OFFSHORE STRUCTURE INCORPORATING A CONDUCTOR DEFLECTING SYSTEM

Abstract: An offshore structure that is supported above the water's surface by at least one substantially vertically dis­ posed leg which extends to the ocean floor. The structure is adapted to accommodate a vertical member or riser conducter (20) having a deflector segment (26) capable of engaging one or more fluid carrying conduits or risers (19) which are lowered therethrough. The defector segment (26) is positioned to engage a lowering riser end so that the riser will be urged outwardly and away from the base of the structure. The riser or risers (19) can thus be readily con­ nected to subsea pipelines which terminate adjacent to the foot of the offshore structure.

Description: Platforms and structures which are used for offshore work in varying depths of water find utility for a number of purposes. Often such platforms are utilized to support equipment and like material for drilling offshore wells to produce gas and/or crude oil. Because the platforms are so expensive, particularly for use in deep water, they are often used as gathering centers for a plurality of remote or dispersed wells in addition to on-platform wells. Thus, while a particular offshore reservoir might embody any number of producing wells, the production flow from the remote wells can be carried through subsea pipelines to a single desired gathering point. Platforms or structures of the type presently contemplated are utilized to gather the crude product, whether it be gas or oil, into a central treating area. From there it can be transshipped by way of vessels or other means, or merely pumped to a central station onshore for further processing. Since the product carrying pipelines are disposed at the ocean floor, it is necessary that they be led from the remote well head to the foot of the offshore structure. From there the pipeline is connected to a suitable extension of the pipeline or riser so that the product can be either pumped or forced by its own pressure upwardly through the riser to the deck of the platform. Platforms of this type are normally provided with a working deck which is supported above the water's surface by at least one, and preferably by a number of heavy support legs. The latter serve not only to position the platform firmly at the offshore site but also provide support and protection to the plurality of on-platform well conductors and the risers which normally extend from one or more pipelines up to the deck. During the fabricating step of an offshore platform, normally the required complement of well conductor guides and risers are preplaced within the structure so that they are an integral part thereof when the platform is installed at the offshore site. However, often the number of risers which are initially built into the structure is insufficient to accommodate the number of remote or dispersed wells that have later been discovered and found to be productive. It therefore may become necessary at a future date to install additional risers for pipelines to be gathered into the foot of the structure. When adding risers not previously planned for, it is necessary to safeguard them against damage which might be caused by water forces or floating objects such as debris, ice and the like. It is also necessary to minimize the weight and size of the added risers and their attachments and supports. In such an instance, the riser can be made as a heavy walled self-protective member. However, this would not minimize weight and size. It is considered more practical to pass one or more risers directly through an existing or added vertical protective member. In platforms with on-platform wells, guides are preinstalled in the structure during fabrication to protect and stabilize the on-platform well conductors. Usually, extra conductor slots are provided beyond the minimum required. In platforms where an extra conductor slot or slots are available and additional pipeline risers are required, the addition of the protective vertical member into the existing unused conductor slot and guides will be most practical. If no conductor slots remain unused, the addition of the protective vertical member with necessary supports may be accomplished in a manner somewhat similar to the on-platform well conductors. The present invention starts from a structure forming part of the older European patent application (EP-A-0 145214). The upright member is provided with upper and lower spaced apart segments which are connected by an intermediate segment forming a connecting element disposed therebetween. Said upright member extends, by said lower segment, to and into the ocean floor. It is, most essentially, capable of permitting a number of risers to be lowered therethrough and which are deflected outwardly in a desired direction or directions. Further, it protects the risers and supports the riser weight. It is possible to provide a structure of said type that is initially fabricated in a manner to be readily adapted in the future by the addition of further fluid carrying risers after the unit has been installed at an offshore site. The offshore structure is provided with means to receive fluid carrying risers longitudinally therethrough in a manner that the risers will be bent or deflected away from their normal downward course during installation according to the opening part of claim 1. DESCRIPTION OF THE DRAWINGS Figure 1 is an elevation view of an offshore structure 10 of the type contemplated. Figure 2 is a cross-sectional view taken along line 2-2 of Figure 1. Figure 3 is a segmentary view on an enlarged scale of a part of the vertical member or riser conductor shown in Figure 1. Figure 4 is a cross-sectional view of a portion of the riser conductor shown in Figure 3. Figure 5 is a segmentary view of a section of the vertical member shown in Figure 3. It is known by US-A-3 474 630 to guide drilling pipes by conical guides within a tubular casing above a partition wall to ensure that the drilling pipe will be sealingly surrounded by a seal ring disposed in alignment below said conical guide when the descending drilling pipe breaks the partition wall. The drilling pipe remains strictly in a vertical position. Finally, it is known by US-A-1 900 163 to use one derrick for drilling a plurality of holes. At first, a main hole is drilled into the bottom of the sea. Then a bit guide is inserted into said hole which guide directs auxiliary drilling crowns and their pipes into angular relation with each other in order to reach different points within the same oil zone. The bit guide comprises a partitioning member and panels with rounded shoulders for deflecting the drilling pipes. The objective of the present invention is to amend the structure as described in EP-A-0 145 214 so that the construction of the intermediate segment is simpler in order to prepare and install it more easily and in order to reach more freedom to deflect risers in different directions without weakening the stiffness of the conductor means formed by a lower and an upper segment and by an integrated intermediate and connecting segment. The invention is claimed in claim 1 and further embodiments are claimed in sub-claims. The present invention fulfills all of the conditions within the objective mentioned above. In achieving the above noted objectives, there is disclosed an offshore platform as shown in Figure 1, which is positioned in water 2. The platform is comprised primarily of deck 11 which is maintained above the water's surface 3, and which holds equipment normally utilized in drilling for offshore wells and for receiving flows of produced fluids. While not presently shown, deck 11 would normally hold a number of storage tanks and similar equipment capable of processing hydrocarbon fluids such as gas and crude oil which are piped from remote wells. Deck 11 is supported in its elevated position above the water 2 by at least one, and preferably by a plurality of elongated legs 12 and 13. The latter are normally constructed of relatively heavy walled steel, and in sufficient numbers to safely support the deck. The respective legs 12 and 13 are provided with the necessary cross bracing 14 and 16 to strengthen the structure as a whole and to assure its integrity for resisting the severe conditions normally experienced at an offshore site where the unit is installed. In the instance of a fluid gathering unit, platform is preferably located at a central or gathering point for a number of pipelines 17. The latter are brought to the structure 10 from remotely positioned wells. Often, such wells are disposed at the ocean floors 1 and flow both gas and crude oil that is produced, through a well head, and which flows through pipeline 17. At the platform, pipeline 17 is connected to a conductor or riser 18, which extends upwardly to deck 11 and terminates at tanks or other processing facilities. The normal form of conductor means 18, utilized for directing fluids to deck 11, is fabricated of steel. As shown in Figure 1, a plurality of the conductor means 18 are initially installed in the structure 10 either for carrying fluids or for directing a drill string into the substrate. However, illustrative of the instant invention, the elongated upright conductor means 20 is positioned in a manner that it can be provided with one or more subsequently installed risers 19. Referring to Figure 3, the conductor 20 is comprised of an upper guiding and supporting segment 21 which extends upwardly to engage deck 11. This segment 21 may optionally include a plurality of longitudinally spaced, conical guides 22, which are fixed in a desired pattern within guide plate 23. A series of optional guide plates 23 are spaced sufficiently apart within conductor 20 to permit a subsequently inserted riser 19 to be lowered from deck 11, and to be held and in substantially vertical alignment. The lower end of the conductor 20 is comprised of lower segment 24. The two segments 21 and 24 are connected and maintained in axial alignment by an intermediate segment 26. Referring to Figures 4 and 5, said intermediate segment 26 in one embodiment includes a plurality of upstanding gusset plates 27, 28, 29 and 31. The latter are joined by welding along a common inner edge, to define an elongated cruciform cross-section. This drawing embodiment illustrates an example of a four chamber cross-section. Other multi-chamber cross-sections are also applicable to the structure as required by the number of risers 19 to be inserted. Although the particular configuration of intermediate segment 26 can be varied, it must of necessity be structurally adequate to function as an integral part of the conductor 20. Thus, the thickness and grade of steel of plates 27, 28, 29 and 31 constitutes primarily a design function. As seen in Figure 4, the respective upright gusset plates 27, 28, 29, 31 of the intermediate segment 26 form longitudinal, radial sectors 32, 33, 34 and 36 therebetween. Preferably said segments will divide the intermediate segment 26 into discrete peripheral compartments for receiving one or more downwardly lowering risers 19. The intermediate segment is rigidly fastened by welding, grouting or bolting into the adjacent spaced apart end openings of respective aligned upper and lower segments 21 and 24. The degree of overlapping of the circular segments 21 and 24 with a cooperating portion of the intermediate segment 26, will be sufficient to assure that it is capable of supporting the subsequently inserted conduits and riser 19, respectively. As shown in Figures 4 and 5, member 26 is provided with means for intercepting and deflecting a downwardly moving riser 19. Said means includes at least one, and if need be, a plurality of deflector shoes or plates 41, 42, 43 and 44. The latter are arranged longitudinally alone one or more of the peripheral compartments in said intermediate segment 26. Each deflector shoe or plate combination such as 41 or 44, is disposed beneath, and in substantial alignment with a conical guide 22. Thus, as riser 19 is lowered from deck 11, it will register in the series of vertically aligned conical guided 22. The riser 19 will then be guided such that further descent will cause its lower end to eventually engage the deflector plate therebeneath. In another embodiment, the shoe or plate, when only one is utilized such as 42, is generally elongated and may incorporate a gradual curvature. At its upper end, plate 42 is disposed adjacent to gusset 28 at a point spaced downwardly from the plate top surface. The deflector plate 42 is further disposed with one longitudinal edge contiguous to the edge surface of gusset plate 29. Thus, as a lowering riser 19 engages the deflecting surface of plate 42, the riser 19 will be restrained from outward movement by the conical guide 22, but will be urged outwardly as shown in Figure 3. The opposing forces acting on the riser 19 will deflect the lower end thereof away from the conductor 20 at a point above the mud line adjacent to the structure 10. In an alternate embodiment of the riser deflector arrangement, a plurality of, or combination of shoes or plates 43 and 45 are disposed within one longitudinal sector 36 of the intermediate segment 26 to form a trough-like path for the riser 19. Thus, as the latter is lowered past conical guide 22, the riser end will engage the junction of the contiguous shoes or plates 43 and 45 and thereby be maintained in relatively accurate alignment. Thereafter, as it is further lowered, its end will be urged outwardly and terminate at a desired point to permit said end of the riser 19 to be connected to a pipeline 17. It is appreciated that the disposition of intermediate segment 26, together with its various conductor deflecting shoes and plates 41, 42, 43, 44, 45, is such as to give the subsequently inserted riser 19 a desired arrangement or disposition adjacent to the mud line. The respective shoes or plates, such as 41, are thus prearranged within said intermediate segment 26 so that the risers 19, if subsequently lowered, will assume a position compatible with contemplated incoming pipelines 17. By varying the angles of deflection and the disposition of the various shoes and plates 41, the risers 19 can be made to deflect in about every predetermined direction to assure they will leave the platform in a desired direction. The respective shoes or plates, such as 42 and 43, as shown in Figure 5 can be braced against distortion by braces 46 disposed rearwardly thereof and spaced to support the deflecting unit.

Claims: Offshore marine structure (10) comprising a deck (11), at least one leg (12) extending from the floor (1) of the water (2) and supporting said deck (11) above the water surface, conductor means (18, 20) for receiving a plurality of conduits and risers (19), respectively, extending between said floor (1) or the water (2) and said deck (11) for conducting hydrocarbon fluids from underwater pipelines (17) to said deck (11), which conductor means (20) includes a lower segment (24), an upper segment (21), and an intermediate segment (26) positioning said former segments in substantial axial alignment with and spaced apart from each other and comprising deflector means (41, 42, 43, 44) urging lower parts of said risers (19) away from the vertical position, wherein said upper segment (21) comprises riser guides (22) for slidable registering a downwardly moving riser (19) in a substantially vertical predetermined position within said upper segment (21), said intermediate segment (26) includes a plurality of uprightly aligned gussets (27, 28, 29, 31) being joined along a common edge and forming a rigid body to be rigidly fastened into the adjacent spaced apart end openings of said upper segment (21) and said lower segment (24) and defining a plurality of longitudinal radial segments (32, 33, 34, 36) therebetween dividing said intermediate member (26) into discrete peripheral compartments, and that said deflector means are formed as deflector plates (41, 42, 43, 44) being arranged longitudinally along said peripheral compartments and being disposed in angular relation to the longitudinal axis of said intermediate segment (26) so that the upper ends of said deflector plates (41, 42, 43, 44) are positioned adjacent to said longitudinal axis while the lower ends thereof are spaced radially away from said longitudinal axis to slidably engage a lowering riser (19) in a trough-like path and to urge said riser (19) radially outward from said longitudinal axis. Offshore structure (10) as claimed in claim 1, characterized in said riser guides (22) are incorporated into at least one leg (12). Offshore structure (10) as claimed in claim 1 or 2, characterized in that said riser guides (22) are conical guides. Offshore structure (10) as claimed in one of the preceding claims, characterized in that a plurality of deflector plates (43, 44) is disposed within one longitudinal sector (36) forming said trough-like path. Offshore structure (10) as claimed in one of the preceding claims, characterized in that said uprightly aligned gussets (27, 28, 29 31) define an elongate cruciform cross-section.

Inventors: LEVERT, FREDERICK JOSEPH, JR., MOTT, GEORGE EDWARD
Applicants: TEXACO DEVELOPMENT CORPORATION
Application year: 1985
Main classification: E21B43
IPC codes: E02B17, F16L1, E21B43, E21B7