such as wellbore interventions and workovers by provision of a dual reciprocating gripper assembly for the installation or removal of pipe or tubing from a wellbore. The gripper assembly forms part of a lifting apparatus comprising a tubing support assembly to which it is operatively connected in use. A control system for the apparatus comprises operational controllers for the gripper assembly and the tubing support assembly. 
         [0005]    In an embodiment of the tubing support assembly, a frame is provided with holding means configured to translate in at least two dimensions and to turn about an axis. The holding means may move laterally in the X-Y plane. The axis may be a vertically aligned axis, typically with regard to facilitating overhead access to the wellbore through the wellhead structure. The holding means may be configured for rotation whilst suspending the weight of a tubing to be recovered and the assembly. The holding means may be slips, particularly dual bore slips adapted for alignment in a centred or off-centred position with respect to the longitudinal axis of the wellhead and wellbore. 
         [0006]    The dual reciprocating gripper assembly may be adapted to pass lines or cables without damaging same, e.g. by provision of slotted parts to enable the through passage of gauge cable or control lines. 
         [0007]    Sensing means may be provided whereby the gripper control system automatically senses an operational event or configuration to facilitate timing of an operational step in the reciprocation cycle. The operational event may be the proximity of the tubular connector and cable clamping device to the gripping means and the operational step may be to open and close the gripping means when appropriate. 
         [0008]    The gripper control system may include means for effecting a rotation of the gripper means e.g. in an operational step of making and breaking of wellbore tubulars to allow controlled application of torque. The apparatus may comprise tubing tongs, to facilitate subsea connection of standard tool joints to make up (or break) wellbore tubulars. 
         [0009]    The dual reciprocating gripper assembly may be reciprocated by main reciprocating cylinders, the function of which can be augmented by provision of high capacity auxiliary cylinders to provide additional lifting force when required, e.g. when unseating the tubing hanger from the wellhead. 
         [0010]    The deployment and recovery of the dual reciprocating gripper may be facilitated by provision of guide lines upon which the gripper assembly can be run down for deployment or run back up for recovery. 
         [0011]    The dual reciprocating gripper assembly may be connected or disconnected remotely underwater. 
         [0012]    A cutting device for the purpose of disconnecting lengths of said wellbore tubular may be operatively associated with the dual reciprocating gripper assembly, e.g. mounted directly below the gripper means so as to act upon a tubular gripped by said gripper means when required. Such a cutting device may be remotely operated e.g. by use of a remotely operated underwater vehicle (ROV). The cutting device provides for severing sections of tubular to form a clean cut end for attachment of a connection mandrel 
         [0013]    In a typical advantageous use of the dual reciprocating gripper assembly of the invention, the dual gripper means are operated such that when deployed at the wellhead, the lower gripper means is engaged with the wellbore tubular to suspend same, whilst at the same time the upper gripper means is operated to locate, secure, axially guide and connect a connection mandrel into said wellbore tubular. 
         [0014]    The connection mandrel may be deployed underwater on coiled tubing from a vessel to connect with the suspended wellbore tubular. 
         [0015]    When said connection mandrel is secured to or moving in the gripper means at the seafloor, said coiled tubing may be maintained on the vessel on an adjustable, constant tension reel. 
         [0016]    Alternatively, the connection mandrel may be deployed underwater on a rope or cable from a vessel e.g. by use of a compensated crane or winch. 
         [0017]    The dual reciprocating gripper assembly of the invention may be operated together with a device for suspending and centring a dual bore tubing with respect to the centreline of said dual reciprocating gripper assembly. 
         [0018]    The dual reciprocating gripper assembly of the invention may be operated together with a device for rotating and orientating a dual bore tubing about the centreline of said dual reciprocating gripper assembly. 
         [0019]    The dual reciprocating gripper assembly of the invention may be deployed on a fixed surface wellhead installation, for example on the drill deck of a land-based rig. Thus the invention, whilst primarily of benefit for remote use at a subsea site, is also of benefit onshore. 
         [0020]    According to a further aspect of the invention, there is provided a dual reciprocating gripper assembly for the installation or removal of a tubular body from a wellbore, said assembly being adapted for removable mounting upon a wellhead structure, and comprising first and second individually controllable gripping devices adapted to selectively engage around a tubular body, said assembly being operatively connected to control means for operating said gripping devices and configured such that during a reciprocation cycle step for installation or removal of a tubular body at least one of the gripping devices is engaged around the tubular body for supporting same, and the other is spaced from the tubular body sufficiently for the gripping to slide over the tubular body to be selectively re-positioned to take up a fresh gripping position on the same or a further tubular body. 
         [0021]    The dual reciprocating gripping devices may be configured to apply torque to the tubular body, and this may be applied during a reciprocation step. 
         [0022]    The dual reciprocating gripper assembly may include gripping devices comprising a plurality of cooperating segments each having a slip face for engaging a tubular, said slip face comprising a plurality of ball bearings pressed onto it, optionally in rows or a random configuration. 
         [0023]    The dual reciprocating gripper assembly may have at least one slot, provided between the segments to permit spacing for cables or lines to pass through the gripper assembly as the gripper assembly is reciprocated. 
         [0024]    The dual reciprocating gripper assembly may have gripping devices comprising cooperating slip face and slip trunnion parts, wherein the cooperating surfaces comprise a plurality of opposed ramps whereby relative longitudinal translation of the ramps results in lateral movement of the slip surface with respect to the slip trunnion. 
         [0025]    The dual reciprocating gripping devices may be mounted in a superposed or tandem configuration in a support assembly comprising a plurality of support posts upon which the gripping devices are adapted to travel, and a plurality of actuators operatively connected to the gripping devices to selectively and independently elevate or lower the respective gripping devices. Guide means may be provide to facilitate travel of the gripping means upon the support posts. The guide means may comprise support plates serving as a mounting for the actuators, which may be hydraulic cylinders. The invention is especially useful for remote operation in a subsea location, and the hydraulic cylinders may be powered by subsea power packs and accumulators mounted upon an associated support assembly. 
         [0026]    The guide means may additionally comprise guide lines leading to and anchored at the wellhead. The guide lines may be run from a surface vessel to the wellhead. 
         [0027]    The sub-sea dual reciprocating gripper assembly may be provided with docking installation guide cones or stab connectors to facilitate deployment at the wellhead. The stab connectors may be hydraulically retractable. 
         [0028]    The respective gripping devices of the gripper assembly can be used to bring together tubulars to be connected using a connection mandrel or to manipulate a running and recovery tool, and to make up or break standard tool joints of wellbore tubulars by rotation .SQ 
         [0029]    In an embodiment the apparatus is configured to sense the orientation of the tubing hanger, effect rotation of the lower slips and subsequent lateral translation of the tubing after the tubing hanger and tail pipe have been removed, so that the tubing can be axially aligned for the connection mandrel. 
         [0030]    According to a further aspect of the invention there is provided a method of pulling a completion tubular from a subsea well comprising retrievably deploying a retrieval tool and a dual reciprocating gripper assembly from a surface vessel to the wellhead, operating the dual reciprocating gripper assembly to bring the retrieval tool into operative contact with a subsea tubing hanger at the wellhead, engaging the tubing hanger with the tool whilst gripping and rotating the tool, running a connection mandrel from the surface vessel to the wellhead, connecting the mandrel to the retrieval tool, operating the dual reciprocating gripper assembly to unlatch the tubing hanger, raising the retrieval tool and tubing hanger whilst supporting the tubular at the wellhead, separating the tubing hanger from the supported tubular, recovering the dual reciprocating gripper assembly and the tubing hanger with connection mandrel and retrieval tool to the surface vessel, re-running the connection mandrel and the dual reciprocating gripper assembly to the wellhead, operating the dual reciprocating gripper assembly to engage the connection mandrel with the supported tubular, and subsequently operating the dual reciprocating gripper assembly to successively engage and pull the tubular, wherein one of the grippers of the dual reciprocating gripper assembly supports the tubular whilst the other re-positions with respect to the tubular to take up the load. 
         [0031]    In an embodiment, the method comprises the steps of sensing the orientation of the tubing hanger, rotating the lower slips as appropriate, and effecting any lateral translation of the tubing required after removing the tubing hanger and tail pipe, so that the tubing can be axially aligned and properly connected to the connection mandrel. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0032]    The invention will be described hereinbelow by way of illustration with reference to the accompanying drawings in which aspects of the invention are represented schematically and operational steps of the invention are represented in a storyboard format, wherein: 
           [0033]      FIG. 1  shows a side view and partial vertical section of a subsea tubular handling system of the invention installed on a subsea wellhead at the seafloor; 
           [0034]      FIG. 2  shows a typical first step in a sub sea work over procedure in which a Blow Out Preventer (BOP) stack and return line is run down to a sub sea wellhead; 
           [0035]      FIGS. 3   a  and  3   b  show respectively, the installed BOP (left hand side of sheet), and a tubing support assembly of the invention connected to the BOP (right hand side of sheet); 
           [0036]      FIGS. 4   a  and  4   b  show respectively, the installed tubing support assembly (left hand side of sheet), and a dual reciprocating gripper assembly of the invention together with tubing hanger running and retrieval tool secured inside the gripper assembly (right hand side of sheet); 
           [0037]      FIG. 5  illustrates the released tubing hanger running and retrieval tool positioned for location into the tubing hanger and having an upper part within the gripper assembly so that the said gripper assembly may re-acquire the tool when necessary; 
           [0038]      FIG. 6  illustrates the deployment of a connection mandrel for attachment to the tubing hanger running and retrieval tool; 
           [0039]      FIG. 7  illustrates the positioning of the gripper assembly to take the load to unseat the tubing hanger, and optional lift capacity provided by additional short stroke cylinders to assist in unseating the tubing hanger from the wellhead; 
           [0040]      FIG. 8  illustrates the setting of slips to support the well tubing, and subsequent cutting operation to sever the tubing hanger from the well tubing whilst preserving the annulus tail pipe; 
           [0041]      FIG. 9  illustrates the release of the connections between the reciprocating gripper assembly and the wellhead, and initial separation for recovery to the surface vessel using a compensated winch or crane (not shown); 
           [0042]      FIG. 10  shows the reciprocating gripper assembly re-run upon the connection mandrel and re-connected at the wellhead to make a connection with the severed well tubing; 
           [0043]      FIG. 11  shows schematically an overhead view of an embodiment of a gripper assembly with a provision for slots that enable the well tubing to be properly suspended on each gripper but allowing the gauge cable, and control line to by-pass the gripping face; 
           [0044]      FIG. 12  shows a second embodiment of a gripper assembly with a spring loaded protection sleeve for cables and/or lines; 
           [0045]      FIG. 13  shows an enlarged view of a slip segment assembly forming part of the reciprocating gripper assembly first shown in  FIG. 1 , in gripping contact with a surface; 
           [0046]      FIG. 14  shows the slip segment assembly of  FIG. 13 , released from gripping contact with a surface to allow the gripper device to slide over the surface during a gripper re-positioning step; 
           [0047]      FIG. 15   a  (left hand side of drawing sheet) shows the gripper assembly of  FIG. 11  in a released mode for re-positioning on a tubular surface; 
           [0048]      FIG. 15   b  (right hand side of drawing sheet) shows the gripper assembly of  FIG. 11  in an engaged mode for gripping on a tubular surface; 
           [0049]      FIG. 15   c  (centre of drawing sheet) shows the gripper assembly of the invention positioned around a wellbore tubular to be recovered to a surface vessel; 
           [0050]      FIG. 16   a  (left hand side of drawing sheet) shows the gripper assembly of  FIG. 11  in a released mode for re-positioning on a tubular surface; 
           [0051]      FIG. 16   b  (right hand side of drawing sheet) shows the gripper assembly of  FIG. 11  in an engaged mode for gripping on a tubular surface to be pulled; 
           [0052]      FIG. 16   c  (centre of drawing sheet) shows the gripper assembly of the invention positioned around a wellbore tubular to be recovered to a surface vessel with the grippers at mid stroke where a reversal of gripping roles is effected; 
           [0053]      FIG. 17   a  (left hand side of drawing sheet) shows the gripper assembly of  FIG. 11  in a released mode for re-positioning on a tubular surface; 
           [0054]      FIG. 17   b  (right hand side of drawing sheet) shows the gripper assembly of  FIG. 11  in an engaged mode for gripping on a tubular surface; 
           [0055]      FIG. 17   c  (centre of drawing sheet) shows the gripper assembly of the invention positioned around a wellbore tubular to be recovered to a surface vessel with both gripper devices at full stroke, at which point the lower gripper device is to be fully opened to pass over cable clamping means; 
           [0056]      FIG. 18  shows a cross-section of a composite coil tubing which may be used for deployment of a connection mandrel 
           [0057]      FIG. 19  shows use of a composite coil tubing for deployment of a connection mandrel which when connected to the well tubing provides a high pressure circulation path into the well tubing; 
           [0058]      FIG. 20  shows use of a compensated crane or winch for deployment of a connection mandrel; and 
           [0059]      FIG. 21  shows the reciprocating gripper assembly set up on a platform wellhead where there are multiple wellheads that are supported on a cellar deck, the gripper assembly being supported on the drill deck. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0060]    Referring initially to  FIG. 1 , a dual reciprocating gripper assembly  1  of this invention is located over and connected to a tubing support assembly  2  which has a through bore into the Blowout Preventer Stack (BOP)  3 . This is connected to the wellhead  4  by an hydraulic connector  5 . A subsea spool piece  6  equipped with two remotely operated valves  7  and a subsea pump  8  are secured to the hydraulic connector  5  at the bottom and at the top to blind shear rams  9  and variable bore pipe rams  10  the BOP. 
         [0061]    The tubing support assembly  2  comprises dual bore slips  11  enclosed in a structural frame  12  which enables said dual bore slips  11  to move laterally in the X-Y plane. The dual bore slips  11  also rotate whilst suspending the weight of well tubing  13  tubing in support assembly  2 . These functions are for aligning the suspended well tubing string  13  with respect to the centreline of the dual reciprocating gripper assembly  1  for retrieval of the well tubing  13  to surface. Attached to said structural frame  12  are subsea power packs  14  and accumulators  15  used in operating the apparatus of the invention and for other operational purposes. These are capable of providing the hydraulic power for the complete assembly. The subsea power packs  14  comprise DC motors powering hydraulic pumps. 
         [0062]    The reciprocating gripper assembly  1  comprises a dual system of upper and lower gripper devices  19 ,  20  respectively, operably mounted within a multiple post support structure, here four such posts  16  being fixed to support plates  17 . The support plates  17  are used to suspend the operating cylinders  18  for the upper reciprocating gripper device  19  and the lower reciprocating gripper device  20 . The gripper devices move up and down the post structures  16  guided by attached travelling plates  21 . 
         [0063]    A cutting device  22  such as a diamond saw, operable externally from a remotely operated vehicle (ROV) can be implemented within the vertical space between the grippers  19 ,  20 . 
         [0064]    One or more of the reciprocating gripper devices  19 ,  20  may be designed and configured for rotational motion about the longitudinal axis so as to apply torque to the well tubing  13  for making and breaking connections. 
         [0065]    A possible operating sequence of the system and use thereof will now be described but it will be appreciated by a person skilled in the art that there are several different ways of employing the equipment described to achieve the objective of pulling and running the well completion including the well tubing  13  without departing from the scope of the invention as set forth in the claims. 
         [0066]    The illustrated system is designed to operate with guide lines  23  but other embodiments may operate in guide line-less mode. 
         [0067]      FIG. 2  shows the typical first operation which is to run the BOP stack  3  down the guide lines  23  from a control site such as a rig or surface vessel  24 . The hydraulic connector  5  latches onto the wellhead  4 . At the same time a return line flexible hose  40  is spooled out from the vessel  24 . 
         [0068]      FIG. 3  shows the tubing support assembly  2  run and connected to the Blowout Preventer Stack  3 . This is latched by means of four hydraulically retractable, stab-in connectors  25 . At the same time all the electro-hydraulic control functions for the equipment are connected. 
         [0069]    Finally the dual reciprocating gripper assembly  1  is run down the guide lines  23  with the tubing hanger running and retrieval tool  26  secured inside of the grippers  18 . The tubing hanger running and retrieving tool  26  is run in this way because its outside diameter will not pass through restriction of the grippers  19 ,  20 . The lowermost gripper  20  is designed to suspend the entire dynamic load of the dual reciprocating gripper assembly  1  on the upper shoulder of the tubing hanger running and retrieving tool  26 . This is illustrated in  FIG. 4 . 
         [0070]    The dual reciprocating gripper assembly  1  is latched in the same way as described above i.e. by means of four hydraulically retractable, stab-in connectors  25 . 
         [0071]    The reciprocating grippers  19 ,  20  manipulate the tubing hanger running and retrieval tool  26  down to locate into the tubing hanger  27 . The gripper assembly  1  can be rotated to provide the necessary orientation of the tubing hanger running and retrieving tool  26  to connect to the tubing hanger  27 . The length of the tubing hanger running and retrieval tool  26  is designed so that when the connection is made to the tubing hanger  27  the upper part of the tool remains in the lowermost gripper  20 . This is illustrated in  FIG. 5 . 
         [0072]    This enables a connection mandrel  28  to be deployed from the vessel  24  down the guide lines  23  using either composite coiled tubing  32  or a compensated lift line  30  and passed through a guide funnel  31  for guidance into the upper gripper  20 . The lower end of the connection mandrel  28  has a gripper and seal that will enable a pressure tight, high tensile, connection to be made to the tubing hanger running and retrieval tool  26 . This is illustrated schematically in  FIG. 6 . 
         [0073]    After the connection mandrel  28  has been connected to the tubing running and retrieval tool  26 , the reciprocating gripper assembly  1  will be used to unseat the locking mechanism in the tubing hanger  27 . 
         [0074]    This may take some considerable tensile load, exceeding the capacity of the cylinders  18 . To avoid this simple short term high load capacity deficit, short stroke, “pancake” auxiliary cylinders  41  will be positioned at the interface between the travelling plate  21  and the fixed support plate  17 . They may be mounted on either one of these support plates  17 . This can easily provide in excess of 100 tons additional tensile capacity. This is illustrated in  FIG. 7 . 
         [0075]    This auxiliary capability is required especially when unseating the tubing hanger  27  from the wellhead  4  when an initial high load demand is placed on the cylinders  18 . 
         [0076]      FIG. 8  illustrates the next step. The tubing hanger  27  and tubing hanger running and retrieval tool  26  are now positioned in the space between the lower four post structure  16  and the tubing support assembly  2 . This enables the dual bore slips  11  to be set and support the weight of the well tubing  13 . 
         [0077]    A remotely operated vehicle (ROV) equipped with a diamond wire saw  42  can now sever the lower tubing hanger  27  connection to the well tubing  13 . If an annulus tail pipe  55  is connected to the tubing hanger  27  care should be taken not to sever this as it can be recovered, attached to the tubing hanger  27 . The tubing hanger  27  plus the tubing hanger running and retrieval tool  26  and the connection mandrel  28  secured in the reciprocating gripper assembly  1  will now be recovered to surface on a motion-compensated crane or winch  39 . To carry out this action the four hydraulically retractable, stab-in connectors  25  will have to be released. This is illustrated in  FIG. 9 . 
         [0078]    The complete assembly can now be recovered to the vessel  24  where the tubing hanger  27  can be removed. The reciprocating gripper assembly  1  can be re-run using the connection mandrel  28  secured to the motion-compensated winch or crane  39 . The four hydraulically retractable, stab-in connectors  25  will once more be connected. 
         [0079]    The connection mandrel  28  can now be run from the vessel  24  in a manner that will be described presently. On landing inside the gripper assembly  1 , the connection mandrel  28  will be reciprocated down to make the connection to the severed well tubing  13  suspended in the dual bore slips  11 . If the well tubing  13  is arranged in dual bore format, it will be necessary to align the well tubing  13  suspended in the dual bore slips  11  with the connection mandrel  28 . This is done by means of operating cylinders that move the dual bore slips  11  only a few centimetres to well centre (to position  11   a ). This is illustrated in  FIG. 10 . 
         [0080]    The well tubing  13  will often have attached a gauge cable  43  or control line  44  attached, normally combined together and secured at each well tubing  13  connection with a cable clamp  45 . To retrieve the well tubing with the attached gauge cable  43  and control line  44  through the upper gripper  19  and the lower gripper  20  requires some special adaptation. 
         [0081]    One embodiment is shown in  FIG. 11 . Here the individual gripper assembly (identical for the upper gripper  19  and the lower gripper  20 ) have a total of six slip segment assemblies  46  with a provision for two slots  47  that enable the well tubing to be properly suspended on each gripper but allowing the gauge cable  43  and control line  44  to by-pass the gripping face.  FIG. 12  shows a second embodiment that makes use of a spring loaded protection sleeve  48  which runs over the well tubing  13  and the cable clamps  45  for the purposes of guiding the attached gauge cable  43  through the gripper assembly. Those skilled in the art will be aware of equivalent means of ensuring the gauge cable  43  and control line  44  are retained in the slots  47 . 
         [0082]    The attachment of the gauge cable  43  and control line  44  may be random. So it may be necessary for the dual bore slips  11  to rotate the well tubing  13  so that it is properly orientated with respect to the slots  47 . The alternative embodiment of this feature is the rotation and alignment of the upper gripper  19  and lower gripper  20 . However this option presents an obvious increase in complexity which though feasible, makes it less preferable. 
         [0083]    The operation of the reciprocating gripper assembly  1  will now be generally explained. One embodiment of the slip segment assemblies  46  is illustrated in  FIG. 13 . The slip face  50  has rows of ball bearings  51  pressed onto it. When gripping, the slip face  50  with the ball bearings  51  pressed into the face, slides down the slip trunion  52  and lightly indents the pipe to ensure the operation of the taper grip mechanism onto the well tubing  13 . 
         [0084]    If the direction of travel is reversed as claimed in  FIG. 14  and the slip face travels back up the taper enabling the slip segment assemblies to slide downwards over the well tubing  13 . 
         [0085]      FIG. 15  illustrates the operation of the reciprocating grippers to remove the well tubing  13  and retrieve the latter to the vessel  24 . Here the upper gripper  19  is engaged to support the weight of the well tubing  13  and the upper cylinders  18  are near the bottom of their strokes and travelling up. 
         [0086]    The lower gripper  20  is open and travelling down on the lower cylinders  18 , sliding over the well tubing  13 , gauge cable  43  and control line  44 . As the cable clamp  45  reaches a mechanical or electrical sensor  49 , it signals the approach of the cable clamp  45  to the control system. 
         [0087]    As the upper gripper  19  travels upwards with the well tubing  13  and the lower gripper  20  travels downwards, the latter meets the cable clamp  45 . In this example illustrated by  FIG. 16 , both the upper and lower cylinders  18  are near mid-stroke. The control system signals the grippers  19 ,  20  to stop and reverse direction. The lower gripper  20  now takes the load of the well tubing  13  and the upper gripper  19  disengages from the well tubing  13  once more, sliding over it. 
         [0088]    At the end of the full stroke of the cylinders  18  the lower gripper  20  now opens up fully to allow the passage of the cable clamp  45 . This is illustrated in  FIG. 17 . This mechanism always ensures that the gripper is always positioned to make a full stroke in the open position to step over the cable clamp  45  and avoid closing on it. 
         [0089]    There are several ways of recovering the tubing to the vessel  24 . 
         [0090]    One embodiment of this invention is to deploy the connection mandrel  28  on composite coiled tubing  32 .  FIG. 18  shows a cross section of such a tube. A thermoplastic liner  33  can form the centre or base tube. Outside this helically wound conductor and fibre optical lines  34  can be installed to provide power and communications. The outer layer of this pipe is constructed from thermoset carbon fibre or glass fibre  35 . 
         [0091]    Composite coiled tubing  32  connected to the well tubing  13  using the connection mandrel  28  provides for a high pressure circulating path into the well tubing  13  for cementing and other wellbore operations. This is illustrated in  FIG. 19 . 
         [0092]    Deployment of the connection mandrel  28  on composite coiled tubing is done from a constant tension reel  36 , so that when the connection mandrel  28  is fixed with respect to the seafloor in the grippers  19 ,  20 ) the constant tension reel  36  provides heave compensation for the vessel movements. This unique feature simplifies the seafloor connection and ensures that the composite coiled tubing  32  is always in tension. If conventional steel coiled tubing was used for this application, it would quickly reach its fatigue limit with the constant cycling back on forth onto and off the constant tension reel  36 . However with composite coiled tubing  32  in this constant tension mode, deployed on a sufficiently large constant tension reel  36 , the fatigue life of the composite coiled tubing  32  would be many million cycles. 
         [0093]    Another advantage of composite coiled tubing  32  is that it does not require the same back tension on the constant tension reel  36  as steel coiled tubing. Typically composite coiled tubing  32  weighs about 1.3 kg/m in water so a minimum tension required in 300 m of water would be 390 kg. The back tension required to ensure proper spooling for the composite coiled tubing  32  on and off the constant tension reel  36  is about 360 kg. Hence in the water depth of 300 m a back tension of 500 kg would be a reasonable minimum. 
         [0094]    Thus, although the composite coiled tubing  32  is kept in tension by the constant tension reel  36  it has a large degree of compliance with respect to the met-ocean conditions. It is critical to ensure that the minimum bend radius of the composite coiled tubing  32  is never violated. Hence a lower bend restrictor  37  is attached to the outside of the composite coiled tubing  32  at the transition to the connection mandrel  28 . An upper bend restrictor  38  will be fixed to the vessel  24  and designed to enable a sliding contact as the composite coiled tubing moves in and out with the movement of the vessel  24 . 
         [0095]    The connection mandrel  28  will normally be equipped with a valve  39  that can be electrically operated from the surface via the helically wound conductor and fibre optic lines  34  integral to the composite coiled tubing  32 . 
         [0096]    The second embodiment of this invention is to deploy the connection mandrel  28  on a heave motion compensated crane or winch  39  which is well known and understood in marine operations. 
         [0097]    In this case the operator can choose the length of well tubing  13  recovered to the vessel  24  in one pass. For example if the met-ocean conditions are benign, it may be possible to recover the length of well tubing  13  corresponding to the water depth to the surface. The main limiting factor is the bending moment applied to the top of the reciprocating gripper assembly  1 . This is illustrated in  FIG. 20 . 
         [0098]    If the well tubing  13  is recovered to surface, it provides direct surface access to the well at the vessel  24 . The well tubing  13  will need to be supported on tensioned elevators  53  with surface pipe cutter  54  to remove and lay down joints of well tubing  13 . 
         [0099]    A further embodiment of the reciprocating gripper assembly  1  is illustrated in  FIG. 21  set up on a platform wellhead  2  where there are multiple wellheads that are supported on a cellar deck  56 . Reciprocating gripper assembly  2  will be supported on the drill deck  57 . The crane  58  is used for handling the pipe that is removed or replaced into the well-bore.