US3653219A

US3653219A - Marine platform

Info

Publication number: US3653219A
Application number: US889379A
Authority: US
Inventors: George E Mott
Original assignee: Texaco Inc
Current assignee: Texaco Inc
Priority date: 1969-12-31
Filing date: 1969-12-31
Publication date: 1972-04-04
Anticipated expiration: 1989-04-04

Abstract

The invention relates to a drilling or production platform adapted to drill one or more submerged wells into an offshore substratum. The platform is self-buoyant to be floated to and from a drilling site, and comprises a work vessel adapted to be detachably connected to the ocean floor by an elongated, rigid mooring and drilling column. The latter is anchored to the ocean floor at a nonrigid connection whereby to permit limited pivotal movement of the column in response to displacing forces. The column houses a number of drill string or casing guides together with flow control means. The column upper end is adapted to detachably engage the vessel whereby to fixedly locate the latter above a subterranean drilling site.

Description

Unite States Patet [151 3,653,219

Mott 1 Apr. 4, 1972 54 MARINE PLATFORM Primary Examiner-Jacob Shapiro [72] lnvemor' George Metame La' Attorney-Thomas H. Whaley and Carl G. Ries [73] Assignee: Texaco, Inc., New York, NY. 22 Filed: Dec. 31, 1969 [57] ABSTRACT Appl. No.: 889,379

The invention relates to a drilling or production platform adapted to drill one or more submerged wells into an offshore substratum. The platform is self-buoyant to be floated to and from a drilling site, and comprises a work vessel adapted to he detachably connected to the ocean floor by an elongated, rigid mooring and drilling column. The latter is anchored to the ocean floor at a nonrigid connection whereby to permit limited pivotal movement of the column in response to displacing forces. The column houses a number of drill string or casing guides together with flow control means, The column upper end is adapted to detachably engage the vessel whereby to fixedly locate the latter above a subterranean drilling site.

4 Claims, 4 Drawing Figures PATENTEDAPR 41972 3,653,219

SHEET 1 OF 2 TIEJ. /9

BACKGROUND OF THE INVENTION In the search for future sources of crude oil and gas, it has become necessary to extend the search area greater distances into deeper offshore waters. While the basic equipment for carrying out exploratory or drilling operations at an offshore location is similar to those for land based units, the marine environment has introduced many problems both unexpected and otherwise.

One of the more prevalent, and frequently unavoidable problems associated with any offshore operation results from natural causes. More exactly, the platform is subjected to continuous exposure to all forms of adverse weather conditions. Thus, the platform is required to operate efficiently in spite of high winds and turbulent waters. In extreme instances such as when a severe storm or hurricane approaches, the drilling operations are of course suspended and personnel evacuated from the platform to safety.

In the instance of offshore platforms rigidly fixed to the ocean floor, such units cannot readily be protected and must be engineered sufficiently strong to withstand expected high winds and turbulent waters. In the instance of floating or anchored vessels, the drill ship relies on the ability of mooring lines and anchors to maintain the ships position. This latter method, although effective to a large extent, does have limitations. For example, quite often moored platforms under severe weather conditions will drag their anchors and be dis placed many miles from the drill site.

The major displacing forces which act against any offshore platform are the wind and surface waves. Relatively minor forces such as water currents and wave effects do exert a minimal force against the under water portions of the platform. However, the latter constitute a relatively insignificant factor as contrasted with the above water forces.

For relatively shallow offshore waters the above noted operating circumstances are normal. As more distant offshore areas become available however, drilling and producing operations must be adapted to deeper waters. At present, the maximum water depth in which a fixed platform can feasibly operate does not often exceed about 350 feet. It is contemplated nonetheless that within the near future, operations at depths up to and beyond 1,000 feet will be considered necessary and even normal. For such deep waters it can be appreciated that the problems associated with any offshore operation will be substantially intensified.

It is therefore one of the objects of the invention to provide a nonrigidly fixed platform for use in deep offshore waters. A still further object is to provide a rigid moving column and conductor housing which is nonrigidly retained at the ocean floor whereby to limit movement of a floating drill vessel attached to the column at the water's surface.

Toward achieving the stated objectives and overcoming the mentioned problems, the hereinafter disclosed marine installation comprises a plurality of separably connected components. These include a floatable vessel adapted to operate at the surface of a body of water, and an elongated mooring column. The latter is disposed at a substantially vertical attitude in the body of water being of sufficient length to extend from the ocean floor to a point at or near the waters surface. The columns lower end is stabilized by anchor means imbedded at least partially into the ocean substratum. A connection between said column and anchor means, comprises essentially a nonrigid union a that affords a degree of pivotal movement to the column about its anchored end. The column is adapted at its upper end to releasably engage the floating vessel or other floating member, whereby to position the latter over a drill site. One or more conductor casings are incorporated into the mooring column to accommodate and protect well conductors or conduits which extend upwardly to the waters surface from a well bore.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a vertical elevation of a marine platform of the type contemplated shown as positioned in a body of water and anchored to the floor thereof.

FIG. 2 is a top view of the marine platform shown in FIG. 1.

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

FIG. 4 is a segmentary view on an enlarged scale illustrating a portion of the platform shown in FIG. 1.

Referring to FIG. 1, a marine installation of the type contemplated is shown, which includes in essence a vessel 10 adapted to perform a drilling and/or producing operation at an offshore location. The vessel is controllably buoyant to regulate its draft by raising or lowering in the water for a particular circumstance.

Elongated mooring column 11 extends in a substantially vertical direction from a position adjacent the waters surface to the marine floor. Said column 11 includes a plurality of

upstanding comer posts

12, 13 and 14 which define a rigid connecting link between vessel 10 and the ocean floor. The column further includes centrally positioned upstanding conductor casings 16 which are disposed parallel to, and spaced inwardly of the columns. An anchor means 17 imbedded into, or resting at the ocean floor, operably engages the lower end of said column 1 1 whereby to permit restrained pivotal movement of the latter about the anchor.

In the usual offshore drilling operation, a well is drilled or produced in a manner similar in many respects to the counterpart operation on shore. The well bore is formed in the conventional manner utilizing essentially a derrick supported drill to form a bore. Well casing is then lowered and connected into the bore. As one well is completed, one or more wells can be further drilled adjacent to the first thereof although spaced a desired distance therefrom. The number and disposition of such wells is of course contingent on the yield ability of the oil source being tapped.

Drilling vessel 10 embodies a buoyant platform or deck 18 which supports an upstanding derrick 19 together with the usual draw-works 21, rotary table, and other necessary equipment ancillary to a drilling operation. Vessel 10 is preferably, although not essentially of the semi-submersible type including discretely arranged tank-like columns 22, disposed about the vessels periphery whereby its buoyancy can be regulated to adjust the disposition thereof in the water. Vessel 10 can thus be raised in the water, floated to a desired drill site, and thereafter by adjusting its buoyancy characteristics, be lowered into the water for engaging mooring column 11 upper end as a prelude to a drilling operation.

Drilling vessel 10 in accordance with the invention, can be of a barge type which is towed to and from location by tugs, tow boats or the like. It can also be of the self-propelled type incorporating a stabilizing system or guidance means whereby to maintain itself at a desired location. The vessel 10 does however embody a docking facility which permits it to be positioned over or adjacent to a mooring column 11.

As shown in FIG. 2, such a facility includes a slotted or indented portion of the deck 18 into which the mooring column 11 upper end is received. Said facility can also embody means forming a side opening in vessel 10 whereby the latter can approach the mooring column and be positioned directly thereabove.

In the instance of a barge type of vessel 10, following the accepted practice, the vessel is anchored by a series of

anchor rodes

23 and 24 that extend outwardly from the vessel to anchors disposed about the latters periphery. By adjusting the tension on the respective rodes, the vessel can be aligned properly to register with the upper end of the mooring column 11.

Vessel 10 is further provided with a plurality of

mooring winches

26, 27 and 28 disposed at the vessels deck in substantial vertical alignment with the upper ends of corresponding connecting points on mooring column 11. Said mooring winches in the instance of unit 28, include a flexible cable 29 having a coupling 31 at the extremity thereof to removably engage a fastening element 32 at the mooring column upper end. Cable 29 is carried on a powered wind-up mechanism whereby the cable can be reeled in to draw the vessel and mooring column 11 into close engagement.

Mooring column 11 is formed of a plurality of upstanding hollow, metal corner posts 12, 13 and 14, which define the columns periphery, and which are disposed in a generally upright position at an offshore location by adjustment of their buoying capabilities. The column lower end is positioned adjacent to but spaced from the ocean floor. The column upper end can further be adapted to support a deck or walkway 36 above the waters surface. Said deck 36 provides ready access to fluid control equipment such as valves 37. The latter is representative of the usual flow regulating and control equipment such as a christmas tree installation normally associated with a gas or oil well head.

The respective corner posts 12, 13 and 14 are presently shown arranged in a triangular pattern. The number and arrangement of corner posts utilized however is contingent on the water depth, the number of wells accommodated, and other factors. The instant three post pattern is found to provide maximum strength and uniform stability to the column under all operating conditions.

The respective corner posts are laterally reinforced at the upper end by

transverse members

38, 38' and 38". The latter are connected to and extend between the respective upright posts, and are preferably of cylindrical metallic construction. The transverse members can further incorporate buoyancy and storage means such as internal tanks which are jointly communicated with a pumping system actuated from deck 36.

The

posts

12, 13 and 14 are commonly braced along their length by intermediate structural elements such as 39 and 41. The latter are so arranged to afford maximum structural rigidity to the column 11 under the most severe expected operation conditions.

Column 11 is further provided with guide means to facilitate a well drilling operation particularly in deep water. The column thus includes a plurality of casing guides 16 which extend substantially the entire column length. Said guide members 16 are formed of elongated cylindrical conduits of sufficient diameter to guide a drill string and bit as the latter is moved between the drill ship and the well bore. Conductor guide 16 is supported within the framework of column 11 and

brace members

42, 43 and 44 respectively.

Each corner post, of which 12 is representative, comprises an elongated tubular member having buoyancy tanks incorporated therein and which are connected with the previously mentioned pumping system. Said corner post 12 is further fabricated to be at least partially water tight by being sealed off, whereby column 11 can be floated to a drilling site. When in the upright installed position, post 12 will be largely submerged in the water with a relatively minor portion of the upper end projecting beyond the waters surface. Because of the elongated submerged portion which is affected relatively little by wave disturbances, the post will maintain a substantially static attitude. Further, this static condition will prevail regardless of wind or water disturbances at the surface.

Comer post 12 thus comprises a hollow lower section 46 which depends from a larger diameter buoyancy belt 47 into which buoyancy tanks are built. Said belt supports a constricted neck 48 which protrudes above the waters surface. The configuration of post 12 upper end 48, because of its narrowness, offers virtually no resistance to displacing forces.

The lower end of post 12 is provided with coupling means for engaging anchor means 17 whereby to permit restrained pivotal movement of column 11 about the anchor. Said coupling means can include a plurality of cables or chains normally maintained under tensional stress, which extend from the columns lower end to the anchor. It can further include a socket formed in the post lower end to slidably engage a mating anchor pillar whereby to permit the required freedom of movement therebetween.

As presently shown post 12 is provided with a cylindrical sleeve 51 extending from the lower end thereof vertically upward. Said sleeve is slidably registered with an upright pillar 52 depending from anchor means 17. The diameter of sleeve 51 is sufficiently large to remain in free sliding engagement with said pillar even though column 1 1 is displaced to an offset, canted position.

Anchor means 17 is disposed at the floor of the submerged drilling site and comprises one or more heavy foundation members. When incorporated into a single unit, anchor means 17 includes a heavy foundation body or pad formed of reinforced concrete or similar material. Said body is provided with passage means extending vertically therethrough to accommodate drill strings and well casing lowered through the casing guide members 16. The upper surface of said anchor means foundation member supports one or more upright pillars 52 which are preferably formed of heavy walled steel, having the lower ends thereof imbedded in the foundation. Said pillars are so spaced apart to register the corresponding column in sleeves depending from the column respective corners posts.

To install the marine structure at an offshore site, column 11 is made buoyant along its entire length by evacuation of buoyancy tanks in both belt 47 and in post lower sections 46. At the site, anchor means 17 is lowered to the ocean floor from a barge or similar transport vessel whereby to dispose the pillars 52 in a substantially upright disposition. The buoyancy of column 11 is thereafter adjusted by flooding of tanks in lower section 46 of the respective corner posts whereby the column will assume a substantially vertical disposition in the water. After aligning the respective sleeves 51 above the pillars 52, the buoyancy of the column is further reduced whereby to lower the entire unit onto the respective pillars thereby establishing the operable coupling between said members.

Vessel 10 is floated as to be disposed adjacent to, or over the upwardly protruding ends 48 of column 11. The attaching cables 29 are lowered from the cable take-up mechanism on vessel 10 to engage the upper ends of the respective corner posts at fastening element 32. By taking in the cable 29 on the wind-up mechanism, the cable thereby draws column 11 and vessel 10 into operable relationship. Simultaneously, the buoyancy of said vessel 10 is adjusted whereby to establish an upward pull on the column and maintain a constant tension thereon.

Obviously, many modifications and variations of the invention, as hereinafter 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.

I claim:

1. The combination in a marine structure for drilling a submerged well in an offshore body of water which includes;

a vessel embodying well drilling apparatus and controllably variable buoyancy therein;

an elongated rigid mooring column having opposed upper and lower ends, said column being normally disposed uprightly in said body of water and having means to controllably regulate the buoyancy of said column in the water,

said elongated rigid column including at least one controllably buoyant corner post, and at least one elongated conductor casing spaced longitudinally from and parallel to said at least one comer post,

said elongated conductor casing having an upper end extending upwardly beyond the surface of said body of water, and having fluid control means carried therein and being operable to regulate the flow of fluid through said conductor casing.

2. In a marine structure as defined in claim 1 wherein said elongated mooring column includes; a plurality of uprightly and spaced buoyant comer posts, lateral bracing means interconnecting said respective corner posts to rigidly position the same, and at least one elongated conductor casing spaced intermediate and extending parallel to said corner posts.

peripherally arranged in a general triangular shape and having said at least one conductor casing disposed centrally of said three posts, said support means extending intermediate and connected to said posts and said at least one conductor casing for positioning the latter.

Claims

1. The combination in a marine structure for drilling a submerged well in an offshore body of water which includes; a vessel embodying well drilling apparatus and controllably variable buoyancy therein; an elongated rigid mooring column having opposed upper and lower ends, said column being normally disposed uprightly in said body of water and having means to controllably regulate the buoyancy of said column in the water, said elongated rigid column including at least one controllably buoyant corner post, and at least one elongated conductor casing spaced longitudinally from and parallel to said at least one corner post, said elongated conductor casing having an upper end extending upwardly beyond the surface of said body of water, and having fluid control means carried therein and being operable to regulate the flow of fluid through said conductor casing.

2. In a marine structure as defined in claim 1 wherein said elongated mooring column includes; a plurality of uprightly and spaced buoyant corner posts, lateral bracing means interconnecting said respective corner posts to rigidly position the same, and at least one elongated conductor casing spaced intermediate and extending parallel to said corner posts.

3. In a marine structure as defined in claim 1 wherein; said plurality of corner posts are peripherally arranged about said mooring column, said at least one conductor casing being disposed inwardly of said peripherally arranged posts.

4. In a marine structure as defined in claim 3 wherein said plurality of corner posts include three of said posts peripherally arranged in a general triangular shape and having said at least one conductor casing disposed centrally of said three posts, said support means extending intermediate and connected to said posts and said at least one conductor casing for positioning the latter.