Underwater variable buoyancy systems and methods

Abstract

An underwater variable buoyancy member includes a tubular configured for underwater disposal and having a longitudinal axis with an internal bore. The internal bore is configured to receive a conduit in coaxial alignment with the longitudinal axis of the tubular, wherein the conduit is configured for conveyance of fluids. The tubular has a wall section configured to contain a gas and a liquid therein. The wall section is configured to receive the gas under pressure to permit selective buoyancy adjustment of the tubular. An underwater variable buoyancy system and method for buoying an underwater conduit.

Description

UNDERWATER VARIABLE BUOYANCY SYSTEMS AND METHODSCross Reference to Related Applications

[0001] Not applicable.Background

[0002] This disclosure relates to the field of underwater fluid conveyance. More particularly, the disclosure relates to methods and devices for establishing a desired buoyancy of an underwater conduit to facilitate near surface separation and connection.

[0003] Marine oil and gas operations entail the conveyance of hydrocarbons from the sea floor to a vessel (e g., a ship or platform) at the water surface. Specially constructed conduits known as “risers” are used to convey fluids between the subsea equipment and the surface vessel. In certain situations, for example emergency situations or hurricane weather conditions, it may be necessary to separate the vessel from the riser. Disconnection or separation may be performed, for example, by uncoupling connection joints near the wellhead after closing one or more pressure control elements in the stack at the sea floor. Separation may include, for example, unthreading threaded connectors, removing coupling bolts from mating flanges and / or releasing a profile connector by rotating components of the stack. Upon separation of the riser from the stack, the riser may be dragged by the vessel as it is tripped to surface. Separation and recovery of the riser to the vessel may take 10-14 days to complete. Reconnection of the conduit between the vessel and the subsea stack also takes some time and requires smooth seas. A need remains for improved conduit separation techniques, especially for separation near the water surface and in a manner that preserves the integrity of the conduit and the connection at the sea floor.Summary

[0004] An underwater variable buoyancy member according to an aspect of this disclosure includes a tubular configured for underwater disposal and having a longitudinal axis with an internal bore. The internal bore is configured to receive a conduit in coaxial alignment with the longitudinal axis of the tubular, wherein the conduit is configured for conveyance of fluids. The tubular has a wall section configured to contain a gas and a liquid therein. The wall section is configured to receive the gas under pressure to permit selective buoyancy adjustment of the tubular.

[0005] An underwater variable buoyancy system according to an aspect of this disclosure includes a conduit disposed underwater and configured for conveyance of fluids from subsurface to a vessel at water surface. A tubular is disposed underwater on the conduit, with the conduit passing through an internal bore in the tubular. The tubular has a wall section configured to contain a gas and a liquid therein. The wall section is configured to receive the gas under pressure to permit selective buoyancy adjustment of the tubular.

[0006] A method for buoying an underwater conduit according to an aspect of the present disclosure includes deploying a conduit underwater, the conduit configured for conveyance of fluids from subsurface to a vessel at water surface. The conduit has a tubular disposed thereon, with the conduit passing through an internal bore in the tubular. Air is injected into a wall section of the tubular configured to contain a gas and a liquid therein to permit selective buoyancy adjustment of the tubular.Brief Description of the Drawings

[0007] The following figures form part of the present specification and are included to further demonstrate certain aspects of the present disclosure and should not be used to limit the claimed subject matter. A more complete understanding of the disclosed embodiments and further features and advantages thereof may be acquired by referring to the following description taken in conjunction with the accompanying drawings, in which like reference numerals may identify like elements, wherein:

[0008] FIG. 1 shows a perspective view of a variable buoyancy member embodiment according to the present disclosure.

[0009] FIG. 2 shows a perspective view of two sectors that form the variable buoyancy member embodiment of FIG. 1.

[0010] FIG. 3 shows an exploded view of two sectors that form a variable buoyancy member embodiment according to the present disclosure.

[0011] FIG. 4 shows a partial perspective view of two sectors that form a variable buoyancy member embodiment according to the present disclosure.

[0012] FIG. 5 shows a perspective view of variable buoyancy member assembly according to the present disclosure.

[0013] FIG. 6A shows a conduit suspended from a vessel at water surface to a well stack at the sea floor according to the present disclosure.

[0014] FIG. 6B shows the conduit of FIG. 6A after a separation event according to the present disclosure.

[0015] FIG. 7 shows a cross-section of an emergency connector embodiment according to the present disclosure.

[0016] FIG. 8A shows a connector equipped with a wet mate connector according to the present disclosure.

[0017] FIG. 8B shows the connector of FIG. 8 A coupled to a conduit according to the present disclosure.

[0018] FIG. 9 shows a series of variable buoyancy members coupled together to form an assembly according to the present disclosure.Detailed Description

[0019] The foregoing description of the figures is provided for the convenience of the reader. It should be understood, however, that the embodiments are not limited to the precise arrangements and configurations shown in the figures. Also, the figures are not necessarily drawn to scale, and certain features may be shown exaggerated in scale or in generalized or schematic form, in the interest of clarity and conciseness. In the development of any actual embodiment, numerous implementation-specific decisions may need to be made to achieve the design-specific goals, which may vary from one implementation to another. It will be appreciated that such a development effort, while possibly complex and time-consuming, would nevertheless be a routine undertaking for persons of ordinary skill in the art having the benefit of this disclosure. The following detailed description of exemplary embodiments, read in conjunction with the accompanying drawings, is merely illustrative and is not to be taken as limiting the scope of the invention.

[0020] FIG. 1 shows an example embodiment of a variable buoyancy member 50 according to this disclosure. The member 50 is formed as an elongated tubular 52 with a longitudinal axis, a first end 54, and a second end 56. An internal bore 58 runs through the entire length of the tubular 52. FIG.2 shows the two separate tubular sectors 52A, 52B forming the variable buoyancy member 50 embodiment of FIG. 1. Each sector 52A, 52B has a series of mating pins 60 and correspondingreceptacles 62 arranged to coincide with one another when the two sector halves are joined to form the unitary tubular 52. Each sector 52A, 52B has a first bracket 54A, 54B at the first end 54, and a second bracket 56A, 56B at the second end 56. The brackets 54A, 54B, 56A, 56B are configured with orifices to receive multiple fasteners 64 (e.g. bolts).

[0021] The embodiment of FIG. 2 also includes connection tubes 66 mounted on the brackets 54A, 54B, 56A, 56B at the end of each sector 52A, 52B. Each bracket 54A, 54B, 56A, 56B is also configured with a centralizing brace 67 mounted on the interior surface of the bracket. As shown in FIG. 1, when the two sectors 52A, 52B are united, the centralizing braces 67 form a collar and the sectors are secured to one another via the fasteners 64.

[0022] FIG. 3 shows an exploded view embodiment of a variable buoyancy member 50. Each tubular sector 52A, 52B is exploded to show the component parts. An curved inner shell 68 is partially disposed within a curved outer shell 70. A series of arc-shaped ribs 72 are mounted in between the inner shell 68 and the outer shell 70 to maintain a uniform semi-annulus spacing 74 between the shells and to provide overall mechanical support for the sector 52A, 52B. The inner ribs 72 have holes 76 formed thereon to permit the passage of gas and liquids through the entire length of the sector. Each sector 52A, 52B includes a pair of flat slats 78 that close the gap between the inner 68 and outer 70 shells. One slat 78 includes the holes forming the receptacles 62 and the other is configured with the pins 60 (see FIG. 1).

[0023] Each sector 52A, 52B also includes an elongated tube 80 positioned within the semiannulus formed between the inner 69 and outer 70 shells. The tubes 80 permit conveyance of liquid and gas between interconnected buoyancy members 50 (See FIGS. 4 and 5). A pair of end arcs 82 close the ends of each sector 52A, 52B, with porting holes 84 to permit the injection of gas and liquids into the wall section forming the semi-annulus 74. Some sector 52A, 52B embodiments may be formed with metal components (e.g. stainless steel) welded together to form fully sealed units, with end ports 84 to permit injection / discharge of gas or liquids within the semi -annulus 74. It will be appreciated by those skilled in the art that other embodiments may be implemented with non-metallic components or a combination of metal and non-metal components (e.g., plastics, composites, etc ).

[0024] FIG. 4 shows the two sectors 52A, 52B fully sealed, with the tubes 80 running through first brackets 54A, 54B at the first end 54. Each bracket 54A, 54B includes ports 86 running through the entire width of the bracket to permit the respective tube 80 to pass through the firstend 54. It is understood the second end 56 of each sector 52A, 52B is similarly configured with the other tube 80 ends passing through the ports 86 formed in the second brackets 56A, 56B at the second end 56 (see FIG. 1).

[0025] FIG. 4 also shows each bracket 54A, 54B outfitted with a centralizing brace 67 mounted on the interior surface of the bracket. When the sectors 52A, 52B are mated to form the tubular 52, the braces 67 form a collar that aids to maintain the conduit (e.g. riser) passing through the internal bore 58 centered and the tubular 52 secured onto the conduit 101 exterior surface (see FIG. 6A). The braces 67 may be affixed to the brackets 54A, 54B in various ways (e.g., fitted within slots in the bracket, welded, via fasteners, adhesives, etc.). The braces 67 may be formed of metal or other materials (e.g. rubber compounds) that are less prone to damage the exterior surface on the conduit 101. The braces 67 may also be formed with one or more channels 88 formed to align with the longitudinal axis of the tubular 52. When the sectors 52A, 52B are joined to form the tubular 52, the channels 88 provide a guide to allow for passage through the tubular 52 of additional hoses, tubing, and cabling (e.g., see 112 in FIG. 8A) that is typically run with subsea conduits 101.

[0026] FIG. 5 shows a series on individual variable buoyancy members 50 coupled together via the fasteners 64. FIG. 5 shows the open end of one of the tubulars 52 making up the buoyancy member 50 string. It will be appreciated that any number of individual tubulars 52 may be coupled together to achieve the desired conduit buoyancy state required for an operation. FIG. 5 also shows the tubular 52 configured with a pair of connection tubes 66 extending from the end of the brackets 54A, 54B. The connection tubes 66 are configured with seals (e.g. O-rings) and allow for fluid- tight injection and conveyance of gas and liquid into and between the coupled members 50.

[0027] FIG. 6A shows a drilling vessel 100 with a conduit 101 suspended therefrom and running to the sea floor 102 for extraction of subsurface hydrocarbons. At the sea floor 102 the conduit 101 is shown coupled to a wellhead and blowout preventer 104. It will be appreciated that the conduit 101 can extend upward for thousands of feet toward the vessel 100 depending on the depth of the producing well.

[0028] As shown in FIG. 6A, the conduit 101 runs through the internal bore 58 of the variable buoyancy member 50 assembly (e.g., one or multiple coupled members 50). In operation, the buoyancy member(s) 50 may be mounted on the conduit 101 before underwater deployment of the conduit 101. Sea water or any desired fluid can be pre-injected into the tubular(s) 52 prior todeployment of the conduit 101 from the vessel 100. Alternatively, fluid can be injected into the tubulars 52 via additional hosing (e.g., see 112 in FIG. 8A) run from the vessel 100 to the connection tubes 66 on the top end of the member 50 string. The fluid is then displaced throughout the individual members 50 via the porting and tubes 80 as described herein.

[0029] FIG. 6A also shows a configuration including a conventional hydraulic connector 106 as known by those skilled in the art. The connector 106 is linked to the conduit 101 above the buoyancy member(s) 50. FIG. 6A also shows the conduit 101 string including an emergency connector 108 coupled into the string above the buoyancy member(s) 50 (further described with respect to FIG. 7 below). When it is required to separate the conduit 101 from the vessel near the water surface (e.g., an emergency hurricane event), air or any other suitable gas is injected into the tubulars 52 via the hosing / valves used to inject the liquid. In this manner, the buoyancy state of the suspended conduit 101 can be varied between neutral buoyancy and maximum buoyancy. For example, the members 50 can be deployed on the conduit 101 partially -filled with water to facilitate deployment of the conduit, and if greater buoyancy is desired, air can be injected under pressure via the hosing to expel the water which is discharged via a conventional escape valve mounted on the tubulars 52 (e.g., mounted to a connection tube 66 at the lower end of the bottom member 50).

[0030] FIG. 6B shows the conduit 101 suspended from the sea floor 102 after the conduit has been separated from the vessel 100 near the water surface. The variable buoyancy member 50 assembly has been filled with sufficient air to put enough buoyancy (represented by the arrow in FIG. 6B) into the conduit 101 string to leave it erect after the separation event. In this manner, the disclosed variable buoyancy members 50 provide an efficient and reliable means for separation of a conduit 101 from a vessel 100 without having to trip thousands of feet of conduit and engage in expensive and time consuming reconnection procedures at the sea floor. The variable buoyancy members 50 provide for easy and effective conduit separation-reconnection operations at a fraction of the time and cost compared to conventional techniques.

[0031] The embodiment shown in FIG. 6A includes a conventional hydraulic connector 106 and an emergency connector 108 mounted on the conduit 101 string. It will be appreciated that embodiments may be implemented with both connector types 106, 108 or only one type of connector disposed on the string. An advantage provided by use of an emergency connector 108 is the practically immediate separation ability of such connectors. Useable emergency connectors108 include the connectors disclosed in, for example, U.S. Patent 11,187,052 and Patent Pub. PCT / US2023 / 033570, both assigned to the present assignee and incorporated herein by reference in their entirety.

[0032] FIG. 7 shows a sample embodiment of an emergency connector 108 from PCT / US2023 / 033570 that may be used in implementations of the present disclosure. In this embodiment, explosively frangible fasteners 40 comprise a bolt configured with an explosively frangible nut 42. Each explosively frangible nut 42 is linked to an electrical lead 24 via a wire 44 coupling the two components. The explosively frangible nuts 42 are protected from the external environment as each nut resides in a recess 46 formed on the connector 108 member 12. In some embodiments, explosively frangible studs, bolts, or other types of explosively frangible fasteners could be used instead of explosively frangible nuts 42. This embodiment allows the first 12 and second 14 coupling members to detach from one another without any hindrance upon activation of the explosively frangible fasteners 40. As shown, embodiments can be implemented with one or more secondary through bores 18 housing a set of sleeves 30A, 30C mounted within the bore. The through bores 18 allow for hoses, tubing, electrical wiring, or other auxiliary lines to pass through the connector 108 body.

[0033] Selective activation of the explosively frangible fasteners 40 can be achieved via a triggering signal sent from a controller 110 configured with electronics and software to convey a signal to the connector 108 when explosive separation of the conduit 101 is required. The controller 110 may comprise any suitable microcomputer programmed to perform the operations disclosed herein. In some embodiments, the controller 110 may be located on the vessel 100 with signal communication conveyed wirelessly or via cabling run along the conduit 101. The controller 110 may also be used to actuate injection of water and air into the deployed variable buoyancy members 50 as described herein. It will also be appreciated that the electric power source to trigger activation of the explosive fasteners 40 may be located locally on the connector 108 (e.g. a battery) or supplied from a remote source via conventional cabling. The controller 110 may also be programmed to autonomously trigger actuation of the explosive fasteners 40 upon activation by an angle detection unit. When implemented with an emergency connector 108, conduit 101 separation can be achieved in seconds. In situations where instantaneous separation is not required, conduit 101 separation can be achieved by manual disengagement of the coupling fasteners on the hydraulic connector 106 by a diver or via a remotely operated vehicle.

[0034] FIG. 8A shows another embodiment of a conventional hydraulic connector 106 that may be implemented with the buoyancy members 50. This embodiment is configured including conventional signal / power connectors for underwater applications known as “wet mate” connectors 110. The wet mate connectors 110 allow for rapid separation and reconnection of the conduit 101 from the vessel 100 while providing a reliable junction for the transfer of actuation signals and / or electrical power from the vessel to the buoyancy member 50 assembly. FIG. 8A also shows the hoses / tubing 112 that may be run with the conduit 101 to provide the gas and liquid to adjust the buoyancy of the buoyancy members 50 as described herein. FIG. 8B shows the connector 106 coupled to the conduit 101 with the wet mate 110 connection engaged.

[0035] FIG. 9 shows a string of variable buoyancy members 50 with a conduit 101 segment disposed therein through the internal bore 58, ready for coupling to the connector 106, 108 at the upper end and to the conduit 101 string at the lower end. It will be appreciated that each buoyancy member 50 may range in diameter (e.g., to approximately 73 inches [185 cm]) and extend to approximately 24 feet (7.3 meters) in length. A string of members 50 may extend for several hundred feet in deep water operations..

[0036] In light of the principles and example embodiments described and illustrated herein, it will be recognized that the example embodiments can be modified in arrangement and detail without departing from such principles. It will be appreciated by those skilled in the art that conventional electronics, software, controllers, and components may be used to implement the embodiments according to this disclosure. It will also be appreciated that embodiments of this disclosure may be implemented for use and operations in the oil and gas industry and in other fields of endeavor. What is claimed as the invention, therefore, are all implementations that come within the scope of the following claims.

Claims

ClaimsWhat is claimed is:

1. An underwater variable buoyancy member, comprising: a tubular configured for underwater disposal and having a longitudinal axis with an internal bore; the internal bore configured to receive a conduit in coaxial alignment with the longitudinal axis of the tubular, wherein the conduit is configured for conveyance of fluids; the tubular having a wall section configured to contain a gas and a liquid therein; and the wall section configured to receive the gas under pressure to permit selective buoyancy adjustment of the tubular.

2. The buoyancy member of claim 1, wherein the tubular comprises multiple sectors configured to couple to one another to form a tubular.

3. The buoyancy member of claim 1, wherein the tubular comprises an inner shell and an outer shell with an annulus formed between the shells.

4. The buoyancy member of claim 3, wherein the annulus forms the wall section configured to contain the gas and the liquid.

5. The buoyancy member of claim 1, wherein the tubular comprises at least one end configured to couple to the end of another tubular.

6. The buoyancy member of claim 5, wherein the at least one end is configured to permit passage of the liquid and the gas between the tubulars.

7. The buoyancy member of claim 1, wherein the tubular comprises at least one port configured to permit discharge of the gas and / or liquid contained therein.

8. The buoyancy member of claim 1, wherein the tubular is configured to maintain the conduit at a selected buoyancy state underwater when the conduit is disposed in the internal bore.

9. A method for buoying an underwater conduit, comprising: deploying a conduit underwater, the conduit configured for conveyance of fluids from subsurface to a vessel at water surface; the conduit having a tubular disposed thereon, with the conduit passing through an internal bore in the tubular; and injecting air into a wall section of the tubular configured to contain a gas and a liquid therein to permit selective buoyancy adjustment of the tubular.

10. The method of claim 9, wherein injecting air into the tubular comprises injecting the air to displace a liquid in the tubular.

11. The method of claim 9, further comprising selectively injecting a liquid into the tubular to adjust the buoyancy of the tubular.

12. The method of claim 9, wherein a connector is coupled to the conduit and configured to permit underwater separation of the conduit from the vessel.

13. The method of claim 9, wherein a connector is coupled to the conduit and configured to permit underwater connection of the conduit to the vessel.

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