US3411303A

US3411303A - Offshore platform with internal flowline

Info

Publication number: US3411303A
Authority: US
Inventors: Richard D Bates; Robert C Visser
Original assignee: Shell Oil Co
Current assignee: Shell USA Inc
Priority date: 1966-12-28
Filing date: 1966-12-28
Publication date: 1968-11-19
Anticipated expiration: 1985-11-19

Description

Nov. 19, 1968 R. D. BATES ETAL 3,411,303

OFFSHORE PLATFORM WITH INTERNAL F'LOWLINE Filed Dec. 28, 1966 y 2 Sheets-Sheet l INVENTORS:

R. C. VISSER R. D. BATES BY: l THEIR AGENT NGV. 19, 1968 E E R, D. BATES ETAL 3,411,303

OFFSHORE PLATFORM WITH INTERNAL FLOWLINE Filed Dec. 28, 1966 2 Sheets-Sheet 2 24 nfZ'a' INVENTORSZ R. C. VISSER R. D. BATES THEIR AGENT United States Patent 3,411,303 OFFSHORE PLATFORM WITH INTERNAL FLOWLINE Richard D. Bates, Anchorage, Alaska, and Robert C. Visser,lSan Dimas, Calif., assignors to Shell Oil Company, New York, N.Y., a corporation of Delaware Filed Dec. 28, 1966, Ser. No. 605,422

9 Claims. (Cl. 61-46) l ABSTRACT OF THE DISCLOSURE An offshore platform provided with at least one internal passage in the structural members of the platform for receiving and protecting a owline from ice floes, water current, debris and the like. The passage, which may be a separate tube within a leg and cross-bracing of the platform, serves to guide the ilowline as it is pulled through the passage from the ocean floor up to the surface of the platform. v

This invention relates to offshore installations of the type having a platform above the surface of the water and more particularly to an installation of this type adapted to protect a flowline extending from the water floor up to the platform from water currents, debris, ice oes, water craft and the like.

The development of offshore oil and gas wells frequently necessitates the use of offshore installations or socalled platforms." These installations are used, for example, for drilling and subsequently for producing a well or wells. Accordingly, it is often desirable to provide one r more owlines from the platform to a remote point, e.g., to shore or another platform. The owlines serve many purposes, the most common being to carry oif the output of oil or gas from a well.

The present practice for handling the ilowlines is to provide a vertical owline riser along the side of the installation extending to the water floor and connect it to a flowline which extends along the oor to the desired destination. This practice leaves the flowline riser exposed and frequently requires divers to make underwater riserto-owlike connections and also to connect the riser to the platform.

Since the riser is exposed, it is subject to damage from water currents, debris, ice oes and the like and, if the riser extends beyond the peripheryof the installation, it is subject to being rammed by water craft attending the installation. Thus, present practice often requires that the riser be made of heavier gauge than the flowline, that it be attached to the installation, that spoilers may belemployed 'to break up eddy currents caused by the water, and even that the riser be encased in a special casing.

The problem is particularly prevalent where large ice floes and rapid currents are encountered, e.g., at the Cook Inlet in Alaska which is icebound much of the year and, due to severe tides, experiences continually cycling ice floes into and out of the inlet.

Accordingly, there is a need for a simple, compact arrangement for connecting an underwater flowline to a platform located above the water surface which fully protects the owline from the above-mentioned edects. It is to this end that the present invention is directed by eliminating the need for a owline riser mounted alongside the installation.

In general, the invention provides an offshore installation supported on the floor of a body of water and having an internal passage for receiving and protecting a flowline extending from the Water oor to the water surface. The passage is adapted to communicate with the body of water near the water floor and extends internally of the installation up to or beyond the water surface so that a Fice owline positioned along the oor of the body of water may be pulled through the passage and up to the surface.

It is therefore a primary object of this invention to provide an offshore installation for protecting a iiowline extending from the ocean floor to the platform of the offshore installation.

It is a further object to provide apparatus for protecting a owline which is carried internally of the structure of the offshore installation.

It is a still further object to provide apparatus which is compact and adaptable to existing installation.

Another object is to provide apparatus which permits the owline to be pulled from the ocean floor up to the platform by means of a drawline.

Still another object is to provide an apparatus which is adaptable to any type of offshore installation.

These and other objects will become apparent from a reading of the following detailed description taken in conjunction with the accompanying drawings in which:

FIGURE 1 is an elevational view of a typical offshore installation to which the present invention is adapted with a ilowline installed;

FIGURE 2 is an elevational view of the same offshore installation with a owline about to be installed;

FIGURE 3 is an elevation of the lower portion of the offshore installation partially cut away to show the flowline receiving tubes of the present invention;

FIGURE 4 is a cross-section of one of the legs of the offshore installation taken along line 4-4 of FIGURE 3; and,

FIGURE 5 is an elevational view taken in perspective of a modified oifshore installation to which the present invention is adapted.

Referring to FIGURE 1, an offshore installation to which the present invention is adapted is indicated generally at 10. As shown, the installation comprises a plurality of support means or legs 11 anchored in the lioor 12 of a body of water `13. A working platform 14 is supported by the legs 11 and is arranged to remain above the surface 15 of the body of Water 13. The platform 14 may be single or multi-decked and normally carries a complement of production equipment necessary toproduce oil or gas from wells drilled, as through the legs 11. As shown, this equipment may include crew `quarters 16, crane 17 and processing equipment 18 which may be surge tanks, separators and the like.

As may be'best seen in FIGURE 4, each leg includes a plurality of conductor tubes 18 which extend the length of the leg and serve as a conductor for drilling operations or for diving anchor pillings to secure the leg to the floor 12. For example, as shown in FIGURE 1, the off-take of a well 19 (previously drilled through one of the conductors 18) is produced through casing 20 positioned in a conductor 18. During the drilling operation a suitable drilling rig (not shown) is located on the platform 14 to perform the drilling operations through the conductors 18. After the drilling is completed the rig may be disassembled and removed. As shown in FIGURE 4 each leg 11 is provided with, e.g., eight conductors, which would thereby give the entire installation a 32-well capability. The present invention, however, is not meant to be limited to a platform in which wells are drilled through the platform legs. The invention could be adapted to a platform in which wells are drilled through individual conductors elsewhere on the structure.

The legs 11 are interconnected by tubular cross-bracing including a horizontal cross-bracing member 21 and an X-shaped cross-bracing member 22 or so-called diagonals between each pair of legs so that the legs and crossbracing from a structure of closed configuration.

The detail of the

supports

21 and 22 and the legs 11 are best shown in FIGURE 3 which illustrates these members partially cutaway to reveal the tubular construction. Each leg of the X-shaped member 22 may carry a flowline receiving tube; one extending axially through the right leg (as viewed) indicated by 23 and the other indicated by 24 although it is not necessary to have both. The

flowline receiving tubes

23 and 24 are preferably secured during fabrication to the inner walls of the member 22 by straps 25 or other suitable means. Similarly, the receiving tubes are suitably secured within the legs 11 and extend to the platform 14 as shown in FIGURE l in which ilowline receiving tube 23 is represented by dotted lines. The lower end `of tube 23 extends through the left leg 11 and terminates with a flanged connector 26. Although the lower end of tube 23 is shown as being canted slightly downward, it may be desirable to curve the lower end so that it terminates in a substantially horizontal position. Accordingly, when the lower end of the tube is so curved, it will be apparent that the flanged connector 26 will also be disposed horizontally rather than as shown.

The tube 23 is attached and sealed to the leg 11 at 27, for example by welding, to secure the tube and prevent sea Water from entering the leg around the tube 23. Thus, it will be seen that the ilowline receiving tube 23 establishes a passage within the structure of the installation from a point near the lioor 12 of the body of water 13 to the platform 14. In addition, other owline receiving tubes may be installed within the leg and cross-bracing of the offshore installation, e.g., the owline receiving tube 24 which is positioned in the other leg of the X-shaped crossbracing member 22. Accordingly, the number of owline receiving tubes employed will be dictated by the flowline requirements of each offshore installation. When the relative size of the flowline receiving tube and the cross-brac ing members permit, more than one tlowline receiving tube can be mounted in parallel. As shown for example, the owline receiving tube 23 is sufficiently smaller than the internal diameter of the X-shaped member 22 so that several tubes could be positioned to follow substantially the same path as tube 23.

Although the offshore installation disclosed is a 4-legged structure, it is contemplated that the subject invention could be practiced with other structure, e.g., single-leg, 3- leg, 6-leg or 8-leg platforms. In FIGURE 5, a single-leg offshore installation is shown incorporating the present invention. The installation comprises a platform 32 carried by a main support leg 39 and a plurality of downwardly sloping support members 29. The leg 39 and one of the members 29 carry a flowline receiving tube for supporting and protecting a owline 31. One end of tube 25 extends through the wall of the support member 29 in the vicinity of the water oor and the other end terminates at the platform 31 where it may be connected to processing equipment to handle the produced gas or oil from wells (not shown) drilled through the leg 39. As mentioned above with reference to the preferred embodiment of FIGURES l-4, the single-leg structure of FIGURE 5 may utilize more than one flowline receiving tube. Each member 29 may be fitted with a tube or a plurality of tubes ma'y be clustered within each member 29.

Referring again to FIGURES 1 4, it will be seen that the flowline receiving tube 23 provides a protective path for a owline 33 and extends from a point near the oor 12 of the body of water 13, through the installation 10 to the surface of platform 14. The flowline 33 is pulled through the tube 23 after the installation 10l is set up by means of a drawline 34 (see FIGURES 2 and 3) secured to'the end of flowline 33 with a suitable connector. Preferably, the drawline 34 is strung through the tube 23 prior to setting up the installation 10.

One end of thel drawing 34 is secured to suitable hoisting means, e.g., a winch 35, as shown in FIGURE 2 and the other end may be brought back up leg 11 to the platform 14 or it may be buoyed off to float in the water for subsequent recovery.

When it is desired to install the flowline 33, the free end of the drawline 34 is secured to the tlowline which may, for example, be laid on the floor of the body of water 13 by means of a reel-type barge 38. As best shown in FIG- URE 2, the drawline 34 is secured to the owline 33 and the barge 35 proceeds away from the installation 10 as the owline 33 is payed out. After sufficient flowline has been laid on the floor 12 to prevent undue bending, the winch 3S is employed to pull the tlowline 33 through the flowline receiving tube 23 and up to the platform 14. As the flowline is being pulled, the barge 38 continues to pay out flowline to provide slackor slack may be provided by laying excess owline in the form of a loop in a suicient amount to permit the flowline to pass the length of tube 23 without bending.

In order to prevent kinking or flattening of the flowline 33 as it is pulled into place, the curvature dictated by the X-shaped cross-bracing member 22 and the right leg 11 (a's viewed) must not be too sharp. Thus, the angle at which the cross-bracing member 22 slopes downwardly away from the leg 11 should be great enough (preferably 30-60) to assure a gradual curve. In addition, the size of the leg 11 will affect the curvature. Accordingly, the angle of member 22 with :respect to leg 11 and the size of leg 11 should be selected to provide at least the minimum radius of curvature permissible for a given size flowline to prevent permanent flattening of the owline.

In order to facilitate the entry of flowline 33 into the tube 23, it is preferable to employ a flared guide 36 on the end of the tube 23. The flared guide 36 is preferably formed with a flanged connector 37 to mate with the connector 26 on the tube 23. Thus, the guide may be fastened to the tube 23 at any time either prior to setting up the installation 10 or once the installation is set up it may be installed by employing divers. The guide is ared outwardly to compensate for any angularity between the flow line 33 and the tube 23 during pulling. The guide 36 may of course be formed integrally with the tube 23 or it may also be attached by other suitable means, e.g., weldlng.

When the guide 36 is installed after the drawline 34 is in place, it will be apparent that the guide must be threaded over the drawline 34 and then suitably secured to the tube 23.

A similar flared guide is also preferably employed with the embodiment disclosed in FIGURE 5. The procedure for pulling the flowline 31 through the flowline receiving tube 30 is essentially the same as described above with reference to the preferred embodiment of FIGURES 1 4.

Up to this point the description of both embodiments has been predicated on the use of a flowline receiving tube through which a flowline is pulled. It is contemplated, however, that the instant invention may be practiced without the necessity of employing such a tube. When the tube is not used the structural members of the installation 10 serve as ilowline carrying means through which the flowline is pulled.

For example, in the preferred embodiment of FIG- URE l the owline could be pulled within the legs 11 and the cross-shaped member 22 without the tube 23. In this case it is preferable to employ a tapered probe or tip (not shown) on the pipeline so that it will pass freely through the legs 11 and cross-shaped member 22 without sticking. In addition, suitable dellectors may be incorporated within the installation at critical turning points, openings, etc., to guide the owline and prevent it from becoming stuck. A flared guide similar to the guide 36 may be secured directly to the platform at the point the owline enters the installation to aid in starting the owline.

Once the owline is installed, it may be connected to any suitable equipment, e.g., the output of a well 19 as shown in FIGURE 1. The flowline, however, may serve other purposes. It may serve to connect two offshore installations to carry the production from one installation to the other or as a supply line, etc. The flowline may extend to shore, to another platform installation or to an underwater collection facility.

The above-described invention provides a fully protected path for a owline extending from the floor of a body of water to an offshore platform above the water surface. The invention protects the ilowline from damage from ice floes, water currents, waves, surface craft and debris and at the same time provides a compact more eicient installation.

Having thus described the invention what is claimed is:

1. An offshore installation positionable on the oor of a body of water and including apparatus for supporting an underwater ilowline connectible to said installation and protecting it from ice, water current, debris and water craft comprising:

substantially vertical hollow support means positioned on the oor of said body of water and extending above the water surface;

platform means supported by the upper end of said support means above said water surface;

independent downwardly sloping hollow owline carrying and containing means having an upper end and a lower end;

said upper end being secured t0 said support means and in open communication with the interior thereof; and,

said lower end terminating near the floor of and being in open communication with said body of water when said offshore installation is operatively positioned on the floor of said body of water;

whereby said hollow owline carrying and containing means and said hollow support means define a closed path between the lower end of said owline carrying and containing means and the upper end of said support means.

2. An offshore installation as defined in claim 1 wherein said flowline carrying and containing means comprise:

iirst passage means in said owline carrying and containing means for receiving a flowline, said rst passage means having one end in communication with the water outside said leg means near the floor of said body of water; and,

second passage means in said leg means in communication with the other end of said rst passage means and extending to the top of said leg means for receiving said flowline;

whereby said rst and second passage means comprise said closed path for said flowline.

3. An offshore installation as defined in claim 2 wherein said hollow support means comprise a plurality of hollow legs.

4. An offshore installation as dened in claim 3 wherein said downwardly sloping ilowline carrying and containing means comprise a hollow cross-bracing member of said offshore installation having the upper end thereof secured to one of said legs and the lower end thereof secured to a second leg; and,

said second leg being provided with opening means in alignment with said rst passage means to provide access through said leg to said first passage means;

whereby said passage means and said opening means comprise an enclosed path for said ilowline between said opening means and said platform.

5. An offshore installation as dened in claim 4 wherein said rst and second passage means are formed by:

a continuous flowline receiving tube; and,

said tube extends through said opening means in said second leg.

6. An offshore installation as defined in claim 5 includlng:

hoist means positioned on said platform means and including a wire drawline attachable to said owline for pulling said flowline through said tube.

7. An offshore installation as dened in claim 6 wherein said hollow cross-bracing member slope downwardly at an angle of 30 to 60.

8. An offshore installation as dened in claim 7 wherein said angle of said downwardly sloping hollow cross-bracing member and the size of said first leg provide at least a minimum radius of curvature of said flowline when pulled through said tube to prevent a substantial change in the cross-sectional shape of said flowline.

9. An offshore installation as deiined in claim 5 ino cluding:

References Cited UNITED STATES PATENTS JACOB SHAPIRO, Primary Examiner.