Patent Publication Number: US-6340273-B1

Title: Support structure for wells, production facilities, and drilling rigs

Description:
FIELD OF THE INVENTION 
     The invention relates to offshore structures and more particularly to a support structure for supporting wells, production facilities, and/or drilling rigs located in a body of water. 
     BACKGROUND 
     In the drilling and production of hydrocarbons and other fluid minerals at offshore sites, offshore platforms are installed for the support of the necessary above water facilities and related equipment to accomplish such drilling and production. Often the size, weight and number of facilities and equipment preclude the use of minimal support structures having less than three legs anywhere between the sea floor and the facilities deck. Support structures having less than three legs must resist eccentric gravity loads and lateral environmental loads such as wind, wave, current and seismic by developing internal bending moment in the legs, whereas the support structures having three or more legs resist the loads primarily be developing internal axial loads. Support structures having three or more legs are stiffer and more efficient than the minimal structures for any loading other than very minimal loads. Production facilities are especially sensitive to motion which occurs under cyclic or intermittent loading and are adversely affected by the motions of the more flexible minimal structures. As is well-known in the art, an active wave zone exists as part of the surface of a body of water. Such wave zone produces loading on production and drilling facilities and other support structures located in a body of water. 
     Given the need for support structures which have three or more legs, current technology has provided conventional pile-supported jackets. Jackets having three legs are called tripods. Decks can be connected to the jacket by conventional methods, including transitions which allow decks to have a different number of legs than the jacket has. 
     Tripods have the advantage of presenting less surface area to wind, wave and current than a structure having more legs. Tripods are, however, inefficient in resisting the applied lateral loads and applied overturning moments. Tripods have the minimum number of piles and thus, each pile must carry more lead than would a structure having a base with more than three legs, assuming both the tripod and the structure with more legs were both evenly loaded. 
     The installation cost of offshore platform jackets is a major factor. A tripod jacket sometimes must be fabricated in a position in which its vertical axis is rotated 70 to 90 degrees toward horizontal, and is transported to the final erection site in that orientation. Tripods are lifted from the transportation vessel and placed in the body of water. Tripods are unstable in water when floating in the rotated position. They tend to roll to one side, which presents safety hazards and causes extra time and costs in rigging the lifting slings, work platforms and other apparatus. Jackets are temporarily supported by mudmats which rest on the ground below the body of water. Mudmats are most effective when placed at the outer corners of the base. The mudmats of a structure having more than three legs are more efficient than the mudmats of a similar sized tripod for the same reasons that apply to efficiency of piles. The combination of a tripod (also called a jacket structure) and base that is more efficient in distributing applied load; more stable when floating; and is more stable when resting on mudmats would be highly desirable. 
     Pile efficiency and jacket efficiency are significantly affected by the geometrical arrangement of piles. Current technology for tripods has piles near or within the jacket legs. Current technology does not use piles or pile groups as effectively as possible by allowing one to transition from a base configuration to a jacket configuration that is different from the base configuration. Consider a triangular base with each side having a length, L, and a rectangular base with each side having a length, L. There would be a pile or pile group at each corner of each base. If each base were to resist the same overturning moment, then the maximum reaction for the triangular base would be 1.4 times the maximum reaction for the rectangular base. The pile foundation must carry vertical loads in addition to overturning moment. Each pile of the triangular base would carry 1.33 times the load for the rectangular base, assuming the vertical load passed through the combined centroid of the piles of the base. The costs for fabrication, handling, and installation of piles would be significantly higher for the triangular base than for the rectangular base. The principles apply to tripods with other types of polygonal bases. 
     The prior art does not disclose improving the efficiency of load distribution to the structure and piles by arranging braces on the faces of the jacket so that well conductors may start outside the face of the jacket above the water line and then pass through the face of the jacket to be inside the perimeter of the jacket the remainder of the way to the ground below the body of water. A jacket design that allows the well conductors to pass through the jacket and terminate outside the jacket above the water&#39;s surface would be highly desirable. 
     It is an object of the present invention to provide a jacket structure having three legs combined with a base which resists applied loads more efficiently. 
     It is another object of the present invention to provide improved efficiency of a support structure and/or piles by configuring the base of the structure such that the base has a larger number of legs than the structure above the base has. 
     It is a further object of the present invention to provide a structure that permits the well conductors to start outside the face of the jacket above the water line and then pass through the face of the jacket to be inside the perimeter of the jacket. 
     SUMMARY OF THE INVENTION 
     A support structure for use in drilling and production operations having one end positioned above a body of water and another end below the body of water on a bed is disclosed. Examples of such structures are deck platforms for supporting drilling rigs and production facilities. The support structure includes a base and a jacket structure having at least three jacket legs and a support means for supporting a structure such as a deck. The base has at least four cylindrical base legs engageably positioned in a generally rectangular pattern on the bed and a base frame connected to the cylindrical base legs. The cylindrical base legs start and terminate below the body of water. Preferably, each of the cylindrical base legs is sized to engageably receive at least one pile, and the pile is adapted to be driven into the bed. 
     The jacket has a first jacket leg, a second jacket leg, a third jacket leg. The first, second, and third jacket legs start below the body of water and terminate above the body of water and are positioned with the support means for supporting a structure above the body of water. The first jacket leg may be attached to one of the at least four cylindrical base legs and the second jacket leg may be attached to another of the at least four cylindrical base legs. The base frame extends between the cylindrical base legs to which the first jacket leg and the second jacket leg may be attached to the third jacket leg to form a triangular shape. The triangular shape, preferably, is a substantially isosceles triangle. 
     The support structure described herein has a base and jacket structure that is supported by piles, also referred to as skirt piles. Skirt pile sleeves are an integral part of the legs of the base of the structure. To secure the base to the bed, skirt piles are driven through the skirt pile sleeves. Each skirt pile is securely connected to a skirt pile sleeve. Methods of connection between pile and sleeve are mechanical, grouted or welded. Each pile is driven into the ground below the body of the water to a distance of penetration calculated sufficient to safely carry the applied loads. 
     The invention provides improved efficiency of the structure and/or piles by configuring the base of the structure such that the base has a larger number of legs than the structure above the base has, and the legs are placed at the outer corners of the base perimeter. The base has at least four legs, at least four sides, and at least four corners. The jacket has three legs. The invention improves the efficiency of the structure and/or piles by also providing a means for conductors to start outside a jacket, pass through the face of the jacket, and be within the perimeter of the jacket at the ground below the body of water The invention has an additional advantage of having more stability than a rotated floating tripod, making installation safer and cheaper than for a standard tripod. The invention is also more stable than a tripod of the same size when resting on mudmats. No extraordinary means or methods of fabrication or installation are required to build the invention and thus no extra costs are incurred. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a further understanding of the nature and objects of the present invention, reference should be made to the following detailed description in which like parts are given like reference numerals and wherein: 
     FIG. 1 is a three dimensional side view of the support structure in accordance with the present invention, and a deck structure supported by the jacket structure; 
     FIG. 2 is a three dimensional perspective view of the support structure in accordance with an embodiment of the present invention; 
     FIG. 3 is a three dimensional partial view of one of the side faces of the jacket structure in accordance with the present invention; 
     FIG. 4 is a three dimensional partial view of the jacket face in accordance with the present invention; 
     FIG. 5 is a plan view taken along the line  5 — 5  in FIG. 1; 
     FIG. 6 is a plan view taken along the line  6 — 6  in FIG. 1; 
     FIG. 7 is a plan view taken along the line  7 — 7  in FIG. 1; 
     FIG. 8 is a plan view taken along the line  8 — 8  in FIG. 1; 
     FIG. 9 is a plan view of the base taken along the line  9 — 9  in FIG. 1; 
     FIG. 10 is a three dimensional view of the base of the support structure in accordance with the present invention; 
     FIG. 11 is an alternate embodiment of the base of the support structure, the base being shown in a plan view; 
     FIG. 12 is an alternate embodiment of the base of the support structure, the base being shown in a plan view; 
     FIG. 13 is an alternate embodiment of the base of the support structure, the base being shown in a plan view; 
     FIG. 14 is an alternate embodiment of the base of the support structure, the base being shown in a plan view. 
     FIG. 15 is a perspective view of the support structure. 
     FIG. 16 is a perspective view of the support structure. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The embodiments of the present invention provide for a support structure  10  for use in drilling and production operations having one end  12  positioned above a body of water  14  having an active wave zone and another end  16  below the body of water  14  on a bed  18 , such as shown in FIG.  1 . Examples of use of such structures are for deck platforms for supporting drilling rigs and production facilities. The support structure includes a base  20 , a jacket structure  22  having, preferably, three legs such as jacket leg or jacket members  36 , and a means or extensions or tubular members  24  for supporting a structure such as a deck  26 . The extensions  24  are attached to the jacket structure  22 . More than three extensions  24  can be used. The extensions  24  extend upward to which a deck or other support structure  26  can be mounted. 
     The base  20  has a top facing towards the active wave zone and a bottom facing towards the seabed and has at least four cylindrical base legs  28  engageably positioned in a generally rectangular pattern on the bed  18  and a base frame  30  connected to the cylindrical base legs  28 . The cylindrical base legs  28  start at the bed  18  below the body of water  14  and terminate above the bed  18  while still in the body of water  14 . Preferably, each of the cylindrical base legs  28  has a hollow interior  29  that is sized to engageably receive at least one pile  32 . The pile is adapted to be driven into the bed  18 , as is well known in the art. 
     The jacket  22  has a first jacket leg  34  (FIG.  2 ), a second jacket leg  36 , and a third jacket leg  38 , where as shown in FIG. 2, said leg  34  and said leg  36  are battered and are co-planer. The plane of said leg  34  and said leg  36  is also battered. The first, second, and third jacket legs  34 ,  36 ,  38  originate below the body of water  14  and terminate above the body of water  14  and are positioned at their upper end as part of the support means  24  for supporting a structure  26  above the body of water  14 . The first jacket leg  34  is attached to one of the cylindrical base legs  28  and the second jacket leg  36  is attached to another of the cylindrical base legs  28 . The base frame  30  extends between the cylindrical base legs  28  to which the first jacket leg  34  and the second jacket leg  36  are attached to the third jacket leg  38  to form a triangle shaped frame. The triangle shaped frame, preferably, is in the form of a substantially isosceles triangle. This configuration allows one to transition from a base having one configuration to a jacket configuration that is different from the base configuration. Thus, the base forms or includes a foundation system for the main jacket legs  34 ,  36 ,  38  which while substantially vertical may be inclined as they rise from the base to the surface of the water and the vertical projections at any time remain within the geometry of the base, as shown in FIGS. 1 and 2. 
     Having a base with at least four legs and a jacket with three legs has several advantages over the current technology. Consider a triangular base with each side having a length, L, and a rectangular base with each side having a length, L. There would be a pile or pile group at each corner of each base. If each base were to resist the same overturning moment, then the maximum reaction for the triangular base would be 1.4 times the maximum reaction for the rectangular base. The pile foundation must carry vertical loads in addition to overturning moment. Each pile of the triangular base would carry 1.33 times the load for the rectangular base, assuming the vertical load passed through the centroid of each pile of the base. The costs for fabrication, handling, and installation of piles would be significantly higher for the triangular base than for the rectangular base. The principles apply to tripods with other types of polygonal bases. 
     In a preferred embodiment, the first jacket leg  34 , the second jacket leg  36  and each of the cylindrical base legs  28  to which the first jacket leg  34  and the second jacket leg  36  are attached are aligned substantially vertically. The first jacket leg  34  has a first end  40  (FIG. 4) that terminates in the cylindrical base leg  28  to which it is attached and a second end  42  that terminates in the support means  24  for supporting a structure  26  (FIG.  1 ). Likewise, the second jacket  36  has a first end  44  that terminates in the cylindrical base leg  28  to which it is attached and a second end  46  that terminates in the means for supporting a structure  26 . (FIG. 4) Thus two of the jacket legs  34 ,  36  are preferably fixedly attached to base legs  28  of the support structure  10 . The inclination of the jacket legs  34 ,  36  above the base  20  may be different from their inclination within the base  20 . 
     FIG. 2 shows a three-dimensional perspective view of the offshore platform shown in FIG. 1, except that the deck structure  26  has been omitted. Mudmats  48  are located near each base leg  28  of the support structure  10  and are connected to adjoining parts of the base frame  30 . 
     With reference to FIG.  3  and FIG. 4, a plurality of angularly extending brace members  50  are arranged between and interconnect the legs  34 ,  36 ,  38  of the jacket  22  and a plurality of lateral brace members  51  also are arranged between and interconnect the legs of the base  20 . Plate members  52 ,  54  are arranged between and interconnect the legs of the jacket  22  structure and base legs  28 . (FIG. 4) 
     An additional plurality of tubular guides and an additional plurality of cross brace members may be provided as may be required for a specific design. The cross brace patterns shown in the figures are for illustrative purposes only. The pattern, number of cross braces, and number of tubular guides will change depending on the design parameters for a specific operation at a specific site. 
     The plurality of angularly extending brace members  50  are connected between the first jacket leg  34 , the second jacket leg  36  and the third jacket leg  38  in a vertically inclined face defined between each pair of jacket legs:  34  and  36 ;  36  and  38 ; and  34  and  38 , to form a multi-sided structure defining a perimeter  56 . The vertically inclined face between, for example, the first jacket leg  34  and the second jacket leg  36  is referred to as a jacket face  58 . The jacket face  58  is formed between the first and second jacket legs  34 ,  36  that are attached to the cylindrical base legs  28 . The first and second jacket legs  34 ,  36  are attached to the base legs  28  using the first plate member  52  and the second plate member  54  as discussed above. Alternatively, the cylindrical base legs  28  can be attached using braces like those used in the base frame  30 . 
     When used in production, the support structure  10  can have a plurality of well conductors  62  attached to the structure. (See FIGS. 1 and 2) Each of the plurality of well conductors  62  have a first end  64 , usually extending above the water line of the body of water  14 , and a second end  66  extending upward from the bed  18 . The plurality of well conductors  62  extend upward toward the surface of the body of water  14 , and intersect the jacket face  58  at an intersection position  60  so that the first end  64  is outside of the perimeter  56  of the jacket  22  and the second end  66  is inside the perimeter  56  of the jacket  22 . 
     In use, the base  20  can have a first plurality of tubular guides  68  (FIG. 9) for receiving and supporting a plurality of well conductors  62  and a first plurality of cross brace members  70  for support. The first plurality of tubular guides  68  are attached to the base frame  30  by the first plurality of cross brace members  70  as illustrated in FIG.  9 . The first plurality of cross brace members  70  are connected at one end to the first plurality of tubular guides  68  and at the other end to the base frame  30 . The second end  66  of the well conductors  62  is received by the first plurality of tubular guides  68 , and as set out above, is positioned inside the perimeter  56  of the jacket  22  near the base  20 . Preferably there is provided, a second, third, fourth and fifth plurality of tubular guides,  72 ,  80 ,  86 ,  92 , attached to the base frame  30  or the jacket structure  22  and positioned to permit the well conductors  62  to penetrate the jacket face  58  as they extend upward. 
     FIG. 8 shows the second plurality of tubular guides  72  positioned inside the perimeter  56  of the jacket  22  and between the bed  18  and the body of water  14 . The second plurality of tubular guides  72  are attached to the jacket  22  by a second plurality of cross brace members  74 . This figure also illustrates a first plurality of cross structural brace members  78  which are arranged between and interconnect the base legs  28  with the first, second and third jacket legs  34 ,  36 ,  38 . 
     FIG. 7 shows the third plurality of tubular guides  80  positioned inside the perimeter  56  of the jacket  22  and between the surface of the body of water  14  and the second plurality of tubular guides  72 . The third plurality of tubular guides  80  are attache to the jacket  22  by a third plurality of cross brace members  82 . This figure also illustrates a second plurality of cross structural brace members  84  which are arranged between and interconnect the first, second and third jacket legs  34 ,  36 ,  38 . 
     FIG. 6 shows the fourth plurality of tubular guides  86  positioned partly outside the perimeter  56  of the jacket  22 , outside the jacket face  58 , and between the surface of the body of water  14  and the third plurality of tubular guides  80 . The fourth plurality of tubular guides  86  are attached to the jacket  22  by a fourth plurality of cross brace members  88 . This figure also illustrates a third plurality of cross structural brace members  90  which are arranged between and interconnect the first, second and third jacket legs  34 ,  36 ,  38 . At this point on the jacket  22 , there is one row of tubular guides outside the perimeter  56  of the jacket  22 . 
     FIG. 5 shows the fifth plurality of tubular guides  92  positioned outside the perimeter  56  of the jacket  22 , outside the jacket face  58 , and between the body of water  14  and the fourth plurality of tubular guides  86 . The fifth plurality of tubular guides  92  being attached to the jacket  22  by a fifth plurality of cross brace members  96 . This figure also illustrates a plurality of cross structural brace members  98  which are arranged between and interconnect the first, second and third jacket legs  34 ,  36 ,  38 , and the support structure  24  for the deck or platform  26 . 
     As shown in FIGS. 1 and 9, the base  20  can have a first base leg  100 , a second base leg  102 , a third base leg  104  and a fourth base leg  106  to comprise base legs  28 , and the base frame  30  can have a first base frame member  108 , a second base frame member  110 , a third base frame member  112 , a fourth base frame member  114 , a fifth base frame member  116 , and a sixth base frame member  118 . In this embodiment, the first base leg  100  is connected to the third jacket leg  38  by the first base frame member  108 ; the first base leg  100  is connected to the second base leg  102  by the second base frame member  110 ; the second base leg  102  is connected to the third jacket leg  38  by the third base frame member  112 ; the fourth base leg  106  is connected to the third jacket leg  38  by the fourth base frame member  114 ; the third base leg  104  is connected to the first base frame member  108  by the fifth base frame member  116 ; and the fourth base leg  106  is connected to the third base frame member  112  by the sixth base frame member  118 . 
     As set out above, preferably, the base  20  further comprises a first plate member  52  (FIG. 2) adapted to attach the first jacket leg  34  to the first base leg  100  and a second plate member  54  adapted to attach the second jacket leg  36  to the second base leg  102 . The first and second plate members add additional strength and stability to the support structure  10 . 
     There are several base configurations that will support the basic jacket structure outlined above and still maintain optimum efficiency and load bearing capabilities. In a second embodiment shown in FIG. 11, the base  20  comprises a first base leg  100 , a second base leg  102 , a third base leg  104  and a fourth base leg  106 . The base also has a first base frame member  108 , a second base frame member  110 , a third base frame member  112 , a fourth base frame member  114 , a fifth base frame member  116 , a sixth base frame member  118 , a seventh base frame member  120 , and an eighth base frame member  122 . The first base leg  100  is connected to the third jacket leg  38  by the first base frame member  108 ; the first base leg  100  is connected to the second base leg  102  by the second base frame member  110 ; the second base leg  102  is connected to the third jacket leg  38  by the third base frame member  112 ; the fourth base leg  106  is connected to the third jacket leg  38  by the fourth base frame member  114 ; the third base leg  104  is connected to the first base frame member  108  by the fifth base frame member  116 ; the fourth base leg  106  is connected to the third base frame member  112  by the sixth base frame member  118 ; the first base leg  100  further is connected to the third base leg  104  by the seventh base frame member  120 ; and the second base leg  102  further is connected to the fourth base leg  106  by the eighth base frame member  122 . Preferably, the third base leg  104 , the third jacket leg  38 , and the fourth base leg  106  are parallel to one another and are positioned in a common plane. 
     In the alternative, the fourth base frame member  114  can have a first portion and a second portion, said first portion being connected between said third base leg  104  and said third jacket leg  38 , and said second portion being connected between said third jacket leg  38  and said fourth base leg  106  to form a V-shape as shown in FIG.  12 . The third jacket leg  38  is positioned between the first base leg  100  and the third base leg  104  so that the point of the V-shape is directed towards the second base frame member  110 . 
     In an alternate base structure shown in FIG. 13, the base  20  comprises a first base leg  100 , a second base leg  102 , a third base leg  104  and a fourth base leg  106 . The base frame  30  comprises a first base frame member  108 , a second base frame member  110 , a third base frame member  112 , a fourth base frame member  114 , a fifth base frame member  116 , and a sixth base frame member  118  as described above. The first base leg  100  is connected to the third jacket leg  38  by the first base frame member  108 . The first base leg  100  is connected to the second base leg  102  by the second base frame member  110 . The second base leg  102  is connected to the third jacket let  38  by the third base frame member  112 . The fourth base leg  106  is connected to the third base leg  104  by the fourth base frame member  114 . The third base leg  104  is connected to the first base frame member  108  by the fifth base frame member  116 . The fourth base leg  106  is connected to the third base frame member  112  by the sixth base frame member  118 . 
     In yet another embodiment shown in FIG. 14, the base  20  comprises a first base leg  100 , a second base leg  102 , a third base leg  104  and a fourth base leg  106 . The base frame  30  comprises a first base frame member  108 , a second base frame member  110 , a third base frame member  112 , a fourth base frame member  114 , a fifth base frame member  116 , and a sixth base frame member  118 . The first base leg  100  is connected to the third jacket leg  38  by the first base frame member  108 . The first base leg  100  is connected to the second base leg  102  by the second base frame member  110 . The second base leg  102  is connected to the third jacket leg  38  by the third base frame member  112 . The fourth base leg  106  is connected to the third jacket leg  38  by the fourth base frame member  114 . The third base leg  104  is connected to the first base leg  100  by the fifth base frame member  116 . The third base leg  104  is connected to the second base leg  102  by the sixth base frame member  118 . Preferably, the first base leg  100 , and the second base leg  102  are substantially vertical and are positioned in a common plane. Additionally, the first base leg  100 , the second base leg  102  and the third jacket leg  38  form a generally triangular pattern. 
     While in accordance with the patent statutes, the best mode and preferred embodiments of the invention have been described, it is to be understood that the invention is not limited thereto, but rather is to be measured by the scope and spirit of the appended claims.