US 3395755 A
Description (OCR text may contain errors)
Aug. 6, 1968 w. F. MANNING BOTTOM ACCESS CAISSON Filed March 30, 1966 WILLIAM F. MANNING INVENTOR BY @45 9, M
ATTORNEY United States Patent 3,395,755 BOTTOM ACCESS CAISSON William F. Manning, Springdale, Conn., assignor to Mobil Oil Corporation, a corporation of New York Filed Mar. 30, 1966, Ser. No. 538,627 Claims. (Cl. 166-.5)
This invention relates to an improved means for obtaining access to submerged wellheads and the like, utilized for the exploitation of subaqueous fluid mineral deposits, more particularly to a removable caisson especially designed for providing an =air-filled working chamber at the submerged wellhead.
Heretofore, when a subaqueous well is proven and is to be placed on production, an above-surface, bottomsupported platform is set over the well with a riser pipe extending from the well to the platform deck and a christmas tree (production wellhead) is mounted on the deck above the surface of the water. A number of directional wells can then be drilled from the deck of the platform. If a large field is being produced, a central separator platform station is often erected and a rudimentary support structure is utilized at the riser pipe of each well. Signal lights and other warning devices must be connected to all of the platforms and well riser supports since otherwise they would create a hazard to navigation. Moreover, since the wells and the production wellhead extend above the water they are still subject to damage by vessels and by wave actions, notwithstanding the warning means. Therefore, it would be desirable to position the production wellhead beneath the surface of the body of water, in fact, near the marine bottom.
Other problems arise when the wellhead is situated far beneath the surface of a body of water. One of the most important of these problems is that of servicing and maintaining the well. Divers, while costly, may be used for actuating the various valves and repairing any malfunctions in connection with the wellhead; however, even in shallower waters, of several hundred feet, the time during which a diver can work under water is limited and his effectiveness is less than that of a man working under atmospheric conditions. With the newly developed capabilities of the offshore industry to drill, and later perhaps produce, wells in the waters of the continental shelf and the continental slope, where the depths encountered range from six hundred to two thousand feet, a diver must be entirely dispensed with.
Therefore, it is an object of this invention to provide atmospheric conditions at subaqueous wells completed far beneath the surface of a body of water.
Another object of this invention is to provide an improved removable access caisson to connect the submerged wellhead with a point above the surface of the body of water.
Other objects and advantages of this invention will be apparent from the following description and the accompany drawings.
Referring to the drawings in which is shown a pre ferred embodiment of the invention:
FIGURE 1 is an elevational cross-sectional view of a bottom-supported caisson of the present invention, taken through line 1-1 of FIGURE 2, fixed over a submerged wellhead and extending above the surface of the body of water;
FIGURE 2 is a cross-sectional view taken through line 22 of FIGURE 1.
Referring now to the drawings, FIGURES l and 2 show a bottom-supported access caisson, generally designated 10, resting on a landing base 12 of a submerged wellhead generally designated 14, and extending above the surface 16 of a body of water 18. The landing base 12, which is directly supported on a marine bottom 20 3,395,755 Patented Aug. 6, 1968 in turn supports the casings and production tubing (not shown) of a well drilled into underlying subaqueous formations. The access caisson 10 is made up of a base section 22 and as many upper caisson sections 24 as are necessary to extend the access caisson above the surface 16 of the body of water 18. The access caisson 10 is of a hollow cylindrical shape, having a solid annulus 27 defined by the outer wall 25 and the inner wall 26 thereof. The inner face of said inner wall 26, defining a cylindrical hollow interior of the access caisson has a circumferential abutment means 28 therewithin, situated near the lower end of the access caisson, the purpose of this abutment means being discussed later.
Formed in the solid annulus 27 of the caisson 10, between the walls, is a pair diametrically opposed access tubes 29 and four elongated buoyancy/ballast tanks 30, equally spaced around the circumference of the annulus. Although the annulus 27 of the caisson, in sectional view FIGURE 2, is a solid thick walled tube, with a number of passages extending .therethrough to form the access tubes 29 and the buoyancy/ballast tanks 30, in actuality the shell of the access caisson 10 may consist of only inner and outer walls with the tubular access passages and buoyancy/ballat tanks being elongated hollow tubes rigidly fixed therebetween.
The base section 22 of the access caisson 10 terminates in a landing portion 32. This landing portion has a contoured inner surface to conform to the hemispherically shaped outer surface of the landing base 12. An O-ring 34 is set in a circumferential groove in the landing portion 32 and cooperates with an outer upstanding circumferential boss 36 integral with the landing base 12 to seal the bottom of the access caisson 10. Flowlines, such as the illustrated flowline 38, enter the wellhead from within the landing base 12 so as to protect the fiowline 38 from being pinched between the complementary surfaces of the landing base 12 and the caisson 10 as the caisson 10 is lowered into place.
The lower ends of each of the well access tubes 29 are connected by a bulkhead port 40 to the cylindrical hollow interior 41 of the cylindrical access caisson 10. The interconnections between the sections of the access tubes 29 and the sections of the buoyancy/ballast tanks 30 within the aligned sections of the access caisson 10 must be watertight. This is accomplished by O-ring seals 43 fitting in circumferential grooves in the abutting surfaces. The remainder of the abutting surfaces need not be contiguous since water leaking into the central well will not affect the operation of the apparatus.
A pair of submersible reversible pumps 42 and 44 are mounted in the lower end of each buoyancy/ballast tank 30. The first pump 42 has a first port 46 opening into the interior of the caisson 10* and a second port 48 opening out into the body of water 18. The second submersible pump 44 has a first port 50 opening into the interior of the buoyancy/ballast tank 30 in which it is situated and a second port 49, also connected to the open body of water 18. A remotely actuatable shut-01f valve 52 is fixed in the upper end of each of the sections of the buoyancy/ballast tanks 30 to compartmentalize the tanks 30. These valves may be electrically operated and controlled by lines connected with an attending surface vessel (not shown). Such a vessel would be necessary, particularly in deep Water, for providing the lateral support necessary to keep the access caisson 10 in the upright position. Such a floating vessel would necessarily be either anchored or dynamically positioned to maintain a minimum of movement at the upper end of the caisson.
When it is desired to maintain or repair a particular submerged wellhead 14, the access caisson 10 of the present invention is shipped out to the area of the wellhead in sections. The sections are floated in quiet water and bolted together to form as long a caisson as required. The assembly of the access caisson 10 may be accomplished by floating the sections of the caisson on their sides in the water, aligning the adjacent sections of the access caisson and bolting together the portions of abutting end flanges of adjacent sections of the caisson that are above the surface of the water, rotating the caisson 10 to submerge that portion then bolted, and bolting an adjacent portion until the Whole circumference of each pair of abutting end flanges of the sections of caissons is bolted together and is rigidly connected. Care must be taken to seal around the sections of the access tubes 28. If the abutting areas between the sections of the buoyancy/ballast tank 30 are not also watertight, it is necessary to include a shut-off valve 52 (not shown) in the lower end of each of the upper caisson sections 24 also. After the access caisson 10 is completely bolted together to the desired length and towed to well site, its buoyancy/ballast tanks 30 are selectively flooded to tip it over until its axis is vertical. This may be done by utilizing the submersible pumps 44 to fill the buoyancy/ ballast tanks 34) in the base section 22 of the access caisson 10. The air entrapped within the sections of the buoyancy/ballast tanks 30 may be exhausted by opening up the shut-off valves 52. If the flooding of the buoyancy tanks in the base section 22 is not enough to orient vertically the access caisson, another section may be controllably flooded by the use of the pumps 44 in conjunction with the valves 52 in the buoyancy/ ballast tanks 30 between the caisson sections. After the access caisson 10 is vertically oriented it is slowly lowered over the wellhead 14 and into alignment with the landing base 12. Television cameras may be mounted on the outside of the access caisson 10 to help the above-surface personnel to position the lower end of the access caisson, and as a further help in final positioning, a television camera may be set on the circular abutment 28 within the cylindrical hollow interior 41. The lower pumps 42, equally spaced around the access caisson 10 in the tanks 30, function as jet positioning means selectively drawing the water from the cylindrical hollow interior 41 of the access caisson 10 and ejecting it through the peripheral ports 48.
Once the access caisson has settled onto the landing base 12, and the O-rings 34 have sealed the caisson and the landing base 12 together, a sealable plug 54 is lowered down through the cylindrical hollow interior 41 on a wireline 56 to seat on the circumferential abutment 28, defining a working chamber 57 in the lower end of the interior of the access caisson 10. The lower end of the wireline 56 beneath plug 54 has a hook 58 for hanging equipment too large and bulky to be brought down by workmen through the access tubes 29. All the pumps 42 are then turned on to evacuate the working chamber 57 of the access caisson 10 beneath the plug 54. The water in the working chamber 57, as well as the connected access tubes 29, will be evacuated. Two access tubes 29 are not necessary for the functioning of the access caisson; however, the providing of two access tubes permits the structure to continue to be utilized even if one of the access tubes springs a leak during use and must be sealed otf from the working chamber 57. Furthermore, equipment may be lowered down the second access tube while personnel are descending or reascending through the other.
The power and control lines for the submersible pumps 42 and 44, as well as for the valves 52, may be supported along the outside of the access caisson 10 or they may be routed through a separate passageway down through the caisson, if the annulus is solid, or directly between the inner and outer walls of the access caisson, if the annulus is hollow, as previously described. With a proper valving arrangement and manifolding system, only one large capacity pump is necessary. This single pump could be .valved to pump water, into all of the buoyancy/ballast tanks 30, from the working chamber 57 of the caisson 10, through appropriate manifolding or alternately to pump water from the working chamber 57 through selected peripheral ports to jet the caisson 10 into position, and through all of the peripheral ports simultaneously to evacuate the working chamber 57. The reversing of this pump could be utilized for reflooding the access tubes 29 and the working chamber 57 of the caisson as well as to evacuate the buoyancy/ballast tanks 30. An intermediate compromise would be to utilize one pump in the lower end of each of the buoyancy/ ballast tanks 30. Such an arrangement would require valving to exhaust or flood either the buoyancy/ ballast tanks 30 or the working chamber 57 but would not require any manifolding. The design of the necessary valving and manifolding is Well within the capabilities of one skilled in the art and will not be discussed in detail.
After the access caisson has been settled onto the wellhead landing base 12, the buoyancy/ballast tanks 30 are flooded just enough to support solidly the caisson thereon, but not enough to drive the landing base structure down further into the marine bottom or to damage it. When it is later desired to remove the access caisson 10, the access tubes 29 and the lower portion of the interior of the caisson 10, below the plug 54, is again flooded. The plug 54 may then be brought back to the surface with any damaged wellhead equipment, or repair or maintenance tools, hanging from the lower end of hook 58.
Although the present invention has been described in connection with details of a specific embodiment thereof, it is to be understood that such details are not intended to limit the scope of the invention. The terms and expressions employed are used in a descriptive and not a limiting sense and there is no intention of excluding such equivalents, in the invention described, as fall within the scope of the claims. Now having described the apparatus and method herein disclosed, reference should be had to the claims which follow.
What is claimed is:
1. An access caisson for providing atmospheric conditions in an area surrounding a submerged wellhead, said access caisson comprising at least one cylindrical caisson section having a cylindrical hollow interior extending the length thereof; means for sealing the lower end of said access caisson to a landing base of a submerged wellhead; means for selectively closing ofl the lower portion of said cylindrical hollow interior above a wellhead extending thereinto to define a working chamber; at least one watertight access tube connecting said working chamber of said access caisson with the upper end of said access caisson when said working chamber is selectively closed off; and means for evacuating water from said working chamber and said access tube when said access caisson is mounted on and sealed to a wellhead landing base set beneath the surface of a body of water.
2. An access caisson, as recited in claim 1, having buoyancy/ballast means associated therewith; and means for flooding said buoyancy/ballast means to lower said access caisson from said surface vertically oriented.
3. An access caisson, as recited in claim 2, wherein said buoyancy/ballast means comprises a plurality of tanks, each extending substantially the length of said access caisson and positioned equidistantly therearound; and pump means mounted in the lower end of each of said buoyancy/ballast tanks for at least evacuating the water from said buoyancy/ ballast tanks whereby the distribution of weight, and the overall weight of said access caisson, in the water, can be controlled.
4. An access caisson, as recited in claim 1, further comprising an outer wall and an inner wall, the inner face of said inner wall defining said cylindrical hollow interior; and at least one access tube extending through an annulus between said inner and outer walls, said access tube being connected to said working chamber of said access caisson whereby a Workman can reach the working chamber from above the surface of the body of water.
5. An access caisson, as recited in claim 4, further comprising at least two caisson sections; means for aligning and rigidly connecting said sections; and means for sealing around at least the said access tube extending through said sections.
6. An access caisson, as recited in claim 4, further comprising inner and outer walls with a hollow annulus therebetween, said access tube being a tubular member rigidly suspended in said annulus between said inner and outer walls of said caisson.
7. An access caisson, as recited in claim 5, wherein sealing means are provided, between said access caisson sections, only at said access tube whereby the problems associated with sealing the large abutting areas of said access caisson sections are circumvented.
8. An access caisson, as recited in claim 6, wherein a plurality of tubular buoyancy/ ballast tanks are suspended in said annulus equally spaced around said cylindrical hollow interior.
9. An access caisson, as recited in claim 8, wherein valve means are provided in at least one of the ends of a portion of each of said buoyancy/ ballast tanks in each access caisson section whereby air can be released when water is pumped in and said buoyancy/ballast tanks can be compartmentalized when a plurality of caisson sections are aligned and rigidly fixed together.
10. An access caisson, as recited in claim 1, wherein said selective sealing means comprises a circumferential flange fixed on the inner face of said inner wall at the upper end of said working chamber; a large plug supported on said circumferential flange, connected to a point above the surface for lowering into said cylindrical hollow interior and onto said flange to seal the upper end of said working chamber; and article carrying means connected to a lower portion of said large plug whereby equipment can be lowered to the working chamber during the sealing of said working chamber.
References Cited UNITED STATES PATENTS 1,048,194 12/ 1912 Mitchell 61-82 2,051,926 8/1936 Weiner 61-82 2,524,382 10/1950 Goodman 6182 2,534,480 12/1950 Shannon -8 2,691,272 10/1954 Townsend et al 175-8 2,854,215 9/1958 Cox et al. 61-82 X 2,965,174 12/1'960 Haeber 1758 X 2,988,144 6/1961 Conrad 61-82 3,020,956 2/1962 Suderow 1755 3,202,216 8/1965 Watts et a1. l66.6 3,202,217 8/1965 Watts et a1. 166-.6
JAMES A. LEPPINK, Primary Examiner.