Articulated Marine Structure With Prepositioned Anchoring Piles

Abstract

The invention relates to a marine structure for use in an offshore body of water where piling is required to hold the structure in place. It relates in particular to a floatable marine structure which is sufficiently buoyant to be floated to an offshore working site carrying a plurality of positioning piles thereon. At the site at least a part of the structure is ballasted to sink to the ocean floor, the prepositioned piles are thereafter sequentially driven into the substratum.

Description

BACKGROUND OF THE INVENTION

A marine platform of the type presently disclosed can serve many purposes and may be utilized by a number of industries. In the specific instance of the petroleum industry, the platform would be positioned in an offshore body of water to drill into and explore the substratum for the purpose of producing crude oil and gas. Normally, in water depths up to several hundred feet such marine platforms would be attached to the drilling site by piles or similar retaining means.

In the instance of marine structures and platforms built for use in Arctic tideland waters the problem of rigidly positioning such a unit is compounded by the presence of floating ice. More specifically, it is known that for most of the year the presence of large ice floes as well as moving sheet ice virtually prohibits the use of any sort of rigidly fixed platform. The permanent structures which have been proposed for use, are built on islands erected at a drilling site, which islands are designed to be of sufficient bulk to resist the displacing force of sheet ice and/or icebergs which are prevalent in areas like those adjacent to Alaska such as the Bering Sea.

It is here proposed however, that as an alternate to the large expenditure involved in such man made islands, the marine platform be designed to resist ice forces by means of piling driven or drilled and cemented into place at relatively high angles of batter. If it is later desired to move the platform it could be disconnected by cutting off the piling below the mud line by means of conventional shaped explosive charges or any of a number of inside cutting devices and thence refloated and moved to a new location.

To utilize a drilling structure of this type to optimal advantage, the latter would have to be mobile to the extent that it could be readily towed to a drilling site and thereafter submerged to assume a fixed position. Thus, either the floatable unit itself, or a portion thereof must be capable of being ballasted to submerge at the site for positioning drilling equipment such as a derrick, rotary table, etc. beyond the water's surface to protect such equipment from the elements.

While it is known in the prior art to utilize piling for anchoring an offshore structure at a drilling site, such platforms are generally of the type wherein the pilings are inserted through the various support legs that extend from the water's surface downwardly to the oean floor. The piling in such an instance can be made of sufficient length to penetrate the substratum to a desired depth. Further, the amount of piling provided for holding the platform is normally carried on a barge or similar vessel which accompanies the platform as it is either carried or floated to a desired site.

Normally, platforms of the type contemplated will carry pile driving or pile drilling apparatus mounted in conjunction with a crane type derrick or with the main drilling structure whereby piles can be individually driven or drilled into the substratum. In achieving such an operation, there are of course problems concerning the piling since the piles must be transferred from a carrying vessel, in lengths which can be easily handled, welded into a continuous length, aligned through a support leg, and thereafter driven into the substratum with or without the aid of a stinger at the pile upper end.

To facilitate the positioning operation of such a platform and to sharply reduce the time for making up and driving the piling, the presently disclosed structure is of the semi-submersible type such that it may be readily floated to a drill site in a buoyed condition. Thereafter, it can be ballasted to sink and rest the lower portion thereof at the ocean floor.

A work deck carried on the structure's upper side can be raised to an elevated working height above the water's surface. Immediately thereafter, a plurality of prepositioned anchor piles can be driven downwardly through the structure's lower end or base and into the substratum for a sufficient distance to rigidly fix said base and prohibit movement thereof in spite of lateral forces exerted by the wind, waves, ice, etc.

Offshore structures of the type described are most commonly used in the drilling for and production of petroleum fluids as crude oil and gas. They are particularly useful in Arctic waters such as those surrounding Alaska which are generally shallow and where heavy ice concentrations prohibit a normal floating or fixed platform operation.

DESCRIPTION OF THE DRAWINGS

In the drawings, FIG. 1 illustrates a marine platform of the type contemplated, floating at the water's surface. FIG. 2 is similar to FIG. 1 showing the platform submerged. FIG. 3 is a top view of FIG. 1. FIG. 4 is an enlarged segmentary view of a portion of the platform in FIG. 2. FIG. 5 is a side view in partial cross section of FIG. 4 and FIG. 6 is an end view of the slide member shown in FIG. 5.

In the drawings, FIG. 1 illustrates a platform 10 of the type contemplated shown in the floating position at the surface of a body of water 11. The platform lower end comprises a base or a hull 12 which conveniently assumes a circular, octagonal or other multi-sided shape. In the normal submerged position, base 12 assumes a generally horizontal position at the ocean floor to facilitate the work from deck 13.

Base 12 carries an upstanding, generally elongated support column 14 which is fixed at its lower end in a cavity or sleeve formed within base 12, and which extends for a sufficient height as to position working deck 13 beyond the water's surface. Thus, for each particular drilling location or site, the length of support column 14 can be adjusted by removal therefrom or by addition thereto of a particular length of column segment.

The primary function of this portion of the marine structure 10 is to properly support working deck 13 in such a manner to permit movement of the latter therealong. Column 14 thereby embodies means for engaging jacks, clamps or similar mechanisms not presently shown whereby the periphery of the column can be releasably engaged with said jacks to elevate the deck a predetermined or desired distance along the column. As mentioned, the essential purpose of this mobile feature is that deck 13 can be elevated beyond the water's surface during a drilling operation. Further, as the structure is being propelled between drilling sites deck 13 is lowered to as close a position as possible with respect to hull 12 whereby to promote the sea worthiness of the entire unit.

The marine structure 10 is provided with means to accommodate a plurality of elongated piles 16 which are supported between hull 12 and deck 13. These piles are so arranged as to be firmly held while they are being transported, and yet readily released so as to be inserted into the substratum.

The number of piles actually used at any particular working site will be determined in accordance with the composition and consistency of the substratum at the working site. Although the lower portion or hull 12 of the structure when in the ballasted condition is relatively heavy to provide a firm foundation for the upper portion, the use of piling is dictated by the adverse ice and soil conditions often encountered in the waters where such platforms are to be used. Such conditions necessitate the safety factor of anchor piling for holding the drilling structure at the site.

Base or hull member 12 comprises in effect a barge-like vessel formed of a plurality of closed, individually controlled buoyancy tanks such as 17 and 18. By regulation of the buoyancy of the respective tanks, both the attitude and disposition of base 12 can be readily controlled between the ocean floor, and the water's surface.

Base 12 is preferably formed of welded steel or reinforced concrete sections of sufficient strength and so reinforced to resist the external forces or pressures expected in the depths of water where platform 10 would normally be positioned. The respective compartments 17 and 18 within the hull, are individually separated by discretely placed bulkheads and panels. Thus, selective adjustments of the buoyancy of said compartments results in the entire unit being raised to a floating position at the water's surface, or lowered to a desired depth, or positioned at a desired attitude.

While not presently shown, each compartment 17 and 18 is connected with a buoyancy system which is controlled from the water's surface and adapted to urge a fluid ballasting medium such as water or drilling mud through the respective compartments. Regulating the flow of said ballasting fluid achieves the purpose of adjusting the disposition of hull 12 as required.

The hull 12 as mentioned, can assume a number of shapes compatible with its function. However, as shown in FIG. 3 in the instant embodiment the hull is formed in a generally circular shape to better accommodate the prepositioned piles 16 when the latter are being transported to the working site.

Elongated support column 14 is positioned centrally of and fastened to the hull 12 for the purpose of properly supporting the deck 13 thereon. Said column 14 in its preferred structure includes a cylindrical, elongated member having sufficient strength to safely bear the compressive weight of working deck 13 together with the ancillary drilling equipment. Column 14 must also be designed to withstand the crushing and bending forces imposed on the unit by moving ice. However, the essential purpose of this unit remains the same, that is to support deck 13 in a desired manner so as to permit the latter to be leveled and vertically adjusted to facilitate a drilling operation.

Column 14 is further provided with means on the outer surface such as indentations or slots or similar facilities, whereby to accommodate the clamping or jacking mechanisms carried on deck 13. The latter are actuatable to engage said column outer surface whereby to adjust the horizontal position of the deck with respect to the water's surface.

As further mentioned, said column 14 can be either elongated or shortened to best accommodate the deck for a particular drilling site. Further, column 14 can be elongated by welding thereto column segments at such time as the platform reaches a working site. Thus, the floatability of platform 10 can be adjusted to make it more seaworthy during the transportation when it is most susceptible to damage by storms, inclement weather, or the like.

Working deck 13 as mentioned, is slidably carried on the column 14 outer surface and guided therealong by jacks on or within the deck. Such apparatus is well known in the art and utilized for the purpose noted of raising a platform or deck on one or more legs which are normally positioned in the floor of a body of water.

Suffice it to say that the respective climbing jacks are individually operable, and so arranged to permit leveling of the deck 13 with respect to the water's surface in such an instance where column 14 is found to be canted from a vertical disposition.

Deck section 13 of course accommodates the normal complement of drilling equipment as is found on any marine structure adapted to this purpose. For example, the deck carries preferably at its center, an upstanding derrick 19 which is so positioned to straddle the upper end of column 14 whereby one or more wells might be drilled down through the column thus protecting the drilling operation from movement of the surrounding waters. Also carried on the deck 13 is the necessary draw works, rotary table and crews' quarters, etc. which will permit a complete, self contained drilling operation.

The deck further supports in the usual manner one or more cranes 21 which are so positioned on the deck to be suspended over the sides to reach a vessel at the water's surface and to assist in the pile driving operations.

During the platform anchoring operation, deck 13 also supports a pile guide means 22 which is operably carried thereon and adjustable to be positioned with respect to a pile 16 as will be herein noted.

The plurality of elongated piles 16 are positioned on the marine structure in such a manner that they can be readily carried to a drilling site and thereafter released as to be in a position to be driven into the substratum beneath submerged hull 12. Toward this end, hull 12 is provided with a number of sleeves or transverse openings 23 adapted to slidably receive a pile 16 therethrough whereby to guide the latter toward its embedded position in the substratum. Thus, the piles 16 which are normally cylindrical in cross section and have a relatively heavy wall, can withstand both the shearing and bending stresses imposed thereon as result of wave and ice action against the platform.

As shown in FIG. 1, the respective piles 16 are carried with the lower end disposed in alignment with the transverse opening or sleeve 23 formed in the hull 12. The respective piles 16 are canted inwardly at their upper ends toward the center of platform 10, and further supported at the periphery of the working deck 13. Toward facilitating the carrying of these anchoring members, deck 13 can be elevated to any desired position along the central or support column 14. The latter is further provided with means for releasably holding the respective piles in a fixed position at the periphery of the deck so as to maintain the stability of the unit even though the latter is subjected to heavy wave conditions which would cause it to pitch and roll.

The mobile pile guide means 22 carried on working deck 13 is such as to be operable along the deck and so positioned at the edge of the latter as to accommodate and guide a single pile as the latter is driven into the substratum. Thus, and as shown in FIGS. 4 and 5 after platform 10 has been propelled to a drilling site, the controlled buoyancy hull 12 is flooded or ballasted so that the latter sinks to the floor of the offshore site. Deck 13 comprises a water tight hull and provides both buoyancy, and a stabilizing effect during the sinking operation. As base 12 is lowered to the bottom, deck 13 is jacked up along column 14. During this operation of course the means securing the piles is adjusted to permit the rising deck 13 to slide along the piles' edges and yet maintain a releasable grip on the latter so that they are not displaced vertically due to the movement of the deck and/or the entire platform.

As hull 12 becomes firmly positioned on the ocean floor, and deck 13 is elevated above the water to the desired elevation, piles 16 become aligned with hull openings 23 and are released and embedded one by one into the substratum. This is achieved by aligning the pile guide mechanism 22 with a pile 16 to be driven and thereafter lowering the latter or adding pile sections thereto should the necessary pile lengths require such operation.

The pile guide mechanism 22 includes carriage 26 which is operably carried on a pair of tracks 27 and 28, and is shown in FIG. 5. The first of said tracks 27 is disposed at the deck upper surface and extends about the periphery thereof. Lower track 28 similarly is disposed at the deck periphery and arranged to exert a horizontal force against the carriage 26 to properly support a pile.

A plurality of support wheels 31 are journaled at the carriage upper end and supported by the circular upper track 27. In a similar manner a plurality of laterally positioned guide wheels 33 and 34 engage track 27 whereby to stabilize the carriage as the latter is moved between operating positions. A similar arrangement is disposed at the lower portion of the carriage 26 embodying a plurality of guide wheels 36 and 37, which engage a flange on the said lower track 28.

In FIG. 6 the elongated pile lead or slide 40 is shown extending outboard from the platform and is supported on the carriage by hinge 35 near the carriage upper end, and connected with pins 39. Thus, said pile lead 40 is so arranged to adjust its vertical angularity whereby to best accommodate a pile as the latter is being driven into the substratum.

The angular disposition of pile slide 40 is regulated by one or more lower hydraulic cylinders 43 or an appropriate mechanical linkage carried on carriage 26, which cylinders or linkages are secured to leads 46 and 47 at the slide undersurface. Thus, by regulating the disposition of the respective cylinders or linkages, the angle of the pile slide 40 is adjustable to support the upper end of a pile 16 during the driving operation.

Said pile lead or slide 40 comprises a pair of parallel extending sides 46 and 47 which are fastened by transverse frames 51 extending therebetween as shown in FIGS. 4 and 6. A plurality of concave faced rollers 52 are disposed along the pile slide, and journaled to permit free movement thereof as a pile 16 is progressively driven downward.

FIG. 7 illustrates a cross section of slide 40 with pile driving hammer 50 operably supported thereon by rollers 48 and 49. The hammer is supported vertically by the pile during the driving operation and is handled on and off the pile by a crane operably guided on tracks 31 and 32.

Operationally, as a pile 16 is restrained in the manner noted along the pile lead 40, it is driven downwardly therethrough by a pile driver 50. The latter comprises an apparatus, although not presently shown, which is well known in the art and is normally structured as to assume a desired angle. In the instant arrangement, it would be adapted to accommodate the particular pile being driven. Thus, the pile driving mechanism is disposed adjacent the pile supporting carriage 26 and the driving mechanism is controllably actuated to drive a pile downwardly along lead 40. As the upper end of the pile reaches the lower end of said lead 40 a removable pile follower can be inserted in the pile and the hammer replaced on the follower to complete the driving operation.

Should the required pile length necessitate the use of additional pile segments, the latter can be added by welding or other suitable connectors known in the industry.

As pile 16 is driven to its desired depth the upper end thereof is fastened within the hull passage or sleeve 23. Such fastening can be by mechanical, or other engaging means between the hull and the pile, or in the conventional manner of utilizing cement for achieving the necessary bond.

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.

Claims

We claim:

1. A floatable marine structure adapted to be fixedly positioned to the floor of an offshore site which comprises;

a hull, including controllable buoyancy means, the latter being operable to regulate the disposition of said marine structure within a body of water,

support means carried on said hull and extending upwardly therefrom,

a working deck operably received on said support means and being longitudinally movable along the latter to regulate the disposition of said working deck with respect to said hull, and

anchor piles removably carried on said marine structure, being aligned in position to be embedded into the substratum beneath said body of water when said hull is submerged to rest on the floor of the latter,

pile guide means operably carried on said working deck and being adjustable to slidably support a pile as the latter is embedded into said substratum, and

a track carried on said working deck adjacent to the peripheral edge thereof, said pile guide means being operably supported on said track.

2. In a marine structure as defined in claim 1, wherein said track includes; a portion thereof being disposed outboard of said deck, and said pile guide means includes a carriage extending between the deck edge to be supported on said track.