Offshore Shallow Water Platforms and Methods for Deploying Same
An offshore structure for drilling and/or producing a subsea well includes a hull having a longitudinal axis, a first end, and a second end opposite the first end. The hull includes a plurality of parallel elongate columns coupled together. Each column includes a variable ballast chamber positioned axially between the first end and the second end of the hull and a first buoyant chamber positioned between the variable ballast chamber and the first end of the hull. The first buoyant chamber is filled with a gas and sealed from the surrounding environment. The offshore structure also includes an anchor fixably coupled to the second end of the hull and configured to secure the hull to the sea floor. The anchor has an arrow-shaped geometry and a central axis coaxially aligned with the longitudinal axis of the hull. The anchor includes angularly-spaced penetration members extending radially from the central axis of the anchor. In addition, the offshore structure includes a topside mounted to the first end of the hull.
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This application is a 35 U.S.C. § 371 national stage application of PCT/BR2021/050383 filed Sep. 6, 2021 and entitled “Offshore Shallow Water Platforms and Methods for Deploying Same,” which claims benefit of U.S. provisional patent application Ser. No. 63/075,360 filed Sep. 8, 2020, and entitled “Offshore Shallow Water Platforms and Methods for Deploying Same,” each of which is hereby incorporated herein by reference in its entirety for all purposes.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENTNot applicable.
BACKGROUND Field of the InventionThis disclosure relates generally to offshore structures for conducting offshore drilling and production operations for the recovery of hydrocarbons (e.g., oil and/or gas). More particularly, this disclosure relates to apparatus and methods for releasably anchoring buoyant adjustable offshore platforms to the sea floor.
Background of the TechnologyMany different types of offshore structures and vessels may be used to drill and produce hydrocarbons from subsea wells. Typically, the type of structure or vessel selected for offshore operations will depend on the depth of the water at the drilling or production site. For example, in water depths less than about 300 ft., jackup platforms may be used for drilling and/or production operations; in water depths between about 300 and 800 ft., fixed platforms are commonly employed for drilling and/or production operations; and in water depths greater than about 800 ft., floating structures such as semi-submersible platforms, spar platforms, and drillships are often used for drilling and/or production operations.
BRIEF SUMMARY OF THE DISCLOSUREEmbodiments of offshore structures for drilling and/or producing subsea wells are disclosed herein. In one embodiment, an offshore structure for drilling and/or producing a subsea well comprises a hull having a longitudinal axis, a first end, and a second end opposite the first end. The hull includes a plurality of parallel elongate columns coupled together. Each column includes a variable ballast chamber positioned axially between the first end and the second end of the hull and a first buoyant chamber positioned between the variable ballast chamber and the first end of the hull. The first buoyant chamber is filled with a gas and sealed from the surrounding environment. In addition, the offshore structure comprises an anchor fixably coupled to the second end of the hull and configured to secure the hull to the sea floor. The anchor has an arrow-shaped geometry and a central axis coaxially aligned with the longitudinal axis of the hull. The anchor includes angularly-spaced penetration members extending radially from the central axis of the anchor. Further, the offshore structure comprises a topside mounted to the first end of the hull.
In another embodiment, an offshore structure for drilling and/or producing a subsea well comprises a hull having a longitudinal axis, a first end, and a second end opposite the first end. The hull includes a plurality of parallel elongate columns coupled together. Each column includes a variable ballast chamber positioned axially between the first end and the second end of the hull and a first buoyant chamber positioned between the variable ballast chamber and the first end of the hull. Each column includes an end wall positioned at or proximal the second end of the hull. At least a first portion of each end wall is oriented at an acute angle α relative to a reference plane oriented perpendicular to the longitudinal axis of the hull. The first buoyant chamber is filled with a gas and sealed from the surrounding environment. In addition, the offshore structure comprises an anchor fixably coupled to the second end of the hull and configured to secure the hull to the sea floor. The anchor has a central axis coaxially aligned with the longitudinal axis of the hull. The offshore structure also comprises a topside mounted to the first end of the hull.
Embodiments of methods for deploying and/or installing an offshore structure are disclosed herein. In one embodiment, a method comprises (a) positioning a buoyant platform at an offshore installation site. The platform includes a hull, a topside mounted to a first end of the hull, and an anchor fixably coupled to a second end of the hull. The anchor includes a plurality of angularly-spaced penetration members extending radially outward from a central axis of the hull. In addition, the method comprises (b) ballasting the hull. Further, the method comprises (c) penetrating the sea floor with the penetration members of the anchor. The method also comprises (d) allowing the platform to pitch about the second end of the hull after (c).
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 embodiments, reference will now be made to the accompanying drawings in which:
The following discussion is directed to various exemplary embodiments. However, one skilled in the art will understand that the examples disclosed herein have broad application, and that the discussion of any embodiment is meant only to be exemplary of that embodiment, and not intended to suggest that the scope of the disclosure, including the claims, is limited to that embodiment.
Certain terms are used throughout the following description and claims to refer to particular features or components. As one skilled in the art will appreciate, different persons may refer to the same feature or component by different names. This document does not intend to distinguish between components or features that differ in name but not function. The drawing figures are not necessarily to scale. Certain features and components herein may be shown exaggerated in scale or in somewhat schematic form and some details of conventional elements may not be shown in interest of clarity and conciseness.
Unless the context dictates the contrary, all ranges set forth herein should be interpreted as being inclusive of their endpoints, and open-ended ranges should be interpreted to include only commercially practical values. Similarly, all lists of values should be considered as inclusive of intermediate values unless the context indicates the contrary.
In the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to . . . .” Also, the term “couple” or “couples” is intended to mean either an indirect or direct connection. Thus, if a first device couples to a second device, that connection may be through a direct engagement between the two devices, or through an indirect connection that is established via other devices, components, nodes, and connections. In addition, as used herein, the terms “axial” and “axially” generally mean along or parallel to a particular axis (e.g., central axis of a body or a port), while the terms “radial” and “radially” generally mean perpendicular to a particular axis. For instance, an axial distance refers to a distance measured along or parallel to the axis, and a radial distance means a distance measured perpendicular to the axis. Any reference to up or down in the description and the claims is made for purposes of clarity, with “up”, “upper”, “upwardly”, “uphole”, or “upstream” meaning toward the surface of the borehole and with “down”, “lower”, “downwardly”, “downhole”, or “downstream” meaning toward the terminal end of the borehole, regardless of the borehole orientation. 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.
Jackup platforms are height adjustable and can be transported between different operation sites, however, as previously described, jackup platforms are limited to about 300 ft. of water depth. Fixed platforms can be used in greater water depth (e.g., up to about 800 ft.), but are not easily transported between operation sites. Floating structures can be used in deep water exceeding 800 ft., but are typically secured in position at the operation site with mooring systems, and thus, are relatively difficult to move between operation sites. In particular, mooring systems typically include mooring lines that extend from the floating structure to relatively large piles driven into the sea bed. The piles may be difficult to manipulate, transport, and install at relatively deep water depths. Moreover, most floating productions systems and especially drillships are relatively expensive and may be economically prohibitive for some operations.
Accordingly, there remains a need in the art for offshore structures suitable for use in water depths greater than about 200 ft. and that are easily moveable between different offshore locations. Such offshore productions structures would be particularly well-received if they were economically feasible for smaller, marginal fields.
Referring now to
Hull 110 has a central or longitudinal axis 115, a first or upper end 110a extending above the sea surface 13 and a second or lower end 110b opposite end 110a. Hull 110 is releasably secured to the sea floor 11 with an anchor 150 fixably coupled to lower end 110b. The length L110 of hull 110 measured axially from end 110a to end 110b is greater than the depth D10 of the water 10 at the offshore installation site. Thus, with lower end 110b disposed at the sea floor 11 and anchor 150 penetrating the sea floor 11, upper end 110a extends above the sea surface 13. In general, the length L110 of hull 110 may be varied for installation in various water depths. However, embodiments of platforms and hulls described herein (e.g., platform 100, hull 110, etc.) are particularly suited for deployment and installation in water depths of 200 ft. to 600 ft.
Hull 110 has a width W110 measured perpendicular to axis 115 in side view. In this embodiment, the width W110 of hull 110 is uniform or constant along the length L110 of hull 110 as measured in any given vertical plane containing axis 115. As previously described, hull 110 is elongate. As used herein, the term “elongate” is used to refer to structures that have a length that is substantially greater than its maximum width. Thus, the length L110 of hull 110 is substantially greater that the width W110 of hull 110.
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Bulkheads 126 close off the axial ends of chambers 130, 131, 133, 134, thereby preventing fluid communication between adjacent chambers 130, 131, 133, 134. Thus, each chamber 130, 131, 133, 134 is isolated from the other chambers 130, 131, 133, 134 in column 120. Chambers 133, 134 are filled with a gas 106 (e.g., air) and sealed from the surrounding environment (e.g., water 10), and thus, provide a minimum and constant degree of buoyancy to column 120 during deployment and installation of hull 110, as well as during operation of platform 100 at installation site 12. As will be described in more detail below, during deployment and installation of hull 110, fixed ballast chamber 130 and variable ballast chamber 131 are also filled with gas 106 and provide additional buoyancy to column 120. However, during installation of hull 110 at site 12, chamber 130 is at least partially filled with fixed ballast 107 (e.g., water, iron ore, etc.) to increase the weight of column 120, orient column 120 upright, and assist in driving drive anchor 150 into the sea floor 11. During drilling and/or production operations with platform 100 at installation site 12, the fixed ballast 107 in chamber 130 generally remains in place and is not adjusted. In addition, during installation of hull 110 at site 12, variable ballast 108 (e.g., water) is controllably added to ballast adjustable chamber 131 to increase the weight of column 120, orient column 120 upright, and assist in driving anchor 150 into the sea floor 11. However, unlike fixed ballast chamber 130, during offshore drilling and/or production operations with platform 100, the relative amounts of gas 106 and ballast 108 in chamber 131 can be controllably adjusted and varied (i.e., increased or decreased) as desired to vary the buoyancy of column 120 and hull 110. In general, fixed ballast 107 can be added to chamber 130, variable ballast 108 can be added and removed from chamber 131, and gas 106 can be added and removed from chamber 131 using techniques known in the art. Although end walls 123, 124 and bulkheads 126 are described as sealing and isolating chambers 130, 131, 133, 134, it should be appreciated that one or more end walls 123, 124 and/or bulkheads 126 may include a closeable and sealable access port (e.g., man hole cover) that allows controlled access to one or more chambers 130, 131, 133, 134 for maintenance, repair, or service.
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Body 153 has a length Lis measured axially (relative to axis 155) from first end 153a to second end 153b, a width W153 measured radially (relative to axis 155) from side 153c to side 153d, and a thickness T153 measured perpendicularly from surface 154a to surface 154b. In embodiments described herein, length L153 is 5.0 m to 12.0 m, and more specifically 8.0 m to 10.0 m; width W153 is 5.0 m to 15.0 m, and more specifically 8.0 m to 12.0 m; and thickness T153 is 5.0 cm to 15.0 cm, and more specifically 5.0 cm to 10.0 cm. In this embodiment, length L153 is 9.0 m, width W153 is 7.0 m, and thickness T153 is 10.0 cm. For most offshore installation sites (e.g., installation site 12), the ratio of the length L153 to the width W153 is between 0.5 and 1.5, and more specifically between 0.8 and 1.2; the ratio of the length L153 to the length L110 is between 5.0 and 20.0, and more specifically between 6.0 and 12.0; and the ratio of the width W110 to the width W153 is between 2.0 and 4.0, and more specifically between 2.5 and 3.5.
As noted above, a plurality of stiffeners 156 extend from body 153. In particular, a plurality of parallel, uniformly laterally spaced stiffeners 156 are positioned between lateral sides 153c, 153d and extend perpendicularly from each planar surface 154a, 154b. In this embodiment, each stiffener 156 is a flat, elongate, rectangular plate fixably attached to body 153 (e.g., by welding) and extending axially (relative to axis 155) from first end 153a to second end 153b of body 153. Thus, each stiffener 156 has a first or upper end 156a at first end 153a of body 153, a second or lower end 156b at second end 153b of body 153, a proximal or fixed lateral side 156c secured to body 153 and extending axially between ends 156a, 156b, and a distal or free lateral side 156d distal body 153 and extending axially between ends 156a, 156b. Each stiffener 156 has a length measured axially (relative to axis 155) between its ends 156a, 156b, a width measured perpendicular to the corresponding surface 154a, 154b between its lateral sides 156c, 156d, and a thickness measured between its planar surfaces. In embodiments described herein, the length of each stiffener 156 is equal to the length L153 of the corresponding body 153 at the location of the stiffener 156; the width of each stiffener 156 is between 0.5 m and 1.2 m, and more specifically between 0.6 m and 0.8 m; and the thickness of each stiffener 156 is between 5.0 cm and 15.0 cm, and more specifically between 5.0 cm and 10.0 cm. As best shown in
Stiffeners 156 provide structural support to the corresponding body 153, thereby enhancing the strength and rigidity of penetration member 152. For example, when anchor 150 is disposed in the sea floor 11 as shown in
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Following offshore drilling and/or production operations at installation site 12, platform 100 may be lifted from the sea floor 11, and then moved to and installed at another installation site. In general, platform 100 is lifted from the sea floor 11 by de-ballasting hull 110 such that at platform 100 is net buoyant. Hull 110 is de-ballasted by increasing the volume of air 106 in chambers 131 and decreasing the volume of water 108 in chambers 131. In response to being net buoyant, platform 100 slowly rises upward, thereby pulling anchor 150 the sea floor 11. Once anchor 150 is fully pulled from the sea floor 11, platform 100 is free floating and may be towed to another installation site and installed at the new installation site in the same manner as previously described.
In the manner described, anchor 150 releasably secures hull 110 and associated platform 100 to the sea floor 11, restricts and/or prevents lateral/horizontal movement of hull 110 and associated platform 100 relative to the sea floor 11, restricts and/or prevents rotation of hull 110 and associated platform 100 about axes 155, 115 relative to the sea floor 11, and allows limited pivoting of hull 110 and associated platform 100 about lower end 110b and anchor 150. As previously described, platform 100 is bottom founded, and thus, anchor 150 facilitates the foregoing functionality without the use of a mooring system.
In the embodiment of hull 110 of platform 100 previously described, columns 120 are spaced apart about 1.0 m to at least allow access therebetween. However, the distance D120 between columns 120 can be increased to allow greater access to the space between columns 120, to accommodate a topside (e.g., topside 160) having a greater footprint (e.g., greater width), to enable alternative deployment and installation techniques, or combinations thereof. Examples of alternative embodiments of hulls 210, 310 that include columns 120 with greater spacing therebetween are shown in
Referring first to
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Similar to hull 110, in this embodiment, axes 125 of columns 120 are parallel to each other and parallel to axis 215 of hull 210 and upper ends 120a of columns 120 define upper end 210a of hull 210. A topside (e.g., topside 160) is attached to upper ends 120a to form an offshore platform for drilling and/or production operations. In this embodiment, hull 210 includes four columns 120 generally arranged in a square configuration. In addition, the four columns 120 are uniformly radially spaced relative to axis 215 and uniformly circumferentially spaced about axis 215 with each column 120 disposed at and defining one corner of the square arrangement. Columns 120 are circumferentially-spaced apart so as not to directly contact each other. In particular, each pair of circumferentially adjacent columns 120 are spaced apart by a minimum distance D120 in top view (
In this embodiment, lower end wall 124 of each column 120 is a plate including radially inner portion 124a and radially outer portion 124b as previously described. Thus, radially inner portions 124a are proximal central axis 215 and disposed in a common plane oriented perpendicular to axes 215, 125, whereas outer portions 124b are distal central axis 215 and oriented at acute angle α relative to the reference plane P124 as previously described (i.e., outer portions 124b generally slope upward moving radially outward relative to axis 215). However, as columns 120 of hull 210 are radially spaced further from central axis 215 than columns 120 of hull 110 are radially spaced from axis 115, no connection plate or other structure is contiguous with and extends between lower end walls 124. In other words, connection plate 127 is not provided in this embodiment. Further, transitions 124c are positioned radially proximal to the radially inner edges of corresponding lower end walls 124 (relative to central axis 215) and radially distal the radially outer edges of corresponding lower end walls 124 (relative to central axis 215). Thus, intersections 124c are not intersected by axes 125, intersections 124c are radially positioned between central axes 125, 215, and intersections 124c do not divide lower end walls 124 in equal halves. For the same reasons as previously described with respect to hull 110, the geometry of lower end walls 124 including outer portions 124b oriented at angles α accommodate pivoting of hull 210 about lower end 210b with anchor 150 penetrating the sea floor 11. During installation of hull 210 and the associated platform at the installation site 12, end walls 124 engage the sea floor 11 and limit penetration of the sea floor 11.
In the installed configuration with a topside (e.g., topside 160) mounted to upper end 210a of hull 210, fixed ballast in chambers 130, variable ballast in at least the lower portions of chambers 131, and the air in buoyancy chambers 133, 134, the resulting platform has a center of buoyancy 205 and a center of gravity 206 positioned below the center of buoyancy 205. This arrangement offers the potential to enhance the stability of the platform when it is in a generally vertical, upright position.
Referring still to
During deployment and installation of hull 210, the fixed ballast chamber of cell 250 may be filled with gas 106 and provide additional buoyancy to hull 210. However, during installation of hull 210 at site 12, the fixed ballast chamber of cell 250 is at least partially filled with fixed ballast 107 (e.g., water, iron ore, etc.) to increase the weight of cell 250 and hull 210, orient columns 120 and hull 210 upright, and assist in driving drive anchor 150 into the sea floor 11. During drilling and/or production operations at installation site 12, the fixed ballast 107 in the fixed ballast chamber of cell 250 generally remains in place and is not adjusted. In general, fixed ballast 107 can be added to the fixed ballast chamber of cell 250 using techniques known in the art. Although end walls 252, 253 seal and isolate the fixed ballast chamber of cell 250, it should be appreciated that one or more end walls 252, 253 may include a closeable and sealable access port (e.g., man hole cover) that allows controlled access to the fixed ballast chamber of cell 250 for maintenance, repair, or service.
Referring still to
Anchor 150 is as previously described and functions in the same manner as previously described. Namely, anchor 150 couples hull 210, and the associated platform, to the sea floor 11 while simultaneously allowing limited pivoting of hull 210 about anchor 150 and restricting rotation of hull 210 and the associated platform about axis 215. As installed at the installation site, anchor 150 penetrates the sea floor 11 with lower end 210b, and in particular lower end wall 253, abutting or adjacent the sea floor 11. The buoyancy of variable ballast chambers 131 of columns 120 are adjusted and controlled such that the total weight of the platform comprising hull 210 exceeds the total buoyancy of hull 210, thereby placing hull 210 in compression and ensuring anchor 150 remains seated in the sea floor 11. Although lower end 210b abuts or is positioned adjacent the sea floor 11, angled radially outer portions 124b, which slope upwardly moving radially outward relative to axes 215, 155, 255 allow a small degree of pivoting of hull 210 and the associated platform about lower end 210b and anchor 150 without damaging lower ends 120b of columns 120 or end walls 124.
In general, hull 210 and a topside to be mounted on hull 210 to form a platform are transported to the offshore installation site (e.g., site 12), assembled at the installation site to form a platform, and installed at the installation site in substantially the same manner as hull 110, topside 160, and platform 100 previously described with the primary difference being the fixed ballast chamber of cell 250 is at least partially filled with fixed ballast during installation after transport to the installation site. In this embodiment, the fixed ballast chamber of cell 250 is generally filled with ballast along with fixed ballast chambers 130 of columns 120 to transition hull 210 into a vertical, upright orientation and subsequently facilitate insertion of anchor 150 into the sea floor 11 as ballast is added to adjustable ballast chambers 131 of columns 120. In addition, hull 210 and the associated platform can be removed from the sea floor 11 and transported to another installation site in the same manner as hull 110 and platform 100 previously described.
In the manner described, anchor 150 releasably secures hull 210 and the associated platform to the sea floor 11, restricts and/or prevents lateral/horizontal movement of hull 210 and the associated platform relative to the sea floor 11, restricts and/or prevents rotation of hull 210 and the associated platform about axes 215 relative to the sea floor 11, and allows limited pivoting of hull 210 and the associated platform about lower end 210b and anchor 150. Hull 210 and the associated platform are bottom founded, and thus, anchor 150 facilitates the foregoing functionality without the use of a mooring system.
Referring now to
Similar to hulls 110, 210 previously described, a topside is mounted to hull 310 to form an offshore platform for performing drilling and/or production operations. Hull 310 is similar to hulls 110, 210 previously described. In particular, hull 310 has a central or longitudinal axis 315, a first or upper end 310a, and a second or lower end 310b opposite end 310a. Hull 310 is sized and configured such that upper end 310a extends above the sea surface 13 when hull 310 is installed an installation site (e.g., installation site 12). In particular, hull 310 has a length L310 measured axially from end 310a to end 310b that is greater than the depth of the water at the offshore installation site. In addition, hull 310 has a width W310 measured perpendicular to axis 315 in side view. In this embodiment, the width W310 of hull 310 is uniform or constant along the length L120 of columns 120 as measured in any given vertical plane containing axis 315.
Referring still to
Similar to hull 110, in this embodiment, axes 125 of columns 120 are parallel to each other and parallel to axis 315 of hull 310 and upper ends 120a of columns 120 define upper end 310a of hull 310. A topside (e.g., topside 160) is attached to upper ends 120a to form an offshore platform for drilling and/or production operations. In this embodiment, hull 310 includes four columns 120 generally arranged in a square configuration. In addition, the four columns 120 are uniformly radially spaced relative to axis 315 and uniformly circumferentially spaced about axis 315 with each column 120 disposed at and defining one corner of the square arrangement. Columns 120 are circumferentially-spaced apart so as not to directly contact each other. In particular, each pair of circumferentially adjacent columns 120 are spaced apart by a minimum distance D120 in top view (
In this embodiment, lower end wall 124 of each column 120 is a plate, however, unlike lower end walls 124 of columns 120 of hulls 110, 210, in this embodiment, lower end wall 124 of each column 120 does not include distinct inner and outer portions (e.g., radially inner portion 124a and radially outer portion 124b), and further, does not include a transition 124c. Rather, in this embodiment, the entirety of lower end wall 124 of each column 120 is disposed in a plane, and further, the entirety of lower end wall 124 of each column 120 is oriented at acute angle α relative to the reference plane P124 as previously described (i.e., the entirety of lower end wall 124 of each column 120 generally slopes upward moving radially outward relative to axis 315). As columns 120 of hull 310 are radially spaced further from central axis 315 than columns 120 of hull 110 are radially spaced from axis 115, no connection plate or other structure is contiguous with and extends between lower end walls 124. In other words, connection plate 127 is not provided in this embodiment. For the same reasons as previously described with respect to hulls 110, 210, the geometry of lower end walls 124 oriented at angles α accommodate pivoting of hull 310 about lower end 310b with anchor 150 penetrating the sea floor 11. During installation of hull 310 and the associated platform at installation site 12, end walls 124 engage the sea floor 11 and limit penetration of the sea floor 11.
In the installed configuration with a topside (e.g., topside 160) mounted to upper end 310a of hull 310, fixed ballast in chambers 130, variable ballast in at least the lower portions of chambers 131, and the air in buoyancy chambers 133, 134, the resulting platform has a center of buoyancy 305 and a center of gravity 306 positioned below the center of buoyancy 305. This arrangement offers the potential to enhance the stability of the platform when it is in a generally vertical, upright position.
Referring still to
During deployment and installation of hull 310, the fixed ballast chamber of cell 250 may be filled with gas 106 and provide additional buoyancy to hull 310. However, during installation of hull 310 at site 12, the fixed ballast chamber of cell 250 is at least partially filled with fixed ballast 107 (e.g., water, iron ore, etc.) to increase the weight of cell 250 and hull 310, orient columns 120 and hull 210 upright, and assist in driving drive anchor 150 into the sea floor 11. During drilling and/or production operations at installation site 12, the fixed ballast 107 in the fixed ballast chamber of cell 250 generally remains in place and is not adjusted.
Referring still to
Anchor 150 is as previously described and functions in the same manner as previously described. Namely, anchor 150 couples hull 310, and the associated platform, to the sea floor 11 while simultaneously allowing limited pivoting of hull 310 about anchor 150 and restricting rotation of hull 310 and the associated platform about axis 315. As installed at the installation site, anchor 150 penetrates the sea floor 11 with lower end 310b, and in particular lower end wall 253, abutting or adjacent the sea floor 11. The buoyancy of variable ballast chambers 131 of columns 120 are adjusted and controlled such that the total weight of the platform comprising hull 310 exceeds the total buoyancy of hull 310, thereby placing hull 310 in compression and ensuring anchor 150 remains seated in the sea floor 11. Although lower end 310b abuts or is positioned adjacent the sea floor 11, angled lower end walls 124, which slope upwardly moving radially outward relative to axes 315, 155, 255 allow a small degree of pivoting of hull 310 and the associated platform about lower end 310b and anchor 150 without damaging lower ends 120b of columns 120 or end walls 124.
In general, hull 310 and a topside to be mounted on hull 310 to form a platform are transported to the offshore installation site (e.g., site 12) in substantially the same manner as hull 110, topside 160, and platform 100 previously described. However, in this embodiment, the topside is mounted to hull 310 in a different manner to form a platform. In particular, hull 310 is designed, and columns 120 are spaced, to accommodate a topside having a relatively large footprint (e.g., width). The topside has a width that is greater than transport vessel 181, and thus, the feet of the topside that sit atop and are coupled to upper ends 120a of columns 120 are disposed on opposite lateral sides of pontoons 182. To mount the topside to hull 310, hull 310 is ballasted so that upper ends 120a of columns 120 are disposed below the feet of the topside, then vessel 181 passes between upper ends 120a to position the feet of the topside above upper ends 120a of columns, and then hull 310 is deballasted and/or vessel 181 is ballasted such that hull 310 engages the topside and lifts the topside from vessel 181. Once the topside is transferred to hull 310 to from the platform, vessel 181 is withdrawn from between columns 120 and the platform is installed at the installation site in substantially the same manner as hull 110, topside 160, and platform 100 previously described with the primary difference being the fixed ballast chamber of cell 250 is at least partially filled with fixed ballast during installation after transport to the installation site.
In this embodiment, the fixed ballast chamber of cell 250 is generally filled with ballast along with fixed ballast chambers 130 of columns 120 to transition hull 210 into a vertical, upright orientation and subsequently facilitate insertion of anchor 150 into the sea floor 11 as ballast is added to adjustable ballast chambers 131 of columns 120. In addition, hull 210 and the associated platform can be removed from the sea floor 11 and transported to another installation site in the same manner as hull 110 and platform 100 previously described.
In the manner described, anchor 150 releasably secures hull 310 and the associated platform to the sea floor 11, restricts and/or prevents lateral/horizontal movement of hull 310 and the associated platform relative to the sea floor 11, restricts and/or prevents rotation of hull 310 and the associated platform about axes 315 relative to the sea floor 11, and allows limited pivoting of hull 310 and the associated platform about lower end 310b and anchor 150. Hull 310 and the associated platform are bottom founded, and thus, anchor 150 facilitates the foregoing functionality without the use of a mooring system.
While preferred embodiments have been shown and described, modifications thereof can be made by one skilled in the art without departing from the scope or teachings herein. The embodiments described herein are exemplary only and are not limiting. Many variations and modifications of the systems, apparatus, and processes described herein are possible and are within the scope of the invention. For example, the relative dimensions of various parts, the materials from which the various parts are made, and other parameters can be varied. 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. Unless expressly stated otherwise, the steps in a method claim may be performed in any order. The recitation of identifiers such as (a), (b), (c) or (1), (2), (3) before steps in a method claim are not intended to and do not specify a particular order to the steps, but rather are used to simply subsequent reference to such steps.
Claims
1. An offshore structure for drilling and/or producing a subsea well, the structure comprising:
- a hull having a longitudinal axis, a first end, and a second end opposite the first end;
- wherein the hull includes a plurality of parallel elongate columns coupled together, wherein each column includes a variable ballast chamber positioned axially between the first end and the second end of the hull and a first buoyant chamber positioned between the variable ballast chamber and the first end of the hull;
- wherein the first buoyant chamber is filled with a gas and sealed from a surrounding environment;
- an anchor fixably coupled to the second end of the hull and configured to secure the hull to the sea floor, wherein the anchor has an arrow-shaped geometry and a central axis coaxially aligned with the longitudinal axis of the hull, wherein the anchor includes angularly-spaced penetration members extending radially from the central axis of the anchor; and
- a topside mounted to the first end of the hull.
2. The offshore structure of claim 1, wherein anchor tapers to a pointed tip at the second end of the anchor.
3. The offshore structure of claim 1, wherein each penetration member comprises a body and a plurality of stiffeners extending from the body.
4. The offshore structure of claim 3, wherein each body is a plate extending axially from the first end of the anchor to the second end of the anchor;
- wherein a first set of the plurality of stiffeners extend from a first planar side of each plate and a second set of the plurality of stiffeners extend from a second planar side of each plate.
5. The offshore structure of claim 4, wherein the plurality of stiffeners are oriented parallel to each other;
- wherein each stiffener is an elongate plate extending axially from the first end of the anchor to the second end of the anchor.
6. The offshore structure of claim 4, wherein the plate of each body has a trapezoidal shape.
7. The offshore structure of claim 3, wherein each penetration member is angularly spaced 90° from each circumferentially adjacent penetration member.
8. The offshore structure of claim 1, wherein the plurality of columns are uniformly circumferentially-spaced about the longitudinal axis of the hull, and wherein the plurality of columns are uniformly radially spaced from the longitudinal axis of the hull.
9. The offshore structure of claim 8, wherein each column is spaced from each circumferentially-adjacent column by a distance D that is at least 1.0 m.
10. The offshore structure of claim 1, wherein each column has a central axis, a first end disposed at the first end of the hull, and a second end proximal the second end of the hull;
- wherein each column includes a radially outer tubular wall extending axially from the first end of the column to the second end of the column and an end plate coupled to the outer tubular wall at the second end of the column; and
- wherein at least a portion of the end plate of each column is oriented at an acute angle α relative to a reference plane oriented perpendicular to the longitudinal axis of the hull.
11. The offshore structure of claim 10, wherein the angle α is between 0° and 20°.
12. The offshore structure of claim 1, further comprising a cell fixably coupled to the plurality of columns and positioned between the plurality of columns proximal the second end of the hull, wherein the cell has a central axis coaxially aligned with the longitudinal axis of the hull;
- wherein the cell comprises a fixed ballast chamber; and
- wherein the first end of the anchor is fixably attached to the cell.
13. A method, comprising:
- (a) positioning a buoyant platform at an offshore installation site, wherein the platform includes a hull, a topside mounted to a first end of the hull, and an anchor fixably coupled to a second end of the hull, wherein the anchor includes a plurality of angularly-spaced penetration members extending radially outward from a central axis of the hull;
- (b) ballasting the hull;
- (c) penetrating the sea floor with the penetration members of the anchor; and
- (d) allowing the platform to pitch about the second end of the hull after (c).
14. The method of claim 13, wherein (d) comprises allowing the platform to pitch to a maximum pitch angle relative to vertical that is less than 10°.
15. The method of claim 13, wherein (a) comprises:
- (a1) transporting the hull and the topside to the offshore installation site;
- (a2) floating the hull at the sea surface in a horizontal orientation;
- (a3) transitioning the hull from the horizontal orientation to a vertical orientation with the first end disposed above the second end; and
- (a4) mounting the topside to the hull above the sea surface to form the platform.
16. The method of claim 13, wherein the hull includes a plurality of circumferentially-spaced, parallel columns disposed about the central axis of the hull, wherein an end wall of each column disposed at or proximal the second end of the hull includes at least a first portion oriented at an acute angle α relative to a reference plane oriented perpendicular to the central axis of the hull to the first portion.
17. The method of claim 16, wherein the first portion of the end wall of at least one column engages the sea floor during (d).
18. The method of claim 16, wherein each end wall includes a second portion oriented parallel to the reference plane, wherein the second portion of the end wall of each column is radially positioned between the first portion of the end wall and the central axis of the hull.
19. The method of claim 16, wherein the entire end wall of each column is oriented at the acute angle α.
20. An offshore structure for drilling and/or producing a subsea well, the structure comprising:
- a hull having a longitudinal axis, a first end, and a second end opposite the first end;
- wherein the hull includes a plurality of parallel elongate columns coupled together, wherein each column includes a variable ballast chamber positioned axially between the first end and the second end of the hull and a first buoyant chamber positioned between the variable ballast chamber and the first end of the hull, wherein each column includes an end wall positioned at or proximal the second end of the hull, wherein at least a first portion of each end wall is oriented at an acute angle α relative to a reference plane oriented perpendicular to the longitudinal axis of the hull;
- wherein the first buoyant chamber is filled with a gas and sealed from a surrounding environment;
- an anchor fixably coupled to the second end of the hull and configured to secure the hull to the sea floor, wherein the anchor has a central axis coaxially aligned with the longitudinal axis of the hull; and
- a topside mounted to the first end of the hull.
21. The offshore structure of claim 20, wherein the acute angle α of the first portion of each end wall is less than 20°.
22. The offshore structure of claim 21, wherein each acute angle α is the same.
23. The offshore structure of claim 21, wherein the end wall of each column includes a second portion oriented parallel to reference plane, wherein the second portion of each end wall is radially positioned between the first portion and the longitudinal axis of the hull.
24. The offshore structure of claim 21, wherein the entirety of each end wall is oriented at the acute angle α.
Type: Application
Filed: Sep 6, 2021
Publication Date: Oct 19, 2023
Applicant: HORTON DO BRASIL TECNOLOGIA OFFSHORE, LTDA. (Rio de Janeiro)
Inventors: Marcelo Igor Lourenço de Souza (Niterói, Rio de Janeiro), Rafael Louzada Bodanese (Rio de Janeiro), Luiz Germano Bodanese (Rio de Janeiro)
Application Number: 18/024,999