US3151594A

US3151594A - Drilling barge anchor system

Info

Publication number: US3151594A
Application number: US212827A
Authority: US
Inventors: Bruce G Collipp
Original assignee: Shell Oil Co
Current assignee: Shell USA Inc
Priority date: 1962-07-27
Filing date: 1962-07-27
Publication date: 1964-10-06
Anticipated expiration: 1981-10-06
Also published as: GB986782A

Description

Oct. 6, 1964 B. s. COLLIPP 3,151,594

DRILLING BARGE ANCHOR SYSTEM 3 Sheets-Sheet 1 Filed July 27, 1962 INVENTORZ B. G. COLL? PP FIG. 2

BYIfi- Hi8 AGENT Oct. 6, 1964 B. s. COLLIPP 3,151,594

DRILLING BARGE ANCHOR SYSTEM Filed July 27, 1962 3 Sheets-Sheet 2 Li a l INVENTORI B. G. COLLIPP BY" fsn mi IS AGENT 1964 B. G. COLLIPP 3,151,594

DRILLING BARGE ANCHOR SYSTEM Filed July 27, 1962 3 Sheets-Sheet 3 FIG. 5

INVENTORZ B. G. COLLIPP United States Patent 3,151,594 DRILLING BARGE Al CHQR SYSTER'E Bruce G. Coilipp, Met-airie, La, assignor to She Oil Company, New York, NFL, a corporation of Delaware Filed July 27, 1%2, Ser. No. 212,327 8 Claims. (Cl. 114-296) This invention relates to apparatus for use in drilling, completing or Working-over oifshore wells, and pertains more to an anchoring system for resiliently anchoring a marine structure in a substantially fixed position against lateral movement in a body of Water.

In recent years, oil Well drilling operations have been carried out at ofishore locations where the water was 100 feet or more in depth. In waters from 100 to about 300 feet deep it is possible to drill a well from a permanentlypositioned structure such as a platform anchored to the ocean floor and extending to a distance above the surface of the water. In Waters deeper than 300 feet it is necessary to drill wells from a floating drilling vessel or platform which is securely anchored in a substantially fixed position throughout the drilling operations. It has been found most difficult to anchor floating barges or deep water platforms against lateral movement due to Wind and Wave forces.

It is therefore a primary object of the present invention to provide an anchoring system for well drilling vessels or deep water permanently-positioned drilling platforms so that the vessel or platform may be resiliently anchored in a substantially fixed position in the water with the anchor systems possessing energy-absorbing characteristics preventing lateral movement of the vessel or platform.

A further object of the present invention is to provide a marine structure with an anchoring system wherein the anchor lines thereof are normally buoyantly supported at all times by means which increase their buoyancy as greater tension is applied to the anchor lines.

Another object is to provide a mooring system that as the forces build up, the configuration of one lines changes and the further build up of forces is carried by an adjacent line. The premature failure of a single line which due to improper setting of anchors or peculiar sea conditions may be carrying most of the load is prevented. (When the buoys submer e further increases in load are transferred to adjacent lines.)

Another object of the present invention is to provide a marine structure with an anchoring system which normally operates in a slack-line condition with the anchor lines being of substantial scope thereby substantially eliminating or minimizing any vertical pull on the anchors.

Still another object of the present invention is to provide a marine structure with an anchoring system which is positioned underwater for the most part to reduce wave forces transmitted to the lines and reduce the possibility of surface vessels becoming fouled in the lines.

A further object of the present invention is to provide a marine structure with an anchoring system employing buoyantiy-supported anchor lines secured to the marine structure in a manner such that a vertical lifting compo nent is normally applied to the marine structure by the anchor lines.

It is also an object of the present invention to provide a marine structure with an anchoring system wherein at least a portion of the anchor lines assume the shape of a catenary curve extending from the anchor to substantially the surface of the Water.

A further object of the present invention is to provide an anchoring system for a drilling platform of the type described in my copending patent application, Serial No. 111,847, filed May 22, 1961.

3,l5i,5%4 Federated Get. 6, 1964 'ice These and other objects of this invention will be understood from the following description taken with reference to the drawing, wherein:

FIGURES 1 and 2 are side and plan views of a typical floating drilling barge provided with a portion of the anchoring system of the present invention;

FIGURE 3 is a diagrammatic view illustrating a crown buoy floating on the surface of a body of water and secured to an anchor sunk in the ocean floor;

FIGURE 4 is a diagrammatic view illustrating a float positioned at the surface of a body of water and being secured in an anchor line of the present system;

FIGURE 5 is a diagrammatic view illustrating a floating vessel and one of its anchors in accordance with the system of the present invention;

FIGURE 6 is a diagrammatic view illustrating a floating drilling vessel provided with another form of buoyant anchor line which is not in accordance with the present invention;

FIGURE 7 is a diagrammatic view illustrating a typical pulley or sheave system for interconnecting a spring buoy of the present anchor system with a marine structure; and

FIGURE 8 is a diagrammatic view illustrating an elongated permanently positioned drilling platform secured to the ocean floor and being provided with an anchor system in accordance with the present invention.

Referring to FIGURES 1 and 2 or" the drawing, a marine structure, such for example as a freely-floating drilling vessel or platform is generally represented by the numeral 11. The drilling vessel may comprise a buoyant hull made up of

hollow legs

12, 13, 14 and 15 in the form of elongated vertical cylinders which may be connected together by hollow horizontal bracing members one of which is shown at 16. The vessel is provided with an operating deck 17, a derrick l8, and other associated equipment (not shown) normally used in well drilling or work-over operations,

In order to resiliently anchor the vessel in a substantially fixed position against lateral movement in the body of water, while permitting vertical movement of the floating structure, a plurality of anchor lines extend from various sides of the drilling vessel which may be, say, 200 feet wide and 250 feet long.

Each anchor line extends from a winch 21 which may be driven by any suitable prime mover means, such for example as an electric motor 22, in order to provide tension on the anchor line as required. The anchor line 20 extends to the edge of the operating platform 17 where it passes over a sheave 23 and then downwardly along the side of the vessel over sheave 24 and then around sheave 25 which is positioned near the bottom of the drilling vessel 11 and is preferably from 5 to feet below the surface of the water 27. From the lowermost sheave 25 the anchor line extends upwardly and is connected to a spring buoy 28 which is positioned outboard of the drilling vessel a distance of, say, to 300 feet or more. If desired, the anchor lines between the lowermost sheave 25 and the spring buoy 28 may pass through a sheave system comprising a pair of double sheave blocks 3 and 31 having four strands of the anchor line 20 running between them and returning up another set of

sheaves

32, 33 and 34- (FIGURE 2) to the deck 17 of the vessel Where the dead end of the line is anchored to the vessel by suitable anchoring means 35. Preferably, a tension or weight indicator 36 is installed in the dead end of the line near the anchor 35. One suitable arrangement is to use a Martin Decker Type E weight indicator and anchor at this point. The sheave block 31 is secured to a single cable 37 which in turn is secured to a suitable connector 38 (FIGURE 4) fixedly attached to the lower portion of the spring buoy Z8.

b A second anchor line connector 42 is secured to the side of'the spring buoy 2S opposite the connector 38 whereby a second anchor line 43 can be connected to the spring buoy 28 and extend outwardly therefrom. For ease and handling or storing the anchor lines 43 when not in use, the anchor line 43 is preferably made up of several sections secured together by cementing links 44. 7

As shown in FIGURE 3 the anchor line 43 is provided at the end thereof with any suitable t pe of anchor which may, for example, be a Baldt light-weight type anchor of ten tons. a

In order to facilitate the removal of the anchor 45 from its holding. position in the ocean floor when it is desired to move the vessel 1?. (FIJURE l) and its anchoring system to another location, a tripping line 47 is connected to the crown 48 of the anchor 45. The other end of the tripping line 47 is connected to a suitable ring or other connector 50 secured to a crown or marker buoy 51. The crown or marker buoy 51 may be much smaller than the spring buoy 28 and need only have sufficient buoyancy to support the tripping line 4-7. The tripping line 4-7 must necessarily be of a length greater than the distance between the anchor 45 on the ocean floor and the surface of the Water 27. Since the retrieving pull on the anchor 45 may run between 50,000 and 100,000 pounds the trip ping line may be of 2-inch wire rope. In order to facilitate reaching the tripping line 47, an auxiliary line 52. is connected between a shackle 53 and the tripping line 47 and a connector 54 on the top of the crown or marker buoy 51.

The capability of any mooring system is dependent on the water depth in which it is to be used. One par .-eter commonly referred to in anchor lines or moorings is scope, which is the length of the anchor or mooring line divided by the Water depth. Thus, a thousand feet of cable would have a scope of 1.0 in one thousand feet of water and a scope of in 100 feet of water. In general, the desired'capabilities of a mooring system improves with scope. A mooring system, in essence, is designed to absorb the kinetic energy of the marine structure which is being moored. In the present system the energy-absorbing ability of the anchor linesincreases with increasing scope, as the anchor line 43 (FIGURE 5) assumes the form of a catenary curve between the springbuoy 2 and the ocean floor 46. In the anchoring sstem of the present invention it is preferred that the scope of the anchor lines be between 3 and 12 or more. Preferably, the length of the anchor'line 43 is sufiicient so that when the anchoring system is in equilibrium at least a portion of each anchor line 43 rests on the ocean floor so that no vertical component is applied through the anchor line which would tend to pull the anchor 45'from its position in the ocean floor.

In the operation of the anchoring system of the present invention, as the vessel 11 (FIGURE 5) moves to the left away from the anchor 45 energy is transferred from the vessel 11 to the anchor line 43 and energy is transformed into the work of raising the anchor line 43 to a position 43a, or a higher or lower position depending upon the tension being applied to the anchor line. Thus, the present system utilizes the desirable qualities of a catenary which" is an exponentially increasing force being applied to return the vessel to its normal position.

By means of the winches 21 a predetermined tension (say 10,000 pounds) is applied to the anchor line it,

which by means of the double sheave blocks and 31 in the four lines therebetween is multiplied to a pretension force of 40,000 pounds between the vessel 11 andthe,

spring buoy 28. The anchor lines 43 may be three-inch wire rope extending several hundred or several thousand feet outwardly from the vessel 11 and assume a catenary curve between the ocean door and the spring buoy 28. In normal sea conditions, wherein there would be very limited movement of the marine structure or vessel 11, the lateral movement of the vessel 11 would be restricted by the energy-absorbing characteristics of the catenary anchor line 43. However, during violent storms the spring buoys 28 would also come into play to a greater extent than normal. Since the spring buoys'23 are floating on the surface of the water under normal conditions, as'increasing tension is applied to the anchor lines by the vessel movirig'ofi its normal position, an increasing buoyancy force is applied vertically upwardly by the spring buoys as the upwardly-directed

anchor lines

37 and 43 tend to pull the spring buoy deeper into the water.

It is well known that in stormy seas one in several hun' dred waves is an extra large wave. By using the anchor system of the present invention the energy of these large waves is dissipated by allowing the vessel 11 to move more with the wave. This is accomplished by one or more of r the spring buoys 28 on the weather side of the vessel dipping below the surface of the Water momentarily and then springing back to the surface of the Water again after the wave has gone past so that the anchor system again enjoys the advantages of the catenary system in effect before the wave passed. If the spring buoys were not employed, there is a danger of the anchor dragging or the anchor line 43 snapping when a big wave comes past;

- upwardly in the water and hence supplement the buoyancy of the vessel itself. At the same time, the anchor line 20 below the lower sheave 25 and the spring buoy 28 is below the surface ofthe waterso that surface vessels can operate close to the drilling vessel 11 as is necessary during the drilling of wells, such for example as in transferring personnel or equipment to the drilling vessel. The'superiority of the anchoring system of the present invention as illustrated in FIGURE .5' may be seen over another form of anchoring system shown in FIGURE 6. In the anchoring system shown in FIGURE 6, the anchor line would pass directly from the sheave 23 ;at the top of the drilling vessel down to thebuoy 28a floating on the surface of the water with the anchor line 43 extending from the buoy 28a to the anchor 45. It will be seen in the arrangement of FIGURE 6 that due to the height of the vessel 11, which may be feet or more above the surface of the water, when the vessel 11 moves off its center point to the left, the tension in the anchor lines may be such as to actually pull the buoy 28ao'ut of the water, as shown in the dotted line configuration, thus adding weight to the anchor line which may cause it to break.

While the anchoring system of the present invention has been described with regard to employing it for anchoring a floating drilling vessel overa drilling location,

it is also to be understood that the present anchoring 7 system could be employed for stabilizing relatively ilexible permanent marine structures such as a platform 60 (FIGURE 8) which may comprise a'plurality of tubular legs sun in the ocean floor and extending a distance above the surface of the water so as to accommodate an operating deck 61 and a derrick 62 or other equip ment. As in the case of the floating vessel, the anchor lines would extend from winches 63 down to the underwater sheave 64 and then upwardly to a spring buoy 65 to which an anchor line 66 would be secured in a manner described with regard to anchor line 43 of FIGURE 5. A series of these buoys 65 would be positioned around the marine structure 60 outboard thereof and in spaced relationship with each other in a manner similar to the spring buoys 28 shown in FIGURE 2 of the drawing.

I claim as my invention:

1. Apparatus for resiliently anchoring a floating marine structure in a substantially fixed position against lateral movement in a body of water while permititng vertical movement of said floating structure, said apparatus comprising (a) a plurality of float means disposed on the surface a distance therefrom and in spaced relationship with each other,

(b) first anchor line means secured at one end to each of said float means in the lower portion thereof and extending in a direction away from said marine structure anchor means secured to the other end of said first anchor line means and adapted to secure said end of said first anchor line means to the floor beneath said body of water,

(d) second anchor line means secured at one end to each of said float means in the lower portion thereof and extending at an angle downwardly therefrom to engage said marine structure at a point below the surface of said body of water, and

(2) means operatively connected to said second anchor line means for applying a predetermined tension at all times in said line means between said marine structure and each of the float means on the surface of said body of water.

2. The apparatus of claim 1 wherein each of said first anchor line means is of a length so that a catenary curve is formed therein between the float means on the surrace of the water and the anchor means on the floor beneath said body of water.

3. The apparatus of claim 2 wherein each of said first anchor line means is of a length so that a portion thereof adjacent said anchor means rests on the ocean floor so that there is no vertical force applied to said anchor means under normal conditions.

4. The apparatus of claim 1 wherein said marine structure is a floating vessel of substantially rectangular configuration in plan with said float means positioned on the surface of said body of water outboard of each corner of said vessel.

5. The apparatus of claim 4 wherein each of said float means comprises a pair of floats in spaced relationship to each other and the vessel at substantially the same distance from said vessel with first and second anchor line means being secured to each float.

6. The apparatus of claim 1 wherein said float means are spaced a distance from said marine structure and said second anchor line means engage the marine structure at a depth suflicient to allow boats to approach and anchor to said marine structure.

7. The apparatus of claim 1 wherein the buoyancy of said float means is sufficient whereby the float means remains at the surface of said body of water while under tension between said first and second anchor line means.

8. The apparatus of claim 7 wherein the buoyancy of said float means is a value selected so that the float means is pulled below the surface of the water with a tension less thn that necessary to break said first and second anchor line means.

References Cited in the file of this patent UNITED STATES PATENTS 1,378,394 Armstrong May 17, 1921 2,604,866 Alcorn iuly 29, 1952 2,986,888 Borrman et a1. June 6, 1961 FOREIGN PATENTS 257,858 Germany Mar. 20, 1913

Claims

1. APPARATUS FOR RESILIENTLY ANCHORING A FLOATING MARINE STRUCTURE IN A SUBSTANTIALLY FIXED POSITION AGAINST LATERAL MOVEMENT IN A BODY OF WATER WHILE PERMITTING VERTICAL MOVEMENT OF SAID FLOATING STRUCTURE, SAID APPARATUS COMPRISING (A) A PLURALITY OF FLOAT MEANS DISPOSED ON THE SURFACE A DISTANCE THEREFROM AND IN SPACED RELATIONSHIP WITH EACH OTHER, (B) FIRST ANCHOR LINE MEANS SECURED AT ONE END TO EACH OF SAID FLOAT MEANS IN THE LOWER PORTION THEREOF AND EXTENDING IN A DIRECTION AWAY FROM SAID MARINE STRUCTURE (C) ANCHOR MEANS SECURED TO THE OTHER END OF SAID FIRST ANCHOR LINE MEANS AND ADAPTED TO SECURE SAID END OF SAID FIRST ANCHOR LINE MEANS TO THE FLOOR BENEATH SAID BODY OF WATER, (D) SECOND ANCHOR LINE MEANS SECURED AT ONE END TO EACH OF SAID FLOAT MEANS IN THE LOWER PORTION THEREOF