US3362170A - Triangular based offshore platform - Google Patents

Description

Jan. 9, 1968 F1 led June -17, 1965 w; F- MANNING 3,362,170

TRIANGULAR BASED OFFSHORE PLATFORM 5 Sheets-Sheet 1 4 III; I, II I I I IIIIIIIIIIIIH,H'IIIIIIIII I h/ in,

kl, AL 32 Y a M 20 in J .4%: I2 Her INVENTOR WILLIAM F. MANNING Jan. 9, 1968 w. F. MANNING 3,352,170

TRIANGULAR BASED OFFSHORE PLATFORM 5 Sheets$heet 2 Filed June 17, 1965 WILLIAM F. MANNING BY cued/w d Jan. 9, 1968 w. I-. MANNING 3,362,170

TRIANGULAR BASED OFFSHORE, PLATFORM I Filed June 17, 1966 3 Sheets-Sheet 3 II I III TIIII IIIIIIIIIIIIIIIIIIIIIIITI rm m l IllllI/IIIIIIIIIII F06 Ill? I/ -\l llllllllll'ljlll IIIIIIIIIIIII!lI/l/IIIITT F06 IIZ INVENTOR WILLIAM F. MANNING BY W -F United States Patent Ofitice 3,362,170 Patented Jan. 9, 1968 ABSTRACT OF THE DISCLOSURE This specification discloses a triangular drilling and/ or production templet, and methods for installing the templet for drilling a subaqueous well and for completing, from a surface structure, an already drilled well terminating in an underwater stubbed-oif conductor pipe. The templet has a vertical leg and a pair of fixedly angled legs forming a triangular base at the marine bottom, and converging upwardly. A buoyancy tank is fixed on the vertical leg near the marine bottom. An above-surface deck is mounted on the upper end of the templet. The templet legs are anchored against axial tension and compression forces by piles extending therethrough into the formations underlying the marine bottom. One or more wells are drilled and/ or completed through the vertical leg which may be a single caisson or two or more rigidly connected parallel caissons.

This invention relates to a compact marine platform to be erected at an offshore submerged or subaqueous well site. More particularly, this invention relates to a prefabricated marine drilling and/or production platform having a hollow vertical support leg which functions to guide a drill string into the ocean bottom or conduct oil or gas from a completed well.

Present developments in the offshore oil industry find exploration and production efforts being extended to areas of extremely deep and unprotected water. For example, drilling in waters of 600 feet is now a reality and the exploration of the continental slope, out beyond the continental shelf, in depths of 1500 feet is close at hand. Different depths provide different problems and types of equipment required. In shallow Water, a submerged barge appears the most practical. Up to 300 feet of water, the rigid, bottom-supported structure has been shown to be the most feasible with the prefabricated templet being the least expensive, and the jack-up rig the most versatile. In depths of over 300 feet, the transparent, or semisubmersible, floating platform is now considered the most desirable by many, while the ship-shape vessel still competes where storms are not violent or continuous.

In the midrange of 100-300 feet of water, where a great deal of activity is centered at this time, there is the most overlap in drilling structures used. The jack up platforms provide a motionless deck with positive continuous location of the hole and depth versatility while the ship-shape provides the most mobility, and the transparent floating platform gives a compromise between the other two. However, one of the problems with jack-up platforms is that with the legs jacked up out of the water, above the platform, for towing, it is unstable in heavy seas. The most pressing problems with floating vessels are keeping them on location and minimizing pitch, roll, and heave.

For drilling in the above-designated midrange depths, it is not always economical to employ a floating vessel which may rent for as much as $12,000 a day, and therefore a light, compact templet would be desirable for drilling. Such a structure should be little more than bracing for a riser or caisson between a point above the surface of the body of water and a point beneaththe bottom thereof and support for a drilling deck. The templet structure should furthermore be capable of being floated to the site and be reasonably stable in the floating state in rough seas while under tow.

For production, in the midrange, the floating designs are impractical, and of the surface equipment under consideration, only bottom-supported structures are seriously contemplated. Due to the fact that a production platform does not have to be especially mobile, the primary consideration is cost. When a platform is to be anchored over a well for years at a time, it becomes incumbent on the designer to devise a structure that will be of minimum cost with sufficient strength to withstand the wind and wave loadings contemplated. The type of structure that best meets these design criteria would be a bare riser and bracing therefor, as described in the preceding paragraph.

Accordingly, it is an object of this invention to provide a relatively lightweight bottom-supported marine platform.

It is another object of this invention to provide a bottom-supported marine platform consisting essentially ofv a supported conductor or riser pipe extending from a.

point above the surface of a body of water to a point beneath the bottom of the body of water. It is a further object of the invention to provide a bottom-supported platform which is stable While being towed to a submerged site.

Other objects and advantages of this invention will be readily apparent from the following description when read in conjunction with the accompanying drawings which illustrate useful embodiments in accordance with this invention.

In the drawings:

FIGURE 1 is a perspective view of a bottom-supported templet structure of the invention with a drilling platform aflixed to the upper end thereof, above the surface of the water;

FIGURE 2 is a perspective view of a similar bottom supported templet structure with a production platform affixed to the upper end thereof, above the surface of the water;

FIGURES 35 illustrate in diagrammatic representations the sequential steps required for installing a production templet, as shown in FIGURE 2, over a previously drilled well.

In accordance with the present invention, the marine drilling and/or production templet comprises a vertical working leg and a pair of fixedly angled support legs, one at each of three corners, to form a structure having a substantially triangular cross section. The legs are widely spaced at the lower end of the structure to form a broad base and converge at the upper end, at approximately the surface of the water. The legs are also interconnected by braces appropriately spaced at intervals along the length of the templet structure. All three legs are anchored by piles driven therethrough into the formations underlying the marine bottom, the legs being rigidly connected to the piles by cementing and/ or welding. The vertical working leg is composed of one or more hollow caissons connected to a point within the formations underlying the marine bottom of the body of water by a hollow pile, each caisson-pile combination serving as a conductor pipe, or riser, for permitting a subaqueous well to be drilled from a deck above the templet structure through each caisson. A cylindrical buoyant tank is fixed to the lower end of the vertical working leg to relieve some of the load on the vertical leg. The axis of the cylindrical buoyant tank is parallel to the axes of the caissons making up the working leg. For a compact arrangement the vertical working leg can extend centrally through the buoyant tank. Each of the support legs is also hollow and can be utilized for production storage. To float the templet to the site, the open ends of the legs are capped, forming large buoyant tanks. The capping of the hollow legs and the later controlled flooding thereof for properly aligning 3 the templet is old in the art and is not a part of the present invention.

When using a templet structure of the type herein disclosed solely as a production platform, after a subaqueous well has been already drilled from a mobile platform, the subaqueous well is left with a stubbed-off conductor pipe extending up out of the subaqueous well, and strong enough to function as a structural piling. The templet structure is towed to the site in a buoyant condition, the caps are removed from the lower ends of the legs and then portions of the templet are sequentially flooded until the templet is submerged, but above the bottom, with the vertical working leg correctly oriented. The templet is then completely flooded by removing the caps from the upper ends of the legs as the templet is lowered with the vertical leg telescoping over the upwardly extending stubbed-off conductor pipe. Piles are driven through the other two legs to anchor them in place. Cement is then injected between each of the fixedly angled support legs and the respective enclosed pile as well as between the vertical working leg and the mated conductor pipe, to cement the three legs in place.

Referring to the drawings, FIGURE 1 illustrates a rigid drilling platform consisting of a triangular templet structure 12 and a drilling deck 14. The drilling platform 10 has a vertical leg 16 formed by a pair of rigidly connected hollow caissons 18 surrounded at their lower ends by a buoyant cylindrical tank 20, and a pair of upwardly converging support legs 22. The legs 16 and 22 are all interconnected by spaced horizontal braces 24 and triangulated for strength by auxiliary braces 26 between each level of horizontal braces 24. The vertical leg 16 alone extends through the deck 14 atop the templet 12, and a drilling rig 28 is centrally located thereover for drilling through one of the hollow caissons 18. The fixedly angled support legs 22 terminate just below the deck 14 where they provide a base for the support braces 30 of the deck 14. To appreciate the size of such a structure, it is calculated that in three hundred feet of water the support legs 22 would be sixty-inch diameter tubes while the caissons 18 would be thirty inches in diameter.

The lower end of each of the legs 22 rests on the bottom 34 and is anchored therein by a pile 32 which is driven down into the formations underlying the marine bottom 34 through the hollow leg 22 before the drilling deck 14 is fixed thereon. A hollow pile 36 is driven through the bottom 34 through each of the caissons 18, making up the vertical leg 16. Grout or any other suitable cementing material is injected between the piles 32 and 36, and the legs 22 and caissons 18 of leg 16, respectively, to cement the piles to the legs 22 and 16. Alternatively the piles 36 and 32, respectively, can be welded within the hollow legs 22 and caissons 18 above the surface of the water at the upper end of the templet structure 12. The piles 32 in legs 22 anchor the legs in place in the formation underlying the marine bottom 34 of the body of water while the piles 36 serve the double function of anchoring the leg 16 and providing water-tight extensions of the caissons 18 for guiding drill pipe into the formations underlying the marine bottom 34 while drilling a subaqueous well.

The drilling rig 28 is set in place over one of the caissons 18 for drilling a subaqueous well therethrough. After the well has been drilled to the desired depth, the rig can be moved a short distance across the deck 14 to be centered over the other caisson 18 and the drilling procedure repeated. Since the structure 10 is of the permanent type, it can be left in place after the drilling has been successfully completed, and then used as a production platform. The drilling rig would then be removed and a wellhead structure commonly termed as Christmas tree (not shown) would be installed on the deck 14 over each caisson 18.

FIGURE 2 illustrates a templet 12 supporting a production deck 14' over a subaqueous well 38. The platform 10 is similar in concept to the drilling platform 10 of FIGURE 1, having a hollow cylindrical vertical leg 16' with a buoyant cylindrical tank 20' concentrically aifixed thereon, and a pair of fixedly angled support legs 22. In the illustrated embodiment the leg 16' is itself the caisson, although the leg 16 could be comprised of several rigidly connected parallel caissons as illustrated in FIGURE 1 and described previously. While the support legs 22' are anchored, as in the first described embodiment, by piles 32' driven therethrough into the formations underlying the marine bottom of the body of water, the vertical leg 16' is telescoped over, or into, an existing stubbed-oif conductor pipe 36 extending upwardly from a drilled subaqueous well in the bottom 34. The production platform 10 of FIGURE 2 is of a lighter and simpler construction than the drilling platform 10 of FIGURE 1 since it is never required to support a drilling rig. The production deck 14' need not be fixed to the templet structure 12 by an extensive bracing structure as shown in FIGURE 1. Instead it can be mounted solely on the upper end of the vertical leg 16', the only portion of the templet structure 12' breaking the surface, thus permitting the smallest possible frontal area to be acted on by wave forces in the turbulent surface water zone. As shown, the production deck 14 Consists of a lower floor 40 and an upper floor 44. The leg 16 extends through the lower floor 40, ending in a Christmas tree 42. The upper floor 44 is an unobstructed fiat area where a servicing helicopter can land. Oil and/or gas may be pumped up through the leg 16 from the well 38 to equipment on the production deck to pressure relieve the produced fluid as well as to separate it into gaseous and liquid components. The products can then be stored in the hollow legs 22.

FIGURES 3-5 graphically illustrate the installation procedure for completing a stubbed-otf subaqueous well to the surface by utilizing the production platform 10. In FIGURE 3 the templet 12' is shown being towed to the subaqueous well site by a ship 46. As previously described, the templet structure 10' can be made buoyant by capping the legs 16 and 22' prior to immersion. The templet 14 lies in the water on a side with the two support legs 22' floating on the surface of the water and the vertical leg 16' in the air between them. Since the vertical leg 16' is centered between the two support legs 22 and is not relatively high in the air, the templet 12' is fairly stable while being towed.

When the templet has been towed to a position adjacent a mobile drilling platform 48, after the drill pipe has been removed from the finished well 52, the capped ends (not shown) are broken away from the lower ends of the legs 16' and 22, and the templet legs 16 and 22 flood, causing the templet 12' to sink. By connecting the upper end of leg 16 to the drilling derrick 50 on the mobile rig 4S centered over the well 52, and holding the other legs 22' by the tow ship 46 to obtain correct orientation, the templet 12' can be held with the leg 16' in a vertical position above the bottom 34. The caps (not shown) covering the upper ends of the legs 16' and 22' can then be removed to complete the flooding. The templet 12' is lowered to telescope the lower end of the vertical leg 16 into the upper end of the stubbed-off conductor pipe 38. Piles 32' are then driven down through legs 22' from the surface into the formations underlying the marine bottom 34 and the piles 32' and the stubbedoff conductor pipe 38 are cemented to their respective legs 22' and 16, respectively.

The production deck 14' is now mounted atop the bottom-supported templet to form a permanent production structure. The Christmas tree 42 is fixed over the leg 16' (if the leg 16' consists of only one caisson, or one is fixed over each of the caissons forming the leg 16 if the leg 16 consists of more than one caisson, whichever is the case). The mobile drilling rig 48 can then be towed away to drill a subaqueous well at another site and the instant well is able to produce oil above the surface of the water.

The drilling platform (FIGURE 1) is installed in a similar manner to that described above for the production platform 10. The templet 12 is also towed to the site in a buoyant condition. However, in most cases the templet 12 can be flooded and set on the site without a derrick overhead to guide it. The location of the working leg is not as critical when a new hole is going to be drilled as when the leg must be stabbed over a conductor pipe extending upwardly from an already drilled well. Another slight variation in the installation procedure is the driving of a pile 36 down through each of the caissons 18 forming the working leg 16 as well as driving piles 32 down through the support legs 22.

Although the present invention has been described in connection with details of specific embodiments thereof, it is to be understood that such details are not intended to limit the scope of the invention. The terms and expressions employed are used in a descriptive and not a limiting sense and there is no intention of excluding such equivalents, in the invention described, as fall within the scope of the claims. Now having described the apparatus and method herein disclosed, reference should be had to the claims which follow.

What is claimed is:

1. A prefabricated bottom-supported templet structure for use in a body of water to support equipment above the surface of the body of water and to provide at least one watertight vertical passage from said equipment above the surface of said body of water to a point within the formations underlying the marine bottom comprising a vertical leg and only two hollow fixedly angled legs for supporting, in part, said vertical leg; said fixedly angled legs being fixedly positioned to form a structure having a substantially triangular cross section; said equipment being located substantially directly over the upper end of said vertical leg; a buoyant tank fixed to said vertical leg whereby the portion of the weight of said above-surface equipment on the vertical leg will be lessened, preventing said vertical leg from being driven further into the forma tions underlying the marine bottom than said angled legs prior to said templet structure being firmly anchored .in the formations underlying the marine bottom; means for sealably connecting and anchoring the lower end of said vertical leg in the formations underlying the marine bottom, said sealably connecting and anchoring means comprising the upper portion of a subaqueous well formed in the underlying formations and extending to producible subaqueous mineral deposits; said support legs being spaced apart at said marine bottom, converging upwardly toward said vertical leg, and terminating at a point adjacent said surface of said body of water; and means for anchoring each of said support legs within the formations underlying said marine bottom against axial compression and tension forces.

2. The prefabricated bottom-supported templet structure of claim 1 wherein said equipment comprises a deck mounted on said templet so as to be above the surface of the body of water in which said templet is located, said vertical leg comprising at least one hollow caisson extending through said deck whereby said watertight vertical passage extends from a point above said deck into the formations underlying said marine bottom.

3. The prefabricated bottom-supported templet structure of claim 1 wherein said vertical leg comprises two parallel hollow caissons rigidly fixed together, forming a pair of separate watertight passages from respective points above the surface of said body of water to respective points within formations underlying said marine bottom and forming extensions of su-baqueous wells in the underlying formations.

4. The prefabricated bottom-supported templet structure of claim 1 wherein said means for sealably connecting and anchoring said caisson into said formations underlying said marine bottom is a hollow pile driven into said formations through said caisson and fixedly cemented therein whereby a drilling rig located directly over said vertical leg on said deck above said surface of said body of Water can drill a subaqueous well through said vertical leg.

5. The prefabricated bottom-supported templet structure of claim 1 wherein said buoyant tank is fixed to the lower end of said vertical leg whereby said buoyant tank is located downward of the turbulent surface water zone.

6. The prefabricated bottom-supported templet of claim 5 wherein said buoyant tank is cylindrical and the axis thereof is parallel to the axis of said vertical leg when fixed thereto.

7. The prefabricated bottom-supported templet of claim 6 wherein said vertical leg extends through said buoyant tank.

8. The prefabricated bottom-supported templet of claim 2 wherein said fixedly angled legs terminate below said surface of said body of water and only said vertical leg extends above said surface of said body of Water.

9. A method for installing an olfshore production platform over a fixed stubbed-off conductor pipe extending up vertically from a previously drilled subaqueous well at a submerged site, wherein said platform comprises the templet structure of claim 2, including the following steps:

(a) flooding said hollow legs Olf said templet to submerge said templet at said site;

(b) positioning said templet during flooding to orient said vertical leg;

(c) guiding said vertical leg into telescoping relationship 'with said fixed upwardly extending conductor w ((1) driving piles into said formations underlying said marine bottom through each of said fixedly angled legs, from the upper ends thereof, to anchor said piles;

(e) fixing each of said piles rigidly within the respective fixedly angled leg to anchor said respective fixed angled leg with respect to said marine bottom;

(f) anchoring said vertical leg by a watertight connection between said vertical leg and said conductor pipe to form a continuous passage through said leg and said conductor pipe into said drilled well whereby said well can be completed so that oil and/or gas may be produced through said vertical leg; and

(g) mounting a working deck on said templet above said surface of said body of water.

References Cited UNITED STATES PATENTS 2,248,051 7/1941 Armstrong 6146.5 2,637,978 5/1953 Evans 6146 2,901,890 9/1959 Hutchison 6146 2,906,500 9/1959 Knapp 6l-46.5 X 3,209,544 10/1965 Borrmann 6146'.5

JACOB SHAPIRO, Primary Examiner. DAVID J. WILLIAMOWSKY, Ex miner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,362,170 January 9, 1968 William F. Manning It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 3, line 55, for "formation" read formations column 6, line 5, for the claim reference numeral "1" read 2 Signed and sealed this 25th day of February 1969.

(SEAL) Attest:

Edward M. Fletcher, Jr. EDWARD J. BRENNER Attesting Officer Commissioner of Patents

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