US3461957A

US3461957A - Underwater wellhead installation

Info

Publication number: US3461957A
Application number: US627126A
Authority: US
Inventors: Francis G West
Original assignee: Shell Oil Co
Current assignee: Shell USA Inc
Priority date: 1966-05-27
Filing date: 1967-03-30
Publication date: 1969-08-19
Anticipated expiration: 1986-08-19
Also published as: GB1118944A

Description

F. 0. WEST UNDERWATER WELLHEAD INSTALLAT ION Aug. 19, 1969 2 sheetsesheet l Filed March so, '1967 INVENTORZ FRANCIS G. WEST United States Patent 3,461,957 UNDERWATER WELLHEAD INSTALLATION Francis G. West, The Hague, Netherlands, assiguor to Shell Oil Company, New York, N.Y., a corporation of Delaware Filed Mar. 30, 1967, Ser. No. 627,126 Claims priority, application Great Britain, May 27, 1966,

27/66 Int. Cl. E21b 33/035, 43/01 US. Cl. 166.5 3 Claims ABSTRACT OF THE DISCLOSURE The present invention relates to an underwater wellhead installation mounted on a tube cemented to a formation underlying the bottom of a body of water.

According to recent practice, the wellhead installations of wells which have been drilled in formations underlying a body of water are mounted at some distance below the surface of the water so as to reduce navigation hazards. These wellhead installations may be remotecontrolled via electric or hydraulic conduits passing from a suitable control center to the installations, or controlled manually by divers operating either freely or by means of diving bells.

Numerous methods are known for drilling such wells through formations underlying a body of water, the wells being completed by means of wellhead installations which are below the surface of the water but above the bottom of the body of water. Control of the operations which have to be performed by the wellhead installations during the production of oil or gas from the wells on which they are mounted is preferably carried out by remote control. Servicing operations on the wellhead or even in the well itself may be carried out by a diver, provided that the depth at which such an installation is located does not exceed the depth at which a diver can work. To service a wellhead installation manually but without the use of divers, it has already been proposed to install the wellhead installation in a water-tight housing which is arranged below the surface of the sea. Access can be gained to such housing by means of a caisson which at its lower end is connected to the housing in a liquidtight manner, and at its upper end communications with the space above the water. By pumping the water out of the caisson, the hatch giving access to the housing can be opened, and a workman can enter via the caisson. The housing can be located fully above the formation underlying the body of water, or it may extend for the greater part into that formation.

Although the application of the above-mentioned housing used for protecting a submerged wellhead installation will certainly reduce navigation hazards as long as the housing is located at a depth greater than the maximum draught of the ships passing through the area where the housing is located, such housing is, however, liable to damage when used in an area where fishing boats are operating. An object of the present invention is to provide a means suitable for protecting an underwater wellhead installation against damage by boats.

A further object of the present invention is to provide Patented Aug. 19., 1969 "ice a means for protecting an underwater wellhead installation, said means being so designed that no damage will be done to fishing nets, tackle, etc., which are being passed through the water by fishing boats, sometimes very close to the sea bed (e.-g., trawl fishing).

According to the invention, an underwater wellhead installation mounted on a tube cemented to a formation underlying the bottom of a body of water, is located in a cellar structure which has its upper wall substantially flush with the bottom of the body of water.

The expression substantially flush with the bottom of the body of water, or in other words substantially flush with the top of the formation underlying the body of water, means throughout the present specification either in the plane forming the lower boundary of the body of water, or in a plane other than that plane, provided that this second plane has a gently curving slope, intersects the lower boundary of the body of water along a closed line, and shows at its intersection with the first plane an angle which is greater than with respect to this lower boundary.

Preferably, the entry to the cellar is formed by an opening in the upper wall or roof portion of this cellar structure, which opening is covered by a removable lid. If desired, the whole roof portion of the cellar structure may be formed by the removable lid.

In the following, three embodiments of the invention will be described by way of example.

FIGURE 1 is a cross sectional view of a metal cellar structure located below the bed of the sea, which cellar structure is provided with a cover closing the entry to the cellar, the top of the cover being in the same plane as the sea bed;

FIGURE 2 is a cross sectional view of an alternative of the construction according to FIGURE 1; and

FIGURE 3 is a cross sectional view of another alternative construction showing a concrete cellar structure located in the bed of the sea, which cellar has a slightly curved roof portion.

The cellar 1, as shown in FIGURE 1 of the drawing, is located in the formation 2 which lies below the sea 3, the bed or floor 4 forming the boundary between the formation 2 and the sea 3. The top surface of the sea is indicated by line 5. The depth of the sea or body of water may be of any magnitude.

The cellar 1 is bounded laterally by a cylindrical side wall 6 made of metal, and at its bottom end by the circular metal plate 7, which is connected to the wall 6, e.g., by welding. An opening is provided in the plate 7, through which opening the conductor 8 is arranged. Conductor 8 and plate 7 are connected together, e.g., by welding.

The top of the cellar 1 is closed by a cover or lid 9 which has a diameter greater than the diameter of the wall 6 and is supported by a ring member 10 welded to the outer face of the wall 6.

The cover '9 is provided with at least one depression 11 in which a means 12 (such as a bar) is arranged, which means is suitable for being connected to a hook or the like for lifting the cover from the side wall 6 of the cellar 1.

In the embodiment as shown in FIGURE 1, no particular sealing means are arranged between the cover 9 and the side wall 6 (or the ring 10), since the Way in which the cover 9 is supported by the ring member 10 ensures that the amount of foreign matter which can enter in this way into the cellar 1 will be extremely small and will in no way hamper the operations to be carried out within the cellar 1. If desired, however, a simple sealing ring may be arranged to close the entry to the cellar to foreign matter, such as sand or silt.

Through the conductor 8, a casing 13 is arranged. Where this casing protrudes from the lower end of the conductor 8, the greater part of it is cemented to the formation 2, and if necessary to any other formation (not shown) below this formation 2. On top of the casing 13, a spool piece 14 is mounted, which spool piece carries a schematically indicated wellhead 15. The production tubing (not shown) arranged within the casing 13 communicates in a known manner with the wellhead.15, and with the flowline 16 connected via coupling 17 with the Wellhead 15. Since the present invention is not directed to any detail of the wellhead, and in fact any type of wellhead may be used, no details are given in FIGURE 1 of the drawing.

A ladder 18 has been mounted on the inner face of the well 6 to enable the diver or divers to descend into the cellar 1 once the cover 9 has been lifted therefrom.

Although in the design of the cellar structure as shown in FIGURE 1 the flow conduit 16 passes through the side wall 6 of the structure, this flowline may if desired in an alternative arrangement, pass through the bottom plate 7.

The sequence of steps to be carried out for installing the wellhead installation according to the invention will now be described in detail.

The borehole, in which the well is to be arranged, is drilled by means (not shown) such as by rotary drilling equipment which is supported by a floating platform or by a platform supported on legs on the sea bed 4. The first tubing to be placed in the drilled borehole is formed by the conductor 8. To this end, the conductor 8 is connected to the cellar structure consisting of the bottom plate 7 and the side wall 6. The assembly thus formed may be lowered from the drilling platform into a hole which has been pre-drilled into the formation 2. If conditions of the formation 2 so allow, the assembly consisting of the side wall 6, the bottom plate 7 and the casing 8 is spudded in by water jets issuing out of conduits (not shown) which are connected to the assembly and have their outlets located at or near the lower end of the casing 8 and near the bottom plate 7. Suitable pumps (not shown) are arranged on the drilling platform for supplying Water under pressure to these conduits.

While being supported in the position as shown in FIGURE 1 of the drawing, the assembly is then cemented to the formation 2 by using cementing equipment which is normally used for cementing conductors in the formation. The cement is passed in a downward direction through the conductor 8 (or a conduit arranged in the conductor 8) to the lower end thereof, and returns in an upward direction along the outer side of the conductor 8 and the outer face of the plate 7 and the side wall 6. After the cement has hardened, a drill bit with drill string is passed through the cellar 1 and the interior of the conductor 8 to drill a hole through the formation 2. Any type of equipment suitable for submerged drilling and completion of wells may be used for the purpose. Thus, guide lines (not shown) extending between the cellar 1 and the drilling platform may be applied for guiding the required equipment to the entrance of the conductor 8. To this end, suitable coupling means (not shown) may be arranged on the upper side of the bottom plate 7 for connecting the lower ends of the guide lines thereto.

After a sufiicient depth has been reached by the borehole, a casing 13 is introduced into the hole, which casing is cemented to the formations underlying the formation 2. If necessary, other casings (not shown) may be placed.

The well is completed by the spool 14 and the wellhead 15, from which a production tubing (not shown) is suspended into the well. The upper end of this production tubing is connected via coupling 17 to the conduit 16 which has been layed by divers below the sea bed 4, and which passes through the side wall 6.

The ladder 18 may be placed in the cellar structure before lowering the latter into the sea, or after the cellar structure is in place.

After the Well has been completed, the entrance to th cellar 1 is closed by the cover 9. If required, this cover can be bolted to the side wall 6 or even locked thereto to prevent unauthorized entry to the cellar 1. The handling of the cover 9 can be effected from the drilling platform by means of a crane, or by divers using gasfilled bags or other buoyant lifting devices tied to the cover.

The interior of the cellar 1 remains filled with sea water. If desired, corrosion inhibiting means may be placed in the cellar 1.

Alternatively, the cellar may be placed first, by other construction equipment, and form part of the well location to which and over which the drilling outfit is brought up.

It will be clear that the invention is not restricted to the manner as shown in FIGURE 1 for supporting the cover 9. In an alternative manner, the cover 9 may have a vertical flange of a diameter smaller than the inner diameter of the Wall 6 and be supported by a ring member attached to the inner face of the wall 6 as shown in FIGURE 2. In addition, the cover may be provided with a socket 19 (see FIGURE 2) cooperating with a spigot 19" attached to the wellhead 15. If desired, the cover 9 may be made of reinforced concrete.

In the embodiment of the invention as shown in FIG- URE 3, the material used for the construction of the cellar walls is reinforced concrete instead of metal. This type of cellar structure is especially useful in areas in which the shape of the sea bed is liable to undergo changes due to currents or tides.

The cellar 20 in FIGURE 3 comprises an integral concrete structure consisting of the side wall 21, the bottom 22 and the curved roof portion 23. The roof portion 23 is larger than the cellar 20 so that it overhangs the cellar and includes an opening which in the position as shown is closed by a cover 24. The periphery of the roof portion 13 is preferably partially buried in the sea bed or floor 25.

Although the cross-section of the roof portion 23 is part of a sphere in the embodiment as shown, it will be clear that any other curved shape may be used. The angle A between the sea bed or floor 25 and the tangent T-T passing through the vertical axis of symmetry S-S and the place where the outer plane of the roof portion 23 and the sea bed 25 intersected is greater than The bottom 22 of the cellar 20 is provided with an opening through which a conductor tubing 26 which is cemented to the formation 27 underlying the sea bed 25 passes in a liquid-tight manner. The upper end of the conductor 26 is not flush with the bottom 22 of the cellar as in the embodiment shown in FIGURE 1, but extends up to a level between the bottom and the to of the cellar 20.

Supported by the conductor 26 and/or by the wall(s) of the cellar 20, a working-platform 28 is arranged at some distance above the bottom 22, thereby creating a space in the lower part of the cellar 20 suitable for the storage of a liquid 35 having a specific gravity greater than the specific gravity of the sea water. 1

A wellhead 29 is mounted on top of the casing 30 and communicates with a conduit 31 which passes through the side wall 21 of the cellar 20 and runs below the sea bed 25 to a place where the product produced from the well can be used or stored.

Also mounted in the cellar 20 is a pump system comprising a suction conduit 32, a pump 33 and a pressure conduit 34, the outlet of which communicates with the tubing system arranged Within the well. By filling the lower part of the cellar 20 with glycol a continuous or interrupted injection of glycol by means of this pump system will prevent hydrate forming if the well produces gas. The energy for activating the pump may be obtained from the gas flowing from the well. If desired, a liquid other than glycol may be stored in the lower span of the cellar 20.

The liquid may be supplied to the cellar 20 by a small pipeline from a control center or by a hose from a supply-boat on the sea surface.

Instead of using an open space for the storage of liquid as indicated in FIGURE 3, a fully formed tank may be situated in the lower part of the cellar 20, thereby creating a space suitable for storing liquids (having a specific gravity either lower or higher than the specific gravity of the sea water) to be used for injection into the well (e.g., an inhibitor or an anti-hydrate formation liquid). Such liquid is then entirely separated from the sea water, and can be pumped to the desired location by a pump system suitable for the purpose. The liquid may be replenished in the same manner as described above with reference to FIGURE 3.

The advantage of the curved roof portion 23 of the cellar 20 will be apparent from FIGURE 3. Even when the material from the upper layer of the formation 27 is displaced, thereby forming hollows in the locality of the cellar structure, this structure does not show any point onto which objects such as anchors or trawl nets being dragged over the sea bed can hook. Damage of the cellar structure as well as anchors or trawl nets is thus prevented.

The concrete cellar structure is preferably placed on fl1e desired location before the drilling operations start. The conductor tubing is then placed in position in a drilled hole by lowering it through the opening provided in the bottom 22. If desired, any other manners of placing the conductor 26 may be applied. The conductor is then cemented to the formation 27, and if necessary, the opening left between the conductor tubing 26 and the bottom 22 may be closed off by divers using suitable sealing material. The operations for placing the casing 30; the wellhead 29 and the flowline 31 take place in a manner similar to that described with reference to FIGURE 1.

It will be clear that the invention is not restricted to cellar structures with curved roof portions 23 extending outside the area enclosed by the side wall 21 as shown in FIGURE 3. If desired, the area enclosed by this wall 21 may be enlarged, and the wall 21 may be connected to the roof portion 23 near the outer edge thereof.

The axis of the well need not necessarily coincide with the axis of the cellar structure as shown in FIGURES 1, 2 and 3. However, the cover or lid closing the opening provided in the roof portion of the cellar must be above the well entry. This cover or lid may be of any shape, but is preferably of circular form.

The interior dimensions of the cellar have to be sufiicient to allow a working space for at least one diver. Preferably, the diameter of the cellar, provided with a cylindrical side wall is used, is about 3 feet. A height of about 3% feet will be sufiicient as working height. If

6 liquid is stored (see FIGURE 3), a greater height of the cellar will be required.

When using a diving bell for servicing the Well, it is preferred to arrange means within the cellar or on the roof portion thereof suitable for centering the diving bell on the cellar structure.

I claim as my invention:

1. An underwater wellhead installation comprising:

a substantially closed cellar structure mounted substantially flush with the floor of a body of water, said cellar including an enclosed vertical wall, a bottom having at least one opening and a top closure;

a well casing conductor extending through said opening in said bottom and extending downwardly into a formation underlying the floor of said body of water;

said top closure having a generally dome shaped roof secured to and overhanging said vertical wall;

said roof being formed with an access opening in communication with the interior of said cellar structure;

a removable cover carried by said roof to close said access opening;

said cellar structure forming an enclosure for a wellhead positionable on the well casing extending through said conductor into a formation underlying said floor of said body of water; and,

wherein the lower portion of said cellar structure comprises a liquid storage chamber.

2. An underwater wellhead installation as defined in claim 1 including:

pump means mounted within said cellar structure and having an inlet in communication with said liquid storage area and an outlet in communication with said well.

3. An underwater wellhead installation as defined in claim 2 including:

a working platform carried by said cellar structure and arranged above said liquid storage chamber.

References Cited UNITED STATES PATENTS 2,729,966 1/ 1956 Lutteke 52169 X 2,747,840 5/1956 Miles -9 2,756,021 7/1956 Townsend et al 175-9 X 2,854,215 9/1958 Cox et al 166-.5 3,063,500 11/ 1962 Logan 166-.5 3,202,218 9/ 1965 Watts et al 166.5 3,247,672 4/ 1966 Johnson 166.5

CHARLES E. OCONNELL, Primary Examiner R. E. FAVREAU, Assistant Examiner