Abstract:
A system for providing motion compensation of a platform attached to an ocean floor. The platform is operatively associated with a riser extending from a subterranean well. The system comprises a frame member positioned on the platform and a deck slidably attached to the frame member, and wherein the deck is attached to the riser. The system further comprises a moving device for moving the frame member relative to the deck. In one of the preferred embodiments, the frame member contains a plurality of guide post and wherein the deck is slidably mounted on the guide post so that the frame member is movable relative to the deck. The moving device may comprise a cylinder member operatively attached to the frame member and a piston operatively attached to the deck and wherein the system further comprises a pressurized recharging vessel configured to direct a pneumatic supply to the cylinder member, and a gas delivery mechanism for keeping the cylinder member within a pressure range. A method of compensating for movement on an offshore platform during well operations is also disclosed.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a structure for compensating motion on an offshore platform. More particularly, but not by way of limitation, this invention relates to a structure and method to compensate for motion of an offshore platform due to tidal, wave, wind and other environmental factors. 
     In the exploration, drilling and production of hydrocarbons, operators search in remote and exotic areas of the globe. Deep water tracts have been explored and drilled with increasing frequency in recent years. Platforms set in waters of 1,000 to 2,000 feet has become common place, and in some instances, wells have been drilled in water depths of 5,000 feet. Different types of drilling and production platforms have been used in these deep waters. One type of platform is a tension leg platform (TLP). In the TLP, a floating platform is connected to the ocean floor via tendons such as steel cables, as is well understood by those of ordinary skill in the art. Another type of structure used in deep water is the spar platform which generally is a floating cylindrical structure that is anchored to the ocean floor with steel cable means. Other types of floating platforms are known in the art. In deep water, a fixed leg type platform is generally not an option due to the extreme water depths. 
     In the deep water drilling of subterranean reservoirs, drillers encounter numerous operational problems. For instance, wave conditions may cause a cyclic buoyant force based on the raising, lowering, heaving and pitching of the platform. Also, tidal conditions may cause a variation in platform height and cause similar buoyant forces. The applied forces will in turn cause motion on the platform and on the work deck of the platform. Additionally, the subterranean well that is drilled will have a riser extending from the sea floor to the platform. In other words, a riser extends from the sea floor to the floating platform. As will be understood by those of ordinary skill in the art, the riser generally does not move in unison with the platform since the riser is fixed to the sea floor by different attachment means and the riser does not experience the same buoyant forces as the floating platform. 
     While an operator is in the midst of performing well work, the motion of the platform can have detrimental effects on the equipment and ongoing operations. For example, a coiled tubing unit that is rigged-up and running a string of tools into the well could be lifted upward and/or downward due to the motion of the platform. This motion could potentially cause serious damage such as breaking the connection of the coiled tubing to the riser which in turn could lead to a catastrophic failure. With prior art designs, operators find it necessary to stop operations and rig down the connection and then reconfigure. Thus, there is a need for a system and method that can compensate for motion of a floating platform while undergoing well intervention procedures. This need, and many other needs, will be fulfilled according to the teachings of the present invention. 
     SUMMARY OF THE INVENTION 
     A system for providing motion compensation of a platform attached to an ocean floor is disclosed. The platform is operatively associated with a riser extending from a subterranean well. The system comprises a frame member positioned on the platform and a deck slidably attached to the frame member, and wherein the deck is attached to the riser. The system further comprises means for moving the frame member relative to the deck. 
     In one of the preferred embodiments, the frame member contains a plurality of guide post and wherein the deck is slidably mounted on the guide post so that the frame member is movable relative to the deck. 
     Also in one of the preferred embodiments, the moving means comprises a cylinder member operatively attached to the frame member and a piston operatively attached to the deck and wherein the system further comprises energizing means for energizing the cylinder member so that the cylinder member extends from the piston thereby moving the frame member. 
     In a preferred embodiment, the energizing means comprises a pressurized (recharging) vessel configured to direct a pneumatic supply to the cylinder member and, valve panel for regulating the pressure delivered to the cylinder member. The energizing means may include a gas delivery mechanism for keeping the cylinder member within a predetermined pressure range and wherein a pressure circuit connects the gas delivery mechanism to the cylinder member. The moving means may further comprise a second cylinder member, and a second piston operatively associated with the second cylinder member. 
     The system may further comprise a track stacker member that is attached to the deck, and an injection head operatively attached to the track stacker member and wherein the frame member is positioned on the floating platform. In one of the embodiments, a coiled tubing is disposed within the injection head, and wherein the coiled tubing extends into the well. 
     The frame member may further comprise a spacer and wherein the spacer is attached to a floating platform in an ocean. In this way, various spacer sections may be included in order to obtain the desired working height from the floating platform. 
     Also, the system may further contain a means for locking the deck to the frame in order to prevent movement of the deck. In one preferred embodiment, the locking means is a pneumatic cylinder with engaging pin for engaging with a latching beam attached to the frame. 
     A method of compensating for movement on an offshore platform during well operations is also disclosed. The method comprises providing a motion compensator on the offshore platform. The motion compensator comprises a frame member attached to the platform, and a deck slidably mounted on the frame member. The method further comprises attaching the deck to a riser that extends from the well to the platform, moving the offshore platform in a first vertical direction, and then sliding the frame member relative to the deck. 
     In one embodiment, the motion compensator further comprises a cylinder connected to the frame member, with the cylinder having a piston disposed partially therein. The piston is attached to the deck and wherein the cylinder is responsive to a pressure. The step of sliding the frame member comprises controlling the pressure into the cylinder with an energizing pressure means to the cylinder and absorbing any force associated with the movement of the offshore platform. 
     In one of the preferred embodiments, an injector head is attached to the deck and wherein the injector head receives a coiled tubing, and the method further comprises lowering the coiled tubing into the riser and performing well work on the well with the coiled tubing. 
     In one of the preferred embodiments, the pressure within the cylinder is set a predetermined balanced pressure and the step of controlling the pressure into the cylinder with an energizing pressure means includes moving the cylinder in a downward direction in response to sea movement, increasing the area within the cylinder which in turn decreases the pressure within the cylinder. A gas is directed into the cylinder so that the pressure within the cylinder increases until the predetermined balanced pressure is reached. 
     In the event the cylinder moves in an upward direction in response to sea movement so that the area is decreased within the cylinder, pressure would be increased within the cylinder. Hence, gas would be directed from the cylinder so that the pressure within the cylinder decreases, and ultimately, the pressure is decreased to the predetermined balanced pressure. 
     An advantage of the present invention is that the system and method can be used on floating platforms. Another advantage is that the system and method provides for motion compensation on a well undergoing well intervention and remedial well work. Still yet another advantage is that the present invention allows for performing coiled tubing well work safely. 
     A feature of the present invention includes the modular design of the components. The modularity allows for ease of transportation, delivery and rig up. Yet another feature includes the ability to build the height needed on specific well applications by simply stacking spacers one on top of the other. 
     Another feature is that motion compensation is provided in the vertical direction. Yet another feature is the pressure control means that regulates the pressure to the cylinders. Still another feature is the use of the plurality of posts that guide the frame structure with respect to the deck during movement of the platform. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is an isometric view of the frame member of the present invention. 
         FIG. 1B  is an isometric view of the motion compensation structure that includes the frame member and associated deck of the present invention shown in a first position. 
         FIG. 1C  is the motion compensation structure of  FIG. 1B  wherein the frame member is shown moved to a second position. 
         FIG. 2  is an isometric view of the track stack structure that is used in conjunction with the motion compensation structure of  FIGS. 1B and 1C . 
         FIG. 3A  is the assembly of the motion compensation structure and track stack structure shown in a first position. 
         FIG. 3B  is the assembly of the motion compensation structure and track stack structure shown in a second position. 
         FIG. 4A  is a schematic illustration of the forces imposed on the floating platform. 
         FIG. 4B  is a schematic illustration of the control means of the present invention. 
         FIG. 5A  is an elevation view the motion compensation structure situated on a platform. 
         FIG. 5B  is the elevation view of  FIG. 5A  wherein the motion compensation structure has compensated due to sea movement. 
         FIG. 6  is a partial side view of  FIG. 1B . 
         FIG. 7  is a partial cut away view of  FIG. 6  depicting the locking cylinder and hook member. 
         FIG. 8  is a partial cross-section taken along line  8 — 8  of  FIG. 6 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to  FIG. 1A , an isometric view of the frame member  25  that includes the base support member  4  and the top support member  6  of the present invention shown in a first position. The support member  4  is rectangular member that has four sides namely a first beam  8 , second beam  10 , third beam  12  and fourth beam  14 . At the corners of support member  4  are attachment plates, namely attachment plate  16 , attachment plate  18 , attachment plate  20  and attachment plate  22 . The base support member  4 , top support member  6  and associated connecting beams is referred to as the frame member  25 . 
       FIG. 1A  shows that extending from the corner of beams  8 ,  10  is the post  24 ; extending from the corner of beams  10 ,  12  is the post  26 ; extending from the corner of beams  12 ,  14  is the post  28 ; and, extending from the corner of beams  8 ,  14  is the post  30 . The post  24  is disposed through the collar  32 ; the post  26  is disposed through the collar  34 ; the post  28  is disposed through the collar  36 ; and, the post  30  is disposed through the collar  38 . The top support member  6  is a rectangular member that consist of a first beam  42 , second beam  44 , third beam  46  and fourth beam  48 . The beam  42  is connected to the collar  32  and  38 ; the beam  44  is connected to the collars  32 ,  34 ; the beam  46  is connected to the collars  34 ,  36 ; and, beam  48  is connected to the collars  36 ,  38  as shown. The beams are connected to the collars via conventional means such as welding, nuts and bolts, pins, etc. The top support member  6  is connected to the posts via conventional means such as welding, by nuts and bolts, pins, etc.  FIG. 1A  further shows latching beam  49   a ,  49   b ,  49   c ,  49   d , and wherein the latching beams  49   a ,  49   b ,  49   c ,  49   d  have openings there through, for instance opening  49   e.    
     Referring now to  FIG. 1B  an isometric view of the motion compensator structure  2  that includes the frame member  25  and associated deck  50  will now be described. It should be noted that like numbers appearing in the various figures refer to like components. The motion compensation structure  2  includes the deck  50  that is slidably disposed on the post  24 – 30 . More specifically, the deck  50  is rectangular with a first beam  52 , second beam  54 , third beam  56 , and fourth beam  58 , and wherein at each corner is a collar that will have disposed there through the respective post. Hence, the collar  59   a  has post  24  there through; collar  59   b  has post  26  there through; collar  59   c  has post  28  there through; and, collar  59   d  has post  30  there through. The collars are attached to the beams via conventional means such as by welding, nuts and bolts, pins, etc. 
     The attachment plate  16  has operatively attached a pressure cylinder  60  with a piston disposed therein and wherein a piston stem  62  extends from the pressure cylinder  60 , and wherein the stem  62  is attached to the deck  50 . The attachment plate  18  has operatively attached a pressure cylinder  64  with a piston disposed therein and wherein a piston stem  66  extends from the pressure cylinder  64  and wherein the stem  66  is attached to the deck  50 . The attachment plate  20  has operatively attached a pressure cylinder  68  with a piston disposed therein and wherein a piston stem  70  extends from the pressure cylinder  68  and wherein the stem  70  is attached to the deck  50 . The attachment plate  22  has operatively attached a pressure cylinder  72  with a piston disposed therein and wherein a piston stem  74  extends from the pressure cylinder  72  and wherein the stem  74  is attached to the deck  50 . As seen in  FIG. 1B , piston stem  62  is connected to the attachment plate  75   a  of deck  50 , piston stem  66  is connected to the attachment plate  75   b  of deck  50 , piston stem  70  is connected to the attachment plate  75   c  of deck  50 , and piston stem  74  is connected to the attachment plate  75   d  of deck  50 . 
       FIG. 1B  further shows attachment plates  75   a – 75   d  will have operatively attached locking cylinders with engagement pins.  FIG. 1B  shows cylinder  76   b  and  76   c . Cylinder  76   c  will extend the engagement pin (not shown here) that will engage the opening  49   e  of latching beam  49   a , thereby locking the deck  50  so that movement would be prevented. Hence, during maintenance and other remedial activity, the deck can be locked and prevented from movement. This feature will described in greater detail later in the application. 
       FIG. 1B  also shows the hook members attached to deck  50 , and more specifically the hook member  77   a  and hook member  77   b  are shown. The hook members will attach to a reciprocal pin member located on the cylinder. The pin members are located on the attachment plates  16 ,  18 ,  20 ,  22 . By latching hooks to the pins, the deck can be prevented from movement. Hence, during maintenance and other remedial activity, the deck can be locked and prevented from movement. This feature will also be described in greater detail later in the application. 
     Referring now to  FIG. 1C , the motion compensation structure  2  of  FIG. 1B  is shown and wherein the frame member  25  is shown moved to a second position relative to the ocean floor, as will be more fully explained later in the application. The level of deck  50  is at the same height in  FIG. 1B  as it is in  FIG. 1A . In other words, deck  50  is the same height relative to the sea floor, but the frame member  25  has moved relative to the deck  50 . The reason that the frame member  25  has moved is due to wave and/or tidal movement of the ocean wherein the frame member  25  has slide downward on the guide post. As seen in  FIG. 1C , the piston stems  62 ,  66 ,  70  and  74  are extended. The deck  50  is held in an essentially stationary position relative to the sea floor during operation, as will be explained later in the application. 
       FIG. 2  is an isometric view of the track stack structure  80  that is used in conjunction with the motion compensation structure  2  of  FIGS. 1B and 1C . The track stack structure  80  is commercially available from Devin International, Inc. under the name Track Stack Jr. The track stack structure  80  is in the form of a rectangular cube and consist of a first leg  82 , second leg  84 , third leg  86 , and fourth leg  88 . An upper beam  90  intermediate beams  92   a ,  92   b , and lower beam  94  connects the legs  82  and  84 . Other members, such as diagonal members, can be added for structural support. An upper beam  102 , intermediate beams  104   a ,  104   b , and lower beam  106  connects the pilings  84  and  86 . The upper beam  108 , intermediate beam  110   a , and lower beam  110   b  connects the pilings  86  and  88 . The upper beam  103 , intermediate beams  105   a ,  105   b  and lower beam  107  connects pilings  82 ,  88 . Also, the table  111   a  is shown, and wherein the table  111   a  is attached to the track stack structure  80 , and generally to beams  90 ,  102 ,  103 ,  108 . 
     The table  111   a  has the opening  111   b  through which will be disposed the riser. In the most preferred embodiment, the table  11   a  can then be attached to an injector head for coiled tubing, and the injector head is attached to the riser thereby in effect attaching the deck  50  to the riser. The means for attaching includes nuts and bolts, welding, pinning systems, etc, which are all very well known in the art. 
       FIG. 3A  is the assembly of the motion compensation structure  2  and track stack structure  80  shown in a first position.  FIG. 3A  additionally depicts a spacer structure  112 , and wherein the spacer structure  112  is a rectangular cube configured structure similar to the track stack structure  80 . The spacer structure  112  is connected to the frame member  25 , and more specifically, spacer structure  112  is connected at the top end to the base support member  4  via conventional means such as welding, nuts and bolts, pins, etc. 
     The spacer structure  112  is modular, and therefore, a number of spacer structures can be stacked one on top of the other, depending on the height required. In other words, different platforms, or perhaps different wells on a platform, may require different working heights. The modular design allows the stacking of these spacer structures to meet the specific requirements for the well intervention work, as will be understood by those skilled in the art. 
     Additionally,  FIG. 3A  schematically shows the pressure control means  114  for controlling the pressure contained within the pressure cylinders  60 ,  64 ,  68 , and  72 . The pressure control means  114  regulates the pressure based on a measured amount of pressure within the cylinders  60 ,  64 ,  68 ,  72 . The pressure control means  114  will be discussed in greater detail in the discussion of  FIGS. 4A and 4B . 
       FIG. 3B  is the assembly of the motion compensation structure  2  and track stacker member  80  shown in a second position. As seen in  FIG. 3B , the piston stems  62 ,  66 ,  70  and  74  are extended due to the downward movement of the platform, as will be explained later in the application. As noted earlier, the track stack structure  80  is attached to the deck  50  and the riser, as will be more fully explained later in the application. According to the teachings of this invention, the motion compensator  2  responds to ocean wave or tidal movement by way of the control means  114 . In the event of wave and/or tidal movement, as noted earlier, the height of the frame member  25  would change. Hence, by controlling the pressure in the cylinders  60 ,  64 ,  68  and  72 , movement of the platform can be compensated thereby reducing the tension that would be applied between the track stacker structure  80  and the riser. 
       FIG. 4A  is a schematic view of the forces being applied to the system herein described. Hence, the floating platform  160  is being subjected to an upward buoyant force F 1  by the ocean while the track stacker structure  80  subjects a downward gravitational force, due to the weight of structure  80 , denoted by F 2 . In the most preferred embodiment, the deck  50  will be positioned with an upward stroke of approximately three feet relative to the frame member  25  and a downward stroke of approximately three feet relative to the frame member  25 . The control means  114 , which will be described with reference to  FIG. 4B , allows the operator to maintain a pressure and uplift/tension balanced state between the track stack structure  80  and the frame member  25  during wave and tidal movement while at the same time maintaining a three foot stroke, from the mid position, in an upward or downward vertical direction.  FIG. 4A  also shows the pad eyes E for attaching a support cable C to the structure for support during operations. 
       FIG. 4B , which is a schematic illustration, depicts the control means  114  of the present invention. In the most preferred embodiment, a reservoir  116  of nitrogen or air pressure filled tanks, or a similar compressed air supply, is connected to the valve panel  118  and wherein the valve panel  118  regulates the amount of pressure that will be directed into the cylinders  60 ,  64 ,  68 ,  72  thereby adjusting the effective upward force and length of exposed pistons stems of the main cylinders  62 ,  66 ,  70 ,  74 . Hence, the pressure is directed from the valve panel  118  via line  120  to the pressure circuit which includes the pneumatic line  122  hose  124  and pressure expansion vessel  126 , which in turn directs the pressure to the cylinders  60 ,  64 ,  68 ,  72 . As used herein, the pressure circuit includes hose  124 , vessel  126 , pneumatic line  122 , cylinder  68 , cylinder  72 , cylinder  64 , cylinder  60 . The reservoir  116  and valve panel  118  acts to charge the pressure circuit with a predetermined minimum pressure setting in order to keep the system in a balanced state. 
     The vessel  126  is connected to the pneumatic line  122  via hose  124 . The vessel  126  acts as a reservoir to collect and transfer pressure from the pressure circuit during operation. It should be noted that the pressure circuit will be set at a balanced pressure state i.e. the pressure necessary to support the weight. In the most preferred embodiment, the pressure within the pressure circuit will be set to allow some additional over tension/pressure so that there is an operating range of pressure within the cylinders  60 ,  64 ,  68 ,  72 . 
     In operation, the control means  114  either directs pressure to the pressure circuit (including hose  124 , vessel  126 , line  122 , cylinder  60 , cylinder  64 , cylinder  68 , cylinder  72 ) or directs pressure from the pressure circuit (including hose  124 , vessel  126 , line  122 , cylinder  60 , cylinder  64 , cylinder  68 , cylinder  72 ) in order to maintain a predetermined upward pressure/force balanced state. The change in position of the cylinders effects the pressure within the cylinders which in turn dictates if pressure should be directed to the cylinders or directed from the cylinders. 
     As noted earlier, the cylinders and pistons have a predetermined extension distance based on a balanced pressure state. This predetermined extension distance allows a stroke distance of either three feet upward or three feet downward. For example, the track stack structure  80  has some specific weight without any outer forces applied thereto, and the cylinders, which are attached to the floating platform, will have a predetermined buoyant force applied thereto, as was shown in  FIG. 4A . Referring again to  FIG. 4B , the pressure circuit, and in particular cylinders  60 ,  64 ,  68 ,  72  are charged to a predetermined pressure to keep the cylinders extended in this balanced state. The track stack structure  80  is attached to the sea floor via the riser  170  and wherein a three foot stroke in an upward direction (see line A) and a three foot stroke in a downward direction (see line B) is allowed while operating within the predetermined balanced state. In effect, the pressure control means  114  acts as a shock absorber (or motion compensator) to the various forces applied during the operation. It should also be noted that biasing means for biasing the cylinders up and down are also possible. Examples of biasing means includes coiled springs contained within the cylinders and about the pistons. 
     A gauge G measures the pressure within the system. In the case where tidal or ocean movement causes the platform to lower, the cylinders would be expanded thereby increasing the cylinder volume which in turn decreases the pressure within the cylinders. In order to maintain the balanced state, pressure from vessel  126  would automatically be applied to the cylinders via hose  124  and valve  146 . This will reestablish the pressure to its balanced state, the downward force applied by the track stack structure  80  is again in equilibrium with a stroke of three feet minus the small drop in overall pressure and force. If pressure were not allowed to increase, the frame member  25  would lower. In the practical application, the control means  114  allows the ability to move upward or downward somewhat thereby decreasing the tension between the frame member  25  and the deck  50  (remember, the deck  50  is in effect connected to the riser). 
     If the tidal or ocean movement causes the platform to rise, then the cylinder area is decreased which in turn would cause a pressure increase. In order to maintain the balanced state, pressure from the cylinders can be directed to the vessel  126  automatically via hose  124  and valve  146 . This will reestablish the pressure to its balanced state while at the same time decreasing the compressive force between the frame member  25  and the deck  50 . 
     Regarding the nitrogen filled tanks  116 , in one of the preferred embodiments, there are 12 or more nitrogen bottles positioned on a rack with a manifold. As noted earlier, the tanks  116  are used to recharge the pressure circuit if the balanced pressure state falls below a predetermined threshold. A gauge  128  is positioned in order to sample the pressure. A ball valve  130  is positioned in the line  132 , wherein the ball valve  130  controls the pressure input to the control panel  118 ; in normal operation, the valve  130  is closed. With respect to the control panel  118 , the control panel  118  includes a pressure gauge  134  for reading the pressure in input line  132 , a ball valve  136  that will then connect to a ball valve  138  that leads to the line  120 . Valve  136  is open and valve  138  is opened for charging the system only. Under normal operation both valves are closed in order to create a redundant sealing of the pressure in the system. A pressure gauge  140  is also included upstream of the ball valve  138  for system operational pressure reading. Also included in one of the preferred embodiments is the relief valve  142  which may be set, for instance, at 1000 psi, in order to release pressure at a predetermined set point determined by the operator as exceeding a safety threshold.  FIG. 4B  also depicts that the control panel  118  can contain the ball valve  144  for releasing pressure if found desirable by the operator; valve  144  would normally be closed. 
     The vessel  126  will have the ball valve  146  associated with the line  124 , as well as the pressure relief valve  148  that can be set at a predetermined threshold pressure of 900 psi in order to relieve any build up in pressure above that amount, as will be understood by those of ordinary skill in the art. In normal operations, valve  146  is open so that the pressure within the pressure circuit communicates with the vessel  126 . 
       FIG. 4B  also depicts the hydraulic system for locking means. More specifically, a hydraulic power unit  191  directs hydraulic fluid to valve  192 , valve  194 , valve  196 , and valve  198 . The valve  192  directs pressure to cylinder  76   a ; valve  194  directs pressure to cylinder  76   b ; valve  196  directs pressure to cylinder  76   c ; and, valve  198  directs pressure to cylinder  76   d . Once pressure is supplied to the cylinders, a pin will extend therefrom and engage with the latching beams in order to lock the deck relative to the frame member, as previously described. Thus, pressure supplied to cylinder  76   a  extends pin  200 ; pressure supplied to cylinder  76   b  extends pin  202 ; pressure supplied to cylinder  76   c  extends pin  204 ; and, pressure supplied to cylinder  76   d  extends pin  206 . Although not shown, it is possible to energize the locking means utilizing the pneumatic system, rather than hydraulics; the pneumatic energizing means would use nitrogen tanks  116 . 
       FIG. 5A  is an elevation view of the motion compensation structure  2  positioned on a tension leg type of platform  160 . The tension leg platform  160  has a plurality of attachment means for attaching the platform  160  to the sea floor  162 .  FIG. 5A  depicts the steel cables  164 ,  166  that have been anchored to the sea floor  162  at a first end, and attached to the platform  160  at a second end. The surface of the sea is denoted at  168 . It should be noted that the present invention is applicable to any type of platform where height variation relative to the sea floor is a factor in operations. Thus, the invention is also applicable to spar platforms, drill ships, and semi-submersible rigs, etc. 
     As seen in  FIG. 5A , a riser  170  extends from the sea floor  162  through the platform  160 . The riser  170  extends from a well  172  that is drilled to a subterranean reservoir as will be understood by those of ordinary skill in the art. The riser  170  will be connected to the track stack structure  80  via the table  11   a . As noted earlier, the track stack structure  80  is attached to the deck  50 . An injector head  174  such that is used on coiled tubing installations is shown along with a cat walk  176  that surrounds the top of the track stacker structure  80 . The injector head  174  is used to direct the coiled tubing into the well  170  as is well understood by those of ordinary skill in the art. 
       FIG. 5B  is an elevation view of  FIG. 5A  wherein the motion compensation structure  2  has compensated due to sea movement. The platform  160  may be experiencing, for instance, a significant wave. In  FIG. 5A , note that the height of the injector head  174  relative to the sea floor  162  is X, while the height from the injector head  174  to the water level is Y. In  FIG. 5B , the platform  160  has lowered relative to the sea floor  162 . Hence, the distance from the sea floor  162  to the injector head  174  is still X, however, the distance from the injector head  174  to the sea level has increased to Y+Z due to the sea and/or tidal movement. Hence, the pressure gauge G (as seen in  FIG. 4B ) will show a decrease in pressure since the volume in the cylinders is decreasing but the pressure will remain within the balanced state range due to the ability of the pressure circuit to communicate with the vessel  126 . 
     Note that in the case wherein the platform  160  is rising (which is seen in  FIG. 5A ), then the area within the cylinders will decrease thereby increasing the pressure within the cylinders due to the decrease in cylinder volume but the pressure will remain within the balanced state range due to the ability of the pressure circuit to communicate with the vessel  126 . 
       FIGS. 6 ,  7  and  8  depict the latching cylinder and hook member of the present invention. The latching cylinders and hook member are means for locking the deck  50  relative to the frame member  25 , wherein movement is prevented. Hence, the latching cylinders represent two different means for locking the deck  50  relative to the frame member  25 . 
     Referring now to  FIG. 6 , a partial side view of  FIG. 1B  will now be described. The latching beam  49   a  and  49   b  is shown. The pin on the cylinders will extend through openings within the latching beams, and more specifically, through opening  49   g  and opening  49   h .  FIG. 6  also shows the hook  77   d  and  77   a . According to the teachings of the present invention, if the pneumatic cylinders, such as cylinder  76   c , are energized, the engagement pin will extend into and engage with the openings, thereby locking the deck  50  relative to the frame member  25 . 
     Referring now to  FIG. 7 , a partial cut away view of  FIG. 6  depicting the locking cylinder  76   c  and hook member  77   d . This view shows that the cylinder  76   c  has extending therefrom the locking pin  204  that is disposed through the opening  49   g . The cylinder  76   c  is pneumatically operated. In one preferred embodiment, there are four pneumatic cylinders as mentioned earlier. Also, the pneumatic cylinders may all be operatively attached to the main pressure source, namely nitrogen tanks  116 . Alternatively, the pneumatic cylinders may have an independent pressure source. While in the most preferred embodiment, pneumatic cylinders have been shown for motion compensation, the cylinders may also be hydraulic or even manually controlled and operated. 
       FIG. 7  also depicts the hook member  77   d . The hook member  77   d  may be manually operated. For activation, the hook member  77   d  is simply rotated so that the hook portion (attached to the deck  50 ) engages a pin  182  on the cylinder  68 . This prevents extension of the inner rod from the cylinder  68 . 
     Both latching mechanisms prevent relative movement of the deck  50  relative to the frame member  25 . In the course of conducting operations, it may be advantageous to prevent movement, for instance during maintenance, remedial work, etc. 
     Referring to  FIG. 8 , a partial cross-section taken along line  8 — 8  of  FIG. 6  will now be described. The  FIG. 8  shows all four hydraulic cylinders  76   a ,  76   b ,  76   c ,  76   d  attached to the attachment plates  75   a ,  75   b ,  75   c ,  75   d . Also, the latching beams  49   a ,  49   b ,  49   c ,  49   d  are shown. 
     Changes and modifications in the specifically described embodiments can be carried out without departing from the scope of the invention which is intended to be limited only by the scope of the appended claims and any equivalents thereof.