Not applicable.
The disclosure relates generally to floating offshore structures. More particularly, the disclosure relates to buoyant semi-submersible offshore platforms for offshore drilling and/or production operations. Still more particularly, the disclosure relates to the geometries of the hulls of semi-submersible offshore platforms, and in particular, the horizontal pontoons of the hull.
In oilfield activities, semi-submersible floating structures or platforms are used for various types of offshore operations including offshore drilling and production of oil and gas, as well as offshore construction operations. Conventional semi-submersible offshore platforms typically include a hull that provides sufficient buoyancy to support a work deck above the surface of the water, as well as rigid and/or flexible piping or risers extending from the platform to the seafloor. The hull often includes a horizontal base that supports a plurality of vertically oriented columns, which in turn support the work deck above the surface of the water. In general, the size of the pontoons and the number of columns are governed by the size and weight of the work platform and associated payload to be supported by the hull.
Embodiments of floating offshore structures are disclosed herein. In one embodiment, a floating offshore structure comprises a buoyant hull including a first column, a second column, and a pontoon coupled to the first column and the second column. Each column is vertically oriented and the pontoon extends horizontally from the first column to the second column. Each column has a central axis, an upper end, and a lower end. The pontoon includes a first tubular member, a second tubular member positioned laterally adjacent to the first tubular member, a first edge plate extending horizontally from the first tubular member, and a second edge plate extending horizontally from the second tubular member. The first tubular member and the second tubular member are disposed between the first edge plate and the second edge plate. Each tubular member has a central axis, a first end coupled to the lower end of the first column, and a second end coupled to the lower end of the second column. The longitudinal axis of the first tubular member and the longitudinal axis of the second tubular member are disposed in a common horizontal plane.
In another embodiment, a floating offshore structure comprises a buoyant hull including a first column, a second column, and a pontoon extending from the first column to the second column. Each column is vertically oriented and has a central axis, an upper end, and a lower end. The pontoon includes a first cylindrical tubular member, a second cylindrical tubular member oriented parallel to the first tubular member, a first heave plate extending horizontally from the first cylindrical tubular member, and a second heave plate extending horizontally from the second cylindrical tubular member. The first cylindrical tubular member and the second tubular member are disposed between the first heave plate and the second heave plate. The first heave plate and the second heave plate are configured to dampen vertical movement of the floating offshore structure. The second cylindrical tubular member is positioned laterally adjacent to the first cylindrical tubular member. Each tubular member is horizontally oriented and has a central axis, a first end coupled to the lower end of the first column, and a second end coupled to the lower end of the second column.
Embodiments described herein comprise a combination of features and characteristics intended to address various shortcomings associated with certain prior devices, systems, and methods. The foregoing has outlined rather broadly the features and technical characteristics of the disclosed embodiments in order that the detailed description that follows may be better understood. The various characteristics and features described above, as well as others, will be readily apparent to those skilled in the art upon reading the following detailed description, and by referring to the accompanying drawings. It should be appreciated that the conception and the specific embodiments disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes as the disclosed embodiments. It should also be realized that such equivalent constructions do not depart from the spirit and scope of the principles disclosed herein.
For a detailed description of the disclosed exemplary embodiments, reference will now be made to the accompanying drawings, wherein:
The following description is exemplary of certain embodiments of the disclosure. One of ordinary skill in the art will understand that the following description has broad application, and the discussion of any embodiment is meant to be exemplary of that embodiment, and is not intended to suggest in any way that the scope of the disclosure, including the claims, is limited to that embodiment.
The figures are not necessarily drawn to-scale. Certain features and components disclosed herein may be shown exaggerated in scale or in somewhat schematic form, and some details of conventional elements may not be shown in the interest of clarity and conciseness. In some of the figures, in order to improve clarity and conciseness, one or more components or aspects of a component may be omitted or may not have reference numerals identifying the features or components. In addition, within the specification, including the drawings, like or identical reference numerals may be used to identify common or similar elements.
As used herein, including in the claims, the terms “including” and “comprising,” as well as derivations of these, are used in an open-ended fashion, and thus are to be interpreted to mean “including, but not limited to. . . .” Also, the term “couple” or “couples” means either an indirect or direct connection. Thus, if a first component couples or is coupled to a second component, the connection between the components may be through a direct engagement of the two components, or through an indirect connection that is accomplished via other intermediate components, devices and/or connections. The recitation “based on” means “based at least in part on.” Therefore, if X is based on Y, then X may be based on Y and on any number of other factors. The word “or” is used in an inclusive manner. For example, “A or B” means any of the following: “A” alone, “B” alone, or both “A” and “B.”
In addition, the terms “axial” and “axially” generally mean along a given axis, while the terms “radial” and “radially” generally mean perpendicular to the axis. For instance, an axial distance refers to a distance measured along or parallel to a given axis, and a radial distance means a distance measured perpendicular to the axis. As understood in the art, the use of the terms “parallel” and “perpendicular” may refer to precise or idealized conditions as well as to conditions in which the members may be generally parallel or generally perpendicular, respectively. Furthermore, any reference to a relative direction or relative position is made for purpose of clarity, with examples including “top,” “bottom,” “up,” “upward,” “down,” “lower,” “clockwise,” “left,” “leftward,” “right,” “right-hand,” “down”, and “lower.” For example, a relative direction or a relative position of an object or feature may pertain to the orientation as shown in a figure or as described. If the object or feature were viewed from another orientation or were implemented in another orientation, it may be appropriate to describe the direction or position using an alternate term. As used herein, the terms “approximately,” “about,” “substantially,” and the like mean within 10% (i.e., plus or minus 10%) of the recited value. Thus, for example, a recited angle of “about 80 degrees” refers to an angle ranging from 72 degrees to 88 degrees.
As previously described, the hull of a floating semi-submersible platform typically includes a horizontal base and a plurality of vertical columns extending from the base. The base usually includes of a plurality of horizontal pontoons (e.g., 3 or more) connected end-to-end to form a closed loop structure with a large central opening. The lower ends of the columns are seated on top of the corners of the base (i.e., at the intersection of each pair of pontoons), and extend therefrom through the surface of the water to the work deck supported on the upper ends of the columns. The pontoons conventionally have a rectangular cross-sectional shape and are composed of flat stiffened panels. Due to the external pressure of water in combination with compressional loads from the weight of the work deck, the columns and pontoons typically require a combination of longitudinal and transversal stiffeners. The use of flat stiffened panels for the pontoons and stiffeners in the pontoons and columns increases manufacturing costs and structural weight. However, as will be described in more detail below, embodiments of floating offshore structures and hulls disclosed herein offer the potential to reduce manufacturing costs, as well as the overall weight of the hull.
During drilling or production operations, it is generally desirable to minimize the motion of the floating offshore structure to maintain the position of the platform over the well site to reduce the likelihood of damage to the risers extending from the structure to the sea floor. One component of offshore platform motion is heave, which is the vertical linear displacement of the platform in response to wave motion. The floating platform preferably has heave characteristics within acceptable limits to minimize riser fatigue and strength requirements. The heave characteristics of many conventional hull designs present unique challenges to the design of riser systems suitable for the induced dynamic loads and associated fatigue. However, as will be described in more detail below, embodiments of floating offshore structures and hulls disclosed herein offer the potential for improved heave characteristics.
Referring now to
Each pontoon 62 extends horizontally between the lower ends of each pair of laterally adjacent columns 64, thereby forming a closed loop base 65 with four corners and a central opening 66. Since pontoons 62 extend between the lateral sides of the lower ends of columns 64, base 65 may be described as being formed by the pontoons 62 and the lower ends of the columns 64. Although base 65 is shown as having a square geometry in this embodiment with each pontoon 62 having the same length, in other embodiments, the base (e.g., base 65) can have a different geometric shape such as rectangular, triangular, etc.
Columns 64 extend vertically from base 65 through the surface of water 52. Topsides 55 is mounted to hull 60 atop the upper ends of columns 64. In general, the equipment used in oil and gas drilling or production operations, such as a derrick, draw works, pumps, scrubbers, precipitators and the like is disposed on and supported by topsides 55. In this embodiment, risers or other conduits (not shown) pass through opening 66 in base 65 to topsides 55. In such embodiments, the risers or other conduits are directly supported at topsides 55. However, in other embodiments, the risers or other conduits may be directly supported by pontoons 62.
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The side-by-side arrangement of multiple cylindrical tubular members 75 reduces or minimizes the vertical height of the corresponding pontoon 62 while simultaneously increasing or maximizing its horizontal width. Such geometry offers the potential to reduce lateral loads experienced by pontoons 62 and platform 50 that may arise due to ocean currents and waves, as well as reduce the heave of the platform 50 by increasing the vertical drag and added mass of pontoons 62. As a result, embodiments of pontoons described herein (e.g., pontoons 62) offer the potential to reduce the performance requirements and associated costs of mooring systems as compared to conventional pontoons designed to manage heave of a similarly sized conventional hull.
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Similar to cylindrical tubular members 75 of pontoons 62, cylindrical tubular members 105 of columns 64 can be formed from a plurality of circular sections 107A joined together end-to-end. In this embodiment, sections 107A are not elongate, however, in other embodiments, each section 107A is elongate. Alternatively, tubular member 105 can be formed from elongate rectangular piece of material (single piece or multiple pieces welded together to form a single piece) that is rolled and then welded lengthwise along a seam.
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The use of an intermediate connection assembly 145 offers the potential to simplify the fabrication of pontoons 62 and the coupling of pontoons 62 to columns 64 by avoiding the complexity of saddle-type connections. As a result, pontoons 62 can be formed from cylindrical tubular members 75 have flat ends 75A, 75b that are closed and sealed by a flat end plate 80 before pontoons 62 are connected to columns 64. Thus, pontoons 62 can be fabricated, sealed, and tested before they are coupled to columns 64.
In this embodiment, each bracket 150 is co-planar with one of the stiffeners 134A, 134B of deck 130 with lower ends 152 coupled to deck 130 (e.g., welded), thereby providing structural continuity between connection assemblies 145, decks 130, pontoons 62, and columns 64. Brackets 150, 160 may be, for example, flat plates welded to members 75, 105 and deck 130 and may installed by any method known in the art. In the example of
In the embodiment shown in
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Column 64 is as previously described. Pontoons 262 are substantially the same as pontoons 62 previously described with the exception of the ends of pontoons 262 and the interface between pontoons 262 and columns 64. More specifically, each pontoon 262 includes a plurality of straight, elongated, horizontally oriented tubular members 275 connected laterally side-by-side. In this embodiment, two parallel, tubular members 275 are connected side-by-side by a horizontal connecting plate 82 as previously described to form the pontoon 262. Pontoon 262 has a linear (i.e., straight) central or longitudinal axis 276, a first end 275A fixably coupled to the lower end of one column 64, and a second end 275B fixably coupled to the lower end of another column 64. Each end 275A, 275B of each tubular member 275 has a concave contoured shape or saddle that mates with and fits partially around cylindrical outer surface 110 of the corresponding tubular member 105. Similar to cylindrical tubular members 75 previously described, in this embodiment, each tubular member 275 includes a cylindrical side wall 277, an inner cavity 78, and a plurality of annular stiffeners 79 axially spaced along the inner surface of wall 277. However, member 275 lacks an end cap or end plate at ends 275A, 275B. Instead, cavity 78 is sealed at the intersection of ends 275A, 275B and the lower end of one of the corresponding column 64, as will be described in more detail below. Tubular member 275 also includes a plurality of axially adjacent ballast tanks defined by axially-spaced bulkheads. In general, tubular members 275 can be formed in the same manner as cylindrical tubular members 75 previously described (e.g., elongate material, possibly rolled and welded lengthwise or from multiple, short circular sections joined end-to-end).
Referring still to
Axes 276 of tubular members 275 are located in the same horizontal plane. As previously described with respect to pontoon 62, the side-by-side arrangement of multiple tubular members 275 reduces or minimizes the vertical height of the corresponding pontoon 262 while simultaneously increasing or maximizing its horizontal width. This geometry offers the potential to reduce lateral loads experienced by pontoons 262 and the associated platform that may arise due to ocean currents and waves, as well as reduce the heave of the platform 50 by increasing the vertical drag and added mass of pontoons 262. As a result, use of embodiments of pontoons described herein such as pontoons 262 offer the potential to reduce the performance requirements and associated costs of mooring systems as compared to those that may be necessary to manage heave of a similarly sized conventional hull.
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Pontoon 362 extends from the lower end of column 364. Similar to pontoon 262, each pontoon 362 includes a plurality of straight, elongated, tubular members 275 as previously described arranged horizontally side-by-side. However, in this embodiment, three parallel, tubular members 275 are connected by horizontal connecting plates 82—one plate 82 as previously described is disposed between each pair of adjacent tubular members 275 of pontoon 362. In addition, pontoon 362 further includes two reinforced, horizontal edge plates 84 extending lengthwise (i.e., axially) along outer regions of the two outermost tubular members 275. In this embodiment, plates 82, 84 are disposed in a common horizontal plane and are vertically positioned at the middle of tubular members 275. Connecting plate 82 and edge plates 84 provide structural integrity for pontoon 362 and provide dampening of vertical motion of platform 50, being thus configured to perform as horizontal heave plates.
Axes 276 of tubular members 275 are located in the same horizontal plane. As previously described with respect to pontoon 62, the side-by-side arrangement of tubular members 275 reduces or minimizes the vertical height of pontoon 362 and increases or maximizes its width in that horizontal plane. This configuration of makes pontoon 362 and hull 360 less susceptible to lateral forces that may arise due to ocean currents and waves. As well, this configuration increases the vertical drag of pontoon 362, configuring it to reduce the heave motions of platform 50. As a consequence, the use of pontoons 362 may allow the use of smaller or less costly mooring systems than would be used for a conventional hull.
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Each pontoon 362 is fixably coupled to a corresponding column 364 with a plurality of connections 285 as previously described-one connection 285 is couples each tubular member 105 to a corresponding tubular member 105. In particular, each tubular member 275 is positioned adjacent one of the vertical tubular members 105 and is coupled to the lower end 105B of that tubular member 105 with one connection 285. As previously described, each connection 285 is a saddle-type connection in which the contoured end 275A, 275B of the tubular member 275 wraps partially around outer surface 110 of the corresponding tubular member 105 and is coupled directly thereto (e.g., welded). In this embodiment, connection 285 does not include any gussets or brackets extending between the coupled members 275, 105, however, in other embodiments, such features may be added.
In the embodiments shown in
Embodiments of pontoons 62, 262, 362 disclosed herein include axially-spaced annular stiffeners 79 disposed along the inner surface of the cylindrical side walls 77, 277 of the cylindrical tubular members 75, 275, but lack internal, longitudinal stiffeners. The circular tubular configuration of members 75, 275 along with the internal, annular stiffeners 79 provide structural integrity and rigidity while the connecting plates 82 and edge plates 84 function as external longitudinal stiffeners that enhance the structural integrity or rigidity of members 75, 275 and pontoons 62, 262, 362, as well as reduce heave.
While exemplary embodiments have been shown and described, modifications thereof can be made by one of ordinary skill in the art without departing from the scope or teachings herein. The embodiments described herein are exemplary only and are not limiting. Many variations, combinations, and modifications of the systems, apparatus, and processes described herein are possible and are within the scope of the disclosure. Accordingly, the scope of protection is not limited to the embodiments described herein, but is only limited by the claims that follow, the scope of which shall include all equivalents of the subject matter of the claims. The inclusion of any particular method step or operation within the written description or a figure does not necessarily mean that the particular step or operation is necessary to the method. The steps or operations of a method listed in the specification or the claims may be performed in any feasible order, except for those particular steps or operations, if any, for which a sequence is expressly stated. In some implementations two or more of the method steps or operations may be performed in parallel, rather than serially. The recitation of identifiers such as (a), (b), (c) or (1), (2), (3) before operations in a method claim are not intended to and do not specify a particular order to the operations, but rather are used to simplify subsequent reference to such operations.
This application is a continuation of U.S. application Ser. No. 15/808,057 filed Nov. 9, 2017, and entitled “Floating Offshore Structures with Round Pontoons,” which claims benefit of U.S. provisional patent application Ser. No. 62/419,828 filed Nov. 9, 2016, and entitled “Floating Offshore Structures with Round Pontoons,” each of which is hereby incorporated herein by reference in their entirety for all purposes.
Number | Date | Country | |
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62419828 | Nov 2016 | US |
Number | Date | Country | |
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Parent | 15808057 | Nov 2017 | US |
Child | 16438133 | US |