US3572044A

US3572044A - Multiunit offshore platform

Info

Publication number: US3572044A
Application number: US809820A
Authority: US
Inventors: Ivo C Pogonowski
Original assignee: Texaco Inc
Current assignee: Texaco Inc
Priority date: 1969-03-24
Filing date: 1969-03-24
Publication date: 1971-03-23
Anticipated expiration: 1988-03-23

Abstract

The invention relates to an offshore platform for use in relatively deep water, being equipped for exploratory purposes and/or for producing crude oil from a subsurface wellhead. The platform comprises a floatable hull section that detachably engages an intermediary jacket. The latter supportedly rests on or near the floor of a body of water and incorporates a removable wellhead structure. After use of the platform for drilling and completion operations at a well site, the jacket and wellhead structure are separated whereby the latter will remain at the site, while the jacket is removed by the hull for further use. The jacket is then raised from the ocean floor by the floatable hull for transfer to another well site.

Description

United States Patent Ivo C. Pogonowski Houston, Tex. 809,820

Mar. 24, 1969 Mar. 23, 1971 Texaco Inc.

New York, N.Y.

Inventor Appl. No. Filed Patented Assignee MULTIUNIT OFFSHORE PLATFORM [56] References Cited UNITED STATES PATENTS 3,201,945 8/1965 Sutton 6l/46.5 3,433,024 3/ I969 Diamond et 6l/46.5

Primary Examiner-Jacob Shapiro Attorneys-K. E. Kavanagh and Thomas H. Whaley ABSTRACT: The invention relates to an offshore platform for use in relatively deep water, being equipped for exploratory purposes and/or for producing crude oil from a subsurface wellhead. The platform comprises a floatable hull section that detachably engages an intermediary jacket. The latter supportedly rests on or near the floor of a body of water and incorporates a removable wellhead structure. After use of the platform for drilling and completion operations at a well site, the jacket and wellhead structure are separated whereby the latter will remain at the site, while the jacket is removed by the hull for further use. The jacket is then raised from the ocean floor by the floatable hull for transfer to another well site.

' PATENTEU ma SHEET 20F 2 MULTIUNIT OFFSHORE PLATFORM The present efforts toward exploration for, and production of crude oil and gas sources, have gravitated to increasingly deeper offshore locations. Much of the developing petroleum technology therefore has been directed to the improvement of, and further advancement of concepts toward facilitating economical removal of the crude product from deep water wells. Generally, such offshore wells are developed utilizing either fixedly anchored platforms, or floating barges, the latter being in effect movably restrained at the waters surface.

In the instance of rigidly anchored platforms, the support structure extends from the ocean floor to a point above the waters surface, and there positions the drilling platform. The latter normally holds a derrick and draw-works, together with the other ancillary equipment characteristic of such offshore drill rigs.

Platforms adapted for offshore work are relatively expensive; in many'instances they are known to exceed several million dollars merely for the building, transporting and locating of the platform at a particular site. It can be appreciated then that the economics of offshore drilling activities become less favorable as the water depth increases. This analogy is due not only. to the greater height of the support platform to maintain the working deck above the water surface, but also to the lack of specific technology which might be relied on in the design of a safe, workable structure.

Since every attempt at finding a productive offshore location does not meet with success, it is economically feasible to in most instances disconnect the platform for the ocean floor and transport the entire unit for use at another drillingsite. The process is thereafter continued whereby exploratory wells may be attempted or completed at a number of sites, utilizing the same platform.

v The actual construction of extra large offshore structures for deep water use suggests numerous problems, prompted mainly by the platforms outlandish size. Notably, while the structure can be readily fabricated on shore, or at a shipyard, the unit must eventually be moved to an offshore working area either by barge or by'self-flotation. Barging has been utilized to a large extent, but the capability of this mode of transportation has limitations. Not the least of these limitations is the difficulty in moving a large completed structure from the shore and onto a barge. For example, there is the inherent strain imposed on the structure by virtue of one or more of the transporting barges being subjected to rocking and tilting in response to the wave action of the water. Further, in the instance where the platform is floated from a building site to a working area, the water immediately offshore of the building site must of necessity be quite deep. This latter condition is rare except where the drydock or construction facility includes a section that has been artificially deepened, which circumstance usually requires firming of the land bank immediately adjacent to the water.

Thus, the technique of constructing an offshore platform and floating the same to a working location, has by and large been contingent on the size of the platform and more specifically on the depths of the water in which it will function. With increased water depth, as a matter of good design practice the lower end or base of the platform support structure must be made increasingly wider that the platform will maintain upright stability under a variety of unfavorable natural conditions prevalent at the drill site.

It is therefore one of the objects of the invention to provide a multiunit offshore platform adapted to be versatile and readily separable into individual components. A further object is to provide a platform of the type described which is easily transferable for reuse at different drilling locations. A still further object is to provide a detachably connected offshore platform adapted to be readily and floatably transported between points of operation. Another object is to provide a separable type platform adapted to removably receive a wellhead structure which is transported to a drilling site at which it remains after the platform itself has been removed to another site. Still another object is to provide a platform adapted for use in a deep water location, which platform is characterized by a relatively widespread base embodying a minimum amount of anchoring. And a still further object is to provide an offshore platform adapted to utilize a central anchoring section which functions, together with a relatively broad base, to firmly position the platform at a drilling site.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings: FIGS. 1, 2 and 3 represent the sequential operations of an offshore unit of the type presently contemplated showing a wellhead structure as used with the drilling platform.

FIG. 4 is an enlarged view of the multiunit platform connected by a plurality of legs which join the surface positioned hull to the floor positioned platform jacket.

FIG. 5 illustrates an embodiment of the jacket member normally positioned at the floor of an under water site.

FIG. 6 is an enlarged segmentary view of a portion of the jacket and wellhead structure connection shown in FIG. 4.

In overcoming the foregoing structural problems and technological operating difficulties, and to further advance the offshore petroleum drilling techniques, the present invention discloses a novel offshore platform adapted principally to deep water use. The platform is fabricated of a multiplicity of detachably connected units including; a floatable hull, a controllably floatable well jacket, and a wellhead structure. At least two elongated legs are operably connected to clamping means on the respective parts. Thus, the hull either supports or is supported by the open frame jacket. The wellhead structure is carried integral with the jacket during drilling and production operations, and is thereafter detached to permit removal of the jacket while leaving the wellhead structure firmly anchored in place.

Referring to the drawings, FIGS. 1, 2 and 3 illustrate a platform of the type contemplated, in a sequence of situations including those in which the platform is floating, at the anchored position, and thereafter further floated without the wellhead structure. The latter is shown remaining in place at the under water wellhead. The platform includes floatable deck section or hull H which is normally disposed at the platform uppermost end. Well jacket J depends from the lower side of bull H, the spacial relationship between the two being adjustably maintained by at least two rigid, elongated legs 15 and I5. Wellhead structure S is incorporated into the framework of jacket .I, being removable to pennit the structure S to be anchored by piling or the like driven into the ocean floor during a drilling operation and thereafter separated from jacket J as the latter is floated to the surface for reuse.

Referring to FIG. 4, hull section H includes an upper deck 11 forming a top working surface. A lower deck 12 spaced from deck 11 defines a storage and flotation section 13, the two decks being normally enclosed and partitioned by steel plate to form watertight compartments. The respective decks are generally formed of steel plates welded into a unit to define a peripheral enclosure. Hull H is provided with an open well 14 preferably at the bull's center although not limited to such location. Well 14 forms an opening to accommodate drill string tools and other equipment supported by derrick l6 and lowered through the well to the ocean floor.

Hull H as shown, is constructed in a triangular configuration to best meet the conditions requisite for floatability and seagoing stability. The geometric shape however is understandably not an absolute requirement to the present invention but is rather exemplary. Each corner of hull H is provided with a leg elevating and locking clamp shown as l7, l8 and I9 respectively. Each clamp further includes suitable mechanism such as a rack and pinidn mechanism adapted for elevating, lowering or locking the leg at a desired disposition.

Hull H is shown in FIG. 4 supported above the ocean floor and elevated beyond the water surface by rigid although adjustable linking means which operably connects the bull to the jacket such as

legs

15, and 15". The leg applicable to the present supporting function in the multiunit platform might assume a number of embodiments. For example, the legs may be of a general elongated tubular disposition formed of end welded tubular short sections. The legs as a matter of practicality, may be fabricated to a predesired length prior to assembling with the platform clamps. Alternately, and more usually, the legs are lengthened during assembly with the hull as the latter supportably lowers jacket J to an anchoring position at the ocean bottom. Also within the purview of the leg structure applicable to the present application is the frequently used triangular sectioned leg formed of an open work structure.

Jacket J includes basically a welded, open framework of steel tubular members including a lower end into which wellhead structure S is incorporated in such manner to permit the latter to be readily removed. A horizontal base section is formed of terminally connected

tubular members

22, 23 and 24. An enlarged plate assembly extending between, and peripherally connected to the respective base sections may be utilized by the jacket as a template which functions as a broad bearing member for jacket J.

Jacket J further includes a plurality of upstanding leg guides 26, 27 and 28 having a flared, frustroconical cap at the upper end adapted to receive and direct the lower end of a support leg stabbed into the guide. Stabbing is normally accomplished by lowering the tubular leg in an upright attitude from the hull H, and manipulating the same to register and fasten within a corresponding leg guide for raising the jacket from its anchored spot. With the leg, as for example 15, restrained at its upper end at clamp 17, and with the lower end fastened into leg guide 26, hull H and jacket J are fixedly disposed with respect to each other. The leg 15 lower end is firmly clamped within leg guide 26 preferably by a contracting jaw arrangement, actuated from the surface. However, cementing to form a rigid collar between the concentrically disposed leg and guide may also be utilized, which operation will necessitate destroying at least part of the leg when it is removed from a guide.

Jacket J further includes a plurality of downwardly extending pile guides 29, spaced about the jacket and formed to receive one or more piles 20. The latter in the usual manner, extend from the pile guide lower end and are imbedded into the ocean substratum to a predetermined depth determined to be suitable for rigidly stabilizing the platform.

A central upright section of jacket J is formed of structural guide members oriented to define an elongated docking facility or cavity. Said facility comprises essentially a guide passage having an enlarged forward opening at the jacket lower end, and extending upwardly to a height commensurate with the height of wellhead structure S. The lower, or forward opening of the docking cavity is adapted to slidably register with and retain a wellhead structure S during the period when the jacket is being transported or lowered into place in contemplation of a drilling operation. Further, when structure S is anchored, it slidably guides a jacket J into place as the latter is lowered prior to commencing a rework or similar operation on a functioning well.

Referring to FIG. 4, one embodiment of the docking facility includes two or

more collars

36 and 37 spaced longitudinally apart and being of a cross-sectional dimension in accordance with the outer dimensions of the wellhead structure. The respective collars are positioned in the jacket by

lateral members

43 and 44 which radiate from, and are connected to the jacket outer elements.

Wellhead structure 8 as shown in FIG. 4, includes a three legged upstanding pylonlike arrangement which is fixedly positioned at the ocean floor by a plurality of leg piles 25. The height of wellhead structure S is best determined in accordance with the height of the water in which the platform is operating. The structure will normally position the usual wellhead flow control equipment 10 to feet above the ocean floor.

Structure S includes a generally triangular formed base comprised of

peripheral elements

51, 52 and 53. Upstanding comer posts 54 and 56 extend from the respective comers of the base, are tapered inwardly to a constricted upper end, and are joined at an upper neck piece 57. Each corner post is provided along its outer surface with a track or slide surface extending the length thereof to facilitate sliding engagement of the wellhead structure with the jacket docking cavity.

Operationally, wellhead structure S is incorporated into the center of jacket J. The respective comer posts 56 and 57 are adapted to closely fit within the longitudinally spaced rubbing

collars

36 and 37 whereby, in fully seated position, the collars will closely fit about the wellhead structure corner posts. To minimize the relative movement between the said members, remotely operated clamping or locking jaws are incorporated into one or both joined members. The locking or engaging members are remotely operable by use of hydraulic lines and ancillary equipment, which, although not presently shown in detail, extend from an actuating mechanism on hull H.

An example of a clamping mechanism usable to achieve the releasable feature of the invention is shown in FIG. 6 and includes a set of jaws 25' depending inwardly from rubbing collar 36, and a second set of said jaws 30 depending from the lower positioned rubbing collar 37. Said upper and lower jaws respectively are incorporated within the docking facility and positioned to engage an upright member 56 of the wellhead structure S. Said clamping jaws are communicated through

hydraulic control lines

40 and 45 with a form of hydraulic actuating means at the'waters surface whereby the jaws can be remotely regulated to engage or disengage with the wellhead structure.

Each

corner post

56 and 57 of the wellhead structure is provided with one or more piles 25 which pass through the post and extend from the bottom end thereof to be firmly and permanently imbedded into the substratum. The function of the piles, as in generally known, is to fixedly implant wellhead structure S in the ocean floor and to concurrently hold jacket J at its ocean floor position.

Referring to FIG. 5, an alternate embodiment of the novel composite jacket and removable wellhead structure, is illustrated and includes the outer jacket section formed essentially of upstanding corner posts 61, 62 and 63 together with the lower

base forming elements

64, 66 and 67. Intermediate, albeit necessary structural elements have been eliminated from the drawing and description to best illustrate the position and arrangement of the shown docking facility as incorporated into the jacket structure.

Said docking facility includes a plurality, and preferably two, concentrically disposed and longitudinally spaced circular guide rings 68 and 69. Bracing members such as 71, 72 and 73 are connected to the respective rings to supportably position the latter with respect to each other and to the jacket. The main structure guide rings as shown, include the upper positioned smaller ring 68, and the larger diameter lower ring 69 so dimensioned to readily receive a wellhead structure when the latter is at a subsea location.

As also shown in FIG. 5, for tall offshore platforms the jacket may be provided with a relatively broad base to assure vertical stability. Toward this end, outrigger members such as 76 and 77 extend downwardly from the jacket upper corners, and terminate in a plane with the jacket base. Horizontal and

vertical braces

79, 81 and 82 reinforce the main outrigger assembly 76 against bending under excessive platform loading due to lateral movement swaying or the like. In this form of jacket structure, the sole anchoring facility is embodied into the docking unit. Thus, the latter includes a plurality of pile guides 83, 84 and 86 which extend from, and are terminally positioned by spaced guide rings 68 and 69. The guides serve to retain piles which are driven into the ocean floor for positioning the jacket. By concentrating the piled section at or near the center of the jacket, and by providing a relatively wide base on the jacket, the amount of piling required is greatly minimized. Further the time and cost expended in piling the platform to the ocean bottom is substantially decreased. V

Referring again to FIG. 4, operationally, the present multiunit offshore platform is adapted for fabrication at one or more shore locations in' the form of discrete and separable members. Afier being fully fabricated, the respective hull, jacket, wellhead structure and linking legs are normally of such a size as to prohibit ease of assembly,-and launching at or close to shore. Thus each individual unit isseparat ely floated by barge or self-flotation to an offshore water depth where'the platform might be conveniently assembled.

The assembly area is normally in relatively shallow water, having an ocean bottom adaptedto support the jacket and wellhead structure without sinking into the substratum. With the hull floating on the, water's surface, the jacket and wellhead structure are controllably submerged by judicious use of buoyancy tanks or similar means incorporated into the jacket structure. This practice of controlled submergence is of course familiar in the art and not considered novel.

Hull H is deployed immediately above the jacket and aligned to position the respective leg clamps 17, 18 and 19 above the corresponding jacket leg guides 26, 27 and 28.

Legs

15, and 15" are individually passed into the corner clamps, lowered into the water, and lengthened by addition of short tubing length as needed. Fastening of the leg lower end to the jacket is achieved by clamping or cementing as herein mentioned, to provide a rigid connection.

With the two or more legs thus connecting the floating hull with the jacket, the legs are drawn up to the hull by' jacks at the respective corner clamps whereby to raise the jacket above the ocean floor. The entire support of the jacket is not necessarily relegated to the floating hull, but may be supplemented by the buoyancy capabilities of the jacket structure itself. With the composite unit now being supported by the floating hull, and by 'the partially buoyant jacket, the entire unit is towed to a water depth, or site at which it is to be used.

- Jacket J is again lowered by lengthening the respective corner legs through addition of leg'lengths, until the jacket lower end rests on the ocean bottom. Anchoring of the platform in the usual manner is achieved by implanting piles which have been prepositioned in the pile guides disposed about either the wellhead structure and/or the jacket. The piling operation as mentioned is limited only to the wellhead structure in the instance where the base of the jacket is sufficiently widened by use of outrigger elements.

Drilling and completion of the well is now achieved in the usual manner. Whether or not the well site is productive will usually determine the disposition of the platform. In the event the well is completed and is a producer or capped as a reserve source, the wellhead structure will be kept in place while the jacket is removed.

The latter is achieved by lowering hull H to a floating position and then shattering the piles holding the jacket in place at the mud line. Where such piles are utilized in the instance where the wellhead structure is the sole anchoring member, the connectors joining the jacket and the wellhead structure might be exploded or actuated, thereby permitting the jacket to be lifted. This is done by retracting the legs upwardlythrough the floating hull jacks and clamps, until the lower surface of the jacket clears the top of the wellhead structure. in such condition the floating hull is again supporting the submerged jacket which might now be safely carried or transported to the shallow water assembly location to be lowered onto and engaged with new replacement wellhead structures.

The, platform is now in readiness to be again towed to a drilling site with the new wellhead structure and whereby the jacket might again be lowered and the previously mentioned procedure followed for the drilling and completion operation.

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

lclaim: l. A multiunlt well drilling platform adapted for fixed positioning at an offshore location in a body of water, said platform including: 1

a. a floatable hull;

b. a jacket normally disposed beneath said hull and having a foundation at the lower end thereof adapted for resting on the floor of said body of water,to function as a base for said drilling platform;

c. a wellhead structure removably connected to and carried by said jacket for mounting fluid control equipment connected to a subsurface well, and including means for anchoring said structure to said floor;

d. adjustable linking means operably connecting said floating hull to said jacket whereby said hull, when floating at the waters surface, will suspend said jacket above said floor, and when said jacket is positioned at said floor, said adjustable linking means will supportably maintain said hull above the waters surface;

e. said wellhead structure being separable from said jacket to remain affixed to said floor when separated from said jacket; and

f. said jacket including a vertically aligned docking facility adapted to slidably register with and connect to said wellhead structure.

2. In a drilling platform as defined in claim 1 wherein, said jacket docking facility includes a plurality of docking guide members disposed therein and vertically oriented to slidably register with and releasably engage said wellhead structure when said jacket is lowered onto said structure.

3. In a drilling platform as defined in claim 1 wherein, said jacket includes remotely actuated clamping means adapted to releasably engage said wellhead structure when the latter is re-- gistered in said jacket docking facility.

4. in a drilling platform as defined in claim 1 wherein, said wellhead structure includes pile guide means depending therefrom, and at least one pile positioned in said pile guide means for imbedment into said floor'to anchor said structure.

5. In a drilling platform as defined in claim 1 wherein, said wellhead structure anchor means includes a plurality of upstanding cylindrical pile guides having at least one pile carried therein whereby, the latter may be imbedded into said floor and fastened into said pile guide to anchor said wellhead structure.

'6. In a drilling platform as defined in claim 1 including peripherally spaced upstanding track members disposed longitudinally of said wellhead structure toslidably engage said jacket docking facility when said jacket is lowered through the water and onto said wellhead structure.

Claims

1. A multiunit well drilling platform adapted for fixed positioning at an offshore location in a body of water, said platform including: a. a floatable hull; b. a jacket normally disposed beneath said hull and having a foundation at the lower end thereof adapted for resting on the floor of said body of water, to function as a base for said drilling platform; c. a wellhead structure removably connected to and carried by said jacket for mounting fluid control equipment connected to a subsurface well, and including means for anchoring said structure to said floor; d. adjustable linking means operably connecting said floating hull to said jacket whereby said hull, when floating at the water''s surface, will suspend said jacket above said floor, and when said jacket is positioned at said floor, said adjustable linking means will supportably maintain said hull above the water''s surface; e. said wellhead structure being separable from said jacket to remain affixed to said floor when separated from said jacket; and f. said jacket including a vertically aligned docking facility adapted to slidably register with and connect to said wellhead structure.

3. In a drilling platform as defined in claim 1 wherein, said jacket includes remotely actuated clampIng means adapted to releasably engage said wellhead structure when the latter is registered in said jacket docking facility.

4. In a drilling platform as defined in claim 1 wherein, said wellhead structure includes pile guide means depending therefrom, and at least one pile positioned in said pile guide means for imbedment into said floor to anchor said structure.

6. In a drilling platform as defined in claim 1 including peripherally spaced upstanding track members disposed longitudinally of said wellhead structure to slidably engage said jacket docking facility when said jacket is lowered through the water and onto said wellhead structure.