Abstract:
An improved motion compensator device that includes a compensated framework for various types of well intervention operations where a stable work area is required that is stationary to the sea bed and equipment in the annulus. The device is intended for use on offshore drilling vessels that are primarily either moored or dynamically positioned and therefore subject to the motions created by the sea. The device is designed to compensate for the vertical motion of the rig by means of two steel frame assemblies, pneumatic compensating cylinders, and a load and motion transfer apparatus.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of and priority to U.S. provisional application No. 61/092,565, filed Aug. 28, 2008. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to an offshore well intervention lift frame and method capable of compensating for the vertical motion of offshore floating or tension leg platforms. 
     BACKGROUND OF THE INVENTION 
     Motion compensator devices have been developed to counteract the motion of offshore floating and tension leg platforms during well intervention procedures. For example, U.S. Pat. No. 6,929,071 is drawn to a motion compensator system and method which includes a frame member positioned on a platform, a deck slidably attached via guide posts to the frame member, (the deck being attached to the riser), and a pressure cylinder and piston assembly which moves the frame relative to the deck. U.S. Pat. No. 7,063,159 is drawn to a coiled tubing handling system that includes a lifting frame, a load compensation system, and a flexible riser system that reduces the load on the wellhead and permits horizontal and vertical movement between the BOPs, coiled tubing stack, and wellhead. U.S. Published Patent Application No. 2008/0099208 A1 is drawn to an apparatus for performing well work on a floating platform which includes a frame assembly, a crown section assembly, a motion compensator means, and a travel head connected to the motion compensator means and to a well intervention device. U.S. Pat. Nos. 6,929,071 and 7,063,159, as well as U.S. Published Patent Application No. 2008/0099208 A1, are each incorporated by reference herein. 
     SUMMARY OF THE INVENTION 
     The present invention is an improved motion compensator device that includes a compensated framework for various types of well intervention operations where a stable work area is required that is stationary to the sea bed and equipment in the annulus. The device is intended for use on offshore drilling vessels that are primarily either moored or dynamically positioned and therefore subject to the motions created by the sea. The device is designed to compensate for the vertical motion of the rig by means of two steel frame assemblies, pneumatic compensating cylinders, and a load and motion transfer apparatus. 
     An embodiment of a motion compensating apparatus of the present invention may include an outer frame having an upper section for attachment to an elevator assembly of an offshore drilling or production rig floating on a surface of a body of water. The apparatus may also include an inner frame in sliding cooperation with the outer frame. The apparatus may have a plurality of compensation cylinders operatively associated with the outer frame and detachably affixed to the inner frame. The apparatus may also contain a capturing assembly detachably connected to the inner frame. The capturing assembly may be capable of supporting well intervention equipment connected to a well. In the apparatus, the plurality of compensation cylinders may be activated to an extended or retracted position to maintain the vertical position of the well intervention equipment despite the rise or fall of the surface of the body of water. 
     The outer frame of the apparatus may have an inverted U-shape with two opposing side walls. The outer frame may have an outer surface and an inner surface. The outer surface of said outer frame includes a lift sub for connection by said elevator assembly. The inner frame of the apparatus may have an inverted U-shape with two opposing side legs. The inner frame may be positioned adjacent to the inner surface of the outer frame and be in sliding cooperation therewith. The side walls of the outer frame may contain or house a portion of the plurality of compensation cylinders. 
     The outer frame of the apparatus may include means for restricting the complete retraction of the plurality of compensation cylinders. The means may comprise one or more safety pins. 
     In the apparatus, the plurality of compensation cylinders may have a distal end and a proximal end. The distal end of the cylinders may be detachably affixed to one of the side legs of the inner frame. 
     The apparatus may contain means for activating said compensation cylinders. The means may comprise a plurality of conduits for transmitting pneumatic fluid to the cylinders. 
     The capturing assembly of the apparatus may be capable of articulation about the point of attachment with the inner frame. The apparatus may be provided with means for preventing articulation of the capturing assembly. The means may comprise one or more anti-rotation pins connecting the inner frame to the capturing assembly. The capturing assembly may include a retaining door having an adjustable opening for placement and support of a lift joint for the well intervention equipment. The retaining door may be hydraulically actuated to open the adjustable opening to receive or release the lift joint or hydraulically activated to close the adjustable opening to grip and support the lift joint and the well intervention equipment attached thereto. The capturing assembly may also include one or more hydraulically actuated bail pins for supporting a bail. 
     Another embodiment of the motion compensating apparatus of the present invention may include an inverted U-shaped outer frame with opposing side walls. The outer frame may include a central lift sub prong for attachment by an elevator assembly of an offshore drilling or production rig floating on a surface of a body of water. The apparatus may also include an inverted U-shaped inner frame with opposing side legs. The inner frame may be in sliding cooperation with the outer frame. The apparatus may further contain two pairs of compensation cylinders operatively associated with the outer frame. Each cylinder may have a proximal end and a distal end. The proximal ends of one of the pairs of cylinders may be housed within one of the side walls of the outer frame and the distal ends of the pair of cylinders may be detachably affixed to one of the legs of the inner frame. The proximal ends of the other pair of cylinders may be housed within the other side wall of the outer frame and the distal ends of the pair of cylinders may be detachably affixed to the other leg of the inner frame. The apparatus may also include a plurality of conduits in fluid communication with the two pairs of compensation cylinders. The apparatus may further contain a capturing assembly detachably connected to the legs of the inner frame. The capturing assembly may have a movable collar for gripping and releasing a lift joint for fixation to well intervention equipment connected to a well. The pairs of compensation cylinders may be activated by pneumatic fluid passing through the plurality of conduits to an extended or retracted position to maintain the vertical position of the well intervention equipment despite the rise or fall of the surface of the body of water. 
     The alternative embodiment of the apparatus may include means for detachably locking said inner frame to said outer frame. The means may comprise a hydraulically actuated locking pin. 
     The alternative apparatus may also include a control panel operatively connected to the apparatus for operating the apparatus. 
     The present invention also is directed to a method of maintaining the vertical position of well intervention equipment connected to a well. The method comprises the step of providing a motion compensating apparatus comprising: an outer frame having an upper section for attachment to an elevator assembly of an offshore drilling or production rig floating on a surface of a body of water; an inner frame in sliding cooperation with the outer frame; a plurality of compensation cylinders operatively associated with the outer frame and detachably affixed to the inner frame; a capturing assembly detachably connected to the inner frame, the capturing assembly capable of supporting said well intervention equipment connected to said well. The method may include the step of attaching an elevator assembly to the apparatus and lifting the apparatus upward within a derrick of the rig. The method may also include the step of causing the capturing assembly to grip and support a lift joint. The method may include the step of attaching the lift joint to the well intervention equipment. The method may also include the step of maintaining the vertical position of the well intervention equipment by activating the plurality of compensation cylinders to either an extended or retracted position depending on the rise or fall of the surface of the body of water. 
     The apparatus used in the method may further include a winch or hoist positioned on the inner frame. The method may include the step of using the winch or hoist to position the well intervention equipment in the capturing assembly. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an embodiment of the lift frame of the present invention in retracted position. 
         FIG. 2  is a front view of the embodiment of the lift frame of  FIG. 1 . 
         FIG. 3  is a side view of the embodiment of the lift frame of  FIG. 1 . 
         FIGS. 4A and 4B  are a sequential front view of an embodiment of the lift frame of the present invention in extended position. 
         FIG. 5  is a perspective view of area “ 5 ” of  FIG. 1  illustrating a jib arm with winch and air/oil reservoir. 
         FIG. 6  is a perspective view of area “ 6 ” of  FIG. 1  illustrating the front trunion mount of a cylinder and safety pins that prevent bottoming out of cylinders. 
         FIG. 7  is a perspective view of area “ 7 ” of  FIG. 1  illustrating a hydraulically activated tubular retaining door. 
         FIG. 8  is a perspective view of area “ 8 ” of  FIG. 1  illustrating cylinder guide brackets and anti-rotation pins. 
         FIG. 9  is a partial perspective view of the backside of the upper section of an embodiment of the lift frame of the present invention. 
         FIG. 10  is a perspective view of area “ 10 ” of  FIG. 1  illustrating the upper handling padeyes. 
         FIG. 11  is a schematic representation of a control panel for operation of an embodiment of the lift frame of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With reference to the figures where like elements have been given like numerical designation to facilitate an understanding of the present invention, and in particular with reference to the embodiment of the present invention illustrated in  FIG. 1 , motion compensator device  10 . Device  10  is shown in a retracted position. Device  10  consists of upper section  12  and lower section  14 . Upper section  12  includes outer frame  16  and slidable inner frame  18 . Both outer and inner frames  16 ,  18  may be substantially U-shaped or more particularly, inverted U-shaped. Upper section  12  also includes two pairs of compensating cylinders  20  and  22 . Compensating cylinders  20 ,  22  are operatively connected to outer frame  16  and slidable inner frame  18 . Compensating cylinders  20 ,  22  are also known as pistons. Outer frame  16  allows for the attachment, travel, and guidance of compensating cylinders  20  and  22  that provide the force necessary for compensation of device  10 . 
     With reference again to  FIG. 1 , upper section  12  and lower section  14  are shown operatively connected. Upper section  12  and lower section  14  may be pinned together via pins  24  to allow for articulation or separation of the sections for either the addition of leg extensions or to assist in the installation of device  10  into a drilling rig derrick. Lower section  14  is designed to support and capture equipment connected to the sea bed. Lower section  14  may be a support/capture system, which includes door device  26  actuated via remote hydraulics or offset attachment points using remote hydraulics for the operation where such equipment such as bails can be attached. 
       FIG. 1  shows that upper section  28  of outer frame  16  may include central lift sub attachment point  30 , which directly connects to the rig&#39;s elevator system to suspend device  10  above the platform of the rig. 
     As seen in  FIGS. 1 and 6 , outer frame  16  may use fixed trunions  32  that attach to the barrel of compensation cylinders  20 ,  22  mounted on the lower frame to transfer the motion. There are also fixed points on outer frame  16  for cylinders  20 ,  22  to react against so that cylinders  20 ,  22  can apply the force necessary to support the given loads during well intervention. 
     The total energy for device  10  may be provided by the use of compressed gas on blind end  34  of cylinders  20 ,  22  via conduits  36 . Under normal circumstances, compressed air is used. But, compressed nitrogen can also be used. A number of deck-mounted air pressure vessels may be used to increase the volume in order to reduce variance in the compensating force. While compressed gas is preferably used to operate compensating cylinders  20 ,  22 , it is to be understood that hydraulic fluid could also be used. 
     With reference to  FIGS. 1 and 5 , device  10  includes small air/oil reservoir  38  on rod side  40  of compensating cylinders  20 ,  22  to act as a lubricant, which travels to cylinders  20 ,  22  via conduits  42 . In case of either a catastrophic or accidental separation of the intervention string, speed control valves will limit the travel velocity as compensating cylinders  20 ,  22  extend. 
       FIG. 8  shows that blind end  34  of cylinders  20 ,  22  are also detachably affixed to lower end  44  of slidable inner frame  18  via cylinder guide brackets  46 . 
     With reference to  FIG. 9 , device  10 , and in particular, outer and inner frames  16 ,  18 , may mechanically lock together in a closed position by means of a hydraulically operated pin  48 . Pin  48  is positioned on slidable inner frame  18 . When locked, pin  48  extend through locking bracket  50  on outer frame  16  as seen in  FIG. 4A ; device  10  no longer compensates but has increase load bearing capacity making it possible for the installation, removal, and transportation of the unit. 
     Device  10  may include fixed mechanical stops that will allow the travel of the unit to stop prior to full retraction of cylinders  20 ,  22 . As seen in  FIG. 6 , outer frame  16  includes safety pins  52  that prevent the bottoming out of cylinders  20 ,  22 . 
     As illustrated in  FIGS. 1 and 8 , articulation of lower section  14  may be controlled by a four pin system. Two large pins  24  carry the main load and allow for rotation of lower section  14 . Two small anti-rotation pins  56 , when in place, prevent the rotation of lower section  14 , but when removed, allow the rotation of lower section  14 . Lower section  14  may be two individual sub-sections that when installed are held to one another. 
     Multiple hoses may be used to carry air pressure from the main air pressure vessels to device  10  when mounted in the derrick. As seen in  FIG. 9 , gooseneck conduits  58  provide a connection means for the multiple hoses. Multiple hoses allow for redundancy in case of hose failure. Should such failure occur, each hose uses manual isolation valves at each end so they may be isolated from the system and still allow device  10  to operate. 
     Device  10  may contain multiple lifting points installed thereon for assistance in handling. For example,  FIGS. 9 and 10  show padeyes  60  on upper section  28  of outer frame  16 . Padeyes  60  serve at attachment points for rig hoist equipment. 
     Device  10  may be made of high strength steel, which reduces the weight of the system. As seen in  FIGS. 1 and 9 , device  10  may contain overhead winch  62 . Winch  62  may be affixed to slidable inner frame  18 . Winch  62  may be used to assist in installing well intervention equipment into lower section  14 . 
     The installation of device  10  will now be described. First, install elevators in the derrick to accept lift sub  30  of device  10 . Position the elevators at an elevation for that purpose. Move device  10  to the area in front of the V-door or on the cat-walk of the rig. Optionally remove two small anti-rotation pins  56  securing lower section  14  that prevent its articulation or rotation. By removing pins  56 , device  10 , and more particularly, lower section  14 , is permitted to articulate as it is pulled into the derrick. Alternatively, pins  56  could be left in place so that device  10  can be lifted by the elevator as one unit. If pins  56  are removed, it is important to re-insert them after device  10  is suspended in the derrick. Install the elevators around lift sub  30  in upper section  28  of outer frame  16  when it reaches the center of the rotary. Attach stabilizing lines to the bottom of device  10  to control it as it hoisted into the derrick. Attach the main air lines and the smaller hydraulic control lines via gooseneck conduits  58 . Charge device  10  with the minimum air required for operation. Unlock slidable inner frame  18  from outer frame  16  by releasing locking pin  48 . Device  10  will remain in its retracted position until compensation to account for the rise or fall of the sea level. 
     Device  10  may be configured for attachment of bails. For using the bail point attachment, retract link pins  64  and bushing at the bottom lower section  14 . Install links into the bottom of section  14  by putting the links in section  14  and re-extending pins  64 . Hoist up device  10  until the links are free of the rig floor. Lower device  10  down to the riser and attach to the links. 
     For using the center capture system  18 , unlock and open the center gate or door  26 . Install a lift joint into the open “U” slot of system  18 . Close and lock the center gate or door  26 . Hoist device  10  using the elevators until the unit is mid position in the derrick or to the required position for operation. Device  10  is now ready to have well intervention equipment installed via the lift joint. Winch  62  may be used to position the well intervention equipment in device  10 . Winch  62  may have a 33K capacity. Winch  62  is commercially available from Lantec under model name LHS330-01. 
       FIG. 11  is a schematic of the control panel that is used to operate device  10 . Line  70  provides passage of fluid (e.g., compressed gas) from standby bottles to device  10 . Pressure gauge  72  is provided in line  70  and measures pressure from 0 to 5,000 psi. Valve  74  is provided in line  70 . Valve  74  may be a ball valve (1½″×3000 psi wp). Line  70  splits into line  76  which powers compensation cylinders  20 ,  22  and line  78  which vents to the atmosphere. Line  76  includes valve  80 , which may be a ball valve (1½″×3000 psi wp). Line  76  also includes pressure gauge  82  with tension indication 0-3000 psi. Line  78  includes valve  84  which may be a ball valve (1½″×3000 psi wp). Line  86  interconnects lines  76  and  78  and includes relief valve  88  which may be set at 2350 psi. Line  90  provides passage of fluid (e.g., compressed gas) from the rig to device  10 . Line  90  includes pressure gauge  92  that measure pressure from 0 to 5,000 psi and valve  94 , which may be a ball valve (1½″×3000 psi wp). Line  90  splits into line or connects to lines  76  and  78 . All lines may be 1½″×3000 psi. 
     Again with reference to  FIG. 11 , line  96  provides for the passage of hydraulic fluid (3000 psi wp) from the rig hydraulic pressure unit to device  10  to lock or unlock lock pin  48 . Line  96  includes two pressure gauges  98 ,  100 , which may measure up to 6000 psi. Line  96  includes valve  102 , which may be a spring center valve (3 pos—4 way ¾″×3000 psi). Line  96  runs from valve  102  to activate lock pin  48  into a locked position. Valve  102  may divert the fluid from line  96  through line  104  to activate lock pin  48  into an unlocked position. Line  106  runs from line  96  to valve  108 . Valve  108  may be a spring center valve (3 pos—4 way ¾″×3000 psi). Line  106  runs from valve  108  to cause the extension of bail pins  64 . Valve  108  may divert fluid from line  106  to line  110  to cause the retraction of bail pins  64 . Line  112  is provided for the return of fluid to a fluid storage tank. Line  114  interconnects lines  96  and  112  and includes relief valve  116  which may be set at 3200 psi. As described, the control panel controls the operation of device  10 . 
     Well intervention devices such as coiled tubing injector heads, blow-out preventor stacks, and lubricators may be affixed to device  10 . To maintain the well intervention devices at a fixed vertical position, compensating cylinders  20 ,  22  may be activated to adjust for the rise and fall of the sea or ocean surface. When the sea or ocean surface rises, cylinders  20 ,  22  are placed in a more contracted position to maintain the vertical position of the well intervention device. When the sea or ocean surface falls, cylinders  20 ,  22  are placed in a more extended position to maintain the vertical position of the well intervention device.  FIGS. 4A and 4B  show device  10  in an extended position. 
     While preferred embodiments of the present invention have been described, it is to be understood that the embodiments described are illustrative only and that the scope of the invention is to be defined solely by the appended claims when accorded a full range of equivalents, many variations and modifications naturally occurring to those skilled in the art from a perusal hereof.