Subsea Riser for Multiple Bore Wells

Multiple bore wells having multibore tubing hangers and christmas trees often utilize multiple tubing strings or "purpose built" multiple bore completion or workover risers. These multiple tubing strings provide access to each individual bore but in deep water locations the multiple tubing strings are cumbersome. Also, the specially built riser to provide access to each individual bore for wirelining is very expensive.

U.S. Pat. Nos. 4,284,142 and 4,474,236 disclose structures of the purpose built type of multiple bore completion/workover risers. These structures provide the multiple bores extending completely through the structure so that access to each bore is available at the water surface.

U.S. Pat. No. 4,291,724 discloses a flowline switching apparatus in which access to a plurality of individual flowlines is provided for through flow line (TFL) tools from a single connection at the top of the structure. This disclosure involves the rotation of a cylinder structure with the flowline extending therethrough being curved to register with the individual bores as the cylinder is rotated.

U.S. Pat. No. 4,319,637 discloses an orienting system for running a multiple string tubing hanger for remote installation, such as an underwater wells.

The present invention relates to an improved riser for a multiple bore subsea well which provides wireline access to each of the bores through a single opening at the upper end of the riser. The improved riser includes an upper tubular member having a single bore, a lower member having multiple bores which mate with the multiple bores of the tubing hanger running tool or the christmas tree running tool which is located at the subsea wellhead, an intermediate section having a rotary portion with a single bore extending therethrough which communicates with the single upper bore and which will communicate with each one of the lower multiple bores individually as the section is rotated to position the lower end of its bore into communication with the upper end of each of such bores and an external housing surrounding said intermediate section and extending between said upper tubular member and said lower member.

An object of the present invention is to provide an improved, reasonably priced subsea riser which provides communication between a single string at the upper end of the riser with individual strings at the lower end of the riser.

Another object is to provide an improved subsea riser which allows independent and separate operations through the riser with each of the multiple bores to which the riser connects.

A further object is to provide an improved subsea riser through which a single bore extends together with the control lines to control the subsea equipment to which the riser connects.

Still another object is to provide an improved subsea riser connecting a single upper bore to multiple lower bores with a housing structural member which can be used as a pressure vessel and protects the control lines and the rotary portion of the riser.

These and other objects and advantages are hereinafter set forth and explained with reference to the drawings wherein:

FIG. 1 is an elevation view of completion riser of the prior art.

FIG. 2 is detail partial longitudinal sectional view of the completion riser shown in FIG. 1.

FIG. 3 is a sectional view taken along line 3--3 in FIG. 1.

FIG. 4 is an elevation view of the improved riser of the present invention.

FIG. 5 is a detailed longitudinal sectional view of the lower part of the riser shown in FIG. 4 and includes FIG. 5A which shows the upper portion of the riser selector, 5B which shows the intermediate or offset portion of the riser selector and 5C which shows the lower portion of the riser selector.

FIG. 6 is a transverse sectional view taken along line 6--6 in FIG. 5 to show the rotational stop structure.

FIG. 7 is another transverse sectional view taken along line 7--7 in FIG. 5 to illustrate the structure of the position indicating apparatus.

Riser 10 illustrated in FIGS. 1, 2 and 3 discloses the completion riser described above in which riser 10 includes a plurality of sections 12 which are connected end to end to provide connection from the water surface to a subsea wellhead 14. Each of sections 12 includes an outer tubular housing 16 and a plurality of strings 18 which provide the connection from the surface to the subsea wellhead 14. As best seen from FIG. 3, riser 10 includes two strings 18a and 18b of large diameter one string 18c having a slightly smaller diameter and a plurality of strings or control lines 18d which extending through tubular housings 16 and are interconnected so that each string 18 and control line 18d extends continuously from the upper end to the lower end of riser 10. This structure provides direct access through the two large diameter strings 18a and 18b to the tubing strings (not shown) within the wellhead 14 for wireline and other operations necessary for completion and workover operations. Each of sections 12 is a complete assembly including all of the tubular members therein to form the complete strings 18. Such structure is expensive and cumbersome.

Improved riser 20 of the present invention is shown in FIGS. 4 through 7. Riser 20 includes a plurality of sections 22 so that it extends from the surface to the subsea wellhead 24. Riser 20 is different from the risers of the prior art in that the upper of sections 22 include single tubular members 26 extending from the water surface to a point near subsea wellhead 24 with control lines 72 being on the exterior of tubular member 26 and preferably suitably attached or secured to member 26 in a well known manner so that they are not damaged by the currents. The lowest section 22 of tubular member 26 is connected to the upper end of riser selector 28. The function of riser selector 28 is to provide ready access to the interior of each of the well tubing strings within wellhead 24 from tubular member 26 for completion and workover operations.

Riser selector 28 includes upper tubular member 30 having suitable means (threaded box) for connecting to the lower end of the lower tubular member 26, housing 32 surrounding all but the upper portion of upper tubular member 30, bearing means 34 between the upper end of housing 32 and tubular member 26, means 36 secured to the lower end of housing 32 and having means 38 for connecting to the subsea wellhead 24, means 40 for limiting the amount of relative rotation of tubular member 30 with respect to housing 32 and means 42 for providing an indication of the relative position of tubular member 30 with respect to housing 32 and connecting means 38. It should be noted that the improved riser 20 can be run with a christmas tree or a tubing hanger running tool on its lower end.

Upper tubular member 30 includes upper external partial groove 44 which is positioned within flange 46 forming the upper end of housing 32, lower groove 48 in which split ring 50 is positioned to support flange 46 at the preselected level on tubular member 30, upwardly facing bearing shoulder 52, tubing extension 54 and skirt 56 both of which extend from the lower portion of annular ring 58 which forms shoulder 52. Flange 46 is secured to bearing ring 60 having inner lip 62 and with upper thrust bearing 64 positioned between upper shoulder 66 on lip 62 and the lower surface of split ring 50 and lower thrust bearing 68 positioned between lower shoulder 70 on lip 62 and bearing shoulder 52. Tubing extension 54 at its upper end is centered with respect to housing 32 and includes offset portion 54a in which tubing extension is gradually bent outward and then returned to a vertical position. This offset portion 54a of tubing extension 54 should be at least ten feet long and is preferred to be thirty feet long so that the bends therein are smooth transitions and allow TFL tools to pass therethrough. Control lines 72 connect through flange 46 into bearing ring 60 in positions communicating with passages 74 therethrough and lines 76 connect into the opposite end of passages 74 and extending downwardly within housing 32 in surrounding relation to skirt 56 to connect into housing ring or member 78 to communicate with passages 80 which extend through housing ring 78 and communicate with their mating passages (not shown) in the wellhead equipment connected to the lower end of riser selector 20.

Housing 32 is threaded onto the exterior of bearing ring 60 at its upper end and is sealed around the upper end of housing ring 78 at its lower end. Snap ring 82 by being in engagement with internal groove 84 in housing 32 and external groove 86 in housing ring 78 retains housing 32 secured to housing ring 78. O-rings 88 positioned within grooves on the interior of housing 32 above groove 84 provide sealing between the interior of housing 32 and the exterior of housing ring 78. Bores 90 and 92 extend through housing ring 78 and communicate with the bore of tubing hangers in the wellhead at their lower ends and terminate at the upper end of housing ring 78 as shown in FIG. 5C. Bore 94 also extends through housing ring 78 and provides communication with the annulus around tubing strings within the wellhead. Plug 96 is positioned with its smaller lower end within bore 94a and has its upper end which is of a larger diameter within bore 94b. Suitable sealing is provided between the exterior of plug 96 and the interior of bores 94a and 94b. Side passage 97 extends through housing ring 78 into communication with bore 94a above the lower seals around the exterior of plug 96 and thus by movement of plug 96 upward can be in communication through bore 94a with the annulus below lower housing 78. Passage 97a through housing 78 communicates with bore 94b above plug 96 and is used to move plug 96 downward into position closing communication between side passage 97 and the lower end of bore 94a. Upper plug 98 is positioned within bore 94c at the upper end of bore 94 and includes spring loaded detent 100 contained therein and projecting upwardly therefrom as shown and hereinafter described.

As described above, tubular extension 54, as best seen in FIG. 5B, is curved from its upper position within the center of housing 32 to its offset lower position which is in alignment with either bore 90 or bore 92, depending on the rotation of upper tubular member 30 with respect to housing 32. As shown in FIGS. 5C and 6, plate 102 is positioned above housing ring 78 within skirt 56 and the lower end of tubular extension 54 extends through opening 104 in plate 102. Skirt 56 surrounds the upper exterior of lower housing 78 and O-rings 105 provide completely sealed and will retain pressure which is exerted therein. Arcuate slot 106 also extends through plate 102 and the upper end of spring loaded detent 100 extends through slot 106 to limit the rotary movement of tubular member 26 and tubular extension 54 to positions in axial alignment with bores 90 and 92. Connecting means 38 is any suitable connecting means to provide the connection of the lower end of riser selector 20 to the upper end of the christmas tree or tubing hanger running tool (not shown in FIG. 5C).

Position indicating means 42 is best seen in FIG. 7 and includes ports 108, 110 and 112 extending through neck 114 of flange 46 and port 110 is always in communication with partial annular groove 44 while ports 108 and 112 are alternately in communication with partial groove 110 depending upon the rotation of upper tubular member 26. By supplying hydraulic fluid to port 110 and connecting ports 108 and 112 to indicating devices sensing pressure of hydraulic fluid at each of the alternate ports, an indication of the position of tubular extension 54 with respect to bores 90 and 92 is provided.

It should be noted that by limiting the length of offset portion 54a of tubular extension 54, the length of riser selector 28 is limited and the major portion of riser 20 is composed of sections of single bore tubular members. This greatly reduces the cost of the riser but does not interfere with the access to the subsea wellhead for completion or workover operations and is not nearly as cumbersome as the risers of the prior art.