US3421579A - Underwater completion - Google Patents

Description

- Jan.14, 1969 NF. MANNING 3,421,579

UNDERWATER COMPLET ION Filed June 17, 1965 FIG I INVENTOR WlLLlAM E MANNING BY CZZQN 12 (6M United States Patent 4 Claims ABSTRACT OF THE DISCLOSURE This specification discloses apparatus for providing a life-sustaining environment in an area adjacent to and surrounding a submerged production wellhead. The apparatus comprises a base structure including an upper and lower base connected by an open framework, and a chamber mounted on the base capable of retaining air. The base structure is either mounted directly on the marine bottom, if the respective wellhead is located just above the marine bottom, or the base structure may be fixed to a caisson structure above the marine bottom, if the wellhead is afiixed atop such a caisson structure for spacing the wellhead above the marine bottom at a convenient diving depth. The chamber is mounted on top of the base and has a scalable entry port above the lower end thereof. The chamber may also be open at the lower end so that a diver-workman can enter through the framework of the base structure which spaces the chamber at least far enough above the marine bottom for such a diver-workman to enter. Means is provided for providing a breathable atmosphere inside the chamber when maintenance operations are necessary. This last stated means can be an air hose connected to a port extending through the wall of the chamber or, if the lower end of the chamber is open, an air hose may be extended therethrough, the other end of the hose being connected to an air pump on a surface vessel floating above. In some instances the chamber may be releasable from the base structure so that it can be lifted to the surface to serve a second function, that of a traveling chamber to transport a workman to the wellhead. When the wellhead is not being serviced, the chamber can be filled with a protective fluid to prevent an attack on the wellhead by sea water and/ or undersea life.

The invention relates to a facility for servicing a submerged production wellhead, more particularly to a facility capable of permitting a workman to service the submerged wellhead without being restricted by personal life-sustainin g equipment.

In coastal offshore waters where fluid mineral deposits, i.e., oil exists in the subaqueous formations underlying the marine bottom, it is usually inconvenient, and many times impractical, to complete a well above the surface of the body of water. In such instances the well can be completed near the marine bottom and the minerals produced through flow lines connected to the submerged wellhead. Although a submerged production wellhead design may successfully overcome some of the design problems previously encountered when the wellhead is extended above the surface, for example, the forces on the wellhead and the depending casing, caused by the action of waves on the wellhead, new problems are created in conjunction with the servicing thereof. Being situated near the bottom of a body of sea water, the wellhead is in a hostile environment. It is under continuous attack from marine life and the corrosive effects of the salt water itself. The equipment must be checked periodically, crustaceous deposits removed, and corroded equipment replaced.

Although robot equipment has been suggested for serv- 3,421,579 Patented Jan. 14, 1969 icing submerged wellheads, it has been found that a workman can do a more efiicient job in a shorter time, particularly if he is not encumbered by personal lifesustaining equipment, such as a diving suit, or limited by the time in which he can work at the required depth. Therefore, one of the new problems created by having the wellhead near the bottom is how to provide an environment in which a man can work on the submerged wellhead without personal Ilife-sustaining equipment. Another is how to protect the production wellhead from the hostile environment.

Accordingly, it is an object of this invention to create an environment, at a submerged wellhead, in which a man can work on the wellhead without the encumbering restrictions of personal life-sustaining equipment.

It is another object of the invention to provide a well servicing facility with a base structure surrounding the submerged well casing, on which a diver may work when servicing the wellhead, and which may serve as support for an air chamber enclosing the production wellhead itself.

It is a further object of the invention to provide a wellhead servicing facility which is designed to allow a diver-workman lowered to the production wellhead to work thereon without personal life-sustaining equipment.

It is another object of the invention to provide a method for servicing a submerged production wellhead with a diver-workman including having the diver-workman enter the air chamber from the surrounding water, seal the chamber, and provide a life-sustaining atmosphere in the chamber whereupon the diver-workman can remove his personal life-sustaining equipment before servicing the production wellhead equipment.

It is still a further object of the invention to provide a protective environment for the production wellhead to reduce maintenance time.

All the objects and advantages of the invention will become apparent from the following description and from the accompanying drawings in which:

FIGURE 1 is a side elevational view of the production wellhead servicing facility of the present invention which includes a base structure and an air chamber, the base structure being shown through section line 11 as indicated in FIGURE 2;

FIGURE 2 is a top plan view of the base structure, taken through line 22 of FIGURE 1, illustrating the framework of the base structure designed to support the air chamber.

In accordance with the present invention, a hollow airretaining chamber encases a production wellhead of a completed well and is supported on a base structure. The base structure consists of an open framework and is anchored by a number of shear plates or spuds rigidly fixed thereto, and driven into the marine bottom. Also, casting slips are operatively connected between the base structure and the well casing, below the wellhead, to help anchor the structure when the chamber is evacuated of water and filled with air. In this connection, the term air is used in the generic sense to connote any breathable mixture of gases. A walk-around platform circumscribes the base structure at the upper end of the framework beneath the base of the air chamber.

The air chamber is a vertical cylinder surrounding the well head and closed at least at its upper end. The air chamber, being spaced from the marine bottom on the open framework of the base structure, is situated so that a diver-workman can enter through an opening in the bottom thereof. A sealable emergency manhole or entry port is formed in the air chamber to permit a man to escape from the enclosed space if the lower end of the air chamber becomes blocked. If the manhole emergency entry port is used to gain entrance to the air chamber,

air must be reintroduced and the water expelled, before the workman can remove his personal life-sustaining equipment in preparation for starting theservicing operation. While in the usual case the air chamber bolts or otherwise rigidly connects to the base structure, the air chamber may be releasably connected to the base structure so that the chamber can be raised to the surface at will. A workman can then descend with the chamber, obviating the need for personal life-sustaining equipment at any stage. In another embodiment, the air chamber is bolted permanently to the supporting structure and when not in use, as a means to permit a diver-workman to service the wellhead Without personal life-sustaining equipment, is filled with a light oil or some other substance which deters marine life from attacking the production wellhead and prevents the corrosive action of the salt water upon the metal parts thereof.

Referring now to the drawings, a submerged well servicing facility, generally designated 10, consisting of a base structure 12 and a substantially cylindrical air chamber 14, is shown surrounding a well casing 18, extending up from beneath the marine bottom and a submerged production wellhead 16 capping the well casing 18. The base structure 12 consists of a framework of beams forming parallel octagonal bases, a lower base 22 and an upper base 24, spaced apart by a number of fixed struts 26 converging upwardly from the larger, lower base 22 to the smaller, upper base 24. A flow line 27 for the produced minerals, and any other necessary lines connected to the wellhead 16, exits from the enclosed air chamber 14 through an opening in the bottom thereof and through the open framework of the base structure to production facilities (not shown). A casing slip assembly 28, which is adapted to grip the well casing 18 adjacent the bottom 20 is centrally mounted within the base structure 12 by means of diverging struts 30 extending upwardly from the perimeter of the casing slip 28 to the perimeter of the upper base 24. The base structure 12 is also anchored on the marine bottom 20 by means of a number of integral spuds 32 depending vertically from the lower base 22 and driven into the formations underlying the marine bottom 20. Between the spuds 32 and the casing slip assembly 28, the platform 12 and air chamber 14 are securely positioned adjacent the marine bottom 20, below the surface of the body of water. To overcome the buoyancy of the air chamber 14, additional weight, such as scrap iron, may be attached to the framework of the base structure 12.

The cylindrical air chamber 14 is fixed atop the upper base 24 adjacent an encircling walk-around platform 34, welded to the base structure 12 and extending radially outward several feet therefrom to provide a solid footing for a diver-workman servicing the wellhead 16. A flooring (not shown) may be included between the bottom of the air chamber 14 and the upper base 24 for a diverworkman to stand on within the air chamber 14. A cover 36, serving to seal releasably entry port 38, formed in the upper end of chamber 14, enables a diver-workman to enter the air chamber 14 while the chamber 14 is submerged and filled with water, or other fluids, as later discussed. The lower end of a buoy line 39 is fixed to the upper end of the air chamber 14 and is connected, at its upper end (not shown) to a buoy for locating the air chamber 14 from the surface.

An air hose (not shown), terminating with a quick release coupling, as well known in the art, is adapted to be operatively connected to the interior of the chamber 14 by a port 40, extending through the outer wall thereof. The port 40 is located in a position where it may be reached by a diver (not shown) standing on the walkaround 34, enabling the diver-Workman to couple the air hose to the port 40 to introduce air into or circulate air through the chamber 14 under the control of pumps on the surface (not shown). If the chamber 14 is bottomless, or at any rate is not completely closed, the air hose may alternatively extend up into the chamber 14 from beneath (not shown). It would be necessary to have an unbroken flooring only if the wellhead 16 were deeply submerged in the water and it would be desirable to have the air in the chamber at less pressure than the water at the working depth.

The base structure 12 is anchored in place prior to the completion of the Well (not shown) and may even be anchored in place prior to drilling the well, being used as a guide means for stabbing in the well casing 18. In any event base structure 12 must be in place before production wellhead 16 is connected to the well casing 18, while the air chamber 14 bolts in place after the well is completed and the well casing 18 is capped by the production wellhead 16. The walk-around 34 may be used by a diverworkman for connecting up the wellhead 16 prior to the introduction of the air chamber 14, since the submerged land adjacent the wellhead 16 is often too soft to provide suitable footing, or the top of the well casing 18 may be too far above the marine bottom 20 to permit installation of the production wellhead 16 by a diver-workman standing thereon. The air chamber 14 secures rigidly to the upper base 24, as discussed above, or connects thereto by a number of releasable locks 42. If the air chamber 14 releasably connects to the base structure 12, it may be brought to the surface for a workman to enter thereinto without the aid of any diving apparatus; the entry port 38 and cover 36 can then be relegated to function only as an emergency escape hatch. In this instance the chamber 14 is brought to a position above the surface and is then ballasted with enough weight so distributed that it will remain in the vertical position as it is lowered through the water filled with air. As the chamber 14 approaches the well the diver-workman inside can guide it over the production wellhead 16, or a number of the various types of guide ropes, or stab-in connections, as shown in the prior art, can be used for guiding the air chamber 14 into connection with the base structure 12. If a floor is constructed on the upper base 24, and sealed to the well casing 18, a circumferential seal (not shown) may also be included around the base of the chamber 14 to provide a watertight connection therebetween, or it may be open beneath the air chamber 14, with air pressure therewithin keeping the water out. Of course, with the air chamber 14 also providing underwater transportation, the releasable locks 42 would be therewithin to obviate need for any operations to be performed in the open water.

An air chamber 14 of the permanently fixed type, may be used, when not occupied by a diver-workman, as an environmental shield containing oil or a noncorrosive gas for preventing an attack on the production wellhead 16 by the corrosive action of the sea water and/ or by barnacles, or other types of undersea life which will quickly cover an exposed device and cause heavy formations on and extensive damage to the wellhead 16.

A wellhead servicing facility 10, such as discussed herein, is designed for use in oifshore or costal areas where the water is approximately feet or so deep. There is no reason, however, why it cannot also be used when the water is much deeper, even 1500 feet. Such a servicing facility 10 may also be used where the water is extremely deep but the well is completed at a point considerably above the ocean floor. In such an instance a large submerged caisson or support structure would extend from the ocean floor to the lower base 22, or the base structure 12 could be held in position solely by casing slips connected to the well casing 18.

Although the present invention has been described in connection with details of the specific embodiments 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 suoh equivalents, in the invention described, as fall within the scope of the claims. Now having described the apparatus and methods herein disclosed, reference should be had to the claims which follow.

What is claimed is:

1. A servicing facility for a submerged wellhead located above a marine bottom and below the surface of a body of water, said wellhead being operatively connected to a well casing extending beneath said bottom of said body of water, comprising an air-retaining chamber, the weight of said chamber being supported beneath said surface on a base structure in a position in which said chamber encases said wellhead, said base structure having at least one casing slip assembly means encircling and gripping said well casing below said wellhead whereby said chamber is held in position by said base structure when said chamber is buoyant as well as when said chamber is not buoyant, means for selectively introducing air into said chamber to fill substantially said chamber surrounding said wellhead, and means for permitting a workman to enter said chamber whereby a workman can service said wellhead without being encumbered by personal life-sustaining equipment.

2. Said wellhead servicing facility of claim 1, wherein said base structure extends from marine bottom to said chamber, and means for anchoring said base structure into said marine bottom.

3. A wellhead servicing facility for a submerged wellhead located above a marine bottom and below the surface of a body of water, said wellhead being operatively connected to a well casing extending into a well beneath said marine bottom of said body of water, comprising; an air-retaining chamber encasing said wellhead and a base structure surrounding said well casing below said chamber for supporting said chamber; said chamber having a cylindrical shape oriented so that its axis of formation is vertical, a closed upper end of said chamber, an entry port in Said closed upper end, a cover for said entry port forming an airtight seal therewith when said entry port is closed by said cover, means for selectively introducing air into said chamber to displace any other fluid therewithin; said base structure being constructed of an upper base and a lower base surrounding said well casing, struts interconnecting said bases to provide an open framework, a casing slip assembly rigidly supported within said base structure and gripping said well casing to prevent upward movement of said base structure, integral spud means depending from said lower base into said marine bottom to anchor said base structure, a circular walk-around platform surrounding said base structure adjacent said upper base, and means for connecting said base structure to said chamber at the lower end thereof.

4. A servicing facility for a submerged wellhead located above a marine bottom and below the surface of a body of water, said wellhead being operatively connected to a well casing extending beneath said body of Water, comprising an air-retaining chamber, said chamber being supported beneath said surface on a base structure in a position in which said chamber encases said wellhead, a circular walk-around platform supported on said base structure adjacent the upper end thereof, said walkaround platform extending outward of said chamber when said chamber is supported on said base structure whereby said walk-around platform can be used by a diver-workman, wearing personal life-sustaining equipment, to connect said chamber to said base structure or to connect said wellhead to said casing prior to the installation of said chamber, means for selectively introducing air into said chamber to fill substantially said chamber surrounding said wellhead, and means for permitting a workman to enter said chamber whereby a workman can service said wellhead without being encumbered by personal life-sustaining equipment.

References Cited UNITED STATES PATENTS 3,353,364 11/1967 Blanding et a1 166-.5 1,948,934 2/ 1934 ORourke 61-69 2,190,330 2/1940 Martine 61-69 2,534,480 12/1950 Shannon -8 2,667,751 2/ 1954 Osborn 61-69 2,747,840 5/1956 Miles 166-.5 X 2,783,970 3/1957 Gillespie 166-.5 X 2,854,215 9/1958 Cox et al. 166-.5 2,906,500 9/1959 Knapp et al 166-.5 3,004,602 10/1961 Kofahl 175-8 3,294,185 12/ 1966 ONeill et al. 166-.5 X

FOREIGN PATENTS 160,865 4/ 1921 Great Britain.

CHARLES E. OCONNELL, Primary Examiner.

R. E. FAVREAU, Assistant Examiner.

US. Cl. X.R.

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