STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not applicable.
BACKGROUND
Field of the Invention
This 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 Technology
Many 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 DISCLOSURE
Embodiments 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.
BRIEF DESCRIPTION OF THE DRAWINGS
For a detailed description of the disclosed embodiments, reference will now be made to the accompanying drawings in which:
FIG. 1 is a schematic side view of an embodiment of an offshore structure in accordance with the principles disclosed herein;
FIG. 2 is a cross-sectional top view of the hull of FIG. 1 taken in section 2-2 of FIG. 1;
FIG. 3 is a cross-sectional view of one column of FIG. 2 taken in section 3-3 of FIG. 2;
FIG. 4 is a partial perspective bottom view of the offshore structure of FIG. 1;
FIG. 5 is an enlarged side view of the lower portion of the hull and the anchor of FIG. 1;
FIG. 6 is an enlarged front view of the lower portion of the hull and the anchor of FIG. 1;
FIGS. 7A-7F are schematic sequential views of the offshore deployment, transport, and installation of the platform of FIG. 1;
FIG. 8 is a schematic side view of an embodiment of a hull for an offshore structure in accordance with the principles disclosed herein;
FIG. 9 is a top view of the hull of FIG. 8;
FIG. 10 is a schematic side view of an embodiment of a hull for an offshore structure in accordance with the principles disclosed herein; and
FIG. 11 is a top view of the hull of FIG. 10.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
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 FIG. 1, an embodiment of an offshore structure 100 in accordance with the principles disclosed herein is shown. Structure 100 functions as a platform from which offshore operations are performed conducted, and thus, may also be referred to as an offshore “platform.” In FIG. 1, offshore platform 100 is shown deployed in a body of water 10 and releasably coupled to the sea floor 11 at an offshore installation site 12. Platform 100 is anchored directly to the sea floor 11 without the use of a mooring system (or associated mooring lines), and thus, is a “bottom-founded” structure, it being understood that bottom-founded offshore structures are anchored directly to the sea floor and do not rely on mooring systems to maintain their position at the installation site (e.g., installation site 12). In general, platform 100 may be deployed and installed at offshore site 12 to drill a subsea well and/or produce hydrocarbons from a subsea well. In this embodiment, platform 100 includes an elongate hull 110 and a topside or deck 160 mounted to hull 110 above the sea surface 13.
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.
Referring still to FIG. 1, hull 110 includes a plurality of elongate parallel cylindrical columns 120. Each column 120 has a central or longitudinal axis 125, a first or upper end 120a, and a second or lower end 120b opposite end 120a. Axes 125 of columns 120 are parallel to each other and parallel to axis 115 of hull 110. Upper ends 120a of columns 120 define upper end 110a of hull 110. Lower ends 120b of columns 120 define lower end 110b of hull 110. Top side 160 is attached to upper end 120a of each column 120, and anchor 150 extends axially from lower ends 120b of columns 120.
As best shown in FIG. 2, in this embodiment, hull 110 includes four columns 120 generally arranged in a square configuration. In particular, the four columns 120 are uniformly radially spaced from axis 115 and uniformly circumferentially spaced about axis 115 with each column 120 disposed at and defining one corner of the square arrangement. Columns 120 are positioned proximal each other but are circumferentially and radially 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 (FIG. 2) and side view (FIG. 1). The minimum distance D120 between each pair of circumferentially adjacent columns 120 is at least 1.0 m to allow inspection of columns 120. In this embodiment, the minimum distance D120 between each pair of circumferentially adjacent columns 120 is the same, and in particular, is 1.0 m, however, in other embodiments described in detail below, the minimum distance D120 may be greater than 1.0 m (e.g., about 40.0 m) to accommodate a larger topside 160 and/or accommodate different types of deployment methods. Each column 120 is coupled to each circumferentially-adjacent column 120 by a plurality of axially spaced plates 121. Each plate 121 extends radially (relative to central axes 125) between the corresponding pair of circumferentially-adjacent columns 120 and extends axially along a portion of the corresponding pair of circumferentially-adjacent columns 120.
Referring again to FIG. 1, each column 120 has a length L120 measured axially between ends 120a, 120b and a width W120 measured perpendicular to its corresponding axis 125 in side view. Length L120 of each column 120 is equal to the length L110 of hull 110. In this embodiment, each column 120 is cylindrical, and thus, the width W120 of each column 120 is equal to its diameter. In this embodiment, each column 120 is identical, and thus, the length L120 and the width W120 of each column 120 is the same. For most offshore installation sites (e.g., site 12), the width W120 of each column 120 is less than 15.0 m, and more specifically between 8.0 m and 15.0 m. In general, the length L120 and the width W120 of each column 120 can be tailored to the particular installation site 12 and associated depth D10 of water 10.
Referring now to FIG. 3, one column 120 is schematically shown, it being understood that each column 120 is the same. In this embodiment, column 120 includes a radially outer cylindrical wall or tubular 122 extending between ends 120a, 120b, a first or upper end wall 123 closing tubular 122 at upper end 120a, a second or lower end wall 124 closing tubular 122 at lower end 120b, and a plurality of axially spaced bulkheads 126 positioned within tubular 122 between end walls 123, 124. End walls 123, 124 and bulkheads 126 are axially spaced apart. In this embodiment, each end wall 123, 124 and each bulkhead 126 is in the form of a rigid plate. End wall 123 and bulkheads 126 are oriented perpendicular to central axis 125 of column 120. As will be described in more detail below, end wall 124 at lower end 120b includes a portion oriented perpendicular to axis 125 of column 120 and a portion oriented at an acute angle relative to axis 125 of column 120. Tubular 122, end walls 123, 124, and bulkheads 126 form a plurality of axially stacked chambers within column 120. Although any suitable number and type of chambers can be provided within column 120, in this embodiment, column 120 includes a fixed ballast chamber 130 extending from lower end 120b, a ballast adjustable chamber 131 axially adjacent fixed ballast chamber 130, and a pair of buoyant chambers 133, 134 axially disposed between upper end 120a and ballast adjustable chamber 131. The number and size (e.g., axial length and width/diameter) of each chamber 130, 131, 133, 134 can be varied depending on conditions at installation site 12, the depth D10 of water 10 at the installation site 12, and desired dynamics for hull 110 and platform 100. At least two buoyant chambers 133, 134 are preferably included in column 120 to provide redundancy and buoyancy in the event there is damage or a breach of one buoyant chamber 133, 134, uncontrolled flooding of ballast adjustable chamber 131, or combinations thereof.
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.
Referring now to FIGS. 1, 2, and 4-6, similar to upper end wall 123 and bulkheads 126, each lower end wall 124 is in the form of a plate. However, unlike upper end wall 123 and bulkheads 126, which are flat plates having parallel, planar upper and lower surfaces oriented perpendicular to the corresponding axis 125, lower end walls 124 are bent and include portions oriented at different angles relative to a reference plane P124 oriented perpendicular to axes 115, 125 (FIG. 5). More specifically, each lower end wall 124 includes a radially inner portion 124a relative to central axis 115 of hull 110 and a radially outer portion 124b relative to central axis 115 of hull 110. Inner portions 124a are proximal central axis 115, whereas outer portions 124b are distal central axis 115. Consequently, each inner portion 124a is radially positioned between central axis 115 and the corresponding outer portion 124b. On each end wall 124, portions 124a, 124b meet and intersect along a transition or intersection 124c defined by an abrupt change in slope of end wall 124. Intersection 124c that extends radially across the wall 124 and between opposite sides of the corresponding column 120. In this embodiment, each intersection 124c intersects central axis 125 of the corresponding column 120, and thus, divides the corresponding end wall 124 into equal halves, each half having a semi-circular shape. In general, each lower end wall 124 can be formed by any suitable technique known in the art such as bending a circular plate along intersection 124c to define portions 124a, 124b or fixably attaching portions 124a, 124b together at intersection 124c (e.g., by welding).
As best shown in the side view of FIG. 5, the lower surfaces of each inner portion 124a is planar and the lower surface of each outer portion 124b is planar, however, the lower surface of each inner portion 124a is not disposed in the same plane as the lower surface of the corresponding outer portion 124b. Namely, each inner portion 124a, and more specifically the lower surface of each inner portion 124a, is disposed in the reference plane P124 oriented perpendicular to axes 115, 125; and each outer portion 124b, and more specifically the lower surface of each outer portion 124b, is oriented at an acute angle α relative to the reference plane P124. Outer portions 124b generally slope upward moving radially outward relative to axis 115, and thus, angles α are measured upward from reference plane P124 to the lower surfaces of outer portions 124b. In this embodiment, each angle α is the same, and further, each angle α is an acute angle between 0° and 20°, and more preferably between 5° and 15°. As shown in FIG. 5, each angle α is 10°. As will be described in more detail below, the geometry of lower end walls 124 including outer portions 124b oriented at angles α accommodates pivoting of hull 110 and platform 100 about lower end 110b with anchor 150 penetrating the sea floor 11.
Referring now to FIG. 4, lower end walls 124 are interconnected at lower end 110b of hull 110 by a connection plate 127. In particular, connection plate 127 is oriented perpendicular to central axis 115, extends radially and circumferentially between inner portions 124a of lower end walls 124, and is fixably attached to inner portions 124a of lower end walls 124. In this embodiment, connection plate 127 is contiguous with lower end walls 124, and thus, connection plate 127 and lower end walls 124 form a single rigid plate-like deck 128 that spans and defines lower end 110b of hull 110. As will be described in more detail below, during installation of platform 100 at installation site 12, deck 128 engages the sea floor 11 and limits penetration of the sea floor 11. In general, connection plate 127 and lower end walls 124 can be fixably attached together by any suitable technique known in the art to form deck 128. For example, connection plate 127 and lower end walls 124 can be monolithically formed as a single piece or formed as separate components that are fixably attached together (e.g., by welding).
As shown in FIG. 1, in the installed configuration, platform 100 has a center of buoyancy 105 and a center of gravity 103. Due to the location of fixed ballast in chambers 130 at lower ends 120b and variable ballast in the lower portion of chambers 131 adjacent chambers 130, and the air in buoyancy chambers 133, 134 proximal upper ends 120a and air in the upper portion of chambers 131 adjacent chambers 133, 134, the center of buoyancy 105 is positioned axially above center of gravity 103 during offshore operations (i.e., once installed). This arrangement offers the potential to enhance the stability of platform 100 when it is in a generally vertical, upright position.
Referring now to FIGS. 1 and 4-6, anchor 150 extends axially from lower ends 110b, 120b of hull 110 and columns 120, respectively. As best shown in FIG. 4, anchor 150 is fixably attached to and extends axially from connection plate 127 of deck 128 disposed at lower end 110b. In this embodiment, anchor 150 has a downward-pointing arrow-shaped, cross or cruciform geometry. In particular, anchor 150 has a central or longitudinal axis 155, a first or upper end 150a fixably secured to lower end 110b of hull 110 via connection plate 127, and a second or lower end 150b opposite end 150a and distal hull 110. Anchor 150 is centered relative to hull 110 and deck 128 with axis 155 coaxially aligned with axis 115 of hull 110. Moving axially downward, anchor 150 generally tapers to a pointed tip 151 at lower end 150b to allow lower end 150b to lead and penetrate the sea floor 11 as anchor 150 is axially advanced into the sea floor 11 during installation at site 12 as will be described in more detail below.
Referring now to FIGS. 4-6, in this embodiment, anchor 150 includes a plurality of angularly-spaced penetration members 152 coupled to lower end 110b and extending radially from central axis 155. In particular, anchor 150 includes four penetration members 152 uniformly angularly spaced 90° apart about axis 155, thereby resulting in the cross or cruciform geometry. Each penetration member 152 is the same, and thus, one penetration member 152 will be described it being understood the other penetration members 152 are identical. In particular, penetration member 152 includes a body 153 and a plurality of stiffeners 156 extending from body 153. Body 153 is a trapezoidal-shaped, flat plate having a first or upper end 153a fixably coupled to end 110b of hull 110 via connection plate 127, a second or lower end 153b distal hull 110, a radially inner lateral side 153c extending axially between ends 153a, 153b, and a radially outer lateral side 153d extending axially between ends 153a, 153b. Sides 153c, 153d extending linearly from end 153a to end 153b, and ends 153a, 153b extend linearly from side 153c to side 153d. In this embodiment, lateral sides 153c, 153d are oriented parallel to each other and central axis 155, first end 153a is oriented perpendicular to sides 153c, 153d and axis 155, and second end 153b is oriented at an acute angle β relative to a plane that is oriented perpendicular to radially inner side 153c and axis 155 as best shown in FIG. 5. Angle β is between 30° and 60°, and in this embodiment, is 45°. As previously described, body 153 is a flat plate. Thus, body 153 includes parallel, planar surfaces 154a, 154b extending between ends 153a, 153b and sides 153c, 153d. Surfaces 154a, 154b face away from each other in opposite directions.
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 FIG. 4, in this embodiment, each stiffener 156 extending from surface 154a is aligned with a corresponding stiffener 156 extending from surface 154b.
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 FIG. 1 and hull 110 pivots about anchor 150 and lower end 110b, the soil resists such pivoting and applies bending moments to the plate-like body 153. Stiffeners 156 reinforce the corresponding body 153, thereby reducing and/or preventing the undesirable bending of the corresponding body 153. It should also be appreciated that by reinforcing body 153 and resisting bending of body 153, stiffeners 156 enable the use of a body 153 with a reduced thickness T153 as compared to an embodiment not including stiffeners 156.
Referring still to FIGS. 4-6, first ends 153a of bodies 153 are coincident with and define end 150a of anchor 150, and second ends 153b of bodies 153 are coincident with and define end 150b of anchor 150. Radially inner lateral sides 153c of bodies 153 are fixably attached together and generally coaxially aligned with central axis 155 of anchor 150, and bodies 153 extend radially outward from central axis 155. Accordingly, bodies 153 are generally oriented parallel to axis 155 and intersect axis 155. Bodies 153 are angularly spaced apart about axis 155. In this embodiment, anchor 150 includes four uniformly angularly spaced bodies 153, thereby resulting in the cross or cruciform geometry in bottom view. However, in other embodiments, three, five, or more than five angularly spaced bodies (e.g., bodies 153) may be provided in the anchor (e.g., anchor 150), and further, the bodies may be uniformly or non-uniformly angularly spaced apart. As previously described, second ends 153b of bodies 153 are oriented at acute angle β relative to a plane that is oriented perpendicular to axis 155, thereby defining the pointed tip 151 of anchor 150.
As shown in FIG. 1 and will be described in more detail below, anchor 150 couples hull 110, and hence platform 100, to the sea floor 11 while simultaneously restricting rotation of hull 110 and platform 100 about axis 115. More specifically, as installed at the installation site 12, anchor 150 penetrates the sea floor 11 with lower end 110b, lower end walls 124, and connection plate 127 abutting or adjacent the sea floor 11, The buoyancy of variable ballast chambers 131 are adjusted and controlled such that the total weight of platform 100 exceeds the total buoyancy of hull 110, thereby placing hull 110 in compression and ensuring anchor 150 remains seated in the sea floor 11. Plate-shaped bodies 153 and stiffeners 156 frictionally engage the sea floor 11. Due to the orientation of plate bodies 153 perpendicular to central axis 115 of hull 110, plate bodies 153 resist lateral (e.g., horizontal) movement of platform 100 and resist yaw (i.e., the rotation of platform 100 about central axes 115, 155). Although lower end 110b abuts or is positioned adjacent the sea floor 11, angled radially outer portions 124b, which slope upwardly moving radially outward relative to axes 115, 155, allow a small degree of pivoting of hull 110 and platform 100 about lower end 110b about anchor 150 without damaging lower ends 120b of columns 120 or end walls 124. In general, the degree of pivoting of platform 100 from vertical (i.e., the angle between axes 115, 155 and vertical) about anchor 150 is generally limited to the angle α as outer portion 124b of one or more end walls 124 will engage and bear against the sea floor 11 when platform 100 pivots from vertical by an angle equal to angle α, thereby preventing further pivoting of platform 100. During installation of hull 110, anchor 150 is urged axially downward into the sea floor 11, and during removal of hull 110 from the sea floor 11 for transport to a different offshore location, anchor 150 is pulled axially upward from the sea floor 11. Variable ballasting of columns 120 via variable ballast chambers 131 is employed to adjust the buoyancy of hull 110 and platform 100 to facilitate installation and removal. In general, the length L120 and the width W120 of each column 120; the length L153, width W153, and thickness T153 of each body 153 of anchor 150; and the length, the width, and thickness of each stiffener 156 may be tailored to the particular installation location, associated water depth, and anticipated environmental loads at the installation location.
Referring again to FIG. 1, topside 160 is coupled to upper end 110a of hull 110. As will be described in more detail below, topside 160 may be transported to the offshore installation site 12 separate from hull 110 and mounted atop hull 110 at the installation site 12. The various equipment typically used in drilling and/or production operations, such as a derrick, crane, draw works, pumps, compressors, hydrocarbon processing equipment, scrubbers, precipitators and the like are disposed on and supported by topside 160.
Referring now to FIGS. 7A-7F, the offshore deployment and installation of platform 100 is shown. FIGS. 7A and 7B illustrate the loadout of hull 110 and topside 160, respectively, from a construction site 15 (e.g., a shipyard); FIG. 7C illustrates the loadout of hull 110 into water 10 after being moved from construction site 15 to an offshore location; FIG. 7D illustrates hull 110 being transitioned from a horizontal orientation to an upright orientation at the offshore installation site 12; FIG. 7E illustrates topside 160 being mounted to hull 110 to form platform 100 at installation site 12; and FIG. 7F illustrates platform 100 being anchored to the sea floor 11 with anchor 150 at installation site 12.
Referring now to FIGS. 7A and 7B, hull 110 and topside 160 are built at construction site 15 and mounted on skids 16 at site 15. Then, hull 110 and topside 160 are separately and independently loaded onto corresponding transport vessels 180, 181, respectively, at site 15. In this embodiment, construction site 15 is an on-shore shipyard, however, in other embodiments, the construction site (e.g., construction site 15) may be a quayside or near shore location. In addition, in this embodiment, both transport vessels 180, 181 are barges. Although FIGS. 7A and 7B illustrate hull 110 being loaded onto barge 180 before topside 160 is loaded on barge 181, in general, hull 110 and topside 160 can be loaded onto corresponding barges 180, 181 in any order.
As shown in FIG. 7A, hull 110 is movably disposed on skids 16 at site 15 in a horizontal orientation (i.e., central axis 115 is horizontally oriented). Transport vessel 180 includes skids 17 and is disposed in water 10 immediately adjacent site 15 with skids 17 aligned with mating skids 16. Next, hull 110 is moved along skids 16 toward vessel 180, and then moved from skids 16 at site 15 onto skids 17 and vessel 180 in the horizontal orientation. With hull 110 loaded thereon, vessel 180 is moved offshore away from site 15. To minimize the weight of hull 110 during loading onto vessel 180 and transport to installation site 12, as well as to ensure hull 110 is net buoyant and will float when offloaded from vessel 180 into water 10 as described in more detail below, chambers 130, 131, 133, 134 are filled with air 106.
Next, as shown in FIG. 7B, topside 160 is movably disposed on skids 16 at site 15. Transport vessel 181 includes skids 18 and is disposed in water 10 immediately adjacent site 15 with skids 18 aligned with mating skids 16. Next, topside 160 is moved along skids 16 toward vessel 181, and then moved from skids 16 at site 15 onto skids 18 and vessel 180. With topside 160 loaded thereon, vessel 181 is moved offshore away from site 15.
Referring now to FIG. 7C, hull 110 can be transported to installation site 12 on vessel 180 and offloaded from vessel 180 at installation site; or transported to an intermediate offshore location (between sites 12, 15) with sufficiently deep water 10, offloaded from vessel 180, and then floated and towed from the intermediate offshore location to installation site 12. In either case, hull 110 can be offloaded from vessel 180 by ballasting vessel 180 until the upper deck of vessel 180 is disposed sufficiently below the sea surface 13 such that hull 110 can float off vessel 180; or by ballasting one end of vessel 180 and/or de-ballasting the other end of vessel 180 to orient vessel 180 and hull 110 disposed thereon at an acute angle relative to horizontal, thereby allowing hull 110 to slide (under the force of gravity) along skids 17 and off vessel 180 into water 10. As previously described, chambers 130, 131, 133, 134 are filled with air 106 during loading onto vessel 180, transport on vessel 180, and offloading from vessel 180, and thus, hull 110 floats in the horizontal orientation once offloaded from vessel 180 into water 10. The floating hull 110 can then be moved away from vessel 180 and/or vessel 180 can be moved away from hull 110.
Moving now to FIG. 7D, topside 160 is transported to installation site 12 on vessel 181, and is lifted from vessel 181 by hull 110. More specifically, as previously described, hull 110 is transported to installation site 12 on vessel 180 and then offloaded into water 10 at installation site 12, or offloaded into water 10 at an intermediate location and then floated out to installation site 12. In either case, hull 110 is transitioned from the floating horizontal orientation to a floating, generally vertical orientation at installation site 12. In particular, fixed ballast chambers 130 are filled with fixed ballast 107 and variable ballast chambers 131 may be partially filled with variable ballast 108. Since buoyant chambers 133, 134 are filled with air 106 and positioned proximal upper end 110a, as the volume and weight of fixed ballast 107 in each chamber 130 increases and the volume and weight of variable ballast 108 in chambers 131 increases, end 110b of hull 110 swings downward, thereby transitioning hull 110 to a substantially vertical orientation. The draft of hull 110 can be controlled and adjusted by adjusting the relative volumes of air 106 and water 108 in chambers 131. Typically, fixed ballast 107 remains in fixed ballast chambers 130 once hull 110 is upright to maintain the center of gravity 103 of hull 110 remains below the center of buoyancy 105 of hull 110.
Moving now to FIG. 7E, topside 160 is lifted from vessel 181 with hull 110 to form platform 100. In particular, vessel 181 includes a pair of laterally spaced apart pontoons 182 upon which topside 160 is supported. Laterally spaced pontoons 182 define a bay 183 extending vertically through vessel 181 and extending from one end of vessel 181. Topside 160 is supported by pontoons 160 and extends over bay 183 between pontoons 182. Bay 183 is sufficiently sized to receive and accommodate upper end 110a of hull 110.
Referring still to FIG. 7E, vessel 181 is deballasted and/or hull 110 is ballasted to raise the position of topside 160 relative to upper end 110a of hull 110 such that hull 110 can be advanced through the open end of vessel 181 into bay 183 and positioned below topside 160. Then, hull 110 and/or vessel 180 are moved to advance upper end 110a through the open end of vessel 181 into bay 183, and position upper end 110a immediately below topside 160. With topside 160 sufficiently positioned over upper end 110a, hull 110 is deballasted and/or vessel 181 is ballasted such that hull 110 moves upward relative to topside 160, engages topside 160, and lifts topside 160 from skids 18, thereby mating topside 160 and hull 110 to form platform 100. Next, platform 100 and/or vessel 181 are moved laterally to remove platform 100 from bay 183, and then platform 100 is positions over the desired installation location at site 12.
Referring now to FIG. 7F, hull 110 is ballasted to lower platform 100 into engagement with the sea floor 11 and push anchor 150 into the sea floor 11. In particular, hull 110 is ballasted until lower end 110b, and in particular, until deck 128 engages and bears against the sea floor 11, at which point further penetration of anchor 150 into the sea floor 11 is restricted and/or prevented. With anchor 150 embedded in the sea floor 11 and deck 128 engaging or adjacent the sea floor 11, the overall weight and buoyancy of platform 100 is adjusted as desired by controlling the relative volumes of air 106 and water 108 in chambers 131. In embodiments described herein, the relative volumes of air 106 and water 108 in chambers 131 are controlled such the weight of platform 100 exceeds the buoyancy of platform 100 (i.e., platform 100 is net negative buoyant) and hull 110 is in compression between ends 110a, 110b. In particular, the total weight of platform 100 is adjusted and controlled to ensure anchor 150 remains sufficiently embedded in the sea floor 11 during subsequent drilling and/or production operations. Thus, platform 100 is secured to the sea floor 11 by ballasting hull 110 and simply penetrating the sea floor 11 with anchor 150. In general, the total weight of the platform 100 will depend on a variety of factors including, without limitation, the weight of topside 160 and the depth Di of the water 10 at the installation site 12, which impacts the size and weight of hull 110. For most offshore applications, the weight of hull 110 (not including any fixed or adjustable ballast) is between about 75% and 100% of the weight of topside 160.
As shown in FIG. 7F, the geometry of deck 128 and specifically the orientation of outer portions 124b at acute angle α in combination with the center of buoyancy 105 being positioned above the center of gravity 103, allows platform 100 to pivot about anchor 150 from vertical relative to the sea floor 11 in response to environmental loads (e.g., wind, waves, currents, earthquakes, etc.). The maximum pitch angle measured from vertical is generally limited to the acute angle α. The relationship between the position of center of gravity 103 and center of buoyancy 105 determines the pitch stiffness and maximum pitch angle θ of platform 100. The pitch stiffness can be varied and controlled by adjusting the relative volumes of air 106 and water 108 in chambers 131 to control the relative locations of center of gravity 103 and center of buoyancy 105. For example, as the volume of water 108 in chambers 131 is increased and the volume of air 106 in chambers 131 is decreased, the center of buoyancy 105 moves upward and center of gravity 103 moves downward; and as the volume of water 108 in chambers 131 is decreased and the volume of air 106 in chambers 131 is increased, the center of buoyancy 105 moves downward and center of gravity 103 moves upward. As the center of gravity 103 and the center of buoyancy 105 are moved apart, pitch stiffness increases; and as the center of gravity 103 and the center of buoyancy 105 are moved toward each other, pitch stiffness decreases. As previously described, the geometry of anchor 150 aids in resisting and/or preventing rotation of platform 100 about axis 115.
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 FIGS. 8 and 10, respectively.
Referring first to FIGS. 8 and 9, an embodiment of an elongate hull 210 for an offshore platform is shown. For example, hull 210 can be used in place of hull 110 previously described to form an offshore platform. Hull 210 is similar to hull 110 previously described. In particular, hull 210 has a central or longitudinal axis 215, a first or upper end 210a, and a second or lower end 210b opposite end 210a. Hull 210 is sized and configured such that upper end 210a extends above the sea surface 13 when hull 210 is installed an installation site (e.g., installation site 12). In particular, hull 210 has a length L210 measured axially from end 210a to end 210b that is greater than the depth of the water at the offshore installation site. In addition, hull 210 has a width W210 measured perpendicular to axis 215 in side view. In this embodiment, the width W210 of hull 210 is uniform or constant along the length L120 of columns 120 as measured in any given vertical plane containing axis 215.
Referring still to FIGS. 8 and 9, hull 210 includes a plurality of elongate parallel cylindrical columns 120 and an anchor 150 fixably coupled to lower end 210b for releasably securing hull 210 to the sea floor 11. Anchor 150 and columns 120 are each as previously described with respect to hull 110, however, the relative positions and spacing of anchor 150 and columns 120 is different as compared to hull 110.
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 (FIG. 9) and side view (FIG. 8). The minimum distance D120 between each pair of circumferentially adjacent columns 120 in this embodiment is greater than the minimum distance D120 between each pair of circumferentially adjacent columns 120 of hull 110 previously described. More specifically, the minimum distance D120 between each pair of circumferentially adjacent columns 120 of hull 210 is greater than 1.0 m, and in particular is 0.5 to 0.6 times the width W120 of columns 120. Due to the increased distance between columns 120 in hull 210 (as compared to hull 110), in this embodiment, each column 120 is coupled to each circumferentially-adjacent column 120 by a plurality of axially spaced braces 221 instead of plates 121. Each brace 221 extends radially (relative to central axes 125) between the corresponding pair of circumferentially-adjacent columns 120. In this embodiment, braces 221 are elongate rigid tubulars. In addition, to enhance structural integrity and rigidity, in this embodiment, braces 221 are fixably attached to columns 120 at axial positions that are aligned with bulkheads within columns 120. The length L120 and width W120 of columns 120 are as previously described, and thus, the length L120 of each column 120 is equal to the length L210 of hull 210.
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 FIGS. 8 and 9, anchor 150 is coaxially aligned with central axis 215 of hull 210 and is coupled to lower end 210b of hull 210 and lower ends 120b of columns 120. However, in this embodiment, anchor 150 is radially positioned between columns 120 and is not coupled to a plate or deck (e.g., connection plate 127 or deck 128) extending radially between end walls 124 of columns 120. Rather, in this embodiment, hull 210 includes a central cell 250 radially positioned between columns 120 to which anchor 150 is fixably attached. Cell 250 has central or longitudinal axis 255 coaxially aligned with central axis 215 of hull 210, a first or upper end 250a, and a second or lower end 250b. In addition, in this embodiment, cell 250 includes a radially outer cylindrical wall or tubular 251 extending axially between ends 250a, 250b, a first or upper end wall 252 closing tubular 251 at upper end 250a, and a second or lower end wall 253 closing tubular 251 at lower end 250b. End walls 252, 253 are axially spaced apart. In this embodiment, each end wall 252, 253 is in the form of a rigid plate. End walls 252, 253 are oriented perpendicular to central axes 255, 215. Tubular 251 and end walls 252, 253 define a fixed ballast chamber within cell 250. As best shown in FIG. 8, in this embodiment, cell 250 extends axially below lower ends 120b of columns 120. Thus, lower end 250b of cell 250 generally defines lower end 210b of hull 210. Anchor 150 is fixably attached to and extends axially from lower end wall 253 of cell 250 in the same manner as anchor 150 is attached to deck 128 of hull 110 previously described.
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 FIGS. 8 and 9, cell 250 is radially positioned and centered between columns 120. In this embodiment, cell 250 is fixably coupled to each column 120 with a rigid connection members 256 that extends radially from cell 250 to a corresponding column 120 as shown in FIG. 9. In this embodiment, connection members 256 are rigid, vertical plates that transfer shear loads between cell 250 and columns 120.
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 FIGS. 10 and 11, another embodiment of an elongate hull 310 with columns 120 spaced apart a distance D120 that is greater than the distance D120 between columns 120 in hulls 110, 210, previously described. As noted above, an increased distance D120 between columns 120 may be employed 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.
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 FIGS. 10 and 11, hull 310 includes a plurality of elongate parallel cylindrical columns 120 and an anchor 150 fixably coupled to lower end 310b for releasably securing hull 310 to the sea floor 11. Anchor 150 and columns 120 are each as previously described with respect to hull 110, however, the relative positions and spacing of anchor 150 and columns 120 is different as compared to hull 110.
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 (FIG. 11) and side view (FIG. 10). The minimum distance D120 between each pair of circumferentially adjacent columns 120 in this embodiment is greater than the minimum distance D120 between each pair of circumferentially adjacent columns 120 of hull 110 previously described, and greater than the minimum distance D120 between each pair of circumferentially adjacent columns 120 of hull 210 previously described. More specifically, the minimum distance D120 between each pair of circumferentially adjacent columns 120 of hull 310 is greater than 1.0 m, greater than the width W120 of each column 120, and in particular between about 30.0 and 50.0 m. In this embodiment, the minimum distance D120 is 40.0 m to allow a barge carrying a topside to pass between upper ends 120a of columns 120 as will be described in more detail below. Due to the increased distance between columns 120 in hull 310 (as compared to hull 110) and similar to hull 210, in this embodiment, each column 120 is coupled to each circumferentially-adjacent column 120 by at least one brace 321 instead of plates 121. Each brace 321 extends radially (relative to axes 125) between the corresponding pair of circumferentially-adjacent columns 120. In this embodiment, braces 321 are elongate rigid tubulars. Similar to braces 221 previously described, to enhance structural integrity and rigidity, in this embodiment, braces 321 are fixably attached to columns 120 at axial positions that are aligned with bulkheads within columns 120. The length L120 and width W120 of columns 120 are as previously described, and thus, the length L120 of each column 120 is equal to the length L310 of hull 310.
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 FIGS. 10 and 11, anchor 150 is coaxially aligned with central axis 315 of hull 310 and is coupled to lower end 310b of hull 310 and lower ends 120b of columns 120. However, in this embodiment, anchor 150 is radially positioned between columns 120 and is not coupled to a plate or deck (e.g., connection plate 127 or deck 128) extending radially between end walls 124 of columns 120. Rather, in this embodiment, hull 310 includes a central cell 250 radially positioned between columns 120 to which anchor 150 is fixably attached. Cell 250 is as previously described. As best shown in FIG. 10, in this embodiment, cell 250 extends axially below lower ends 120b of columns 120. Thus, lower end 250b of cell 250 generally defines lower end 310b of hull 310. Anchor 150 is fixably attached to and extends axially from lower end wall 253 of cell 250 in the same manner as anchor 150 is attached to deck 128 of hull 110 previously described.
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 FIGS. 10 and 11, cell 250 is radially positioned and centered between columns 120. In this embodiment, cell 250 is fixably coupled to each column 120 with a plurality of rigid connection members 356 that extend radially from cell 250 to each column 120 as shown in FIG. 10. In this embodiment, connection members 356 are elongate rigid tubulars.
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.
Patent Application
20230331356
