WO2003021079A1

WO2003021079A1 - Method and device for the extraction and transport of gas hydrates and gases from gas hydrates

Info

Publication number: WO2003021079A1
Application number: PCT/EP2002/009385
Authority: WO
Inventors: Wilhelm Althaus; Jürgen Grän-Heedfeld; Adam Hadulla; Stefan SCHLÜTER; Heyko Jürgen SCHULTZ; Tim Schulzke
Original assignee: Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V.
Priority date: 2001-08-28
Filing date: 2002-08-22
Publication date: 2003-03-13
Also published as: DE10141896A1

Abstract

The invention relates to a method for the extraction and transport of gases contained in gas hydrates and gas hydrates, from deposits arranged below the ground or water surface, whereby a) a fluid is introduced using a sink device (2), which reaches from above the surface of the ground or water down to the deposit (3), b) the fluid at least partly destabilises the gas hydrate such that the gas is released and c) the released gas and/or the gas hydrate is drawn off from the deposit to above the ground or water surface by means of at least one riser (1).

Description

Method and device for extracting and conveying gas hydrates and gases from gas hydrates

The subject of this invention is a method for the extraction and production of flammable, hydrocarbon-containing gas and gas hydrate from gas hydrate deposits of all kinds for the purpose of material and energetic use. The main application is the deep-sea mining of methane gas from submarine gas hydrate deposits and permafrost areas. The invention also relates to the associated device. The process works using the mammoth pump principle. In addition, preventive removal of unstable or metastable gas hydrate can be carried out with the invention for ecological and safety reasons.

Gas hydrates are solid, ice-shaped cage structures in which gas molecules are enclosed by a "cage" made of water olecules. These connections will be chemically counted among the clathrates. The range of possible enclosed gas molecules is wide, C0 ₂ , H ₂ S, simple hydrocarbons such as methane, whereby methane hydrate is the largest part of the gas hydrates (> 90%) and is the most interesting from an economic and ecological point of view. Under standard conditions, one cubic meter of methane hydrate contains approximately 164 standard cubic meters of gaseous methane and approximately 0.8 standard cubic meters of liquid water. Estimates of global gas hydrate deposits vary between 3 and 7600 trillion m ³ . So far rough estimates indicate that there is approximately twice as much carbon in gas hydrates worldwide as in all known fossil fuel deposits (coal, oil, natural gas) combined.

Gas hydrates are formed when there is high pressure, low temperatures, sufficient gas and water. The following options are generally suitable for extracting gas from gas hydrates:

1. lowering the pressure;

2. increase in temperature; 3. addition of chemicals / inhibitors (methanol, glycol, NaCl, special polymers, etc.); 4. The fourth mining method is "mining" mining.

The gas can be extracted directly on site. As an alternative to this, mining of the gas hydrates and subsequent gas extraction in a separate plant is conceivable.

Gas hydrates are found in and on the sediments of the ocean floor at depths of more than approx. 300- 500 m, depending on the latitude. The lower limit of the gas hydrate stability zone is determined by the heat rising from the earth's core, which destabilizes the clathrates or prevents formation. In places, gas hydrated layers several meters thick have formed on the seabed. As is known from drilling, the gas hydrates serve as cement in the pore spaces of the sediment, but also occur in layers or tubers. The sediment layer that is permeated by them can be up to about 1000 m thick. There are also gas hydrate deposits in the permafrost soil of Siberia, Canada, Alaska, etc. The deposits in the permafrost originated in earlier oceans and have been well preserved since then.

In addition to an enormous energy content, gas hydrates, especially the submarine deposits, have a potential hazard. Warm underground currents can, for example, destabilize gas hydrate deposits on and in the seabed. A sudden release of large amounts of the gas bound in clathrates can cause landslides on the sea floor and undersea mudslides. Crater fields on the seabed indicate the instability of gas hydrate veins. These craters, also called "pock arks", can be 100 to 200 m wide and up to 20 m deep. Slides and explosive gas releases could result in tsunamis (giant waves) in coastal areas. The landslides also pose a threat to deep-sea cables and drilling platforms. Communication lines can be cut and oil rigs capsized by tsunamis. In addition, methane gas releases can have a lasting negative ecological impact, since methane as a greenhouse gas has a strong influence on the global climate. Methane is between 20 and 60 times more climate active than C0 ₂ . An increased introduction into the atmosphere increases the greenhouse effect.

It becomes clear that the extraction or production of gas hydrates and gas from gas hydrates is very interesting in terms of energy, is a safety-related undertaking and affects both economic and ecological concerns.

Previous approaches for the promotion of gas hydrates or gas from gas hydrates primarily consider the purpose of energetic use. Many process proposals for funding are questionable in terms of safety and environmental protection.

Methods for obtaining gas hydrate or gas from gas hydrate are described, for example, in WO / 00 47832. Here, chunks of methane hydrate are to be torn off from the sea floor by means of compressed air and conveyed to the sea surface by a tube which widens upwards.

DE 198 49 337 AI proposes a production process in which methanol or a mixture containing methanol is introduced into the gas hydrate deposit, as a result of which the hydrate is dissolved and the gas bound in it is released. The resulting methanol-gas-water mixture is then to be promoted.

JP 91 58662 recommends the introduction of heated sea water (through the waste heat from a nuclear reactor placed on the sea floor) into a gas hydrate deposit, the gas obtained by melting the gas hydrate being withdrawn from the deposit via a second borehole. From WO / 98 44078 a method is known for the degradation of surface gas hydrates on the seabed, wherein various collector arrangements can be applied to the seabed, collect chunks of gas hydrate and released gas and bring them with an impressed flow in a tube-like arrangement to the sea surface, where the obtained Local gas is converted into liquid hydrocarbons for better transport.

US 4,424,858 describes a device which contains two tubes arranged one inside the other, the upper end of the inner tube being below the sea level and sucking in sea water, which is conveyed into a deposit in order to dissolve gas hydrate there. The resulting gas is transported to the surface of the sea through the outer tube. The inner tube can extend deeper into the reservoir than the outer one and may be perforated to allow gas from different

Being able to collect depths. The outer tube also contains a side arm, which is below the sea level and can be closed for the start-up process, in order to discharge cooled sea water that has risen with the gas.

US 4,007,787 proposes to convey light hydrocarbons into the deposit which do not form hydrate under deposit conditions, in order to thereby release the gas from the hydrates. A freezing point depressant can also be injected into the reservoir to accelerate gas production.

US Pat. No. 3,969,834 also shows a possibility of using the airlift principle for liquids, suspensions, To promote sions and slurries of seabeds and river beds. In the method, a pipe is run from the water surface to the bottom. At the lower end of the pipe a collector is attached, which is placed on the medium to be pumped and has a side arm, which allows ambient water to be sucked in. Air is blown into the first pipe via a second pipe and a mixer. This air rises in the pipe and sucks material lying on the floor with it.

Proceeding from this, it is the object of the present invention to propose a method with which it is possible to promote gas hydrates and gases from gas hydrate layers, especially methane gas, in an economically and technically as well as ecologically safe and controlled manner. Another object of the present invention is to provide a corresponding device for carrying out such a method.

The object is achieved in relation to the method by the characterizing features of patent claim 1, in relation to the device for carrying out the method by the features of patent claim 14. The subclaims show advantageous developments.

Far-reaching advantages are associated with the method and the device according to the invention.

The extraction of gases from gas hydrates forms a future-proof alternative to the use of conventional fossil raw materials. The controlled destabilization and use of methane contained in natural gas hydrates can stabilize the global energy supply in the long term and by replacing it whose fossil fuels and CO ₂ reduction reduce global climate change.

The material use of controlled destabilized methane from gas hydrates can lead to massive resource savings in the area of classic fossil raw materials such as hard coal and especially oil.

Furthermore, with the proposed invention

Preventive removal of methane from unstable deposits and use it and convert it to a lower climate potential by using it in highly effective gas and steam power plants with efficiencies> 50%, before it enters the atmosphere uncontrollably and possibly environmental or Climate catastrophes.

There is also the possibility of enriching the seawater to be extracted with substances, in particular C0 ₂ , which are thermodynamically easier to form gas hydrates than methane and to be pumped into the methane hydrate deposit. On the one hand, this favors the destabilization of methane hydrate, because for thermodynamic reasons, for example, carbon dioxide hydrate is formed rather than methane hydrate and, on the other hand, there is a simultaneous possibility of transferring and depositing climate-active substances such as C0 ₂ in particular.

The invention permits the extraction and extraction of gas hydrates and gas from gas hydrates from all types of gas hydrate deposits. The extraction of free gas and liquid hydrocarbons that are also present in the deposits can also be carried out by the above beaten equipment can be realized.

The invention represents a structurally simple, economical, safe, controllable and environmentally friendly method for obtaining gas hydrates and gas from gas hydrates. The process is largely self-sustaining, and part of the methane gas obtained can be used to heat the circulating water.

With the proposed invention, not only the deposits lying directly on the sea floor can be developed, but also the gas hydrate layers lying in deeper sediment and soil areas. Degradation of gas hydrate in permafrost areas is also possible.

The cavern formed when the gas hydrates stored in the sea floor are broken down is filled with water and therefore mechanically stabilized. Deposit gas (leakage current) flowing out of the side of the cavern is cooled on the way through the sediment and forms gas hydrate again, whereby the deposit area is additionally cemented and solidified. Due to the new formation of the gas hydrate, no leakage current enters the atmosphere. In contrast to surface degradation, the ecosystems that cover the sea floor are preserved.

The introduction of chemicals, additives, inhibitors, etc. can be dispensed with, the dissolution process can take place through the use of other physical phenomena (temperature increase, pressure reduction). The seawater extracted into the deposit contains dissolved NaCl as a natural hydrate inhibitor, which reduces the destabilization of the gas hydrate. supports.

The invention is described below with reference to FIGS. 1 to 4 explained in more detail.

Fig. 1 shows the basic principle of a erfindungsge ^¬ MAESSEN device in which the Abströmer is arranged coaxially in the Aufströmer.

FIG. 2 shows an embodiment of the device according to FIG. 1, in which a specific separating device and an oil separator are additionally provided in the collecting container.

Fig. 3 shows the embodiment in which the upstream and downstream flow is spaced apart.

FIG. 4 shows a further alternative of the solution according to the invention, in which the upflow is arranged coaxially in the outflow.

In Fig. 1 the basic principle of the invention is shown. A pipe arrangement, represented here by a double pipe arrangement 1, 2, is introduced into the sea floor 8 up to the gas hydrate deposit 3. The inner tube 2 can be as long as the outer 1 or longer. It can therefore also be embedded deeper into the sea floor. Based on the design of the airlift loop reactor, the two tubes form the up and downflow area.

In Figs. 1 and 2 is the inner tube 2 of the outflow, the outer tube 1 of the upflow. Advantages of this design are the larger collecting area (outer tube = inflow) for the controlled destabilized lized gas 16 and a lower heat loss to the surrounding sea water 6, since the warm water is led through the inner tube into the deposit and is thus isolated from the surrounding influx from the colder sea water.

The reverse flow guidance is shown in Fig. 4. Here the outer tube is the outflow 32 and the inner tube is the upflow 33.

The bottom or deflection area of the airlift loop reactor is formed by the storage area 3. The head of the reactor is formed by the gas collecting container 4, which can be both an oil rig and a mobile drilling vessel and is also described below as a "sea vehicle".

The mode of operation is described in more detail below.

Water (sea water) heated by a heat exchanger 24 is conveyed through the outflow region into the deposit. There, the temperature is increased by the energy introduced, and the solid gas hydrate is thus destabilized and degassed / evaporated in a controlled manner. The released gas 16 rises in the upstream and is caught in the seacraft and separated from the water. The gas obtained can be used for direct recycling, chemical conversion or transport, the separated water can be circulated and returned to the deposit, which means less heating energy is required than when using "fresh" sea water. The process is self-sustaining after the start-up phase, since the circulating flow is induced by the resulting density difference. The amount of gas released can be safely controlled by the energy brought into the deposit.

The additional details shown in FIG. 1 provide more detailed information about the head region 4. A part of the water conveyed into the deposit remains there and fills up the cavern formed and thus contributes to mechanical stabilization. There is therefore a loss of water flow which can be compensated for by a fresh water flow 9 led into the head 4 via the pump 23. The product gas 11 obtained can be fed via the valve 25 to a direct recycling, a chemical conversion or a transport device, a partial flow of the gas 12 can be passed via the valve 26, for example, into a burner 13 or other energy generator. The hot combustion gas 14 is used directly or indirectly to heat the outflowing water. The alternative heating of the outflowing water by means of other types of heating and energy sources is also the subject of the invention, for example use of the gas obtained is also conceivable by means of a fuel cell or a gas engine for generating electrical current and heat. A liquid overflow 10 at valve 27 prevents the head collection tank 4 from overflowing with water.

An embodiment is shown in FIG. 2 in which the structure of the sea vehicle has been changed. 2 shows the great variability of the method and the device.

Likewise, in the variant shown in FIG. 2, a solid phase 17 that rises with the dissolved gas and circulating water is taken into account with torn up solid gas hydrate and / or rock and sediment. The solid particles enter the collecting tank 4 of the sea vehicle with gas and circulating water and can be separated there by various separating devices 19. The possible separating devices are represented in FIG. 2 by way of example by separating plates which collect and separate the solid particles via sedimentation processes. The use of other apparatuses such as hydrocyclones for the separation process described here in the illustrated process is also an object of the invention. The solid particles 20 can be removed from the collection areas by means of the pump 28. It is also possible to put the solid particles back into the cavern or the borehole via the outflow or other devices. Adding solids into the outflow area leads to the maintenance or reinforcement of the driving density difference that maintains the process. Solid gas hydrate pieces rising in the upstream are destabilized by the reduction of the hydrostatic pressure and by the indirect heating of the rising suspension by the heated outflowing circulating water and dissolve.

Gas hydrates and their deposits often also contain longer-chain, liquid hydrocarbons (hereinafter referred to as "oils"). Under certain circumstances, these oils 18 are also conveyed into the collecting tank 4 of the reactor and float there due to their lower density. Another object of the invention are separation devices of all kinds, which separate the oil phase from the circulating water and remove it from the reactor head via the pump 29. The oil can be directly used, chemically converted, or transported through the oil drain 22 be fed. The separating device is exemplified in FIG. 2 by an oil trap with separating plates.

Another object of the invention is the isolation of the individual reactor components. The insulation of the pipe structure is particularly important for the use of the conveyor device according to the invention in permafrost soil.

According to the invention, the constructive design of the upstream and downstream flow is preferably carried out by means of tubes pushed into one another, also of different cross-sectional shapes (oval, round, angular, rectangular, etc.), preferably round, preferably concentric. The

Pipe diameters can range from 1 cm to 50 m. Dimensions are preferably used as are known from the field of oil drilling, etc. The use of several upstream and downstream streams connected in parallel is possible, as is the use of satellite drilling, i.e. Boreholes at a spatial distance from the main drilling site, for additional, one-sided delivery of water heated to hydrate destabilization into the gas hydrate deposit.

The gas hydrates in the deposit can be destabilized by the conveying device according to the invention, in addition to the temperature increase, also by reducing the pressure (applying negative pressure) and using (chemical and physical) destabilizing additives. These possibilities are also conceivable for the start-up process, but in principle not necessary for the self-sustaining process based on the mammoth pump principle. For the

Start-up phase are also those marked with 30 to provide supporting pumping devices.

The favorable structural design prevents the inflow area from becoming blocked by gas hydrate forming in the pipe from the inflowing gas and water (if the formation conditions occur locally), since the outflowing warm circulating water indirectly contributes to heating the inflow area, and the gas hydrate formation conditions are consequently avoided ,

The structural design of the pipe arrangement can be of various types, as long as it is carried out according to the mammoth pump principle and is also the subject of this invention. The pipe arrangement of the upstream and downstream areas can e.g. as already mentioned and in FIGS. 1 and 2 are shown as a double pipe arrangement, but can also be carried out, for example, by an arrangement in which the pipes are spatially separated from one another (FIG. 3). The upstream and downstream flow areas can also reach into the deposit at different, spatially separated locations (two or more separate boreholes), so that controlled destabilization occurs at the point at which the outflow plunges into the deposit. the released gas flows through the deposit and is directed into the head through the upstream borehole. In this way, an interaction of the upstream and downstream flow is achieved.

Claims

claims

1. Process for the extraction and extraction of gases and gas hydrates contained in gas hydrates from deposits which are arranged under the surface of the earth or water, that is, due to their use,

a) that a fluid is introduced by means of at least one outflow device which extends into the deposit from above the surface of the earth or water,

b) that the fluid at least partially destabilizes the gas hydrate so that the gas escapes,

c) that the escaping gas and / or the gas hydrate is discharged via at least one inflow which leads from the deposit to the surface of the earth or water.

2. The method according to claim 1, characterized in that the ascending through the upstream gas and / or gas hydrate in a lying above the earth or water surface and the gas is separated from the water.

3. The method according to claim 2, characterized in that an additional separation of entrained solids takes place.

4. The method according to claim 2 or 3, characterized in that an additional separation of substances with a lower density than water, in particular oils, takes place.

5. The method according to at least one of claims 1 to 4, characterized in that seawater, surface water, groundwater, melted ice or melted snow is used as the fluid.

6. The method according to at least one of claims 1 to 5, characterized in that the fluid additives such as C0 _{2 are} supplied which form gas hydrates more easily than methane.

7. The method according to at least one of claims 1 to 6, characterized in that the fluid is heated before being fed into the outflow.

8. The method according to at least one of claims 1 to 7, characterized in that the gas obtained is used at least partially for heating the fluid.

9. The method according to at least one of claims 1 to 8, characterized in that gases and / or gas hydrates from gas hydrate layers, which lie on and in the sea floor, are obtained and promoted.

10. The method according to at least one of claims 1 to 8, characterized in that gases and / or gas hydrates from gas hydrate layers, which lie in sediment and / or soil areas, are obtained and promoted.

11. The method according to at least one of claims 1 to 10, characterized in that hollow bodies, in particular pipes, are used as the upstream and / or downstream flow.

12. The method according to at least one of claims 1 to 11, characterized in that a cavern is formed in the gas hydrate layers before the gases and / or gas hydrates are conveyed.

13. The method according to claim 12, characterized in that the cavern is formed by generating a negative pressure, heating or mining excavation by chemical additives.

14.Device for extracting and conveying gases and gas hydrates enclosed in gas hydrates from deposits which are arranged below the surface of the earth or water, consisting of an outflow in which a fluid is supplied to the gas hydrates and an upstream to collect the separated gas and / or gas hydrates, characterized in that at least one outflow (2, 32), the head end of which is above the surface of the earth or water (5) and which extends into the deposits (3) of the gas hydrates, and at least one upstream (1, 33) on the head above the surface of the earth or water (5) is connected to a gas collecting container (4) and which leads up to the deposits (3) of the gas hydrates, are arranged interactively.

15. The apparatus according to claim 14, characterized in that the collecting container (4) is provided with a solids separation device (19).

16. The apparatus according to claim 14 or 15, characterized in that the collecting container (4) is provided with an oil separating device (21).

17. The device according to at least one of claims 14 to 16, characterized in that the gas collecting container (4) is designed in the form of an oil rig.

18. The device according to at least one of claims 14 to 17, characterized in that the gas collecting container (4) is designed in the form of a drilling ship.

19. The device according to at least one of claims 14 to 18, characterized in that the outflow (2, 32) is connected on the head side to a heat exchanger (24).

20. The device according to at least one of claims 14 to 19, characterized in that the outflow (2, 32) on the head side is connected to an energy generator (13).

21. The device according to at least one of claims 14 to 20, characterized in that the upstream and / or downstream flow (1, 2, 32, 33) is tubular.

22. The apparatus according to claim 21, characterized in that the cross section is oval, round or angular.

23. The device according to claim 14 and 22, characterized in that the diameter of the tube is in the range of 1 cm to 50 m.

24. The device according to at least one of claims 14 to 23, characterized in that the cross section of the outflow (2) is smaller than the cross section of the upstream (1).

25. The device according to claim 24, characterized in that the outflow (2) is arranged concentrically or eccentrically in the upstream (1).

26. The device according to at least one of claims 14 to 23, characterized in that the outflow (32) has a larger diameter than the upstream (33).

27. The apparatus according to claim 26, characterized in that the upflow (33) is arranged concentrically or eccentrically in the outflow (32).

28. The device according to at least one of claims 14 to 23, characterized in that the upstream and downstream flow are arranged spaced apart.

29. The device according to at least one of claims 14 to 28, characterized in that the upstream and / or downstream (1, 2, 32, 33) and / or the collecting container (4) is at least partially insulated.