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(11) | EP 0 263 722 A2 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Casing guide for well template |
| (57) A casing guide apparatus includes a subsea well template 12 having a well opening
(44) defined therein, and a cylindrical well casing (32) received through the well
opening. A casing guide bushing (68) is operably associated with the template (12)
and the casing (32) for permitting relative vertical movementt between the template
and the casing and for preventing relative lateral movement between the template and
the casing at the well opening. |
[0001] This invention relates generally to offshore hydrocarbon production, and more particularly, to a casing guide apparatus for connecting a well casing to a subsea well gravity base template.
[0002] With the gradual depletion of subterranean and shallow subsea hydrocarbon reservoirs, the search for additional petroleum reserves is being extended to deeper and deeper waters on the outer continential shelves of the world. As such deeper reservoirs are discovered, increasingly complex and sophisticated production systems have been developed.
[0003] It is projected that in the near future, offshore exploration and production facilities will be required for probing depths of 10,000 feet or more. Since bottom founded compression structures are generally limited to water depths of no more than about 1,200-1,500 feet because of the sheer size of structure required, other, so-called compliant structures have been developed.
[0004] One type of compliant structure receiving considerable attention is a tension leg platform (TLP). A TLP comprises a semisubmersible-type floating platform anchored to the sea bed through vertical members or mooring lines called tension legs. The tension legs are maintained in tension at all times by insuring that the buoyancy of the TLP exceeds its operating weight under all environmental conditions. A TLP is compliantly restrained in the lateral directions allowing sway, surge and yaw while vertical plane movements such as heave, pitch and roll are stiffly restrained by the tension legs.
[0005] In the first commercially installed TLP built for the Hutton Field in the U.K. North Sea, installed in 485 feet of water, separate piled anchor templates were provided for anchoring the tensioned mooring elements extending from each of the four corner columns of the floating tension leg platform. A separate well template was also provided on the sea bed.
[0006] It has also been proposed to utilize a gravity base well template for the anchoring of a TLP and to serve as a guide template for wells located below the TLP. A gravity base well template is a massive structure which is held in place on the sea floor by gravity, rather than by anchored pilings.
[0007] One feature of a gravity base subsea well template which must be accommodated, however, is the tendency of such a massive gravity structure to gradually settle downward in the ocean floor throughout the operating life of the gravity base well template.
[0008] The present invention provides a casing guide particularly designed for use with a gravity base well template to permit the gravity base well template to settle downward relative to the casing extending upward from the well, while at the same time providing firm lateral support to the casing where it passes through the well template.
[0009] The casing guide includes a bushing means, operatively associated with the template and the casing, for permitting relative vertical movement between the template and the casing and for preventin relative lateral movement between the template and the casing at a well opening defined through the template. This permits the gravity base template to settle into the ocean floor relative to the casing without imposing substantial compressive loads on the upper portion of the casing, thus eliminating a danger of buckling of the upper portion of the casing upon settling of the gravity based template.
[0010] The bushing preferably includes a cylindrical bushing member having a cylindrical inner bushing bore within which the casing is closely received. The bushing means preferably also includes a latch means, operatively associated with the bushing member and the well opening of the template, for latching the bushing member into a fixed position within the well opening upon insertion of the casing and bushing means downwardly into the well opening of the template.
[0011] An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:
FIG. 1 is a schematic elevation view of a TLP anchored to a gravity base well template.
FIG. 2 is a plan view of the gravity base well template.
FIG. 3 is a partly sectioned elevation view of the gravity base well template of FIG. 4 is an enlarged schematic elevation view of a segment of the gravity base well template with an upper portion of a well casing received therein. The lower portion of the well casing is received in and cemented in place within a well bore extending into the ocean floor.
FIG. 5 is an elevation patly sectioned view of the upper end of the casing as received in the well template, showing the details of construction of the casing guide of the preferred embodiment.
[0012] Referring now to the drawings, and particularly to FIG. 1, a tension leg platform 10 is anchored to a gravity base well template 12 by a plurality of tethers 14.
[0013] The gravity base well template 12 sits on an ocean floor 16 defining the bottom of a body of water 18.
[0014] The TLP includes a work deck 22 supported on four corner columns 24 which are connected by horizontal pontoon members 26.
[0015] A plurality of production risers 28 extend from subsea well heads 30 defined on the upper end of well casings 32. Each of the production risers 28 terminates in a well head apparatus 34 commonly referred to as a Christmas tree 34 located upon the work deck 22.
[0016] FIGS. 2 and 3 are plan and elevation/section views, respectively, of the gravity base template 12. The particular form of gravity base template shown in FIGS. 2 and 3 is described in detail in pending United States Patent Application Serial No. 840,235, filed March 17, 1986, for UNITIZED TLP ANCHOR TEMPLATE WITH ELEVATED WELL TEMPLATE of Charles N. White and Andrew F. Hunter, and assigned to the assignee of the present invention. The details of construction of the template 12 as set forth in Application Serial No. 840,235 are incorportated herein by reference.
[0017] The template 12 is primarily constructed from reinforced concrete, and as seen in FIG. 2, includes the four corner columns 24, eight small storage tanks 36, four larger storage tanks 38, interconnecting web portions such as 40, and a structural steel grid work 42 defining a plurality of well openings such as 44 therein.
[0018] The concrete portion of the template 12 includes a skirt piling 116 which extends downward around the outer perimeter of template 12 and penetrates the ocean floor 16 upon initial placement of the gravity base well template 12 on the ocean floor 16.
[0019] On the top of each of the corner columns 24 is an anchor template 46 to which the tethers 14 are attached.
[0020] FIG. 3 is a schematic elevation section view of the gravity base well template 12 of FIG. 2 taken along line 3-3 of FIG. 2.
[0021] In FIG. 3, one of the well casings 32 is shown, having its lower portion 48 cemented in place at 50 within a well bore 52. An upper portion 54 of casing 32 extends upward from the well bore 52 above the ocean floor 16 to the structural grid portion 42 of gravity base well template 12.
[0022] The upper portion 54 of casing 32 extends through lower and intermediate loose-fitting conductor guides 55 and 57, respectively, which are supported by frame members 59 and 61, respectively, of template 12. The guides 55 and 57 and frame members 59 and 61 are shown in a schematic fashion in FIG. 3.
[0023] FIG. 4 is an enlarged elevation sectioned schematic view somewhat similar to FIG. 3, which shows in greater detail the construction of the grid work 42 of template 12, and the manner in which the upper portion 54 of casing 32 is received therein.
[0024] The grid work 42 includes a plurality of upper and lower horizonal members 56 and 58, respectively, connected by vertical members 60.
[0025] The well opening 44 is defined within a cylindrical template housing 62 which is supported from the upper and lower horizontal members 56 and 58 by smaller horizontal and diagonal structural members 64 and 66, respectively.
[0026] Each casing housing such as 62 is located in the center of four guide posts such as 67 to which are connected guide lines (not shown) for use in guiding tubular members such as the casing 32 when they are lowered from the TLP 10 to the template 12.
[0027] FIG. 5 is a still further enlarged section elevation view of those portions of the grid work 42 of template 12 immediately surrounding one of the template housings 62, along with the upper end of casing 32 and the apparatus of the preferred embodiment providing for connection between the casing 32 and the template 12. The well casing 32 typically will be a thirty-inch diameter casing.
[0028] A bushing means 68, shown in FIG. 5, is operably assiciated with the template housing 62 of template 12 and the casing 32, for permitting relative vertical movement between the template 12 and the casing 32 and for preventing relative lateral movement between the template 12 and the casing 32 at well opening 44.
[0029] The bushing means 68 includes a cylindrical bushing member 70 having a cylindrical inner bushing bore 72 within which the casing 32 is closely received. The bushing member 70 is preferably constructed from two semicylindrical halves which are connected together about the uppermost section of casing 32. Bushing member 70 is constructed from a material which is compatible cathodically with the material of the template 12.
[0030] The bushing member 70 has a tapered lower end 71 to avoid hanging up of the bushing member 70 as it is inserted downward into template housing 62. Bushing member 70 also has a radially outward extending annular lip 73 at its upper end.
[0031] Bushing means 68 further includes a latch means 74 operably associated with the bushing member 70 and with the well opening 44 of template 12, for latching the bushing member 70 into a fixed position within the well opening 44 upon insertion of the casing 32 and bushing means 68 downwardly into the well opening 44 of template 12.
[0033] The latch means 74 includes upper and lower annular latching grooves 76 and 78, respectively, defined in the well opening/housing bore 44.
[0034] Latch means 74 further includes upper and lower radially outwardly biased locking means 80 and 82, respectively, connected to the bushing member 70 and extending radially outward from the bushing member 70 for receipt in the upper and lower latching grooves 76 and 78, respectively, of the well opening/housing bore 44 of housing 62 of well template 12.
[0035] Upper groove 76 is shown as having a tapered lower annular surface 77 for allowing lower locking means 82 to pass downward past upper groove 76.
[0036] The well template 12 further includes an upwardly open conical guide means 84 concentrically disposed about the well opening/housing bore 44 above the well opening/housing bore 44. A downwardly open conical guide means 85 extends downward below well opening/housing bore 44 to prevent hanging up of bits, underreamers and the like which may be passed upward through well opening/housing bore 44.
[0037] The bushing member 70 has a cylindrical outer surface 86 closely received in the well opening/housing bore 44 of template housing 62.
[0038] The upper and lower locking means 80 and 82 shown in FIG. 5 may be expandable snap rings which are carried by upper and lower grooves 88 and 90 defined in outer surface 86 of bushing member 70.
[0039] A releasable connecting means 100 is operably associated with the casing 32 and bushing member 70 for initially limiting vertical movement of the bushing member 70 relative to the casing 32 until the bushing member 70 is latched into the fixed position illustrated in FIG. 5 within the well opening/housing bore 44 of well template 62. The releasable connecting means 100 preferably is a means for initially preventing any substantial vertical movement of the bushing member 70 relative to the casing 32, but could also be designed to allow some limited movement of the bushing member 70 relative to the casing 32.
[0040] In the preferred embodiment illustrated in FIG. 5, the releasable connecting means 100 includes a plurality of shear pins such as 102 and 104 connected between the casing 32 and the bushing member 70.
[0041] The casing 32 includes a sleeve 106ʹ fixedly connected thereto and sleeve 106 snugly but slidably positioned therebelow, sleeves 106 and 106ʹ together defining an outer cylindrical surface 108 thereof. The sleeve 106ʹ is snugly received in the inner bushing bore 72. Sleeve 106ʹ is stiff enough so as to prevent any substantial lateral movement of the casing 32 relative to the bushing member 70. The snug fit of sleeve 106 in bore 72 does, however, permit vertical sliding motion of the casing 32 and the sleeve 106 thereof relative to the bushing member 70.
[0042] The sleeve 106 preferably is made from metal or a hard elastomeric-composite material which is shrink-fitted or bonded to the casing 32, whilst sleeve 106 which is made of the same material is simply fit snugly upon casing 32. One purpose of sleeves 106 106ʹ is to provide a more concentric outer surface 108 than is present on typical casing which may be slightly out-of-round. The sleeve 106 includes a radially outwardly extending tapered lip 109, located below tapered lower end 71 of bushing member 70, to aid in preventing hanging up of bushing member 70 as it is inserted downward into template housing 62 and, more importantly, to avoid undesired contact by an external member with bushing member 70 that might prematurely shear the pins 102 and 104.
[0043] The shear pins such as 102 and 104 have their radially inner ends contact-welded to an outer surface 110 of casing 32, and extend through the sleeve 106ʹ into engagement with blind bores drilled radially into the bushing bore 72 as seen in FIG. 5.
[0045] First, the gravity base well template such as 12 having a well opening 44 defined therein is placed upon the subsea floor 16.
[0046] The bushing means 68 is assembled with the well casing 32 which is then lowered from the TLP 10 down through the well opening/housing bore 44 of template 12 until the lower portion 48 of casing 32 is received in the well bore 52.
[0047] Upon downward insertion of the casing 32 and bushing means 68 into the well opening/housing bore 44 of template 12, the upper and lower locking means 80 and 82 connectably engage with the upper and lower grooves 76 and 78 defined in well opening/housing bore 44 so that the bushing means 68 is substantially fixed relative to the template 12 for preventing lateral movement of the casing 32 relative to the template 12 at the well opening/housing bore 44.
[0048] During the period of time that the casing 32 and bushing means 68 are being lowered into position, the bushing means 68 is held fixed to the casing 32 by the releasable connecting means 100.
[0049] Once the bushing means 68 is connectably engaged with the template 12 as illustrated in FIG. 5, the releasable connecting means 100 may be released by applying a vertical load to the casing 12 thus shearing the shear pins 102 and 104 and allowing the casing 12 with its elastomeric sleeve 106 to slide vertically within the bushion bore 72, and slidable sleeve 106 can slip down casing 32 as necessary when contacted by bushing 70.
[0050] Then the lower portion 48 of casing 32 is fixed in the well bore 52 by cementing as indicated at 50.
[0051] During the operational life of the well template 12, it will tend to gradually settle into the ocean floor. This settling in some cases may be up to approximately ten inches over the operating life of the template 12.
[0052] With a gravity base well template 12 like that illustrated in FIG. 3, the upper unsupported portion 54 of casing 32 extending from the ocean floor 16 to the grid work 42 of template 12 may have a length on the order of thirty to fifty meters. Accordingly, if the gravity base template 12 were fixedly attached to the casing 32 at the well opening/housing bore 44, the compressive loads applied to the unsupported upper portion 54 of casing 32 during settling of the gravity base well template 12 would present a real danger of buckling the upper portion 54 of casing 32.
[0053] The bushing means 68 of the illustrated embodiment, however, allows the gravity base well template 12 to settle downward into the ocean floor relative to the casing 32 without imposing substantial compressive loads upon the upper portion 54 of casing 32 thus eliminating the danger of buckling of the upper portion 54 of the casing 32.
[0054] At the same time, however, it is necessary that a firm lateral support be provided to the casing 32 at the well opening/housing bore 44.
[0055] As schematically illustrated in FIG. 3, an upper end 112 (see FIG. 5) of casing 32 is connected to one of the production risers 28 by a connector 114.
[0056] As will be appreciated by those skilled in the art, the production riser 28 is subject to substantial lateral forces from currents and from movement of the TLP. If the casing 32 is not firmly supported against lateral movement at the well opening/housing bore 44 defined through the grid work 42 of template 12, the dynamic response of the production riser 28 could result in potentially damaging impacts between the casing 32 and the template 42. Additionally, dynamic forces could be transmitted to the upper portion 54 of the casing 32 and to other tubular members contained therein which could over a long period of time lead to fatigue failure of these items.
[0057] The bushing means 68 of the preferred embodiment provides the necessary lateral support, while at the same time allowing the gravity base well template 12 to settle into the ocean floor without imposing dangerous compressive loads upon the unsupported upper portion 54 of casing 32.
[0058] Thus it is seen that the apparatus and methods of the present invention readily achieve the ends and advantages mentioned as well as those inherent therein. While certain preferred embodiments of the invention have been illustrated for the purposes of the present disclosure, numerous changes in the arrangement and construction of parts may be made by those skilled in the art which changes are encompassed within the scope of the present invention as defined by the appended claims.
1. A casing guide apparatus, comprising: a well template having a well opening defined
therein;
a well casing received through said well opening; and
bushing means, operably associated with said template and said casing, for permitting relative vertical movement between said template and said casing and for preventing relative lateral movement between said template and said casing at said well opening.
a well casing received through said well opening; and
bushing means, operably associated with said template and said casing, for permitting relative vertical movement between said template and said casing and for preventing relative lateral movement between said template and said casing at said well opening.
2. The apparatus of claim 1, wherein:
said template is a gravity base template which will gradually settle into a floor of a body of water during its operating life;
said casing has a lower portion thereof cemented within said floor of said body of water, and said casing has an upper portion thereof extending above said floor and through said well opening of said template; and
said bushing means is further characterized as a means for permitting said gravity base template to settle into said floor relative to said casing without imposing substantial compressive loads on said upper portion of said casing, thus reducing the danger of buckling of said upper portion of said casing upon settling of said gravity base template.
said template is a gravity base template which will gradually settle into a floor of a body of water during its operating life;
said casing has a lower portion thereof cemented within said floor of said body of water, and said casing has an upper portion thereof extending above said floor and through said well opening of said template; and
said bushing means is further characterized as a means for permitting said gravity base template to settle into said floor relative to said casing without imposing substantial compressive loads on said upper portion of said casing, thus reducing the danger of buckling of said upper portion of said casing upon settling of said gravity base template.
3. The apparatus of claim 1 or 2, wherein said bushing means includes:
a cylindrical bushing member having a cylindrical inner bushing bore within which said casing is closely received; and
latch means, operably associated with said bushing member and said well opening of said template, for latching said bushing member into a fixed position within said well opening upon insertion of said casing and said bushing means downwardly into said well opening of said template.
a cylindrical bushing member having a cylindrical inner bushing bore within which said casing is closely received; and
latch means, operably associated with said bushing member and said well opening of said template, for latching said bushing member into a fixed position within said well opening upon insertion of said casing and said bushing means downwardly into said well opening of said template.
4. The apparatus of claim 3, wherein:
said template includes a template housing having a housing bore therethrough defining said well opening; and said latch means includes:
an annular latching groove defined in said housing bore; and
radially outwardly biased locking means, connected to said bushing member and extending radially outward from said bushing member, for receipt in said latching groove of said housing bore of said template.
said template includes a template housing having a housing bore therethrough defining said well opening; and said latch means includes:
an annular latching groove defined in said housing bore; and
radially outwardly biased locking means, connected to said bushing member and extending radially outward from said bushing member, for receipt in said latching groove of said housing bore of said template.
5. The apparatus of claim 4, wherein:
said template further includes upwardly open conical guide means concentrically disposed about said housing bore above said housing bore.
said template further includes upwardly open conical guide means concentrically disposed about said housing bore above said housing bore.
6. The apparatus of claim 4 or 5 wherein:
said bushing member has a cylindrical outer surface closely received in said housing bore of said template housing.
said bushing member has a cylindrical outer surface closely received in said housing bore of said template housing.
7. The apparatus of any of claims 3 to 6, further comprising: releasable connecting
means, operably associated with said casing and said bushing member, for initially
limiting vertical movement of said bushing member relative to said casing until said
bushing member is latched into said fixed position thereof within said well opening
of said template.
8. The apparatus of claim 7, wherein:
said releasable connecting means is further characterized as a means for initially preventing any substantial vertical movement of said bushing member relative to said casing.
said releasable connecting means is further characterized as a means for initially preventing any substantial vertical movement of said bushing member relative to said casing.
9. The apparatus of claim 8, wherein:
said releasable connecting means includes a plurality of shear pins connected between said casing and said bushing member.
said releasable connecting means includes a plurality of shear pins connected between said casing and said bushing member.
10. The apparatus of any of claims 3 to 9 wherein:
said casing includes a sleeve fixedly connected thereto and defining an outer cylindrical surface thereof, said sleeve being snugly received in said inner bushing bore so as to prevent any substantial lateral movement of said casing relative to said bushing member and so as to permit vertical sliding motion of said casing and said sleeve relative to said bushing member.
said casing includes a sleeve fixedly connected thereto and defining an outer cylindrical surface thereof, said sleeve being snugly received in said inner bushing bore so as to prevent any substantial lateral movement of said casing relative to said bushing member and so as to permit vertical sliding motion of said casing and said sleeve relative to said bushing member.
11. A bushing apparatus for a casing of a subsea well, comprising:
a cylindrical bushing member having a cylindrical inner bushing bore defined therein for slidably receiving said casing;
latch means, operably associated with said bushing member and adapted to engage a subsea well template, for latching said bushing member into a fixed position within a well opening of said well template upon insertion of said casing and said bushing member downwardly into said well opening; and
releasable connecting means, operably associated with said bushing member and adapted to be connected to said casing, for initially limiting vertical movement of said bushing member relative to said casing until said bushing member is latched into its said fixed position thereof within said well opening of said template.
a cylindrical bushing member having a cylindrical inner bushing bore defined therein for slidably receiving said casing;
latch means, operably associated with said bushing member and adapted to engage a subsea well template, for latching said bushing member into a fixed position within a well opening of said well template upon insertion of said casing and said bushing member downwardly into said well opening; and
releasable connecting means, operably associated with said bushing member and adapted to be connected to said casing, for initially limiting vertical movement of said bushing member relative to said casing until said bushing member is latched into its said fixed position thereof within said well opening of said template.
12. The apparatus of claim 11, wherein:
said releasable connecting means is further characterized as a means for initially preventing any substantial vertical movement of said bushing member relative to said casing.
said releasable connecting means is further characterized as a means for initially preventing any substantial vertical movement of said bushing member relative to said casing.
13. The apparatus of claim 12, wherein:
said releasable connecting means includes a plurality of shear pins means for frangibly connecting said bushing member and said casing.
said releasable connecting means includes a plurality of shear pins means for frangibly connecting said bushing member and said casing.
14. The apparatus of any of claims 11 to 13, wherein:
said latch means includes a radially outwardly biased locking means, connected to said bushing member and extending radially outward therefrom, for engagement with a latching groove defined in said well template about said well opening.
said latch means includes a radially outwardly biased locking means, connected to said bushing member and extending radially outward therefrom, for engagement with a latching groove defined in said well template about said well opening.
15. A method of constructing an underwater well, said method comprising the steps
of:
(a) placing a well template having a well opening defined therein on a floor of a body of water;
(b) assembling a bushing means with a well casing;
(c) lowering said well casing downward through said well opening of said template until a lower portion of said casing is received in a well bore;
(d) connectably engaging said bushing means with said well template so that said bushing means is substantially fixed relative to said template for preventing lateral movement of said casing relative to said template at said well opening;
(e) fixing said lower portion of said casing into said well bore; and
(f) allowing said bushing means to slide downward relative to said casing as said well template settles into said floor, thus reducing the danger of buckling of an upper portion of said casing upon settling of said well template.
16. The method of claim 15, wherein:
step (b) is further characterized by releasably connecting said bushing means and said casing and thereby initially limiting vertical movement of said bushing means relative to said casing; and
said method further comprises a step, after step (d), of releasing said bushing means so that said bushing means is free to slide vertically along said casing.
step (b) is further characterized by releasably connecting said bushing means and said casing and thereby initially limiting vertical movement of said bushing means relative to said casing; and
said method further comprises a step, after step (d), of releasing said bushing means so that said bushing means is free to slide vertically along said casing.
17. The method of claim 16, wherein;
step (b) is further characterized as initially preventing vertical movement of said bushing means relative to said casing.
step (b) is further characterized as initially preventing vertical movement of said bushing means relative to said casing.
18. The method of claim 17, wherein:
step (b) is further characterized as frangibly connecting said bushing means and said casing with a plurality of shear pins; and
said releasing step is further characterized as applying a vertical force to said casing to shear said shear pins.
step (b) is further characterized as frangibly connecting said bushing means and said casing with a plurality of shear pins; and
said releasing step is further characterized as applying a vertical force to said casing to shear said shear pins.
19.The method of claim 16, 17 or 18 wherein:
said releasing step is performed prior to step (e).
said releasing step is performed prior to step (e).
20. The method of any of claims 15 to 19 wherein:
said step (e) is further characterized as cementing said lower portion of said casing into said well bore.
said step (e) is further characterized as cementing said lower portion of said casing into said well bore.