US3453830A - Method and apparatus for alleviating scouring about legs of a marine structure - Google Patents

Description

METHOD AND APPARATUS FOR ALLEVIATING SCOURING ABOUT LEGS OF A MARINE STRUCTURE July 8, 1969 A c. MITCHELL. JR 3,453,830

Filed March 13, 1968 Sheet I of 2 INVEN'TOR ALBERT C. MITCHELL, JR.

mdz%m ATTORNEY A.,C. MITCHELL. JR METHOD AND APPARAT Filed March 13, 1968 July 8, 1969 7 3,453,830 US FOR ALLEVIA'I'ING SCOUHING ABOUT LEGS OF A MARINE STRUCTURE Sheet FIG. 2

FIG. 3

INVENTOR ALBERT C. MITCHELL, JR.

ATTORNEY United States Patent US. 'Cl. 61--46.5 11 Claims ABSTRACT OF THE DISCLOSURE A method and apparatus for placing antiscouring materials or objects about the lower end of an extendible leg of a marine structure to alleviate scouring wherein said lower end of said leg is positioned on the bottom of a body of water and the upper end supports a work platform. The invention includes at least one pallet attached to the leg. An extendible means such as a net is attached to each pallet; the net normally lying flat on the pallet when unextended and having a pyramidal configuration when extended. The antiscouring material or objects are piled on the net while it is in a flattened condition and prior to the positioning of the leg on the bottom. The net is extended by a cable after the leg is positioned to force the antiscouring material or objects off the pallet to place the objects around the leg.

Background of the invention This invention relates to a method and apparatus for alleviating scouring about the legs of a marine structure and, more particularly, relates to a method and apparatus for placing antiscouring materials or objects about the legs of said structure.

The drilling of underwater wells in search of oil or other minerals is now commonplace. In carrying out such drilling operations, different types of marine structures are used depending primarily upon the depth of water encountered. One of the most common of these structures is one which is used in depths of water between 40 and 300 feet and is commonly referred to in the art as a jack-up rig.

A typical jack-up rig is comprised of a floating barge or work platform on which is carried the drilling derrick, drawworks, mud tanks and pumps, and the other associated equipment necessary for the actual drilling of an underwater well. Spaced about the periphery of the platform and extending through openings or guides therein are a plurality of skeletal legs. These legs are normally retracted and supported in a position above the platform whenever the rig is floated from one location to another. Once the rig has been positioned over the desired drilling site each leg is lowered through its respective platform opening or guide until it engages the bottom of the water where it partially embeds itself in the soil. In some instances, a spud can may be provided at the lower end of each leg to aid in embedding the legs in the bottom. When each leg is in its desired position on the bottom, jacks on the rig are actuated to lift the platform out of the water and onto the legs. By being supported above the surface of the water on legs which are effectively anchored to the bottom of the water, the platform normally provides a stable base for drilling operations.

Unfortunately, however, in some bodies of water the platform does not remain stable due to the scouring of soil from around the embedded portions of the legs. This scouring, which is believed to be caused by tides, waves, and/or strong underwater currents, may shift or move large volumes of sand, gravel, or other material from around the legs in relatively short periods of time. This 3,453,830 Patented July 8, 1969 undermining of the legs allows one or more of said legs to shift or sink further into the bottom thereby causing the platform to tilt or shift which in turn may snap drilling lines, dislodge valuable equipment, or destroy the platform itself. In view of this, it is obvious that the problem of scouring is one which must be: considered when jack-up rigs or like structures are used in underwater operations.

In the past, various approaches have been taken to prevent scouring of soil from around the legs of such structures. These approaches have included, for example, 1) using rigid barriers around the legs such as steel pilings or scouring skirts; (2) consolidating the soil around the legs by use of hardening resins, concrete, Or other soil solidifying material; and (3) surrounding the exposed areas of the legs on the bottom with piles of unconsolidated, insoluble material or objects, such as large size gravel, concrete blocks, anchored willow mats, of sandbags.

Of these approaches, the latter one of using piles of unconsolidated material or objects to surround the lower ends of the legs is one of the most commonly used. This antiscouring material or objects being unconsolidated have a tendency to fall into any undermining or excavations caused by scouring, thereby maintaining a relatively firm foundation around the legs and preventing any serious shift of the legs. Also, by using unconsolidated material or objects instead of material which solidifies around the legs, the rig can be moved more easily at the completion of drilling operations.

It has been found that larger, unconsolidated, antiscouring objects, such as concrete blocks and preferably sandbags, will resist scouring better than smaller material (e.g., gravel) since due to their weight they cannot be moved as easily from around the legs by scouring action of underwater currents. However, in the past due to the bulk of these objects, considerable time was required to lower and place them in their proper positions. Also since this placement involved the efforts of underwater divers for relatively long periods, it has been a relatively expensive procedure to follow.

Summary of the invention In accordance with the present invention, there is provided a new and improved method and apparatus for the placement of large, unconsolidated, antiscouring materials or objects such as sandbags or the like about the legs of an underwater drilling structure to alleviate the scouring of soil from about said legs. In carrying out the present invention, one or more pallets are fixedly secured on each leg of the platform. Each of these pallets is provided with a flexible, extendible means which is preferably a specially shaped net or the like. The net which lies flat on the pallet when in an unextended or collapsed position has a pyramidal configurationwhen raised or pulled to an extended position, said pyramidal configuration having a base which substantially conforms to the periphery of the pallet and which is attached thereto. A cable or rope is attached to the apex of the pyramidal net and is operable from the platform when the structure is in position. The antiscouring materials or objects to be placed about the legs are piled onto the flattened net prior to the legs being finally positioned in the water. When the legs are in position, the net is pulled to an extended position by the cable attached to the net. As the net is extended it forces the antiscouring materials or objects ofl the sides of the pallet so that they fall downward around the corresponding sides of the leg. As is obvious from the above, the invention provides a quick and efilcient means of placing antiscouring objects about the legs of an underwater drilling structure which requires neither the time interval nor the extensive efforts of underwater divers previously required in other placement procedures. If desired, a diver can be employed to check the final placement of the objects and slightly reposition some of of them, if necessary; but the time required will be only a fraction of that previously needed.

The actual construction, operation, and the apparent advantages of the invention will be better understood by referring to the drawings in which like numerals identify like parts and in which:

Brief description of the drawings FIGURE 1 is a perspective view, partly broken away, of an underwater drilling structure employing the present invention;

FIGURE 2 is a perspective illustration of the present invention; and

FIGURE 3 is a perspective view taken along lines 33 of FIGURE 2 with the invention in an extended position.

Description of the preferred embodiments Referring more particularly to FIGURE 1, an underwater drilling structure is shown in operational position in a body of water 11. The drilling structure shown in the figure belongs to the class of marine structures commonly known as jack-up rigs and this type of rig is widely used in underwater drilling operations. The structure 10 is comprised of a fioatable barge or work platform 12 having a plurality of extendible, skeletal legs 13 spaced about the periphery thereof. Structure 10 is shown as having four legs 13, but it should be recognized that some rigs may have only three while others may have more than four. In any case, the number of legs does not affect the present invention. Drilling derrick 14, work cranes 15, and other necessary drilling equipment are mounted on platform 12 as is well known in the art. Legs 13 extend through guide members 16 which are mounted on or form part of the platform 12. Legs 13 are normally retracted (not shown) and extend above platform 12 whenever the structure is floated to or from a drilling location. Legs 13 are preferably comprised of a plurality of tubular members 20 connected together by cross members 21 to form a polygon cross-sectional configuration. Legs 13 are illustrated as having three tubular members 20 which give legs 13 a triangular cross section, but more than three members 20 could be used if desired. Additional vertical braces 22 are normally used to strengthen the legs as is well known in the art. Spud can 23 is provided at the lower end of each leg to improve the penetration ability of each leg and also to aid in removal of the legs when drilling operations are completed. Use of spud cans for this purpose is well known.

In accordance with the present invention, at least one pallet 25 is provided on each leg 13 of the drilling structure 10. Referring more particularly to FIGURES 2 and 3, pallet 25 is comprised of a plurality of brace members 26 joined together to form a base having substantially the same configuration as that of the cross section of skeletal legs 13; e.g., in the present illustration the base will be triangularly shaped. The base is secured to cross members 21 at the desired level of legs 13 by means of a plurality of clamp means 27. The triangular base is completely covered by heavy bridge timbers 28 or the like which are secured thereto to form a solid foundation for pallet 25. A flexible, extendible means 29 is provided for each pallet 25. This means 29 is preferably comprised of a heavy netlike material formed from nlyon or wire but can also be comprised of solid materials such as heavy cloth or canvas, reinforced plastic material, or any other similar material. Means 29 or net 29, as it will hereinafter be referred to, is constructed so that it will form a pyramidal configuration when it is in its extended position. The base 29a (FIGURE 3) of the pyramidal configuration substantially conforms to the configuration and dimensions of pallet 25 and is secured to the periphery of pallet 25 by bradding, bolting, gluing, or any other means well known in the art. In the present instant, the

base of net 29 is a triangle but if leg 13 were comprised of four tubular members instead of three, the base would be rectangular and so on. A rope or cable 30 is secured to the apex 29b of net 29 by means of a hook and eye (not shown) or similar means and extends upward to platform 12 for a purpose explained below.

Net 29, being flexible, will be fiat on pallet 25 when in an unextended or collapsed position. The antiscouring material or objects, e.g., sandbags 31, to be placed about legs 13 are then piled or loaded onto net 29 while it is in the flattened condition.

Operation of the present invention is as follows: Skeletal legs 13 of a standard-type, jack-up marine structure 10 are equipped with pallets 25 as explained above. As is well known in the art, leg 13 will be retracted and will extend upward from platform 12 while structure 10 is floated into position over a desired drilling site. Prior to or upon reaching the proposed site, sandbags 31 or other desired antiscouring material is loaded onto pallet 25 and hence flattened net 29. Legs 13 are then lowered until spud cans 23 engage the bottom 17. Spud cans 23 can be used to wash-in the lower portions of leg 13 if the soil is otherwise too hard to allow legs 13 to become partially embedded therein. When legs 13 are positioned on bottom 17, jacking units (not shown) cooperate with legs 13 to lift platform 12 out of the water to a position above the surface thereof where it is supported entirely on legs 13.

Next, cable 30 is pulled upward by means of a Winch (not shown) or the like to raise net 29 to an extended position. As net 29 is extended to its pyramidal configuration, it forces sandbags 31 off each of the sides of pallet 25 so that sandbags 31 will fall downward around spud can 23 as shown in FIGURE 1. Due to the weight of sandbags 31 and the relatively short distance which they travel, most of the sandbags will assume a proper position about spud cans 23. If desired, a single diver can inspect the actual position of the sandbags and reposition some of them, if necessary.

Although a particular embodiment of the subject invention has been illustrated and described, the disclosure is intended to cover all changes and modifications therein which do not constitute departure from the spirit and scope of the invention. For example, the present invention has been described in conjunction with a drilling rig but it should be recognized that it would work equally as well with other similar marine structures such as workover rigs or the like. Also, although only one pallet is shown on each leg, several pallets could be provided by securing them, one above the other, to respective cross members 21 and then diverting individual cables from each associated net 29 by means of pulleys so that the cables would run up the sides of tubular members 20 to platform 12.

What is claimed is:

1. In a marine structure of the type comprising a floatable platform having a plurality of extendible, skeletal legs having a polygonal cross section which are normally retracted to a position above the platform when said structure is being moved on a body of water and which engage the bottom of said water when said legs are extended, means for positioning material or objects about the lower ends of said legs to prevent scouring comprising:

at least one pallet having substantially the same canfiguration as said polygonal cross section of said skeletal legs secured to each of said legs at a point which will lie below the surface of said water when said leg is extended,

an extendible means which, when extended, has a pyramidal configuration having base dimensions conforming to the periphery of said pallet, said extendible means being attached to said periphery of said pallet and normally lying fiat on said pallet when in an unextended or collapsed position, said means being adapted to receive said material or objects to be positioned while said means is flat on said pallet; and

means connected to said extendible means and operable from said platform to extend said extendible means to an extended position when said skeletal legs engage the bottom of said water.

2. The structure of claim 1 wherein:

said means to extend said extendible means includes a cable connected to said extendible means and extending to said platform.

3. The structure of claim 2 wherein:

said extendible means is comprised of netlike material.

4. The structure of claim 1 wherein:

said marine structure is a jack-up structure.

5. In a marine structure comprising a platform having extendible leg means thereon which is normally retracted to a position above the platform during movement of said structure and which engages the bottom of a body of water when in an extended position, means for placing material or objects about the lower end of said leg means to prevent scouring:

support means on said leg means adapted to receive and support said material or objects prior to said leg means being extended, said support means being positioned on said leg means so that it will lie below the surface of the water when said leg means is extended; and

means on said support means to displace said material or objects from said support means when said leg means is extended.

6. The structure of claim 5 wherein:

said support means is a pallet.

7. The structure of claim 6 wherein said means to displace said material or objects includes:

an extendible means which, when extended, has a pyramidal configuration attached to said pallet, said extendible means normally lying flat on said pallet when in an unextended or collapsed position, said extendible means adapted to receive said material or objects to be positioned while said means is flat on said pallet; and

means connected to said extendible means and operable from said platform to extend said extendible means to an extended position.

8. The structure of claim 7 wherein: said means to extend said extendible means includes a cable connected to said extendible means and extending to said platform. 9. The structure of claim 8 wherein: said extendible means is comprised of netlike material. 10. A method of positioning antiscouring material or objects about the lower end of a leg of a marine structure to alleviate scouring around said leg wherein said lower end of said leg is positioned on the bottom of a body of water and the upper end of said leg supports a work platform or the like, the method comprising:

securing at least one pallet to said leg at a position on said leg so that said pallet will be below the surface of the water when said lower end of said leg is positioned on the bottom of said body of water; attaching a flexible means having a pyramidal configuration when in an extended position to said pallet, said flexible means lying substantially flat on said pallet when not in an extended position; placing said antiscouring material or objects on said flexible means while said flexible means is in a flattened position on said pallet prior to the positioning of said leg in said body of water; and extending said flexible means to said extended position after said leg is positioned on the bottom of said body of water whereby said antiscouring material or objects are displaced by said flexible means from said pallet to fall to a position about the lower end of said leg. 11. The method of claim 10 wherein: said antiscouring materials or objects are sandbags.

References Cited UNITED STATES PATENTS 2,940,266 6/1960 Smith 61--46.5 3,312,069 4/1967 Jorda 61-1 X 3,394,553 7/1968 Vidal 61-46.5

JACOB SHAPIRO, Primary Examiner.

U.S. Cl. X.R. 6l-50, 52

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