WO2015065412A1

WO2015065412A1 - System and method for methane production

Info

Publication number: WO2015065412A1
Application number: PCT/US2013/067690
Authority: WO
Inventors: James REWERTS; Carlos Ortiz; Vijo Varkey THEEYATTUPARAMPIL; Hermano C. FERREIRA
Original assignee: Siemens Energy Inc
Current assignee: Siemens Energy Inc
Priority date: 2013-10-31
Filing date: 2013-10-31
Publication date: 2015-05-07
Anticipated expiration: 2016-04-30

Abstract

A system (10) and method for production of methane (18) from a methane hydrate formation (12). A flexible gas harvesting dome (14) is positioned over the methane hydrate formation to collect methane released within the formation by action of a methane production stimulation device (16). A methane gas removal system (26) transfers the methane gas from the dome to a nearby processing platform (40) where the gas may be converted to liquid methane (30) for eventual transfer to market. Analysis of the formation enables prediction of the flow path of the released methane to the surface of the formation for optimal positioning of the dome.

Description

SYSTEM AND METHOD FOR METHANE PRODUCTION

FIELD OF THE INVENTION

The present invention relates to methane production from the release and capture of methane from methane hydrates, and in particular embodiments, to offshore methane production.

BACKGROUND OF THE INVENTION

Methane hydrates are mineral deposits formed from water and methane. Under high pressure and low temperatures, methane molecules are stored in a cage of interlocking water molecules which encapsulate the methane. Methane hydrates can contain a very high concentration of methane. For example, 160 cubic feet of gaseous methane may be contained within one cubic foot of methane hydrate. Thus, methane hydrates have the potential for being a significant fuel source if processed efficiently.

There are four environments that have the requisite temperature and pressure conditions for the formation and maintenance of methane hydrate formations. They include sediment and sedimentary rocks below Arctic permafrost; sedimentary deposits along continental margins; deepwater sediments of inland lakes and seas; and under Antarctic ice. Typically, the methane hydrate deposits are within a few hundred meters of the sediment or ice surface.

To release the methane from the fixed grid network of the methane hydrates, known processes heat or depressurize the methane hydrate formation. In other processes, compounds such as C0₂ are injected into the methane hydrate formation to displace and release methane from the methane hydrates. There are a number of disadvantages associated with the above techniques. For one, these techniques are utilized in combination with conventional oil drilling techniques, including heated water and steam injection, for production of the methane gas from methane hydrates.

Conventional oil techniques necessarily generate a significant amount of waste, including drilling fluid chemicals, oil-based and water-based drilling muds. In addition, drilling a well bore for injection of components and capture of the desired product contribute to high capital expenditures. Furthermore, conventional techniques for methane production from methane hydrates require complex separation techniques to recover the desired methane gas product from the drilling fluids.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in the following description in view of the sole figure that schematically illustrates a system for methane gas production in accordance with an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The present inventors have developed systems and methods for producing methane from methane hydrate deposits. Advantageously, the systems and methods provide for the efficient and cost-effective release of significant quantities of methane gas from such methane hydrate formations, and the subsequent capture of the released methane gas without complex separation techniques. Embodiments of the invention take advantage of the natural tendency of methane to float in water or air, due to its low density, by collecting released methane within a flexible gas harvesting dome disposed over a methane hydrate deposit. When properly stimulated, methane is released from the deposit, rises due to natural buoyancy, and is collected in the dome for subsequent processing.

Referring to the sole figure, there is shown a system 10 for offshore production of methane from a methane hydrate deposit or formation 12 disposed within a seabed 32 under a body of water 31 . A gas harvesting dome 14 is positioned over the methane hydrate formation 12. A methane production stimulation device 16 is used to cause release of methane gas 18 from the methane hydrate formation 12. The methane gas 18 rises up through the seabed 32 and floats upward in the water 22 and is collected in a cavity 20 defined within the dome 14. The methane gas 18 causes the gas harvesting dome 14 to inflate into a methane capture configuration 24, as shown in the figure, while it is retained in position by an anchoring device such as cables 36 secured to the seabed 32.

The system 10 also includes a methane gas removal system 26 for transferring the collected methane gas 18 from the cavity 20 to a floating platform 40. In some embodiments, the system 10 further includes a liquification system 28 on the floating platform 40 for conversion of the methane gas 18 to liquid methane 30.

The gas harvesting dome 14 may be dimensioned and positioned to optimally capture the methane gas 18 as it is produced from the methane hydrate formation 12. A larger methane hydrate formation (by area, concentration, or volume) may require a larger gas harvesting dome. Thus, contrary to conventional techniques, which utilize the same equipment without regard to the size of the methane hydrate formation, aspects of the present invention can be tailored to the methane hydrate formation being harvested. The identification and location of a methane hydrate formation may be accomplished by standard simulation software or techniques used in the oil and gas industry. Moreover, the path of released methane gas 18 flowing within the formation 12 and seabed 32 are modeled to predict the location(s) of escape of the gas 18 into and through the seabed 32, with the dome 14 being positioned accordingly to optimize the collection of the released gas 18. In some embodiments, the gas harvesting dome 14 may be from 50 to 1000 meters in a longest dimension, but larger or smaller sizes are contemplated depending on the particular application.

The gas harvesting dome 14 may be formed from any gas impermeable material so as to maintain the methane gas 18 within the cavity 20. For example, the dome 14 may be formed from a polymeric material, such as polyurethane, polyethylene, polystyrene, polyvinyl chloride, polytetrafluoroethylene (PTFE), reinforced rubber, or a combination of such materials. In addition, the dome 14 may be of any suitable thickness appropriate to provide the desired strength while still facilitating its

manufacture, transportation and deployment.

As noted above, the methane hydrate formation 12 may be located at sediment and sedimentary rocks below Arctic permafrost; sedimentary deposits along continental margins; deepwater sediments of inland lakes and seas; and under Antarctic ice. Since methane rises in water and in air, the concept of a collection dome may be used for both subsurface and terrestrial methane production. It is appreciated that the dome 14 should be properly anchored not only to resist the uplift force created by the methane gas 18 but also to accommodate any currents or wind existing in the surrounding fluid. For high current applications, a frame structure (not shown) may be used in

combination with the anchoring cables 36. For terrestrial applications, it would be important to prevent the egress of air into the dome, such as by providing a seal between the dome and the surface, in order to prevent the creation of a flammable mixture within the dome. In water body embodiments, a portion of the gas harvesting dome 14 may be submerged and a portion of the dome 14 may rise above the surface of the water 22.

The methane hydrate stimulation device 16 may be any suitable system, equipment, and/or process for causing release of at least some of the methane gas 18 from the methane hydrate formation 12. In various embodiments, the methane hydrate stimulation device 18 may be configured to cause release of methane gas 18 from the methane hydrate formation 12 via the application of heat, pressure reduction, introduction of a displacement gas, and/or or via application of an electric current to the methane hydrate formation, or through any other technique available at the time of production. As the methane gas 18 migrates upward following release, it encounters the gas harvesting dome 14 and causes it to inflate and to rise through buoyancy as illustrated in the figure. Advantageously, this process separates the methane gas 18 while preventing ingress of ambient air.

Heating of the methane hydrate formation 12 to release the methane gas 18 may take place according to any suitable method known in the art, for example as set forth in U.S. Patent No. 7,963,328, incorporated by reference herein. In an embodiment, the heating may take place via the introduction of preheated or superheated, water, steam, carbon dioxide or other fluid and/or by providing electrically driven heat, e.g. resistance heating or electrochemical heating to the methane hydrate formation. Advantageously, the stimulation device 16 may be powered from the floating platform 40, such as by providing electrical energy, heated air, water or steam from the platform 40. In one embodiment, the power source 50 may be a generator fueled by methane produced by the system 10, itself. In other embodiments, the methane hydrate stimulation device 16 may be configured to provide electromagnetic heating as described in U.S. Patent Application Publication No. 20120312538, or by introducing a fluid that disturbs the thermodynamic equilibrium in the methane hydrate formation 12 as described in United States Patent Application Publication No. 2004/0060438, each of which are

incorporated by reference herein. The gas removal system 26 may include a conduit 38 formed from a relatively flexible and impermeable material such as polyurethane, polyethylene, polystyrene, polyvinyl chloride, polytetrafluoroethylene (PTFE), or appropriate materials, sized appropriately for the expected flow of methane. The methane gas 18 is delivered to the floating platform 40 where the gas 18 may be further processed and/or stored. For example, separation/filtration 42 may be provided for further removing any water or other contaminants from the gas 18. The platform 40 may contain a liquification system 28 for converting gaseous methane 18 to liquid methane 30. The liquid methane 30 may be retained in a storage device such as an insulated tank 44. In an embodiment, the floating platform 40 defines a floating liquefied natural gas (FLNG) facility 46. The platform 40 will float above or adjacent the methane hydrate formation 12 such that the FLNG facility 46 will produce, liquefy, and store liquid methane 30 at sea before offloading it to a tanker 48 or otherwise transferring it to market.

It may be appreciated that multiple stimulation devices 16 and multiple gas removal systems 26 may be serviced from a single floating platform 40. Moreover, for methane hydrate deposits 12 located near a shoreline or under Antarctic ice, the processing platform 40 may be a modular design and skid mounted or otherwise made portable.

While various embodiments of the present invention have been shown and described herein, it will be obvious that such embodiments are provided by way of example only. Numerous variations, changes and substitutions may be made without departing from the invention herein. Accordingly, it is intended that the invention be limited only by the spirit and scope of the appended claims.

Claims

CLAIMS The invention claimed is:

1 . A system for production of methane from an underwater methane hydrate formation, the system comprising:

a floating processing facility;

a methane production stimulation device powered from the floating processing facility and effective to cause release of methane gas from the methane hydrate formation;

a gas harvesting dome disposed over the methane hydrate formation and defining a cavity for collection of the methane gas escaping from the formation;

a gas transfer duct interconnecting the gas harvesting dome and the floating processing facility for transferring the collected methane gas from the cavity to the processing facility.

2. The system of claim 1 , wherein the floating processing facility further comprises a Hquification system for conversion of the collected methane gas to liquid methane.

3. The system of claim 1 , wherein the floating processing facility comprises a liquid methane storage device.

4. The system of claim 1 , wherein the dome comprises a flexible

impermeable material.

5. The system of claim 1 , wherein the methane production stimulation device comprises a device effective to apply heat to the methane hydrate formation.

6. The system of claim 1 , wherein the methane production stimulation device comprises a device effective to apply a pressure reduction to the methane hydrate formation.

7. The system of claim 1 , wherein the methane production stimulation device comprises a device effective to introduce a replacement gas into the methane hydrate formation.

8. The system of claim 1 , wherein the methane production stimulation device comprises a device effective to apply an electrical current to the methane hydrate formation.

9. The system of claim 1 , wherein the gas transfer duct comprises a non- pressurized and flexible conduit.

10. The system of claim 1 , further comprising a plurality of anchors attached to the gas harvesting dome for positioning the gas harvesting dome at a location over the methane hydrate formation selected to optimize the collection of the methane gas escaping from the formation.

1 1 . A method for recovering methane from a methane hydrate deposit, the method comprising:

selecting a location of the methane hydrate deposit where methane gas released from within the deposit is expected to escape the deposit;

disposing a gas harvesting dome over the selected location;

stimulating release of methane gas from within the deposit;

collecting the released methane gas within the dome; and

transferring collected methane gas from the gas harvesting dome to a processing facility via a gas transfer duct.

12. The method of claim 1 1 , further comprising sizing and positioning the gas harvesting dome in response to a modeled prediction of methane gas escape paths.

13. The method of claim 1 1 , wherein the gas harvesting dome is anchored to a seabed comprising the methane hydrate deposit.

14 The method of claim 13, further comprising converting the collected methane gas to liquid methane at the processing facility floating above the seabed.

15. The method of claim 13, wherein the stimulating release of methane gas is accomplished via application of a displacement gas, pressure reduction, heat or electric current from the floating processing facility.