US3685300A

US3685300A - Marine platform with curved support leg

Info

Publication number: US3685300A
Application number: US81950A
Authority: US
Inventors: George E Mott; Johnnie J Ziober
Original assignee: Texaco Inc
Current assignee: Texaco Inc
Priority date: 1970-10-19
Filing date: 1970-10-19
Publication date: 1972-08-22
Anticipated expiration: 1989-08-22

Abstract

The invention relates to a marine platform for use in drilling wells at an offshore body of water. The platform includes one or more vertically spaced decks that are raised beyond the water''s surface by a plurality of downwardly extending support legs. The respective legs are interconnected one to the other along their length and form an outwardly divergent pattern with respect to the decks. At least one of the legs is structured with an arcuate configuration. Said curved leg further encloses an elongated pile or piles that extend from the platform and are imbedded in the substratum. The piles, which are also curved, thereby function as guide members to bend a descending drill string in a desired direction. The string is thus deviated from a vertical disposition to achieve an initial direction preliminary to the boring of a directionally drilled well.

Description

United States Patent Mott et al.

[15] 3,685,300 [451 Aug. 22, 1972 1 MARINE PLATFORM WITH CURVED SUPPORT LEG [72] Inventors: George E. Mott, Metairie; Johnnie J. Ziober, Morgan City both of La. N

[73] Assignee: Texaco Inc., New York, NY.

[22] Filed: Oct. 19, 1970 g [21] Appl. No.: 81,950

Attorney-Thomas H. Whaley and Carl G. Reis 5 7] ABSTRACT The invention relates to a marine platform for use in drilling wells at an offshore body of water. The platform includes one or more verticallyspaced decks that are raised beyond the water's surface by a plurality of downwardly extending support legs. The respective legs are interconnected one to the other along their length and'form an outwardly divergent pattern with respect to the decks. At least one of the legs is structured with an arcuate configuration. Said curved leg further encloses an elongated pile or piles that extend from the platform and are imbedded in the substratum. The piles, which are also curved, thereby function as guidev members to bend a descending drill string in a desired direction. The string is thus deviated from a vertical disposition to achieve an initial direction preliminary to the boring of a directionally drilled well.

6 Claims, 5 Drawing figures [52] US. Cl. .....6l/46.5, 175/7, 175/9 [51] .Int. Cl. ....E02b 17/00, E02d 21/00, E2lb 15/02 [58] Field ofSearch ..6l/46.5,46, 50; l75/7',9

[56] References Cited UNITED STATES PATENTS 3,434,293 3/1969 Brown ..6 H465 3,004,612 10/1961 Kofahl ..175/7 3,457,728 7/1969 Pogonowski ..6l/46.5 3,516,259 6/1970 Tokola ..61/465 3,474,630 10/1969 Pogonowski ..6l/46.5 3,209,544 l0/l965 Bormann ..6l/46.5 3,315,473 4/1967 Hauber et al. ..6l/46.5

Ts T

PATENTEDwczz I972 SHEET 1 [IF 2 MARINE PLATFORM WITH CURVED SUPPORT LEG BACKGROUND OF THE INVENTION In the drilling of an offshore field for the purpose of determining the fields potential productivity, it is expedient to provide as many exploratory and/or producing wells as possible. In the instance of a floating drill ship, the ship is merely floated from one location to another and anchored, whereby a series of vertical wells can be readily drilled. In the instance of a stationary, anchored platform however, the problem of obtaining maximum exploratory coverage from a single location embodies some difficulties.

To obtain maximum exploratory or producing coverage of any oil rich reservoir, it has been found feasible to employ the technique of drilling a number of wells from a single, fixed base. The usual fixed facility or base comprises an upstanding platform which is rigidly positioned to the floor of the body of water and which extends partially above the waters surface. With a platform so anchored, presently known drilling techniques permit a plurality of wells to be directionally oriented whereby to in essence, radiate away from the drilling center.

When the potentially oil productive area is relatively close to the ocean floor, it is difficult to properly orient a drill string to have the well bore enter the substratum at a desired angle. This is true since, for directionally adjusting the limitedly flexible drill string in any operation, such an adjustment must be made gradually, thereby necessitating a predetermined depth of solid substrate through which to drill.

One expedient sometimes used for economically forming a number of directionally drilled wells, is to provide a platform having straight, although sloping drill conductors, which commence at the platforms deck. These directed drill conductors are set at a predetermined angle to the ocean floor. The drilling technique, however, necessitates the use of I deck mounted equipment, such as derrick, pipe holders, etc., which are capable of being adjusted from a vertical disposition to align with the drill conductor. Such equipment is considered a specialty item, and consequently is relatively expensive in contrast to the normal equipment designed.

Toward overcoming the herein stated problems, there is presently provided a drilling apparatus adapted for progressively deviating an offshore well bore away from a vertical disposition. Said apparatus includes a marine platform capable of being anchored at an offshore location whereby to form one or more wells in a direction and number as required. The disclosed structure includes in essence, a work deck which is disposed above the waters surface and normally comprises two or more levels. A plurality of support legs extend downwardly from the deck and are connected at the lower end thereof to the ocean floor.

Structurally, the marine platform includes a plurality of cross members arranged between the respective support legs providing each of the latter with mutual lateral bracing. At least one, and preferably a plurality of the legs are so shaped to define a uniform arcuate configuration, being substantially vertically disposed at the upper end such that the leg is curved a predetermined degree of deviation from vertical as the leg progresses toward the ocean floor.

At least two legs of the structure are straight and may be vertical and parallel, or may be inclined. Straight legs embody the advantage of permitting the structure to be floated to a job site without excessive draft.

Each leg including the curved ones, is further provided with anchoring piles which extend longitudinally thereof, and are imbedded into the penetratable sea floor. In the instance of curved legs, each of said anchoring piles thereby assumes substantially the same curvature as the leg while enclosed within the latter. With respect to the drilling operation, each curved anchoring pile thus serves as an elongated drilling guide into which a drill string can be vertically lowered such that the string will be gradually urged into a direction away form the platform.

DESCRIPTION OF THE DRAWINGS In the drawings,

FIG. 1 is a vertical elevation of an elongated marine platform of the type contemplated, illustrating one arcuately curved and one straight, but inclined leg for positioning the platform at the ocean floor.

FIG. 2 is an enlarged segmentary view of a portion of the curved leg shown in FIG. 1, with a part of the wall removed to illustrate the legs inner construction.

FIG. 3 is a section taken along line 33 in FIG. 2.

FIG. 4 is a segmentary view on an enlarged scale and in cross-section, showing pile type drill guides positioned within a curved support leg.

FIG. 5 is an enlarged segmentary view in cross-section, illustrating a drill string disposed within a curved drilling guide extending through the platform support leg.

Referring to the drawings, FIG. 1 depicts elongated marine platform 10 of the type contemplated, as normally submerged in an upright position at an offshore body of water. A working deck 11 comprises at least two spaced apart levels, which deck supports drilling equipment needed for boring a well into the ocean floor. Such equipment includes primarily a vertical derrick 12, draw works 13, and a rotary table 14. While not presently illustrated in detail, the drilling mechanism including derrick 12 and rotary 14 is horizontally movable and adapted to be positioned at various locations along the deck surface whereby to be selectively, vertically aligned over any one of the platform legs.

Deck 11 is fixed a predetermined distance beyond the ocean surface to maintain the deck 11 as well as drilling equipment, out of immediate contact with surrounding water. Said deck 11 is so supported by at least one, and preferably a plurality of downwardly extending

legs

16 and 17. The latter are generally disposed at three or four comers of the deck and arranged to provide a firm anchoring and foundation means for platform 10. The curved legs are aligned in substantially vertical orientation at the level of the upper deck 11. Said legs are further contoured in an arcuate curvature such that at the lower end, the leg is directed at a predetermined number of degrees from the vertical.

While the present arrangement of FIG. 1 illustrates one curved, and one straight leg extending from platform 11, it is understood that as many of said curved legs will be provided as is deemed necessary under the drilling circumstances at a particular location. For example, platform 11 might be further supported by other, substantially straight legs which extend downwardly to, and are imbedded in the ocean floor, as are the curved legs.

Normally, marine platforms of the present type are fabricated at a shore facility and are thereafter conveyed to an offshore drilling side. The platform can be carried on barges if the size of the platform and the size of the barge or barges so permit. More often however, for larger platforms the latter are provided with internal, controllable buoyancy means whereby they can be self floated and towed to the desired drilling site. Thereafter, by regulation of the platforms buoyancy, the entire unit is caused to first assume an upright floating stance and then to descend to the desired site at the ocean floor.

To assure firm anchoring under adverse weather conditions, the respective support legs are caused to penetrate the floors upper substrate. The degree of penetration achieved is dependent on the consistency of the substrate as well as the desired depth of penetration. For example, in a relatively deltaic substrate characterized by the Gulf of Mexico, each leg would normally be designed to sink a greater depth than they would in a less penetratable or more consolidated soil.

For the purpose of the present disclosure, the lower ends of the

respective platform legs

16 and 17 are both illustrated as being imbedded into the substrate. When so immersed, they tend to stabilize deck 11 in a substantially horizontal plane.

As shown in FIG. 2, the respective support legs 16, for example, are formed of a plurality of axially aligned, hollow segments which are end welded or otherwise fastened together to form a continuous, elongated hollow member. The leg is preferably shaped with a tubular cross-section as a matter of convenience and economy in fabrication. Normally, such legs are fabricated of short rolled lengths of tubing segments, which segments are joined by welding until a predetermined length of leg is achieved.

As shown in FIG. 3, physically the support leg comprises an outer cylindrical casing 18 which can be on the order of magnitude of from 3 to feet in diameter. The wall thickness of the leg will be in accordance with such engineering factors as the expected stress to be placed on the leg by the particular platform, the weight carried, and the water depth. In larger diameter legs, an inner shell 19 is spaced inwardly of casing 18 to define an annular intermediate space 20 extending substantially the length of the leg. Said annular space 20 defines the area in which a plurality of elongated piles 21 are positioned, and driven from the leg lower end into the substratum.

As further shown in FIG. 2, the respective support legs are provided with longitudinally spaced pile guides 22 and 23. The latter when properly aligned, form a series of

longitudinal openings

25 and 25a within the leg. Said openings 25 are peripherally spaced to register a desired number of anchoring piles whereby to afford the necessary holding capability to the respective legs. Each pile guide opening 25 is provided with a receiver having an upper guide edge adapted to accommodate the end of a downwardly moving pile whereby to guide the latter as it is driven from above. Normally, the respective piles 25 are positioned within a leg after the platform has been set on the ocean bottom. However,

sections of pile may be prepositioned in a leg during the fabrication period. Thereafter, the respective piles 21 are driven by a pile driver or other means at the deck level into the penetratable floor. As the penetration progresses, additional lengths of pile segment are welded to the pile upper end and the operation is continued until the pile achieves a predetermined depth of penetration.

Anchoring piles 21 as shown, and in accordance with usual practice, comprise a series of heavy wall tubular segments generally fabricated of rolled steel. The pile lower end is open to facilitate passage thereof as it is driven or sunk further into the ocean floor. In the instance of curved lengths, to provide the curved piles with the desired arcuate curvature, the end of each pile is cut in such a manner that when welded together, adjacent segments form a chord of said desired curvature. As the pile is lowered into a leg, it will slide along and be guided by aligned pile guides 22 and 23.

Referring to FIG. 2, while only two pile guides 22 and 23 are presently shown, it is understood that a sufficient number of such members will be provided within each leg to accomplish the desired guidance and lateral support of the circularly arranged piles. In an altemate embodiment, and as shown in FIGS. 3 and 4

shoes

27 and 28 are secured to the upper face of disc-

Iike panels

32 and 33 respectively, having a center opening which engages and fastens to shell 19. Said panel 32 includes a peripheral edge that similarly engages the inner wall of casing 18 usually at a welded joint, whereby to be rigidly sustained in place and to maintain the cylindrical shape of casing 18 and shell 19.

Each panel 32 is provided with the peripherally arranged, and equispaced receivers 27 aligned with guide openings 29. The latter are of sufficient diameter to slidably receive a pile as the latter is lowered. When the piles are initially inserted into the platform leg during installation, they must be correctly oriented so that the pile curvature conforms with the leg curvature. The piles then will tend to position themselves correctly, and register with the proper shoe throughout the length of the leg.

As a matter of economy, each support leg is usually provided with only the necessary number of piles required to anchor the platform and to form the number of wells desired to be drilled. By varying the pile diameter, wall thickness and material strength, the number of piles can be made to provide drilling conductors for the desired number of wells.

Referring to FIG. 4 subsequent to the pile in any one leg being properly imbedded in the substrate, the piles are fastened to the leg at a rigid joint. The latter consists of a collar 31 formed of hardened cement which is poured into the leg lower end and permitted to solidify. Collar 31 is formed between outer casing 18 and shell l9, together with the respective

transverse panels

32 and 33. To form a proper seal and hold fluidized cement in collar 31, guide openings 29 in lower panel 33 are provided with resilient, peripheral rings 40 against which the piles will slidably fit to form a fluid tight oint.

The annular space about the respective piles is com municated with one or more external fittings 34 adapted to engage a conduit 36, which is in turn communicated with a source of fluidized cement. In making the cement collar, an initial laver of the fluidized material is pumped into annular space with the piles 21 in place, and thereafter allowed to harden. This initial layer forms a solid base across the panel 33 to seal the lower end of the compartment. A second injection of cement through a higher positioned fitting 39 causes the annular space 20 to fill with the fluidized material, the excess flowing through openings 37 in the upper panel 32. As the upper layer of cement hardens, the prepositioned piles 21 will be firmly locked in place to maintain the platform steady at the ocean floor for the drilling operation.

With the piles thus set, the normal procedure for introducing a drill string and bit into the respective piles will follow the conventional way of drilling a well bore. Thus, and referring to FIG. 5, drill string 41 is lowered vertically from the derrick 12 into pile 21. The string will gravitate by its own weight downwardly through the curved pile, bearing against walls of the latter to conform to the curvature of said pile. As drill bit 42 emerges from the pile lower end, the well bore will be started by rotating the entire string 42. Since drill bit 43 is now oriented in a desired direction, and at an angle to the vertical, by altering the drill speed and pressure the direction of the bore can be regulated to reach a desired location.

In the normal manner, as the bore progresses, drilling mud is pumped through the drill string and thereafter returned through the well bore and the pile 21, where it is directed to a collecting tank at the waters surface prior to being recirculated.

Other modifications and variations of the invention, as hereinbefore set forth, may be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.

We claim:

1. In a marine platform for drilling wells into the ocean floor at an offshore body of water, said platform including; a work deck holding well drilling equipment, and a plurality of elongated legs engaging and extending downwardly from said work deck to the floor of said body of water whereby to be fixed to the latter and support the deck beyond the waters surface,

at least one of said elongated legs having the upper end thereof retained in a substantially vertical disposition, said at least one leg being contoured along its length to define a substantially uniform arcuate configuration, said at least one contoured leg further including an outer cylindrical shell,

a casing disposed concentrically of said shell and spaced inwardly of the latter to define an annular passage extending the length of said shell,

a lateral positioning pile guide means fixed within said annular passage and comprising a plurality of pile guide members spaced longitudinally apart and disposed normal to the axis of said shell,

said pile guide members further including a plurality of circularly arranged and peripherally spaced openings, the latter being arranged in axial alignment with openings in adjacent of said pile guide members,

elongated anchor pile means extending longitullll illffilffil2 sf ffi to urge a pile into a contoured configuration corresponding to the contour of said leg, and means forming a cylindrical passage in said anchor pile of a sufficient diameter to slidably receive a drill string and bit passed therethrough, whereby said drill string will follow the contour of said passage and be urged into a desired direction deviated from the vertical, prior to entering the substrate beneath said pile.

2. In a marine platform as defined in claim 1, wherein said elongated anchor pile means comprises a plurality of said piles positioned in said annular passage.

3. In a marine platform as defined in claim 2, wherein said respective anchor piles are prebent to conform to the arcuate contour of said platform leg.

4. In a marine platform as defined in claim 1, wherein positioning means in said annular passage engages said respective anchor piles subsequent to the latter being embedded in said substrate.

5. In a marine platform as defined in claim 4, wherein said positioning means includes; a hardened fluid mass at the lower end of said annular passage, engaging said piles and said leg, whereby to position the respective piles with respect to said shell and easing.

6. In a marine platform as defined in claim 1, wherein said at least one contoured leg is aligned in a direction outwardly away from said marine structure.

Claims

1. In a marine platform for drilling wells into the ocean floor at an offshore body of water, said platform including; a work deck holding well drilling equipment, and a plurality of elongated legs engaging and extending downwardly from said work deck to the floor of said body of water whereby to be fixed to the latter and support the deck beyond the water''s surface, at least one of said elongated legs having the upper end thereof retained in a substantially vertical disposition, said at least one leg being contoured along its length to define a substantially uniform arcuate configuration, said at least one contoured leg further including an outer cylindrical shell, a casing disposed concentrically of said shell and spaced inwardly of the latter to define an annular passage extending the length of said shell, a lateral positioning pile guide means fixed within said annular passage and comprising a plurality of pile guide members spaced longitudinally apart and disposed normal to the axis of said shell, said pile guide members further including a plurality of circularly arranged and peripherally spaced openings, the latter being arranged in axial alignment with openings in adjacent of said pile guide members, elongated anchor pile means extending longitudinally of said contoured leg and being registered in the respective axially aligned openings, whereby to urge a pile into a contoured configuration corresponding to the contour of said leg, and means forming a cylindrical passage in said anchor pile of a sufficient diameter to slidably receive a drill string and bit passed therethrough, whereby said drill string will follow the contour of said passage and be urged into a desired direction deviated from the vertical, prior to entering the substrate beneath said pile.

5. In a marine platform as defined in claim 4, wherein said positioning means includes; a hardened fluid mass at the lower end of said annular passage, engaging said piles and said leg, whereby to position the respective piles with respect to said shell and casing.