MXPA97006375A

MXPA97006375A - Support of a catena upper pipe

Info

Publication number: MXPA97006375A
Application number: MXPA/A/1997/006375A
Authority: MX
Inventors: David Finn Lyle
Original assignee: Deep Oil Technology Incorporated
Priority date: 1996-08-22
Filing date: 1997-08-21
Publication date: 1998-02-01

Abstract

The present invention relates to a support pipe of the catenary riser that receives the riser pipe and is joined to the structure exposed to the floating sea water. The support tube is attached to the structure exposed to floating seawater in a vertical angle to be in line with the natural angle that the installed catenary support tube assumes on a calm day. The support tube is attached to the structure exposed to floating sea water at different points along the length of the support tube and thus flexes at its points of attachment to the floating structure. This minimizes the pressures in the catenary riser

Description

ASSEMBLY OF AN UP-TUBE CATHENARIO DESCRIPTION OF THE INVENTION This invention relates generally to the production of hydrocarbons from forms below sea level and more particularly to riser pipes using such production. When producing hydrocarbons from formations below sea level, it is common for a number of wells to be drilled on the sea floor at positions that are not directly below or substantially between the contour of the structure used during production operations . The hydrocarbons produced are subsequently exported by means of pipes below sea level. This results in the production and export of riser tubes that have a catenary curve in the risers between the structure and the sea floor. The flotation movement of the production platforms causes corresponding flexion and pressure in the riser tubes. The state of the art has accommodated the flexing in the risers by incorporating ball joints in suitable locations in the joints between the pipe segments in the riser pipe. Ball joints present the problem of being more expensive and less secure than the pipe segments that are welded together.

The invention addresses the above need. Which provides a supporting tube of the catenary riser that receives the riser pipe and joins the structure exposed to the floating sea water. The support tube is attached to the structure exposed to the floating sea water at a vertical angle to be in line with the natural angle that the installed catenary riser can assume on a calm day. The support tube is attached to the structure exposed to floating sea water at different points along the length of the support tube and thus flexes at its points of attachment to the floating structure. The support tube extends outwardly from the floating structure in such a way that the first attachment point is located at a distance from the lower end of the support tube. The additional flexibility in the support tube is attached by locating the second point of attachment to the floating structure at a key distance in addition to the end of the support tube. The support tube can be provided with a flexural stiffness that varies from the first point of attachment to the lower end of the support tube. BRIEF DESCRIPTION OF THE DRAWINGS For a further understanding of the nature and objects of the present invention, reference is made to the following description, taken in conjunction with the accompanying drawings in which like parts are given with like reference numerals, and where : Figure 1 is a schematic side sectional view illustrating the invention in a structure exposed to floating sea water. Figure 2 schematically illustrates the shape of a support tube embodiment of the invention. In Figure 1, a structure exposed to floating sea water 10 is held in position by a plurality of mooring lines 12. The mooring lines 12 are attached to one end of the floating structure 10 and at the end opposite the anchors or stakes not shown on the sea floor 14. The catenary riser tube 16 extends from the sea floor 14 upwards through a central well 18 provided in the floating structure 10 for production facilities not shown. The support for the catenary riser tube is provided in the form of a support tube 20. The support tube 20 has an internal diameter of a size to receive the catenary rising tube 16 therethrough. The support tube 20 is attached at its upper end to the floating structure 10, indicated by A, at a small angle to the vertical to be in line with the natural angle that the catenary riser tube 16 assumes when it is in its installed position. the calm sea. The support tube 20 has a length extending outwardly from the lower end of the floating LO structure and is attached to the lower end of the floating structure 10., indicated by B, at predetermined points indicated by the letters C, D and E. The number and location of the junction points between the support tube 20 and the floating structure 10 is determined by the desired flexibility in the tube 20. of support. For example, greater flexibility towards the lower end of the support tube 20 can be achieved by moving the attachment point C away from the attachment point B at the lower end of the floating structure. Allowing the support tube 20 to be flexible at its points of attachment so that the floating structure 10 maintains the pressure in the catenary riser tube 16 within the allowable limits. The support tube 20 can be provided with greater flexibility progressively from the attachment point B to its lower end by varying the wall thickness and / or the diameter of the tube. As seen in Figure 2, the support tube 20 can be constructed in combination of the curved and linear sections incorporated in its shape, such that the upper end of the support tube is substantially vertical and directs the catenary riser to a desired upper water location in the floating structure in a substantially vertical orientation. In this example of one embodiment of the invention, the section 22 of the support tube 20 is linear, the section 24 is curved, and the section 26 is linear. The floating structure 10 is fifty-four point ninety meters (one hundred and eighty feet) high. Section 22 of the support tube is nine point fifteen meters (thirty feet) long, section 24 is twenty-seven point forty-five meters (ninety feet) long and section 26 is eighteen point three meters (sixty feet) long . Section 24 has a radius of one hundred thirty-one point seventy-six meters (four hundred thirty-two feet), which results in a twelve-degree exit angle at the bottom of the floating structure 10 to accommodate the natural catenary curve of the rising tube 16. It should be understood that in Figure 2 it is merely used as an illustration of a possible configuration of the invention and that the total length of the back support tube 20 of the floating structure 10 is not shown. Three different methods can be used to install the catenary riser 16 in the support tube 20. In the pre-break method, the riser pipe is placed on the sea floor 14 before the floating structure 10 is moored at the site. Once the floating structure 10 is secured in position, the end of the rising tube 16 is placed at the lower end of the support tube 20 and pulled through a point where the end of the rising tube 16 is above the water. . During the pull-in phase, the angle of the riser 16 and the support tube 20 can assume other angles than in the natural neutral catenary position (no bending pressure). During the initial phase of pulling, the angle may be less than the desired neutral position. At the end of the pull phase, the exit angle may be equal to the desired neutral position or may be greater than the neutral angle. If the exit angle is greater than the desired neutral position once the end of the riser 16 reaches the surface, additional sections of the riser pipe can be added. The upper end of the now higher riser is decreased, adding as many segments as necessary, until the neutral angle of the desired calm day is reached at an exit point of the support tube 20. Additional adjustments to the exit angle can be made by moving the floating structure 10 horizontally to the surface. It may also be possible with some floating structures to tilt the structure, and the support tube 20 attached, using ballasts and in this way more accurately accommodating the catenary angle of the neutral elevated tube at the entry point for the support tube during installation. In the method of resting, the installation container of the riser, not shown, can approach the floating structure 10 as soon as the installation container rests in the riser pipe on the sea floor. The end of the riser 16 can be lowered with wire ropes from the installation vessel until the riser tube is at the entry point for the support tube 20. A wire rope entangled through the support tube can then be used to pull the riser 16 through the support tube to a point above the surface of the water. The installation can then be completed as described above. In the far-rested method, the riser 16 can be pulled from the riser installation vessel by wire wires entangled through the support tube 20. The appropriate length of the riser pipe is suspended between the riser pipe installation vessel and the outer floating structure 10 to maintain the proper neutral entry angle at the entry point for the support pipe -20. With this method, it is not necessary to add segments of the riser pipe at the end of the riser pipe in the floating structure. The invention eliminates the need for costly sea level bending joints and pipe fittings of the riser pipe. With the pre-break method, the pipe of the riser can be installed immediately after the floating structure is placed and in this way it can be ready for immediate use. This allows the production of oil and gas to reach the nearest stream. Also, all welded pipe is generally considered to be safer than pipes with mechanical connections and flexible joint elements. Since many varied and different modalities can be elaborated within the scope of the inventive concept taught here and since many modifications can be made in the detailed modalities here according to the descriptive requirement of the law, it is understood that the details here are interpreted as illustrative and not in a limiting sense.

Claims

CLAIMS - 1. In a structure exposed to floating sea water to produce hydrocarbons where a catenary riser extends from the sea floor to the floating structure, a support for the catenary riser, characterized in that the support comprises a tube attached to predetermined locations in the structure exposed to floating seawater such that the support tube leaves the lower end of the floating structure at an angle from the vertical, the tube extending outward from the lower end of the structure exposed to water of floating sea and that has a size to receive the catenary rising tube through the tube. The support tube according to claim 1, characterized in that the portion of the tube extending outward from the lower end of the structure exposed to the floating sea water is curved to substantially equalize the natural curve of the catenary riser received in the same. The support tube according to claim 1, characterized in that the portion of the tube extending outwardly from the lower end of the structure exposed to the floating sea water progressively increases the flexibility toward the lower end of the support tube. 4. The support tube according to claim 1, characterized in that the support tube is formed of a combination of curved sections and linear sections in such a way that the upper end of the support tube is substantially vertical and the lower end "of the tube Support substantially equalizes the normal installed angle of the catenary riser in the calm sea.