US3224204A

US3224204A - Method of anchoring an offshore structure

Info

Publication number: US3224204A
Application number: US302418A
Authority: US
Inventors: Christian H Siebenhausen
Original assignee: Shell Oil Co
Current assignee: Shell USA Inc
Priority date: 1963-08-15
Filing date: 1963-08-15
Publication date: 1965-12-21
Anticipated expiration: 1982-12-21

Description

Dec. 21, 1965 c. H. SIEBENHAUSEN 3,224,204

METHOD OF ANCHORING AN OFFSHORE STRUCTURE Filed Aug. 15, 1963 5 Sheets-Sheet 1 FIG. I

INVENTOR:

C.H. SIEBENHAUSEN HIS AGENT D 1965 c. H. SIEBENHAUSEN 3,224,204

METHOD OF ANCHORING AN OFFSHORE STRUCTURE Filed Aug. 15', 1963 Y s Sheets-Sheet 5 INVENTOR:

C.H. SIEBENHAUSEN HIS AGENT United States Patent 3,224,204 METHOD OF ANCHORING AN OFFSHORE STRUCTURE Christian H. Siebenhausen, Midland, Tex., assiguor to ghelll Oil Company, New York, N.Y., a corporation of e aware Filed Aug. 15, 1963, Ser. No. 302,418 7 Claims. (Cl. 61-465) The present application is a continuation-in-part of copending application, Serial No. 65,308, filed October 27, 1960.

This invention relates to offshore structures of various types adapted to be anchored to the ocean floor for use in offshore operations. More particularly, the invention is directed to a structure such as an oil well drilling platform or production platform which may be secured to the ocean floor in a relatively simple and inexpensive manner which permits the structure to be subsequently readily moved and anchored at another location.

In drilling and producing wells at offshore locations, large structures are employed which are positioned in the ocean floor and extended upwardly above the surface of the water generally to a distance equal to the maximum wave height to be encountered in that area. An offshore structure generally comprises a footing or base element, which may be in the form of a framework or a pontoon which rests on the ocean floor, with a plurality of vertical legs extending upward-1y above the surface of the water where an operating platform is secured thereto for supporting various pieces of equipment. If the platform is to be used for drilling of wells, drilling equipment including a drill rig and auxiliary equipment as well as living quarters for the crew and storage facilities are usually mounted on top of the platform. If the platform is to be used for production purposes, various m'anifolding equipment, storage tanks, meters and treating apparatus are generally mounted on the platform. Platforms of this type are relatively large in size and may range up to 300 feet in length. A typical platform for use in the drilling of wells may have a footing or pontoon that is 80 feet wide, 140 feet long and 15 feet high.

After an offshort structure of the above-described type has been positioned on the ocean floor at a selected location, it is the general practice to anchor the structure to the floor by driving piles down through the vertical legs of the structure so that they penetrate up to 300 feet or more in the ocean floor. In general, the depth to which the piles are sunk depends on the nature of the soil on the ocean floor. Thus, the harder the formation beneath the structure the shorter the piles that are used. While some of the piles that are driven through the legs of the structure are cut off at the level of the top of the legs of the structure and then welded or otherwise connected to the leg, it is also a practice at times to install stub piles in the bottoms of the legs and through the footing of the structure. Stub piles are piles that do not extend to the surface of the water. Usually they only extend up to the top of the footing of the offshore structure, thereby providing support for the structure without causing an obstruction to the wave action.

In shallow water, piles may be satisfactorily driven into the ocean floor with conventional tools employed, such as with a pile driver. However, in deep water, as the mass and the unsupported length of a pile increases, the efficiency of a driving hammer is reduced. In driving a stub pile into the ocean floor it is necessary to install a follower pipe or section of pile which extends from the top of the stub pile to above the surface of the water so that it can be contacted by a driving hammer. When 3,224,204 Patented Dec. 21, 1965 a stub pile has been driven to the desired depth, the follower pile is removed together with the driving mechanism and the stub pile is then usually cemented in place with the top of the stub pile being cemented to the footing of the offshore structure. If it is later desired to remove the offshore structure, for example in the case of a dry (non-productive) well, the stub piles can be cut off at a point below the footing of the structure in any conventional manner and the offshore structure may then be used at another location. However, prior to using the offshore structure at another location, it is necessary to remove the top of the stub pile which is still cemented in the footing or leg of the structure. In order to carry out this operation it is often necessary to tow the structure back to a harbor or dry dock.

It is, therefore, a primary object of the present invention to provide an offshore structure which may be readily anchored to the ocean floor by means of stub pile and later disconnected readily from the stub piles and moved to another location where it is again readily anchored to a second set of stub piles without the necessity of carrying out any major construction or repair work on the offshore structure.

A further object of the present invention is to provide a method and apparatus whereby an offshore structure may be readily connected and disconnected from stub piles at a series of offshore locations.

Another object of the present invention is to provide a method whereby an offshore structure having a plurality of legs may be anchored to the ocean floor without installing piles in the legs, so that the legs may be employed more efficiently, such as to form fluidtight chambers which aid in floating the structure to its location, or serve as housing means for various service lines or pipes for flooding or evacuating a fioatable base secured to the bottom of the substructure.

These and other objects of this invention will be understood from the following description taken with reference to the drawing, wherein:

FIGURE 1 is a diagrammatic view illustrating a platform structure positioned on the ocean floor and anchored thereto by means of piles extending through anchor jackets;

FIGURE 2 is a diagrammatic view taken in partial longitudinal cross-section of one stub pile shown as anchored to an anchor jacket;

FIGURE 3 is a diagrammatic view taken in partial longitudinal cross-section of the stub pile and anchor jacket of FIGURE 2 after they have been disconnected from each other but while they still remain positioned together;

FIGURE 4 is a diagrammatic view taken in partial longitudinal cross-section of the anchor jacket of FIGURE 3 after it has been partially raised off the stub pile which remains in the ocean floor;

FIGURE 5 is a diagrammatic view taken in partial longitudinal cross-section of a portion of a stub pile after it has been cut off and partially raised out of the anchoring jacket in the footing of the offshore structure; and

FIGURE 6 is a view taken in partial longitudinal crosssection of another form of a well jacket and its position in a footing of an offshore structure.

Referring to FIGURE 1 of the drawing, an offshore structure is shown as comprising a plurality of support members or

legs

11, 12 and 13 interconnected by means or bracing members 14and fixedly secured to a base member 15 which rests on the ocean floor 16. While a threelegged structure is shown from ease of illustration, it is to be understood that the structure could employ any number of legs which are usually arranged to outline a geometrical figure having a closed perimeter. Also, in some cases, instead of employing a plurality of legs extending upwardly from the base member or footing 15,

there may be a single large diameter leg or caisson extending upwardly from the base member or footing to support a deck thereon. The

legs

11, 12 and 13 are generally tubular, being legs formed of large diameter pipe. However, in some circumstances they may be solid members, such as I-beams. The base member 15 is shown as being a unitary structure comprising a series of interconnecting members which serve to reinforce it. In some structure the base member 15 may be covered with sheet metal or other material to form a buoyancy tank adapted to be flooded or evacuated so as to form a float by which the entire structure may be raised or lowered in the water. Mounted on top of the

legs

11, 12 and 13, at a suitable distance above the surface of the water 17, is an operating platform or deck 18.

Fixedly secured to the base member or footing, preferably near the outer edge thereof, are a series of

anchor jackets

20, 21 and 22 which may take the form of short sections of tubular pipe having an upper portion that preferably extends above the base member or footing 15 while the lower portion of the jacket is fixedly secured, as by welding, within the base member or footing 15 or on the outer edge thereof. The

anchor jackets

20, 21 and 22 are shown as containing

stub piles

23, 24 and 25 which have been driven into the ocean floor 16 in any conventional manner. Elements 26 represents any suitable pile driver or drilling mechanism for driving or drilling the piles into the ocean floor. During this drilling or driving operation a follower pile 27 may have been employed to get the top of the stub pile 23 down to the desired depth. Alternatively, the stub pile 23 could be cut off at the top when it had reached the desired depth with the upper cut off portion of the pile being withdrawn to the platform or drilling barge again.

In FIGURE 2 the anchor jacket is shown as being provided on the inner surface thereof with anchoring means in the form of a series of anchoring rings 30 which may be secured to the inner wall of the anchor jacket 20 in any suitable manner, as by welding or bolting. Although anchoring elements 30 in the form of rings are preferred, the anchoring elements may take the form of partial rings or merely blocks of metal secured to the inner wall of the anchor jacket 20 in axial spaced relationship. Preferably the space between each two metal rings is at least equal to the height of the ring element itself. The number of anchoring rings to be employed depends upon the number of times it is desired to connect the anchor jacket 20 to the pile 23 and subsequently to other piles. Preferably a pipe guide or collar 31 is securely anchored within the lower part of the anchor jacket 20. In installing a pipe 23 within the anchor jacket 20, a pile 23 is selected having a diameter only slightly smaller than the internal diameter of the anchoring rings 30.

In order to connect the top of the pile 23 to the anchor jacket 20, an expander tool of any suitable type, which may take the form of a mechanically or hydraulically actuated device or one containing an explosive charge, is lowered into the top of the pile 23 until it is positioned opposite the upper anchoring rings 30. Upon actuation of the expander device the pipe wall of the stub pile 23 near the top thereof is deformed and expanded into the space between the anchor rings at the top of the anchor jacket 20, as shown in FIGURE 2. It is preferred that the wall of the stub pile be expanded between as few of the anchor rings as possible and yet obtain their rigid connection. Thus the lower rings may be utilized at subsequent installations. Various types of expander tools may be used. One example would be a tool employing expanding dogs as in the hydraulic tool manufactured by Daily Oil Tools (see p.1552 of l9601961 Composite Catalog of Oil Field Equipment, Gulf Publishing Company). Controlled explosive charges to expand the pipe could be used as they are in daily use in oilfields for setting production tubing packers on a wire line (see 1960-1961 Composite Catalog, p. 546 and 586).

In the event that a well was drilled from the platform and it was found to be a dry hole, the platform structure of the present invention could be readily moved to another offshore location in the following manner. A pipe cutter of any well known design can be lowered into the top of the pile 23 or, alternatively, outside the upper portion of the anchor jacket 20 to cut off the top of the pile 23 and the anchor jacket 20 as shown in FIGURE 3 of the drawing. With the stub pile 23 and its anchoring jacket 20 now disconnected as shown in FIGURE 3, the base member or footing 15 and its anchor jacket 20 can be removed from the stub pile 23 by raising or floating the base member 15 upwardly in a conventional manner, leaving the stub pile 23 in the ocean floor as illustrated in FIGURE 4. The entire offshore structure is then moved to another location where new stub piles are driven through the portion of the anchor jacket 20 (FIGURE 3)" which remains secured to the footing 15. The secondstub pile would then be attached to the upper two or three anchoring rings of the anchor jacket 20 in a manner similar to that described with regard to FIGURE 2. The anchor jacket and pile could subsequently be disconnected for a second time when desired and the entire offshore structure moved to a third location where it would be anchored and disconnected in a similar manner. One type of an inside pipe cutter manufactured by Hunt Tool Company is illustrated in the 196061 Composite Catalog p. 2744. Available outside pipe cutters are described on pages 776-7, 928 and 2742 of the 196061 Composite Catalog.

Rather than cut off the top of both the pile 23 and its anchor jacket 20 as shown in FIGURE 3 and leave the top of the stub pile 23 protruding above the ocean floor 16 as shown in FIGURE 4, it may be desired to cut off the stub pile 23 below the ocean floor. This could be accomplished by inserting an inside pipe cutter into the stub pile 23 of FIGURE 3 and cutting it below the ocean floor. Thus, when the offshore structure and footing 15 were raised in a manner shown in FIGURE 4, the short section of stub piles still within the anchor jecket 20 would drop out of the jacket and onto the ocean floor 16. Alternatively, as illustrated in FIGURE 5, an outside pipe cutter could be employed to cut the anchor jacket 20 at a point represented by numeral 32 in FIG- URE 5, while an inside pipe cutter culd be run down through the stub pile 23 and cut it at a point represented by numeral 33. Subsequently tool fishing would be lowered to pull out the top section of the stub pile 23 to which the upper cut off part of the anchor jacket 20 is illustrated as attached.

In the previously described arrangements of a stub pile and an anchor jacket, the anchor jacket 20 has been shown as extending upwardly above the base member or footing 15 of the platform structure so that an outside pipe cutter could be lowered down over the anchor jacket to cut it at a desired level. In FIGURE 6 another arrangement of an anchor jacket 34 is shown as being entirely contained within the base member or footing 15 of an offshore platform structure. In this arrangement an annular space 35 is provided around the upper portion of the anchor jacket 30 for containing the anchoring rings 36. By providing an annular space 35, an outside pipe cutter can be lowered at any time around the upper end of the anchor jacket 34 to cut it off while an inside pipe cutter may be lowered at any time through the stub pilo 37 to cut it at the desired height.

Thus, it may be seen that the present invention pro vides a method and apparatus for installing and anchoring stub pile to the base or footing of an offshore platform at; successive locations to which the platform is moved, with-. out returning the platform to dry dock to have other anchoring means provided or to remove old portions of stub pile.

I claim as my invention:

1. A method of installing at an offshore location amarine structure having a base with a plurality of pile jackets for receiving concentric stub piles therethrough and a plurality of vertically-displaced anchoring means on each jacket for each of said piles, said method comprising:

positioning said marine structure with its base on the driving piles through the pile jackets of said base structure, said piles being arranged so that their upper ends are below the Water surface;

connecting each of said piles to said base by at least one but less than all of said plurality of anchoring means for each pile contained within an anchoring jacket;

subsequently serving each of said piles and said jacket with said anchoring means connected thereto at a point below the connection between the pile and the anchoring means;

raising said marine structure and moving it to another location;

again lowering said marine structure to the ocean floor;

again driving a second series of piles through said jackets of said base structure; and,

connecting said second series of piles to said base structure by at least some of the remaining anchoring means in each of said jackets.

2. The method of claim 1 wherein said piles are connected to said anchoring means of said base by the step of expanding each of said piles against cooperating anchoring means.

3. The method of claim 2 including the steps of lowering a pile expanding tool down through each of said piles to a position opposite the uppermost anchoring means and actuating said tool to expand said piles against said anchoring means.

4. The method of claim 2 including the steps of lowering an explosive charge into each of said piles to a position opposite the uppermost anchoring means and detonating said explosive charge to expand said piles into locked engagement with said anchoring means.

5. The method of claim 1 wherein said piles and engaged anchoring means are severed by lowering a cutting tool to a point below the engagement of said pile with said anchoring means and cutting ofi? said pile and said anchoring means at a level below said anchored point.

6. The method of claim 5 including the steps of lowering a pile severing device through said pile to a point below said marine structure base and severing said pile at this point also.

7. The method of claim 1 wherein said marine structure is floated when it is moved from one location to another.

References Cited by the Examiner UNITED STATES PATENTS 2,772,539 12/1956 Sandberg 61--46.5

CHARLES E. OCONNELL, Primary Examiner. EARL J. WITMER, JACOB SHAPIRO, Examiners.

Claims

1. A METHOD OF INSTALLING AT AN OFFSHORE LOCATION A MARINE STRUCTURE HAVING A BASE WITH A PLURALITY OF PILE JACKETS FOR RECEIVING CONCENTRIC STUB PILES THERETHROUGH AND A PLURALITY OF VERTICALLY-DISPLACED ANCHORING MEANS ON EACH JACKET FOR EACH OF SAID PILES, SAID METHOD COMPRISING: POSITIONING SAID MARINE STRUCTURE WITH ITS BASE ON THE OCEAN FLOOR; DRIVING PILES THROUGH THE PILE JACKETS OF SAID BASE STRUCTURE, SAID PILES BEING ARRANGED SO THAT THEIR UPPER ENDS ARE BELOW THE WATER SURFACE; CONNECTING EACH OF SAID PILES TO SAID BASE BY AT LEAST ONE BUT LESS THAN ALL SAID PLURALITY OF ANCHORING MEANS FOR EACH PILE CONTAINED WITHIN AN ANCHORING JACKET; SUBSEQUENTLY SERVING EACH OF SAID PILES AND SAID JACKET WITH SAID ANCHORING MEANS CONNECTED THERETO AT A POINT BELOW THE CONNECTION BETWEEN THE PILE AND THE ANCHORING MEANS;