Patent Publication Number: US-9410381-B2

Title: Riser tension protector and method of use thereof

Description:
This application claims priority to Australian patent application No. 2014221195 filed on Sep. 2, 2014, the entire contents of which is incorporated herein by reference. 
     BACKGROUND 
     A riser tension protector and a coiled tubing lift frame assembly with over tension protection and back-up heave compensation are disclosed for use on floating drilling vessels such as drilling ships and semi-submersible drilling vessels. 
     As oil and gas offshore exploration and production operations are increasingly established in deeper waters, it has become more common for drilling activities to be performed from rigs that float on the surface of the water, such as drilling vessels or semi-submersible drilling rigs. Unlike fixed rigs or jack-up rigs, floating rigs are subject to wave motion, causing up-and down motion, which must be compensated for during drill, well completions, well testing, well interventions and other operations. Wave motion is of particular concern during “locked-to-bottom” operations (i.e., well completion, well testing and well intervention) where a completions workover riser or landing string (alternatively referred to as a ‘riser’) is physically connected to the subsea well at the seabed. It will be appreciated that, depending on the nature of the operations, the riser may be connected to a tubing hanger at the well-head, to a subsea tree or other infrastructure at the top of the well. Loss of heave compensation can lead to severe consequences. 
     Apart from the operational difficulties arising from the up-and-down motion of the floating rig, significant safety issues also arise, in particular the potential for the riser to fracture or buckle, resulting in loss of well containment and potential blowout. Indeed, safety standards in offshore operations demand that a heave compensation system be regarded as an essential component of a floating rig during locked-to-bottom operations. 
     Known heave compensation systems may be described as employing passive heave compensation or active heave compensation. 
     A simple passive heave compensator is a soft spring which effectively strokes in and out in response to string loads as the vessel heaves up and down while effectively holding constant tension on the string. Exemplary types of simple passive heave compensators are crown-mounted compensators or inline passive drill string compensators. Passive heave compensators employ hydraulic cylinders and associated gas accumulators to store and dissipate the energy as the vessel heaves up and down. 
     Active heave compensation differs from passive heave compensation by having an external control system with external inputs from motion reference units that actively tries to compensate for any movement at a specific point. Exemplary types of active heave compensation include active heave draw works which employ electric or hydraulic winch systems to raise and lower the top drive in response to the vessel motion. 
     Active-passive compensation systems consist of a primary passive compensation system with secondary actively driven hydraulic cylinders to reduce tension variations and improve efficiency. Two independent active and passive systems are generally not employed. The essential nature of the heave compensation function to a floating rig is such that safety standards also demand that they be designed such that no single component failure shall lead to overall failure of the system. They should also be “fail to safety” meaning that in the event of any predictable failures, the system defaults to a compensating state, which is the safest state during locked-to-bottom operations. While active heave draw works have numerous benefits for normal drilling operations, they fail to a “locked condition”, which is undesirable for well completions, well testing and well intervention operations. Passive compensation systems (e.g. crown mounted compensators) are also not immune to failures. Safe operations and industry standards require additional means of safety to be implemented in the system/equipment configuration. Additional means of safety may include a standard in-line tensioner or traditional compensated coiled tubing lift frame, design of a weak link in the riser/landing string, weaklink bails, limiting operation parameters to be within the stretch limit of the riser, and so forth. 
     Generally, these operating parameters place constraints on operators which have direct impact on productivity and efficiency. All these existing options have limitations. In the case of a standard inline tensioner or conventional compensated coiled tubing lift frame, there are concerns about the how the system behaves when run in series with the active heave draw works. In the case of the weak link in the riser and weaklink bails, they typically only provide protection in an over-tensioned case and once broken, they provide no support to the landing string thereafter. In the case of limiting operating parameters to within the stretch of the riser, this can impose considerable downtime during offshore operations. 
     It would be advantageous to provide an inline tensioner or a back-up compensator which can be fully locked under normal operating loads so that it did not interfere with the operations of the primary compensator, but which is capable of automatic and rapid activation to provide compensation if axial load on the riser exceeds normal operation limits, which may occur in event of failure of the rig&#39;s primary compensator. 
     It would also be desirable to have an inline tensioner or a back-up compensator that may be actuated without the need for control valves to control fluid flow through fluid lines. Control valves add complexity into the back-up compensator, introducing additional failure points and restricting the actuation speed of the back-up compensator. 
     There is therefore a need for an alternative or improved heave compensation apparatus which may operate as a back-up to the rig&#39;s drill string compensator in the event of failure or disablement of the rig&#39;s drill string compensator. 
     There is also a need for an improved heave compensation apparatus which can be used as a lift frame for the installation of intervention pressure control equipment (i.e. coiled tubing or wireline equipment) during well testing/well intervention work, as those components are installed in the congested space of the drilling derrick. 
     The above references to background art do not constitute an admission that the art forms a part of the common general knowledge of a person of ordinary skill in the art. The above references are also not intended to limit the application of the heave compensation and tensioning apparatus as disclosed herein. 
     SUMMARY 
     Generally, a riser tension protector, a coiled tubing lift frame assembly including said riser tension protector, and a method of use thereof, are disclosed. The coiled tubing lift frame assembly may be employed as a back-up to a floating vessel&#39;s primary compensator in the event of failure or disablement of the rig&#39;s primary compensator. The primary compensator may be in the form of a crown mounted compensator, active heave drawworks, or other type of drill string compensator. 
     According to one aspect, there is disclosed a riser tension protector for a riser used in operations on a floating vessel, said protector comprising: 
     a pair of pneumatic cylinders spaced apart from one another, the pneumatic cylinders having a respective cylinder barrel and a piston rod translatable therein, a free end of the piston rods being operatively associated to a top drive system and a lower end of the cylinder barrels being fixed relative to a flowhead assembly; 
     wherein the pneumatic cylinders are charged to a pneumatic pressure sufficient to cause the piston rods to remain retracted and stationary in said barrels when an axial load on the riser is under a predetermined operating load threshold and to extend on an upheave of the floating vessel when the axial load on the riser exceeds the predetermined operating load threshold. 
     In the event of failure of the rig&#39;s primary compensator on an up heave of the floating vessel, the axial load may increase to or above the predetermined operating load threshold, causing the piston rods to automatically extend in said barrels. On a subsequent down heave of the floating vessel, the piston rods will retract in said barrels in response to a decreasing axial load on the riser. The piston rods may then remain retracted and stationary within the barrels until the predetermined operating load threshold is exceeded again. 
     It will be appreciated that the pneumatic pressure charged to the pneumatic cylinders and the predetermined operating load threshold may be varied to suit the planned operation. 
     In one embodiment, the pneumatic cylinders are arranged to be in fluid communication with one another in a manner whereby the pneumatic pressure in each cylinder is the same. The provision of the same pneumatic pressure in each cylinder ensures that the respective piston rods extend simultaneously in response to the axial load. 
     In another embodiment, the piston rods may be hollow. The hollow piston rod may define a cylindrical cavity. The cylindrical cavity may also be charged to the same pneumatic pressure as the pneumatic cylinders. The cylindrical cavity of the hollow piston rod may be in fluid communication with a rod side of the cylinder barrel via one or more apertures in a piston rod wall. The rod side of the cylinder barrel defines an annular cavity. The annular cavity may be charged to the pressure sufficient to cause the piston rods to remain retracted in said barrels when the axial load on the riser is under the predetermined operating load threshold. 
     In a further embodiment, respective upper ends of the cylinder barrels may be interconnected by a cross member. The free ends of the piston rods may be fixed to an upper frame section adapted for attachment to the top drive system. 
     According to a second aspect, there is disclosed a coiled tubing lift frame assembly, said assembly comprising: 
     a frame having an upper frame section adapted for attachment to a top drive system and a lower frame section adapted to interface with a flowhead assembly; 
     a pair of pneumatic cylinders spaced apart from one another, the pneumatic cylinders having a respective cylinder barrel and a piston rod translatable therein, a free end of the piston rods being fixed to the upper frame section and a lower end of the cylinder barrels being fixed to the lower frame section; 
     wherein the pneumatic pressure in said cylinders is charged to a pressure sufficient to cause the piston rods to remain retracted and stationary in said barrels when an axial load on the riser is under a predetermined operating load threshold and to extend on an upheave of the floating vessel when the axial load exceeds the predetermined operating load threshold. 
     The upper frame section may be attached to the top drive system by means of coupling elements, such as elevator bails. 
     In one embodiment, the lower ends of the cylinder barrels may be fixed to the lower frame section by means of coupling elements, such as elevator bails. In an alternative embodiment, the lower ends of the cylinder barrels may be fixed directly to the lower frame section. In this particular embodiment, the lower end of the cylinder barrel may define a rigid section. In these embodiments, respective upper ends of the cylinder barrels may be interconnected by a cross member. 
     The disclosure also describes a method for providing back up compensation for a riser used in operations on a floating vessel in the event of failure of, or operability issues with, a primary compensator, the method comprising: 
     providing the riser tension protector as defined above; 
     locating the pair of pneumatic cylinders of the riser tension protector between the top drive system and the flow head assembly in a manner whereby the free ends of the piston rods are operatively associated with the top drive system and the lower ends of the cylinder barrels are fixed relative to the flow head assembly; 
     charging the cylinders to a pneumatic pressure sufficient to cause the piston rods to remain retracted and stationary in said barrels when an axial load on the riser is under a predetermined operating load threshold and to extend on an upheave of the floating vessel when the axial load on the riser exceeds the predetermined operating load threshold; and, 
     in the event of failure of, or operability issues with, the rig&#39;s primary compensator and the axial load on the riser exceeding the predetermined operating load threshold, allowing the piston rods to extend to compensate for an upheave of the floating vessel. 
     In one embodiment the piston rods may be purposefully extended to a mid-stroke position so that the piston rods may extend or retract, respectively, thereby providing compensation on both an up heave and a down heave, respectively, maintaining relatively constant axial load on the riser. Axial load variations are compensated for by gas compression and expansion in the cylinders. 
     It will be appreciated that if the piston rods are purposefully extended to the mid-stroke position, the axial tension will increase as the piston rods extend. The riser tension protector is configured to allow an operator to remotely decrease the pneumatic pressure in the cylinders to reduce the axial load lower than the predetermined operating load threshold. Similarly, the pneumatic pressure in the cylinders may be increased by a remote operator. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Notwithstanding any other forms which may fall within the scope of the riser tension protector and coiled tubing frame assembly as set forth in the Summary, specific embodiments will now be described, by way of example only, with reference to the accompanying drawings in which: 
         FIG. 1  is a partial schematic representation of a derrick and drill floor of a floating vessel showing a riser tension protector and coiled tubing lift frame assembly in accordance with one embodiment configured in-line with various components used in locked-to-bottom operations for oil and gas reserves offshore; 
         FIG. 2  is a schematic representation of a riser tension protector for a floating vessel in accordance with the disclosure, wherein the piston rods of said protector are shown fully retracted; 
         FIG. 3  is a schematic representation of the riser tension protector shown in  FIG. 2  with piston rods shown in phantom; 
         FIG. 4  is a longitudinal cross-sectional representation of the riser tension protector shown in  FIGS. 2 and 3 ; 
         FIG. 5  is a perspective view of an upper frame section of the riser tension protector shown in  FIGS. 1-4 ; 
         FIG. 6  is a perspective view of a cross beam section of the riser tension protector shown in  FIGS. 1-4 ; 
         FIG. 7  is a perspective view of one embodiment of a lower frame section of the coiled tubing frame assembly shown in  FIGS. 1-6 ; 
         FIG. 8  is a perspective view of another embodiment of a lower frame section of the coiled tubing frame assembly shown in  FIG. 9 ; 
         FIG. 9  is a partial schematic representation of a derrick and drill floor of a floating vessel showing a riser tension protector and a coiled tubing lift frame assembly in accordance with an alternative embodiment configured in-line with various components used in locked-to-bottom operations for oil and gas reserves offshore. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of a riser tension protector for a riser used in operations on a floating vessel and a coiled tubing lift frame assembly will now be described by way of example only, and with particular (though not exclusive) reference to drilling and completions for oil and gas reserves offshore. 
     Referring to  FIGS. 1 and 9 , there is shown a partial and schematic view of a derrick  100  and a drill floor  200  of a floating vessel used in locked-to-bottom operations for oil and gas production offshore. The derrick  100  extends upwardly above the drill floor  200  and supports the main hoisting and drilling components used in drilling operations. 
     The derrick  100  may support a hoisting assembly, such as a block and tackle, for raising and lowering a completions/workover riser or landing string  110  (alternatively referred to as a ‘riser’) which may be configured to pass through the drill floor  200  and facilitate well completions/well testing/well intervention of a subsea production well. A lower end of the riser  110  may be fixed to the wellhead at the seafloor by means of a tubing hanger in what may be termed ‘locked-to-bottom’ operations. The upper end of the riser may be fixed to a flowhead assembly  130  above the drillfloor  200 . A top drive system  120  may be provided to also facilitate lowering or lifting of the riser  110 . 
     The hoisting assembly may be provided with a primary heave compensator. The primary heave compensator may be an active heave drawworks system or a passive heave compensator mounted on the top of the derrick  100 . As discussed above, if this primary heave compensator fails or becomes inoperative, the fluctuation in the vertical position of the floating vessel relative to the seafloor due to wave motion will place the riser  110  under alternating compression and tension. 
     The riser tension protector  10  and the coiled tubing lift frame assembly  12 , in the embodiment described herein, provides a back-up or secondary heave compensator which is configured to compensate for excessive axial load on the riser  110  in an upheave of the floating vessel when the primary heave compensator fails. This particular embodiment provides ‘over tension protection’. 
     The coiled tubing lift frame assembly  12  incorporates the riser tension protector  10  and may be configured in-line below the rig&#39;s primary heave compensation system. The coiled tubing lift frame assembly  12  may be operatively associated at one end thereof with the top drive system  120  and fixed relative to the flowhead assembly  130 . Installed in this way, the coiled tubing lift frame assembly  12  may be suspended above the drill floor  200  of the floating vessel. 
     In normal inline operation, the coiled tubing lift frame assembly  12  may be disposed in a fixed length mode, as will be described later whereby respective piston rods of the pneumatic cylinders of the riser tension protector  10  remain stationary and substantially fully retracted in respective cylinder barrels, and the primary heave compensator accounts for the heave of the floating vessel. In the event of failure of the primary heave compensator, however the piston rods of the pneumatic cylinders automatically extend to prevent excessive axial load on the riser  110  in response to an upheave of the vessel. 
     Referring generally to  FIGS. 2 to 4 , where like reference numerals refer to like parts throughout, there is shown the riser tension protector  10  as described herein. 
     The riser tension protector  10  includes a pair of pneumatic cylinders  14  spaced apart from one another. Each pneumatic cylinder  14  has a cylinder barrel  16  having an upper end  18  and a lower end  20 , and a piston rod  22  translatable within the cylinder barrel  16  between a retracted mode and an extended mode. In some embodiments, the piston rod  22  may have a stroke of up to 3 m, even up to 4.5 m, the fully extended mode being defined by a physical end stop of the cylinder barrel  16 . Under normal operating conditions, whereby the primary heave compensator is operable, the piston rods  22  may remain retracted and stationary in the cylinder barrel  16 . In the event of failure of the primary heave compensator and in response to a load on the riser  110  in excess of a predetermined axial load, however, the piston rods  22  may extend to prevent excessive tension on the riser  110  on an upheave of the vessel, and will subsequently retract on a down heave of the vessel. 
     The upper ends  18  of the cylinder barrels  16  are interconnected by a cross member  24 , as will be described in more detail with reference to  FIG. 6 . The cross member  24  provides rigid structural support for the pair of pneumatic cylinders  14 . 
     The lower ends  20  of the cylinder barrels  16  are arranged, in use, to be fixed relative to a flowhead assembly  130 , preferably by means of a lower frame section  26 ,  26 ′ adapted to couple to the flowhead assembly  130 , as will be described in more detail with reference to  FIGS. 7 and 8 . In one embodiment, as shown in  FIG. 1 , the lower ends  20  of the cylinder barrels  16  are fixed to the lower frame section  26  by coupling elements  28 . In an alternative embodiment, as shown in  FIG. 9 , the lower ends  20  of the cylinder barrels  16  may be fixed directly to the lower frame section  26 ′. 
     The piston rod  22  has a free end  30  with a clevis  32  associated therewith. In use, the clevis  32  of each piston rod  22  is operatively associated with an upper frame section  34 , as will be described in more detail with reference to  FIG. 5 . 
     An opposing end  36  of the piston rod  22  is associated with a piston head  38 . The piston head  38  is translatable within the cylinder barrel  16 , thereby defining a first pneumatic chamber  40  on a blind side  42  of the cylinder barrel  16  and a second pneumatic chamber  44  on a rod side  46  of the cylinder barrel  16 . The first pneumatic chamber  40  will generally define a cylindrical cavity in the cylinder barrel  16  and the second pneumatic chamber  44  will generally define an annular cavity in the cylinder barrel  16 . It will be appreciated that the volume of the first and second pneumatic chambers  40 ,  44  will vary depending on the stroke of the piston rod  22 . 
     The piston rod  22  may be hollow, defining a third pneumatic chamber  48  therein. The third pneumatic chamber  48  may be in fluid communication with the second pneumatic chamber  44  via one or more apertures  50  in a piston rod wall  52 . 
     The first pneumatic chamber  40  on the blind side  42  of the cylinder barrel  16  has a low pneumatic pressure in a range of 0.5 bar to 10 bar, depending on the stroke length. The second and third pneumatic chambers  44 ,  48  on the rod side  46  of the cylinder barrel  16  and within the piston rod  22 , respectively, are charged with a relatively higher pneumatic pressure than the first pneumatic chamber  40 . 
     The pneumatic pressure in the second and third pneumatic chambers  44 ,  48  may be sufficient to cause the piston rods  22  to remain retracted and stationary in the cylinder barrels  16  when an axial load on the riser is under a predetermined operating load threshold. When the axial load on the riser exceeds the predetermined operating load threshold, for example if the primary heave compensator fails on an upheave of the floating vessel or the upheave of the vessel exceeds the normal operating swell, in response thereto the piston rods  22  extend, thereby preventing excessive axial load on the riser  110 . In these particular embodiments, in the fully retracted mode the pneumatic pressure in the second and third pneumatic chambers  44 ,  48  may be in a range of 150-200 bar. In an extended mode, the pneumatic pressure in the second and third pneumatic chambers  44 ,  48  may increase up to 280 bar. In some embodiments, the second pneumatic chamber  44  on the rod side of the cylinder barrel  16  may be provided with one or more pressure relief valves  54  to vent pressure at a pre-set value, allowing the piston rods to extend while maintaining constant pressure in the second and third pneumatic chambers  44 ,  48  and hence constant axial load on the riser on an up heave of the floating vessel. 
     Following the upheave of the vessel, subsequently on a down heave of the vessel the axial load on the riser may reduce to or below the predetermined operating load threshold, thereby allowing the piston rods  22  to retract into the cylinder barrels  16 . It will be appreciated that the pneumatic pressure in the second and third pneumatic chambers of the cylinder barrels  16  and the predetermined operating load threshold may be varied to suit the planned operation. 
     The pneumatic cylinders  14  may be arranged to be in fluid communication with one another in a manner whereby the pneumatic pressure in the second and third pneumatic chamber  44 ,  48  of each cylinder  14  is the same. Fluid communication between the spaced apart pneumatic cylinders  14  may be provided by a conduit  56  extending between and interconnecting the second pneumatic chambers  44  of the cylinder  14 . Advantageously, the provision of the same pneumatic pressure in each cylinder  14  ensures that the respective piston rods  22  retract or extend simultaneously in response to the axial load on the riser. 
     The pneumatic cylinders  14  may be in intermittent fluid communication with a control unit  150  typically located on the drill floor  200  via an umbilical  160 . The control unit  150  is configured to provide an air fill function to the pneumatic cylinders  14  via a hose (contained within the umbilical  160 ). Air fill may be provided by the rig&#39;s high pressure air supply or by standalone high pressure air vessels on the deck, regulated to provide the desired pneumatic pressure to the pneumatic cylinders  14 . The control unit  150  may also be configured to provide an air vent function which is remotely operable via the control unit  150  with a pilot hose to the pneumatic cylinder  14 . The pilot hose may be contained within the umbilical  160 . The air vent may be associated with double pilot actuated isolation ball valves, spring applied to close, and a silencer. The air vent may be associated with an inline orifice on the vent line to limit vent rate. Further, the double pilot actuated isolation valves may be configured to provide a local manual override to provide a manual air bleed function. It will be appreciated that under normal operating conditions, the hose need not be connected to the pneumatic cylinders  14  as high pressure air adjustment is not normally required. It is envisaged that hoses will only need to be connected in the event that a remote air fill/vent is required. 
     The coiled tubing lift frame assembly  12  includes the riser tension protector  10  described herein. The coiled tubing lift frame assembly  12  includes a frame with the upper frame section  34  adapted for attachment to the top drive system  120  and the lower frame section  26  which is adapted to interface with the flowhead assembly  130 . The free ends of the piston rods  22  of the riser tension protector  10  are fixed to the upper frame section  34  as will be described below. The lower frame section  26  may be adapted for fixing the lower ends  20  of the cylinder barrels  16  by means of coupling elements  28 , such as elevator bails, as shown in  FIG. 1  and in more detail in  FIG. 8 . Alternatively, the lower frame section  26 ′ may be adapted so that the lower ends  20  of the cylinder barrels  16  may be directly fixed thereto, as shown in  FIGS. 8 and 9 . 
     Referring now to  FIG. 5 , there is shown a detailed perspective view of the upper frame section  34  of the riser tension protector  10  and coiled tubing lift frame assembly  12 . The upper frame section  34  is adapted for attachment to the top drive system  120  via coupling elements  140 , such as elevator links. 
     The upper frame section  34  comprises a cross member  200  in the form of a spreader beam. The cross member  200  may be a pair of parallel plates  202  spaced apart from one another. Each plate  202  has an upper edge  204 , a lower edge  206 , and opposing side edges  208 . An end plate  210  extends between respective internal faces  212  of the parallel plates  202  at opposing side edges  208 , thereby defining a cavity  214  between the pair of parallel plates  202 . 
     The upper frame section  34  further comprises an attachment member  216  in the form of a lug. In this embodiment, the attachment member  216  upwardly extends from the upper edge  204  of the cross member  200  and is disposed substantially equidistantly from the opposing side edges  208  of the cross member  200 . 
     In some embodiments, the attachment member  216  may be integrally formed with the parallel plates  202  of the cross member  200  or may be welded to the parallel plates  202 . 
     However, in the particular embodiment shown in  FIG. 5 , the attachment member  216  has a body  218  that is inserted into the cavity  214  between the pair of parallel plates  202  and secured therebetween by fasteners  220 . The fasteners  220  may take the form of a pin that is inserted through correspondingly aligned apertures  222 ,  224  in the parallel plates  202  and the body  218  of the attachment member  216 , respectively. Advantageously, this particular arrangement provides the attachment member  216  with limited rotation, helping to reduce member forces on the attachment member  216  due to unequal bail lengths and skew loading thereon. 
     The attachment member  216  may be configured to be coupled to the top drive system  120  by various coupling elements  140 , such as bail arms or elevator links. In this embodiment, the attachment member  216  is provided with a pair of downwardly inclined ears  226  spaced from the upper edge  204  of the cross member  200 . In use, as shown in  FIG. 1 , respective lower ends of the bail arms  140  are engaged with the downwardly inclined ears  226  while respective upper ends of the bail arms  140  are coupled to the top drive system  120 . 
     In one particular embodiment, maintaining engagement of the lower ends of the bail arms with the downwardly inclined ears  226  may be achieved with a retainer  228  in the form of a pair of L-shaped brackets. In use, after engagement of the bail arms  140  with the downwardly inclined ears  226 , the arms of the L-shaped brackets may be connected (such as with bolts, threaded screws, and so forth), respectively, to the upper edge  202  of respective parallel plates  202  and side edges  230  of the downwardly inclined ears  226 . In this way, if there is a recoil event or the load decreases, the lower ends of the bail arms are prevented from disengaging the downwardly inclined ears  226  and, consequently, the upper frame section  34  is prevented from detaching from the top drive system  120 . 
     The upper frame section  34  is also adapted to be operatively associated with the piston rods  22  of the cylinders  14 . The parallel plates  202  of the cross member  200  may be provided with a pair of apertures  232 . Each aperture  232  is spaced apart from opposing side edges  208  of the cross member  200 . The apertures  232  are configured, in use, to receive a pin which is inserted through a respective clevis  32  associated with the free end  30  of the piston rod  22  of the cylinder  14 , thereby fixing the free end  30  of the piston rod  22  to the upper frame section  34 . 
     The upper frame section  34  may also comprise a first pair of opposing plates  234  laterally extending from the parallel plates  202  of the cross member  200  and a second pair of opposing plates  236  laterally extending from the parallel plates  202  of the cross member  200 . The first pair of opposing plates  234  is disposed adjacent to the upper edge  204  of the parallel plates  202 . The second pair of opposing plates  236  is disposed adjacent to the lower edge  206  of the parallel plates  202 . 
     Referring now to  FIG. 6 , there is shown a detailed perspective view of the cross member  24  of the riser tension protector  10 . In this particular embodiment, the cross member  24  takes the form of a spreader beam  300 . 
     The cross member  24  comprises a pair of spaced apart hollow cylindrical members  302  interconnected by an upper plate  304  and a lower plate  306 . 
     The cylindrical members  202  are each provided with a flange  308  concentrically disposed at a lower end  310  thereof. The cylindrical members  302  are spaced apart from one another such that the flanges  308  are configured, in use, to receive and couple with respective upper ends of the cylinders  14  so that the piston rods  22  of the cylinders  14  may reciprocally translate concentrically within the hollow cylindrical members  302 . In this way, the intermediate member  300  provides structural rigidity to the cylinders  14 . 
     The upper plate  304  is disposed at respective upper ends  312  of the hollow cylindrical members  302 . In use, when the piston rods  22  are fully retracted, the upper plate  304  provides a landing for the upper frame section  34 , as shown in  FIGS. 1-3 . 
     Referring now to  FIG. 7 , there is shown a detailed perspective view of the lower frame section  26  of the coiled tubing lift frame assembly  12 . In this particular embodiment, the lower frame section  26  is adapted to be connected to the cylinders  14  of the riser tension protector  10  by means of coupling elements  280  such as long bails or elevator links. 
     The lower frame section  26  comprises a cross member  400  in the form of a spreader beam. The cross member  400  comprises a cylindrical member  402  having an upper edge  404 , a lower edge  406 , an outer cylindrical wall  408 , and an inner cylindrical wall  410 . The lower frame section  26  also comprises a pair of opposing side plates  412  outwardly extending from respective opposing sides of the outer cylindrical wall  408 . 
     The lower frame section  26  further comprises a pair of split insert members  414  which are locked in place by a collar member  416 . The split insert members  414  comprise a pair of semi-cylindrical members  414   a ,  414   b  which are disposed to abut each other at facing edges  418  thereof. The cylindrical members  414   a ,  414   b  are concentrically disposed to abut the inner cylindrical wall  410  of the cylindrical member  402 . The pair of split inserts  414   a ,  414   b  is advantageously formed to interface with any one of a plurality of general flowhead assemblies  130 . The collar member  416  is advantageously formed with a wedge type cross section, holding the split inserts  414  securely with the cylindrical member  402  in tension without the need for additional securing bolts. 
     In use, the flowhead assembly  130  is interfaced with the lower frame section  26  by coupling the flowhead assembly  130  with the split inserts  414  and the collar member  416  proximal to the lower edge  406  of the cylindrical member  402 . In this way, the lower section  26  is capable of locking directly to the flowhead assembly  130 . 
     The lower frame section  26  may be also adapted to engage the cylinders  14 . The cross member  400  may be provided with a pair of downwardly depending ears  420 . The downwardly depending ears  420  outwardly extend from the opposing side plates  412  in longitudinal alignment therewith. In use, as shown in  FIG. 1 , respective lower ends of the bail arms  28  are engaged with the downwardly inclined ears  420  while respective upper ends of the bail arms  28  are coupled to the lower ends of the cylinder barrels. 
     In one particular embodiment, maintaining engagement of the lower ends of the bail arms with the downwardly inclined ears  420  may be achieved with a retainer  422  in the form of a pair of L-shaped brackets. In use, after engagement of the bail arms  28  with the downwardly inclined ears  420 , the arms of the L-shaped brackets  422  may be connected (such as with bolts, threaded screws, and so forth), respectively, to the opposing side plates  412  and the downwardly inclined ears  420 . 
     The lower frame section  26  may also comprise a first pair of opposing plates  424  laterally extending from the cylindrical member  402  and the side plates  412  of the cross member  400  and a second pair of opposing plates  426  laterally extending from the cylindrical member  402  and the side plates  412  of the cross member  400 . The first pair of opposing plates  424  is disposed adjacent to the upper edge  404  of the cylindrical member  402 . The second pair of opposing plates  426  is disposed adjacent to the lower edge  406  of the cylindrical member  302 . 
     Referring now to  FIG. 8 , there is shown a detailed perspective view of the lower frame section  26 ′ of the coiled tubing lift frame assembly  12 . In this particular embodiment, the lower frame section  26 ′ is adapted to be directly connected to the cylinders  14  of the riser tension protector  10 . 
     The lower frame section  26 ′ comprises a cross member  500  in the form of a spreader beam. The cross member  500  comprises a cylindrical member  502  having an upper edge  504 , a lower edge  506 , an outer cylindrical wall  508 , and an inner cylindrical wall  510 . The lower frame section  26 ′ also comprises a pair of opposing side plates  512  outwardly extending from respective opposing sides of the outer cylindrical wall  508 . The side plates  512  may be outwardly tapering. 
     The lower frame section  26 ′ further comprises a pair of split insert members  514  which are locked in place by a collar member. The split insert members  514  comprises a pair of semi-cylindrical members  514   a ,  514   b  which are disposed to abut each other at facing edges  518  thereof. The cylindrical members  514   a ,  514   b  are concentrically disposed to abut the inner cylindrical wall  510  of the cylindrical member  502 . The pair of split inserts  514  is advantageously formed to interface with any one of a plurality of general flowhead assemblies  130 . The collar member is advantageously formed with a wedge type cross section, holding the split inserts  514  securely with the cylindrical member  502  in tension without the need for additional securing bolts. 
     In use, the flowhead assembly  130  is interfaced with the lower frame section  26 ′ by coupling the flowhead assembly  130  with the split inserts  514  and the collar member proximal to the lower edge  506  of the cylindrical member  502 . In this way, the lower frame section  26 ′ is capable of locking directly to the flowhead assembly  130 . 
     The lower frame section  26 ′ may be also adapted to directly engage the cylinders  14 . The cross member  500  may be provided with a pair of opposing shafts  519 . The shafts  519  outwardly extend from the opposing side plates  512  in longitudinal alignment therewith. In use, the shafts  519  are configured to engage the spherical bearings in the lower end of the cylinders  14  in a manner whereby the cylinders  14  are directly fixed to the lower frame section  26 ′. 
     The lower frame section  26 ′ may also comprise a first pair of opposing plates  520  laterally extending from the cylindrical member  502  and the side plates  512  of the cross member  500  and a second pair of opposing plates  522  laterally extending from the cylindrical member  502  and the side plates  512  of the cross member  500 . The first pair of opposing plates  520  is disposed adjacent to the upper edge  504  of the cylindrical member  502 . The second pair of opposing plates  522  is disposed adjacent to the lower edge  506  of the cylindrical member  502 . A plurality of substantially vertical brace members  524  may extend between the first and second pairs of plates  520 ,  522  to provide additional strength and rigidity to the lower frame section  26 ′ and to provide additional handling points. The vertical brace members  524  may be equidistantly spaced with respect to one another. 
     The lower frame section  26 ′ may be further provided with a pair of load bearing lugs  526  in the form of padeyes. The load bearing lugs  526  upwardly extend from the first pair of opposing plates  520 . The load bearing lugs  526  may be integrally formed with substantially vertical brace members  524  extending between the first and second pairs of opposing plates  520 ,  522 . The load bearing lugs  526  and the vertical brace members  524  are equidistantly spaced apart from opposing sides of the cross member  500 . Advantageously, the load bearing lugs  526  may be used to lift the coiled tubing lift frame assembly  12 . 
     In use, the riser tension protector  10  and the coiled tubing lift frame assembly  12  may be employed as a backup compensator for a primary compensator in the form of a drill string compensator. The coiled tubing lift frame assembly  12  may be installed by first charging the pneumatic pressure of the pneumatic cylinders to a pressure sufficient to cause the piston rods  22  of the cylinders  14  to remain fully within the cylinder barrels under normal operating conditions (i.e. under normal swell). The upper frame section may then be coupled to the top drive system  120  by various couplers, such as bail arms or elevator links  140 . The flowhead assembly  130  may then be interfaced with the lower frame section  26  by coupling the flowhead assembly  130  with the split inserts and the collar member proximal to the lower edge of the spreader beam. 
     In the event of the rig&#39;s drill string compensator failing, on an upheave of the floating vessel the axial load on the riser may exceed a predetermined operating threshold load. In these circumstances, the piston rods  22  in the cylinders  14  will extend in response to, and to compensate for, heave of the vessel. 
     Numerous variations and modifications will suggest themselves to persons skilled in the relevant art, in addition to those already described, without departing from the disclosure. All such variations and modifications are to be considered within the scope of the disclosure. 
     For example, the piston rods  22  of the pneumatic cylinders  14  may be solid. Consequently, in this alternative embodiment, the pneumatic cylinders  14  are not provided with a third cylindrical cavity whose pneumatic pressure may be charged at an overpressure. 
     In the claims which follow, and in the preceding description, except where the context requires otherwise due to express language or necessary implication, the word “comprise” and variations such as “comprises” or “comprising” are used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the apparatus and method as disclosed herein.