Abstract:
A floating, offshore drilling and/or production platform is equipped with a rail-mounted transport system that can be positioned at a plurality of selected positions over the well bay of the vessel. The transport system can move a drilling riser with a drilling riser tensioner system and a blowout preventer from one drilling location to another without removing them from the well bay of the vessel. Using the transport system, the drilling riser is lifted just clear of a first well head and positioned over an adjacent, second well head using guidelines. The transport system may then move the upper end of the drilling riser (together with its attached tensioner and BOP) to a second drilling location. A dummy wellhead may be provided on the seafloor in order to secure the lower end of the drilling riser without removing it from the sea while production risers are being installed.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/543,663, filed on Oct. 5, 2011, and U.S. Provisional Application No. 61/606,031, filed on Mar. 2, 2012, and U.S. Provisional Application No. 61/610,805, filed on Mar. 14, 2012. The disclosure of each of these three provisional applications is hereby incorporated by reference in its entirety. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT: Not Applicable 
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    This invention relates to offshore drilling and production platforms. More particularly, it relates to a method and apparatus for drilling a plurality of wells at a single platform (or vessel) location and installing production risers on those wells. 
         [0004]    2. Description of the Related Art including information disclosed under 37 CFR 1.97 and 1.98. 
         [0005]    Both tension leg platforms (TLP&#39;s) and semi-submersible floating vessels (“semis”) can be used for offshore drilling and production operations, 
         [0006]    A tension leg platform (TLP) is a vertically moored floating structure typically used for the offshore production of oil and/or gas, and is particularly suited for water depths greater than about 1000 ft. 
         [0007]    The platform is permanently moored by tethers or tendons grouped at each of the structure&#39;s corners. A group of tethers is called a tension leg. The tethers have relatively high axial stiffness (low elasticity) such that virtually all vertical motion of the platform is eliminated. This allows the platform to have the production wellheads on deck (connected directly to the subsea wells by rigid risers), instead of on the seafloor. This feature enables less expensive well completions and allows better control over the production from the oil or gas reservoir. 
         [0008]    A semi-submersible is a particular type of floating vessel that is supported primarily on large pontoon-like structures that are submerged below the sea surface. The operating decks are elevated perhaps 100 or more feet above the pontoons on large steel columns. This design has the advantage of submerging most of the area of components in contact with the sea thereby minimizing loading from wind, waves and currents. Semi-submersibles can operate in a wide range of water depths, including deep water. The unit may stay on location using dynamic positioning (DP) and/or be anchored by means of catenary mooring lines terminating in piles or anchors in the seafloor. Semi-submersibles can be used for drilling, workover operations, and production platforms, depending on the equipment with which they are equipped. When fitted with a drilling package, they are typically called semi-submersible drilling rigs. 
         [0009]    The DeepDraftSemi® vessel offered by SBM Atlantia, Inc. (Houston, Tex.) is a semi-submersible fitted with oil and gas production facilities that is suitable for use in ultra deep water conditions. The unit is designed to optimize vessel motions to accommodate steel catenary risers (SCRs). 
       BRIEF SUMMARY OF THE INVENTION 
       [0010]    A floating, offshore drilling and/or production platform is equipped with a rail-mounted transport system that can be positioned at a plurality of selected positions over the well bay of the vessel. The transport system can move a drilling riser with a drilling riser tensioner system and a blowout preventer from one drilling location to another without removing them from the well bay of the vessel. Using the transport system, the drilling riser is lifted just clear of a first well head and positioned over an adjacent, second well head using guidelines. The transport system may then move the upper end of the drilling riser (together with its attached tensioner and BOP) to a second drilling location. A dummy wellhead may be provided on the seafloor in order to secure the lower end of the drilling riser without removing it from the sea while production risers are being installed. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S) 
         [0011]      FIG. 1  is a perspective view of an isolated well bay on an offshore drilling platform according to one particular embodiment of the invention that provides for 27 production riser tensioners and up to nine locations of a moveable drilling riser tensioner and blowout preventer. 
           [0012]      FIG. 2  shows the well bay illustrated in  FIG. 1  installed in the lower deck (“production deck”) of a TLP. 
           [0013]      FIG. 3  shows both a production riser tensioner and surface tree assembly as well as a drilling riser tension joint, drilling riser tensioner and blowout preventer assembly on a transport trolley according to the invention. 
           [0014]      FIG. 4  shows various views of an adapter frame in the retracted (drilling) position within a transport trolley according to the invention. 
           [0015]      FIG. 5  shows various views of an adapter frame in the extended (transfer) position within a transport trolley according to the invention. 
           [0016]      FIG. 6  shows various views of a transport trolley according to the invention. 
           [0017]      FIG. 7  shows various views of an adaptor frame drilling riser support insert) according to the invention. 
           [0018]      FIG. 8  illustrates the sequential steps used in transferring a drilling riser between adjacent wells on the seafloor in a method according to the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0019]    The invention may best be understood by reference to one particular preferred embodiment whose apparatus is illustrated in  FIGS. 1-7  and an associated method of use is illustrated in  FIG. 8  as a sequence of steps. The drawing figures outline general equipment and methodology for drilling multiple wells from a floating unit, and the installation of production risers, while minimizing or eliminating the need to retrieve the drilling riser when moving between wells. 
         [0020]    The system shown is intended for use on a well pattern which is essentially rectangular in shape, but it should be understood that similar methodology could be adapted to well patterns of a more square shape or other patterns. 
         [0021]    One particular feature of the system is a transfer trolley, which is suspended from the lower deck (the production deck) of the floating platform. The transfer trolley is set to run down the length of the well pattern. The position of the transfer trolley is held side to side by fixed rails, or similar, which may form part of the deck structure. The end-to-end position of the transfer trolley may be shifted using a rack-and-pinion arrangement with the pinion(s) turned by hydraulic motors or the like. The end-to-end position of the transfer trolley may be controlled by other means—for example by a pair of opposing winches used to translate the transfer trolley. 
         [0022]    The transfer trolley may be used to transport the assembled drilling riser together with an associated tensioner and blowout preventer (BOP) between well bay positions. 
         [0023]    The production deck (the lower deck) of the floating structure may contain discrete (separate) tensioners  42  for the near-vertical production risers. These tensioners may be arranged in a regular geometric pattern, as shown in  FIGS. 1 . It should be noted that the spacing of the well bay on the structure may be chosen to be consistent with the physical requirements to fit production tensioners, surface trees, connection jumpers, and other required equipment for drilling, production, work over and so forth. The wells may be spaced on the seafloor to provide access space as required for various seafloor activities related to drilling, production, etc. The seafloor and surface spacing may not necessarily be identical (due to different space requirements) but may be established in a way to minimize the offset angles between corresponding seafloor and surface locations. 
         [0024]    Referring in particular to  FIGS. 1 and 2 , the TLP includes provision for installation of a total of 27 riser tensioners in a 9-by-3 array of well slots  20  on the rawer deck  82  of a TLP. The drilling riser is deployed only from the central of the three columns, with the ability to reach each of the 27 subsea well head locations from at least one of the nine positions within the central column. For certain well patterns, less than the full 9 central column positions may be needed to reach each of the wells on the seafloor. The central column may initially be open to allow translation of the hanging drilling riser to locations appropriate for reaching the well heads. Production risers in the two outer columns may be installed first, with tensioners  42  and surface trees  40  mounted on the lower deck (production deck)  82 . As additional risers are added, inserts may be placed in the central column to allow installation of production riser tensioners therein. Tree access platforms  16  may be provided in production deck structure  18 .  FIG. 1  shows the outer columns with all production risers installed, a single production riser installed at one end of the central column, and the drilling riser  36  near the midpoint of the central column.  FIG. 1  also shows a smaller BOP  28  (used for well completion) on a Production Riser Tensioner  42  (connected to production riser tension joint  44 ) in the outer row adjacent to the larger drilling BOP  26 , confirming adequate clearance between the two BOP&#39;s. 
         [0025]      FIG. 2  shows the production deck  82  of a TLP equipped with a drilling riser transport system according to the invention viewed from the opposite end of the well bay as that shown in  FIG. 1  and with the topsides structure (drilling deck) in place, The two winches  22  shown at the near end of the opening in the lower deck  82  are for the drilling riser guidelines  24 , This view also shows the routing of the production  10 , annulus  14  and control jumpers  12  for each of the surface trees. These jumpers are routed outward on the two outer columns of wells. The boxes  84  above the central (open) column represent the tie off locations for the central wells. Note that there is ample clearance for hook up of hard piping to the drilling BOP  26 . 
         [0026]    The leftmost illustration in  FIG. 3  is a side view of a drilling riser assembly comprising drilling riser tension joint  36 , a drilling riser tensioner system  30  and a high-pressure blowout preventer (BOP)  26  supported in a drilling riser transfer system  32  according to the invention. 
         [0027]    As shown in the uppermost view of  FIG. 3  (a top plan view), the support inserts for both the production tensioners  42  and drilling riser tensioner  32  may rest on brackets  38  extending outward from the main beaus  64  along the edges of the opening in the lower deck. The drilling riser  36  may be moved by means of a transporter  32  which fits around the Drilling Riser Transport (DRT) support insert  66  and can lift it clear of the support brackets  38 . 
         [0028]    Also shown in the top and side views of  FIG. 3  are winches  22  for guide wire ropes  24 . Winches  22  may be constant tension winches Guide wire rope  24  may be routed around sheave  86  and through openings in drilling riser tensioner  30  and hole  62  (see  FIG. 6 ) in transport trolley  32 , 
         [0029]    As illustrated in  FIG. 4 , the transporter  32  may move the drilling riser assembly ( 26 + 30 + 32  in  FIG. 3 ) on rails  34  ( FIG. 1 ) by means of a rack-and-pinion drive system, located on the edges of the opening in the lower deck. Rack  70  may be attached to well bay support beam  64  and/or track  72  and pinions  68  may be mounted on transport trolley  32  and connected to hydraulic drive motors  52 . The transporter may be supported by Hillman rollers  54  (Hillman Inc., Marlboro, N.J. 07746) resting on horizontal tracks  72 . As shown in  FIG. 4 , the drive system of the illustrated embodiment uses four drive motors. In addition, the motion of the transporter may be controlled by guide rollers (not shown) reacting on the sides of the track on one or both sides of the opening in the lower deck. 
         [0030]    In  FIG. 4 , adaptor frame  66  is shown in the retracted position. The extended position of the adaptor frame  66  is shown in phantom in the lower left view of Figure.  4 . When in the retracted position, the adaptor frame e  66  is supported by deck support brackets  38  and not (to any significant degree) by transport trolley  32 . It will be appreciated that the retracted position of adaptor frame  66  is that used during drilling operations. When in the retracted position, the reactive force of the drilling riser tensioner system  30  is transmitted to the deck structure  64  via deck support brackets  38 . The supports of transport trolley  32  (e.g., Hillman rollers  54  and support arms  88 ) are not exposed to the dynamic loads of heave compensation imposed by tensioner system  30 , 
         [0031]      FIG. 5  is similar to  FIG. 4 , but with adaptor frame  66  in the extended position. As shown in  FIG. 5 , the DRT support insert  66  may be lifted relative to the transporter  32  by four hydraulic cylinders  66 , two on each side of the insert. The geometric shape of the support insert and the transporter may be such that overlap between the two parts provides guidance as the support insert rises, limiting lateral loads on the hydraulic cylinders. 
         [0032]    Extending adapter frame  66  results in lifting the drilling riser assembly sufficiently to clear the wellhead on the seafloor to which is was connected. This permits the drilling riser assembly to be moved horizontally within the well bay without disconnecting either the drilling BOP  26  or the drilling riser tensioner system  30 . Moreover, the drilling riser itself may remain in the sea. In certain embodiments, a dummy wellhead may be provided on the seafloor for landing and securing the lower end of the drilling riser while production risers are run. This can help to prevent collisions between the risers. 
         [0033]      FIG. 6  contains four views of a transport trolley  32  according to one embodiment of the invention—an isometric view, a top plan view, a side view and an end view. Adapter frame lift cylinders  60  are shown within transport trolley  32 . Also shown are openings  62  for guidelines  24  which may be sized to also permit passage of the remote ROV guide post tops (see  FIG. 8 ). 
         [0034]      FIG. 7  contains four views of an adapter frame  66  according to one embodiment of the invention—an isometric view, a top plan view, a side view and an end view. Adapter frame  66  has a central opening  67  with a perimeter rim  74  which may project into opening  67 . Rim (or flange)  74  may be sized and configured to fit drilling riser tensioner system  30 . Drilling riser tensioner system  30  is supported on rim  74 . Load brackets  80  are sized and configured to engage deck support brackets  38 . Lift extensions  78  are sized and configured to engage adapter frame lift cylinders  60 . In a system according to the invention, the static load of the drilling riser assembly is borne on lift extensions  78  when transport trolley  32  is moved horizontally but the static and dynamic loads are borne by load extensions  80  when the drilling riser is connected and tensioned by tensioner system  30 . As shown in  FIG. 7 , load extensions  80  may be reinforced with gussets  90 . 
         [0035]    Specific design parameters for one particular preferred embodiment of a drilling riser transport system according to the invention are:
       The transporter  32  may be supported by four sets of Hillman rollers  54 .   The top of the DRT support insert  66  is level with the top of the support rails when the transporter lift cylinders  60  are retracted.   The DRT  30  fits within the inner opening  67  of the support insert  66 , and is supported by a ledge  74  around the perimeter of the opening.   Lift of the DRT support insert  66  relative to the transporter  32  is sufficient to clear the well head and its associated guide posts.   Maximum load carried by the DRT support insert  66  is carried through the brackets  80 .   Static load only is carried by the transporter  32  during lift and movement of the drilling riser.   The transporter  32  carries no load when the DRT support insert  66  is resting on the brackets  80 .   The transporter may be driven by a rack  70  and pinion  68  system powered by hydraulic drive motors  52 .       
 
         [0044]    As shown in the sequence illustrated in  FIG. 8 , the transfer method according to the invention begins at Step 1 with the drilling riser and its associated tieback connector attached to a home position wellhead. At Step 2, the guidelines are slackened so that the ROV can unlock the upper section of the guideposts (“guide post tops”) and move them to the adjacent wellhead. If not already deployed, the guide arms may be folded down (using the ROV) and the guidelines reattached to the drilling riser by positioning the guidelines in the lower guide arms via gates in the guide arms. In Step 3, the tieback is disconnected from the home position wellhead and lifted by extending the adapter frame lift cylinders  60 . This provides sufficient clearance to move the tieback connector from the home position wellhead to the adjacent wellhead by applying a selected amount of tension to the guidelines  24  using guide line winches  22  (which may be constant tension winches). The transporter  32  may concurrently move the drilling riser to the closest available drilling position over the target wellhead. The lower guide arms may be free to swivel around the tie back connector to align and connect with the guidelines and guideposts. The guide arms may be sized such that, in the folded position, they may pass through passageways in the drilling riser tensioner and openings  62  in drilling riser transfer trolley  32 . After full positioning tension is applied to the guidelines thereby realigning the tieback connector over the adjacent well (Step 4), the drilling riser may be lowered (Step 5) by retracting hydraulic lift cylinders  60 , and the tie back connector landed and locked on the adjacent wellhead. 
         [0045]    Although particular embodiments of the present invention have been shown and described, they are not intended to limit what this patent covers. One skilled in the art will understand that various changes and modifications may be made without departing from the scope of the present invention as laterally and equivalently covered by the following claims.