SYSTEM

Background

[0001] This disclosure relates to the field of collection of and transport of fluids produced from the bottom of a body of water. More specifically, the disclosure relates to devices that can be towed to a specific location along a body of water, deployed on the bottom of the body of water at the specific location, and then operated to extract less dense fluids than the water, such as methane gas trapped as hydrate on the water bottom.

[0002] So called “unconventional” accumulations of hydrocarbons include methane ice hydrate in solid form that accumulates on the sea floor at specific ranges of temperature and pressure. See, for example, Maja Sojtaric, Domes of frozen methane may be warning signs for new blow-outs, Centre for Arctic Gas Hydrate, Environment and Climate, June 6, 2017. Methane has may be released from methane hydrate by localized heating. Current investigation for the purpose of producing methane from methane hydrate in commercial quantities is described in, Japan, U.S. to test methane hydrate extraction in Alaska, Kyodo News, Sept. 9, 2020.

[0003] Methods and apparatus used to evaluate commercial feasibility of methane production from methane hydrate include drilling wells through methane hydrate accumulations and heating the methane hydrate from such wells to enable released methane to migrate into the wells for retrieval at the water surface. Methane hydrate accumulations are known to occur at very shallow depths below, or on the sea floor, making well-based techniques for methane extraction impractical.

Summary

[0004] One aspect of the present disclosure is a gas hydrate gas production system. A system according to this aspect of the disclosure includes a radially expandable support frame and an impermeable, flexible barrier material disposed on the support frame to define an enclosed volume on one side of the support frame. At least one heating element is deployable from the support frame. A conduit extends from the one side of the support frame to a vessel deployed on a surface of a body of water. The conduit defines a fluid flow path from the enclosed volume to the surface.

[0005] In some embodiments, the at least one heater comprises an electrical resistance heating element.

[0006] In some embodiments, the conduit comprises an electrical cable extending along a length of the conduit, the electrical cable electrically connected to the electrical resistance heating element.

[0007] In some embodiments, the electrical resistance heating element comprises an electrical resistance heater cable.

[0008] In some embodiments, the radially expandable support frame comprises a central support tube, a support rod actuator movable longitudinally along the central support tube, a plurality of circumferentially spaced apart extension rods pivotally coupled at one end to the support rod actuator, and a plurality of circumferentially spaced apart support rods each pivotally coupled at one end to the central support tube and at another longitudinal end to a longitudinal end of one of the extension rods.

[0009] Some embodiments further comprise a float disposed proximate one longitudinal end of the central support tube and a weight having a selectably floodable compartment disposed proximate another longitudinal end of the central support tube.

[0010] Some embodiments further comprise an anchor disposed at a longitudinal end of each support rod opposed to the longitudinal end pivotally coupled to the central support tube.

[0011] In some embodiments, each anchor comprises an internal heating element.

[0012] In some embodiments, each internal heating element comprises an electrical resistance heater. [0013] Some embodiments further comprise a winch coupled to each of the plurality of support rods, each winch longitudinally movable along the respective support rod, each winch comprising an electrical resistance cable spooled thereon.

[0014] In some embodiments, the conduit forms part of an umbilical line, the umbilical line comprising an electrical cable.

[0015] A method for producing gas from a gas hydrate according to another aspect of the present disclosure includes towing a gas hydrate production system by a vessel to a location proximate a gas hydrate deposit on a bottom of a body of water. The gas hydrate production system is lowered into the body of water at the end of an umbilical line to proximate the bottom of the body of water. A support frame in the gas hydrate production system is operated to open an impermeable, flexible barrier to define an enclosed volume on one side of the barrier. A heating element in the gas hydrate production system is operated to fuse part of the gas hydrate deposit. Gas from the fused gas hydrate is collected in the defined enclosed volume and moved to the vessel along the umbilical line.

[0016] In some embodiments, the operating the support frame comprises moving a support rod actuator longitudinally along a central support tube, thereby moving a plurality of circumferentially spaced apart extension rods pivotally coupled at one end to the support rod actuator. Thereby a plurality of circumferentially spaced apart support rods each pivotally coupled at one end to the central support tube and at another longitudinal end to a longitudinal end of one of the extension rods is extended. As a result, the impermeable, flexible barrier attached to the support rods and is thereby extended to define the enclosed volume.

[0017] In some embodiments, the lowering the gas hydrate production system comprises flooding a weight chamber disposed at one end of the central support tube with water to orient the production system vertically in the body of water and extending the umbilical line from the vessel. [0018] In some embodiments, the operating the heating element comprises deploying a plurality of electrical resistance cables from the support frame into contact with the gas hydrate deposit and energizing the plurality of electrical resistance cables.

[0019] Other aspects and possible advantages will be apparent from the description and claims that follow.

Brief Description of the Drawings

[0020] FIG. 1 shows an example embodiment of a production system according to the present disclosure disposed on the sea floor.

[0021] FIG. 2 shows the example embodiment of FIG. 1 in more detail.

[0022] FIG. 3 shows an example embodiment of a production system according to the present disclosure.

[0023] FIG. 4 shows another example embodiment of a production system according to the present disclosure.

[0024] FIG. 5 shows another example embodiment of a production system according to the present disclosure.

[0025] FIG. 6 shows an example embodiment of a support frame and associated components that may be used in various embodiments of a production system according to the present disclosure.

Detailed Description

[0026] FIG. 1 shows an example embodiment of a production system 10 according to the present disclosure disposed on the bottom 20 of a body of water 22 such as an ocean. There are two separate production systems 10 shown in FIG. 1, which may be identical to each other. Each production system 10 may comprise an impermeable barrier 12 (“barrier”), which may be in the form of flexible, impermeable fabric such as cloth fabric treated with a fluid-impermeable material such as rubber, or a flexible plastic film such as MYLAR film. MYLAR is a registered trademark of El du Pont de Nemours and Co., Wilmington, Delaware, USA. The barrier 12 may be supported by a foldable frame, to be described in more detail below with reference to FIG. 6. The production system 10 may comprise anchors 14, which in some embodiments may be heated, e.g., by electrical resistance heating to enable the anchors 14 to penetrate the top of a methane hydrate deposit 18 and afterward allow resolidification of the methane hydrate and consequent locking the anchors 14 in place.

[0027] The production system 10 may comprise one or more heating elements 16, such as electrical resistance heating elements, which may be deployed onto the surface of the methane hydrate deposit 18. When the heating elements 16 are operated, methane may be released from the methane hydrate deposit 18. Released methane may displace water under the barrier 12 and accumulate therein. Accumulated methane may migrate from under the barrier 12 along a conduit forming part of an umbilical line 11, whereupon the methane may be retrieved at the water surface such as on a vessel or platform (not shown). The umbilical line 11 may comprise an electrical cable (not shown separately) to provide power to operate the heating elements 16 and to communicate control signals such as may be used to switch on and off the heating elements 16 and to control operation of various components of the frame, as will be further explained with reference to FIG. 6. The electrical cable (not shown separately) may also provide electrical power to operate the heating elements 16 and if so provided, electrical heating elements in the anchors 14.

[0028] FIG. 2 shows the example embodiment of the production system 10 of FIG. 1 in more detail. The barrier 12 may be supported by support rods 32, which will be explained in more detail with reference to FIG. 6 to provide, on one side of the barrier 12 an enclosed volume into which released methane may migrate upwardly by gravity. Each of the support rods 32 may pivot open about a central point proximate an upper end of each support rod 32 to expand the enclosed volume, and pivot closed to minimize the volume for deployment and retrieval of the production system 10 in the water 22. Each of the support rods 32 may have connected thereto one of the heating elements 16. The heating elements 16 may be coupled to the support rods 32 such that the heating elements 16 contact the methane hydrate deposit 18 when the production system 10 is deployed to the water bottom 20. The anchors 14 may be internally heated such that as the heating elements 16 and the heated anchors 14 fuse the methane hydrate 18, the entire production system 10 may remain in contact with the existing surface of the methane hydrate 18. As will be appreciated, such existing surface will drop as the methane is released from the methane hydrate deposit 18. The umbilical line 11 may be coupled to the production system 10 using a disconnect 13, such as a tension operated connector, to enable recovery of the umbilical line 11 in the event the production system 10 becomes trapped on the water bottom (20 in FIG. 1).

[0029] As methane is released from the methane hydrate deposit 18 by heating, it migrates upwardly by gravity to the volume enclosed by the barrier 12 and may then move to surface through conduit (not shown) in the umbilical line 11.

[0030] FIG. 3 shows an example embodiment of a production system 10 according to the present disclosure. The example embodiment shown in FIG. 3 may have an electrical resistance cable 19 attached to any part of the frame (see FIG. 6) and may be caused to rest on the surface of the methane hydrate deposit 18 when the production system 10 is deployed proximate the water bottom 20. The electrical resistance cable 19 may be energized to release heat, which heat fuses the methane hydrate deposit 18 as described above with reference to FIGS. 1 and 2.

[0031] FIG. 4 shows another example embodiment of a production system 10 according to the present disclosure which may comprise a plurality of electrical resistance cables 19 as in the embodiment of FIG. 3 for more extensive areal coverage of the methane hydrate deposit 18 for production purposes.

[0032] FIG. 5 shows another example embodiment of a production system 10 according to the present disclosure. The example embodiment of FIG. 5 may comprise one or more “sonde” type electrically operated heaters 21, or other type of heaters such as chemical reaction heater or combustion heaters. The sonde type heaters 21 may have a heat source (not shown separately) enclosed in a pressure tight housing for deployment on the surface of the methane hydrate deposit 18.

[0033] FIG. 6 shows an example embodiment of the support frame stated with reference to FIG. 1, shown at 10A in FIG. 6. The support frame 10A and associated components as shown may be used in various embodiments of a production system according to the present disclosure. The support frame 10A may comprise a central support tube 30. The central support tube 30 may provide a surface along which a support rod actuator 34 may move longitudinally. The support rod actuator 34 may be caused to move along the exterior of the central support tube 30 by a linear actuator (not shown separately) such as a worm gear/bail nut combination, an hydraulic or pneumatic cylinder and ram combination, or a cable and pulley system (none shown separately).

[0034] The support rod actuator 34 may have pivotally coupled to its exterior one longitudinal end of each of a plurality of circumferentially spaced apart extension rods 36. Each of the extension rods 36 may be pivotally coupled at its other longitudinal end to a corresponding support rod 32 at a convenient position along the length of each support rod 32. Each support rod 32 may be pivotally coupled at one of its longitudinal ends to the central support tube 30. Thus, longitudinal movement of the support rod actuator 34 will cause radial extension of the free ends, i.e., those opposed to the end coupled to the central support tube 30, of the support rods 32. As may be inferred from the description of FIG. 1, the barrier (12 in FIG. 1) may be supported by the support rods 32 such that when the support rods 32 are laterally extended, the enclosed volume is created; when the support rods 32 are laterally retracted, the enclosed volume is reduced and the production system (10 in FIG. 1) may move freely within the body of water.

[0035] In some embodiments such as the present example embodiment, the heating elements may be electrical resistance cables 19 as explained with reference to FIG. 4. Each electrical resistance cable 19 may be stored on a winch 42. Each winch 42 may be coupled to a respective support rod 32 to enable longitudinal movement of each winch 42 along its respective support rod 32 as indicated by the arrows next to each winch 42. In the present example embodiment, the electrical resistance cables 19 may be deployed by simultaneously unspooling from the respective winches 42 and moving the winches 42 longitudinally along the respective support rods 32. In this way, the electrical resistance cables 19 may be deployed on the surface of the methane hydrate (18 in FIG. 4) in a radial spoke pattern for high effective surface areal coverage of the methane hydrate (18 in FIG. 4). [0036] The anchors 14 are shown in FIG. 6 as connected to respective support rods 32.

The anchors 14 may in some embodiments be internally heated, such as by electrical resistance heating.

[0037] The central support tube 30 may have a float 38 or other buoyant device coupled proximate the longitudinal end of the central support tube 30 that is coupled to the umbilical line 11. Thus, when deployed in the water, the float 38 will urge the central support rod 30 to orient as shown in FIG. 6, that is, vertically. The other longitudinal end of the central support tube 30 may have coupled thereto weight 40 having an enclosed chamber 40A that may be selectively flooded and evacuated with surrounding water. When evacuated, the weight 40 will be buoyant such that the production system 10 will oriented horizontally in the water. When the support frame 10A is closed, and the weight chamber 40A is evacuated, the production system 10 will be disposed horizontally proximate the water surface and may thereby be towed by a vessel (not shown) to any chosen location for deployment.

[0038] For deployment, the chamber 40 A may be flooded to orient the production system

10 vertically in the water and then lowered by the umbilical line 11 to the water bottom (20 in FIG. 1). The support rod actuator 34 may then be operated to open the support frame 10A. The winches 42 may then be operated as explained above to deploy the electrical resistance cables 19. The electrical resistance cables, and in some embodiments, electrical heating elements in the anchors 14 may then be energized to heat the methane hydrate (18 in FIG. 4) and to produce and accumulate methane as explained with reference to FIG. 1.

[0039] When production at the specific sea floor location is completed, the production system 10 may be retrieved from the sea floor by reversing the above described deployment actions, and the production system then may be moved to a different location.

[0040] 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. The foregoing discussion has focused on specific embodiments, but other configurations are also contemplated. In particular, even though expressions such as in “an embodiment," or the like are used herein, these phrases are meant to generally reference embodiment possibilities, and are not intended to limit the disclosure to particular embodiment configurations. As used herein, these terms may reference the same or different embodiments that are combinable into other embodiments. As a rule, any embodiment referenced herein is freely combinable with any one or more of the other embodiments referenced herein, and any number of features of different embodiments are combinable with one another, unless indicated otherwise. Although only a few examples have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible within the scope of the described examples. Accordingly, all such modifications are intended to be included within the scope of this disclosure as defined in the following claims.