US3650114A

US3650114A - Method and apparatus for connecting a flowline to an offshore installation

Info

Publication number: US3650114A
Application number: US11716A
Authority: US
Inventors: William J Neal
Original assignee: Shell Oil Co
Current assignee: Shell USA Inc
Priority date: 1970-02-16
Filing date: 1970-02-16
Publication date: 1972-03-21
Anticipated expiration: 1989-03-21

Abstract

A method and apparatus for connecting a flowline having a major portion adapted to lie along the floor of a body of water to an offshore installation of the type having a substantially vertical support positioned on the floor of a body of water and a platform carried by the support. The flowline is positioned at the water surface adjacent the installation and terminated a distance beyond the installation approximately equal to the depth of the water. The portion of the flowline adjacent the installation is slidably connected to the support and the flowline is lowered to the floor of the body of water while gradually bending the flowline at a plurality of locations therealong in such a manner that the portion of the flowline between the support and its terminal end is substantially parallel to the support when the flowline reaches the floor of the body of water. The terminal end of the flowline is subsequently connected to the platform. In this manner, the flowline has a sufficient curvature to prevent buckling thereof.

Description

Neal

ited States Paten METHOD AND APPARATUS FOR CONNECTING A FLOWLINE TO AN OFFSHORE INSTALLATION William J. Neal, Manvel, Tex.

Shell Oil Company, New York, NY.

Feb. 16, 1970 Inventor:

Assignee:

Filed:

Appl. No.:

References Cited UNITED STATES PATENTS [451 Mar. 21, 1972 Primary Examiner-Jacob Shapiro Attorney-Louis J. Bovasso and J. H. McCarthy [57] ABSTRACT A method and apparatus for connecting a flowline having a major portion adapted to lie along the floor of a body of water to an offshore installation of the type having a substantially vertical support positioned on the floor of a body of water and a platform carried by the support. The flowline is positioned at the water surface adjacent the installation and terminated a distance beyond the installation approximately equal to the depth of the water. The portion of the flowline adjacent the installation is slidably connected to the support and the flowline is lowered to the floor of the body of water while gradually bending the flowline at a plurality of locations therealong in such a manner that the portion of the flowline between the support and its terminal end is substantially parallel to the support when the flowline reaches the floor of the body of water. The terminal end of the flowline is subsequently connected to the platform. In this manner, the flowline has a sufficient curvature to prevent buckling thereof.

10 Claims, 3 Drawing Figures PATENTEUHAR21 I972 SHEET 1 BF 3 INVENTOR:

WlLLIAM J. NEAL HIS ATTORNEY PATENTEDMARZI m2 SHEET 2 [IF 3 FIG. 2

INVENTOR:

W'LLIAM J. NEAL HIS ATTORNEY PAIENTEDMARm I972 SHEET 3 [IF 3 FIG. 3

INVENTOR:

WlLLiAM J. NEAL BY M ms ATTORNEY METHOD AND APPARATUS FOR CONNECTING A F LOWLINE TO AN OFFSHORE INSTALLATION BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to underwater flowlines and, more particularly, to a method and apparatus for connecting an underwater flowline to an offshore platform."

2. Description of the Prior Art The development of offshore oil and gas wells frequently necessitates the use of offshore installations or so-called 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 or more flowlines from a platform to a remote point, for example, to shore or to another platform. The flowlines may serve many purposes, the most common being to carry off the output of oil or gas from a well. Since the flowline (also referred to as a pipeline) lays in a substantially horizontal position along the floor of the body of water in which the platform is located, a problem arises in establishing fluid communication between the flowline and the surface of the platform which is above the surface of the body of water. It will be thus apparent that either the flowline must be bent from its horizontal position on the ocean floor to a vertical position extending to the upper surface of the platform or a separate vertical extension must be installed and connected to the flowline on the ocean floor. The vertical portion is generally referred to as the flowline riser.

The present practice for installing the riser" is to provide a vertical flowline or pipeline segment along the side of the platform which extends to the floor of the body of water and is connected to the underwater flowline by divers. However, this is a generally cumbersome and expensive operation, particularly in relatively deep water where the divers effectiveness is severely impaired.

At greater than diver depths, connections cannot be made by divers on the ocean floor. In this case, it is known to first connect the riser" to the flowline and lower the assembly down a leg of the platform while simultaneously laying the flowline from a barge proceeding away from the platform. However, the procedure also has drawbacks in that the lowering and laying operation must be carefully programmed to prevent damage to the pipeline and/or riser. In addition, the method is only applicable where a pipeline is laid away from a platform and cannot be readily and easily employed where a pipeline approaches a platform.

SUMMARY OF THE INVENTION It is an object of this invention to provide a method and apparatus for installing a flowline riser to an offshore platform which eliminates the need for making an underwater connectron.

Another object of this invention is to provide a method of installing a riser in which the underwater flowline and the riser may be formed of one continuous pipelinev A further object of this invention is to bend the underwater flowline to provide an upstanding portion which serves as a riser.

A still further object of this invention is to bend the flowline to form a riser while maintaining the radius of curvature above a predetermined minimum so as to prevent buckling of the pipeline.

These and other objects are preferably accomplished by a flowline having a major portion adapted to lie along the floor of a body of water to an offshore installation of the type having a substantially vertical support positioned on the floor of a body of water and a platform carried by the support. The flowline is positioned at the water surface adjacent the installation and terminated a distance beyond the installation approximately equal to the depth of the water. The portion of the flowline adjacent the installation is slidably connected to the support and the flowline is lowered to the floor of the body of water while gradually bending the flowline at a plurality of locations therealong in such a manner that the portion of the flowline between the support and its terminal end is substantially parallel to the support when the flowline reaches the floor of the body of water. The terminal end of the flowline is subsequently connected to the platform. In this manner, the flowline has a sufiicient curvature to prevent buckling thereof.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a vertical view of an offshore installation showing a flowline connected thereto in accordance with the teachings of my invention;

FIG. 2 is a side view of the installation of FIG. 1; and

FIG. 3 is a vertical view similar to FIG. 1 showing the final step in carrying out the teachings of my invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawing, FIG. 1 shows an offshore installation 10 having a substantially vertical support means in the form of a plurality of legs (only

legs

11 and 12 being shown in FIG. 1 for convenience of illustration) adapted to rest on the floor 13 of a body of water 14, such as an ocean. A generally horizontal platform 15 is carried by the legs extending above the water surface 16. A plurality of rails, as for example, rails 17 and 17a, extend generally from platform 15 to the ocean floor 13 and are connected thereto in any suitable manner. Although rails 17 and 17a are shown as separate elements in FIG. 1, they may form two or more of the legs of the support means and are thus considered to be part of the support means for supporting platform 15. Suitable bracing means 18 may be provided between the legs for bracing the installation 10. The rails 17 and 17a may be fastened to bracing means 18 so that they are generally parallel to each other.

At least a pair of slidable clamps l9 and 20 are associated with each rail 17 and 17a, respectively. These

clamps

19 and 20 are in turn fixedly connected to a generally horizontal and rigid cross bar 21. A suitable blow-down ballast 22 is fixed to bar 21 in any suitable manner so that clamps l9 and 20 may be lowered along rails 17 and 17a to the ocean bottom 13 in the manner to be discussed further hereinbelow.

A flowline support derrick 23 is pivotally attached to bar 21 through a pivotal connecting sleeve 24. The opposite end of derrick 23 carries an elongated flexible shoe 25 having a flowline 26 passing therethrough. Flowline 26 is adapted to be lowered to the ocean floor l3 and extends to installation 10 from a suitable remote location, such as an onshore installation, an offshore gathering station, etc., (not shown). The flowline 26 is positioned at the water surface 16 adjacent installation 10 and is terminated as at its terminal end 27, at barge 28, a distance beyond the installation 10 approximately equal to the depth of the water 14. A suitable flowline tensioning device 29 is disposed on barge 28 for tensioning flowline 26.

A tensioning barge or similar vessel 30 is coupled to the installation 10 through an anchor line 31 attached to platform 15. A plurality of

floats

32 and 33, two being shown for convenience of illustration, are connected to anchor line 31, and float on water surface 16.

Floats

32 and 33 are in turn coupled to

suspension cables

34 and 35, respectively, which are coupled to flowline 26 through conventional

automatic release clamps

36 and 37 at spaced positions along flowline 26. Suitable takeup winches (not shown) may be included in

floats

32 and 33 for raising and lowering flowline 26. In this manner, as indicated by the arrows at both vessels 28 and 30 and at

cables

34 and 35, the flowline 26 may be supported when tension is released and the assembly (i.e., flowline 26, cross brace 21,

cables

36 and 37, etc.) is lowered down rails 17 and 17a to the ocean floor 13. A plurality of flowline locking clamps 38 are preferably disposed along leg 12 of installation 10 at a plurality of spaced intervals for reasons to be discussed further hereinbelow.

A plurality of flexible shoes 39, similar to shoe 25, are pivotally attached to bar 21 by means of a plurality of rods 40 coupled to a common connecting sleeve 41 (FIG, 2), similar to sleeve 24, on bar 21. The rods 40 and pistons 42 are pivotally connected to sleeve 41 as at pad eye 46 (FIG. 2). Each rod 40 has associated therewith a hydraulically actuated blow-down piston 42 at atmospheric pressure for reasons to be discussed further hereinbelow. The actuating means for the pistons 42 may extend through rods 40 and may be actuated, as for example, by a pump (not shown) on the platform 15.

Suitable winches

43 and 44 may be disposed on platform 15. Winch 43 is coupled to clamp 20 through winch line 45, for raising and lowering bar 21 on rails 17 and 17a.

In operation, the initial position of flowline 26 is at the water surface 16 adjacent installation 10. The terminal end 27 of flowline 26 is extended past installation to vessel 28, a distance approximately equal to the depth of the body of water 14 from surface 16 to the ocean floor 13. The portion of flowline 26 adjacent the installation 10 has slidably connected thereto

shoes

25 and 39 in which flowline 26 can slide (see FIG. 3). Upon addition of ballast to ballast 22, the

clamps

19 and 20, and bar 21, attached thereto, slide down rails 17 and 17a to the ocean floor 13 (FIG. 3). Winch 44 and line 46 permit easy control of the bar 21. As the bar 21 moves down the rails 17 and 17a. the rods 40, and support derrick 23, pivot about pad eye 46 (FIG. 2) and gradually bend the flowline 26 to the dotted line positions of FIG. 2.

Floats

32 and 33, and the

cables

34 and 35, attached thereto and their associated takeup winches, permit control of the flowline 26 as it is being swung out and downwardly and lowered to the ocean floor 13. When the flowline 26 reaches the ocean floor 13, hydrostatic pressure may be used to close pistons 42 to their stop position and lock shoes 39 into their position. The final position of flowline 26 is shown in FIG. 3. It can be seen that a substantially vertical "riser" portion of flowline 26 has been formed. The floats 34 and 35 and their associated cables and winches may then be released. Barge 28, having a conventional bending shoe 47 attached thereto, may be used to push the terminal end 27 of flowline 26 while winch 44, with line 48 coupled thereto, pulls flowline 26 into locking engagement with clamps 38 on installation 10. The terminal end 27 of flowline 26 may then be coupled to platform 15 by any suitable means (not shown) known in the art.

In this manner. the vertical or riser" portion of the flowline 23 extending to the upper surface of the platform 15 may be connected to processing equipment handling the output of a well drilled through one of the legs of the platform (not shown) or may be connected directly to a well or to another pipeline leading to the platform. Although the riser is shown in a vertical position. it should be understood that the riser may be installed at any angle from the horizontal (i.e., generally or substantially vertical to installation 10) without departing from the spirit of the invention. For example, the flowline 26 could be bent to a 45 angle and then joined with another section to provide communication with the upper surface of the platform 15. In addition, the riser need not extend to the surface. It may, for example, extend only a short distance past the upper end of the

flowline bending shoes

25 and 39. Pipe lengths could subsequently be added to the terminal end 27 of the flowline 26 to form a riser extending to the surface of the platform 15.

The degree of curvature or bending of the flowline 26 may be predetermined from techniques well known in the pipeline art so as to maintain the radius of curvature of flowline 26 above a predetermined minimum so as to prevent buckling thereof. For example, the techniques disclosed in U.S. Pat. No. 3,466,882 may be used.

I claim as my invention:

1. A method of connecting a flowline having a major portion adapted to lie along the floor of a body of water to an offshore installation of the type having substantially vertical support means positioned on the floor of a body of water and platform means carried by the support means, said method comprising the steps of:

positioning said flowline at the water surface of said body of water adjacent said offshore installation said flowline extending to and past said installation;

terminating said flowline past said installation a distance approximately equal to the depth of said water from said water surface to the floor thereof;

connecting the portion of said flowline adjacent said installation to said support means; and

lowering said flowline to the floor of said body of water by gradually swinging said flowline outwardly from said installation and downwardly so that the portion of said flowline between the lower end of said support means and its terminal end assumes a position substantially parallel to said support means when said flowline reaches the floor of said body of water.

2. The method of claim 1 wherein said support means includes a plurality of flowline bending shoe means, each of said bending shoe means including a connecting rod having a bending shoe at one end adapted to be connected to said flowline and pivotally attached to said support means at the other end, said pivotal attachment being slidably movable along said installation from the water surface to the floor of said body of water wherein the step of connecting said flowline to said installation includes the step of connecting said flowline to each of said bending shoes.

3. The method of claim 2 wherein the step of lowering said flowline to the floor of said body of water includes the step of slidably moving said pivotal attachment down said installation while swinging said plurality of bending shoes outwardly from said installation and downwardly thereto so that the portion of said flowline between said support means and its terminal end bends about said bending shoes and assumes a position substantially parallel to said support means when said flowline reaches the floor of said body of water.

4. The method of claim 1 including the step of connecting the terminal end of said flowline to said platform means.

5. The method of claim 3 including the step of maintaining under tension the end of said flowline opposite said terminal end leading away from said platform while lowering said flowline to the floor of said body of water.

6. The method of claim 5 including the step of supporting under tension the terminal end of said flowline while lowering said shoe means to the floor of said body of water.

7. Apparatus for connecting a flowline to an offshore installation comprising:

substantially vertical support means positioned on the floor of a body of water;

platform means carried by the support means;

a plurality of flowline bending shoe means pivotally attached to the support means and slidably movable downwardly on said support means from a position adjacent the water surface of said body of water to the floor thereof, each of said flowline bending shoe means including a flowline bending shoe for connecting a flowline thereto; and

rotating means operatively engaging each of said bending shoe means for rotating each of said bending shoe means from a position, whereby a flow-line connected to each of said bending shoes is adapted to be substantially parallel to said water surface at said water surface and substantially perpendicular to the floor of said body of water at said floor when said pivotal attachment is moved downwardly along said support means from the water surface to the floor thereof.

8. The apparatus of claim 7 wherein said support means includes rail means and the pivotal attachment of said bending shoe means is slidably movable down said rail means.

9. The apparatus of claim 7 including flowline support means operatively engaging said installation and adapted to support under tension a flowline being lowered from the water surface to the floor thereof.

10. The apparatus of claim 7 wherein each of said flowline bending shoe means includes hydraulically actuated blowdown piston means at atmospheric pressure when said flowline is at the water surface and at hydrostatic pressure when said flowline is at the ocean bottom.

Claims

1. A method of connecting a flowline having a major portion adapted to lie along the floor of a body of water to an offshore installation of the type having substantially vertical support means positioned on the floor of a body of water and platform means carried by the support means, said method comprising the steps of: positioning said flowline at the water surface of said body of water adjacent said offshore installation said flowline extending to and past said installation; terminating said flowline past said installation a distance approximately equal to the depth of said water from said water surface to the floor thereof; connecting the portion of said flowline adjacent said installation to said support means; and lowering said flowline to the floor of said body of water by gradually swinging said flowline outwardly from said installation and downwardly so that the portion of said flowline between the lower end of said support means and its terminal end assumes a position substantially parallel to said support means when said flowline reaches the floor of said body of water.

7. Apparatus for connecting a flowline to an offshore installation comprising: substantially vertical support means positioned on the floor of a body of water; platform means carried by the support means; a plurality of flowline bending shoe means pivotally attached to the support means and slidably movable downwardly on said support means from a position adjacent the water surface of said body of water to the floor thereof, each of said flowline bending shoe means including a flowline bending shoe for connecting a flowline thereto; and rotating means operatively engaging each of said bending shoe means for rotating each of said bending shoe means from a position, whereby a flow-line connected to each of said bending shoes is adapted to be substantially parallel to said water surface at said water surface and substantially perpendicular to the floor of said body of water at said floor when said pivotal attachment is moved downwardly along said support means from the water surface to the floor thereof.

10. The apparatus of claim 7 wherein each of said flowline bending shoe means includes hydraulically actuated blow-down piston means at atmospheric pressure when said flowline is at the water surface and at hydrostatic pressure when said flowline is at the ocean bottom.