JP2003193787A - Method and system for collecting gas hydrate by boring - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and system for collecting gas hydrates by boring, for enhancing the efficiency of collection and transportation by enhancing the handleability of gas hydrates. <P>SOLUTION: The method of digging a hydrate layer H existing within sea ground G to collect gas hydrates into an offshore structure 10 includes digging the hydrate layer H, feeding sea water near the surface of the sea into the hydrate layer H, and raising a mixture of the gas hydrates and the sea water onto the offshore structure 10 as a gas-hydrate slurry. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an excavation and recovery direction and an excavation and recovery system for excavating and recovering gas hydrate existing in the ground of a water bottom such as the seabed.

[0002]

2. Description of the Related Art Natural gas is a gas layer formed in the ground.
Exists in a gaseous state inside (called "free gas layer")
Are often drilled from these free gas layers
It is generally used. But apart from this,
Solid state hydrates produced by hydration of natural gas
And may exist. This natural gas hydrate (below
Below, "gas hydrate") is the inclusion compound
(Clathrate compound), a type of water molecule
(H₂O) a three-dimensional cage-shaped clathrate lattice (K
Lathrate contains methane (C
H_Four), Ethane (C₂H ₆) And other molecules enter and are included
It has a crystalline structure. Such gas hydrate
Has a high density of natural gas inside.
ing. Theoretically, gas hydrate 1m³Inside the standard
Approximately 170m when converted to gas in the state³Natural gas
Will be included as a next-generation energy source
It has received a great deal of attention.

Since the gas hydrate can be stably generated by being generated under the conditions of low temperature and high pressure, it forms a layer in the ground that meets these conditions ("gas hydrate layer", or simply (Called the "hydrate layer"). Specifically, it has been found that it is widely distributed in the lower part of the permafrost layer in the Arctic Circle, the Antarctic Circle, etc., or in the seabed ground with a depth of about 300 m or less. In addition, it is considered that a large amount will exist in the seabed ground near Japan, such as the Nankai Trough, and investigations or excavation and recovery thereof are about to be carried out sequentially.

[0004]

The excavation and recovery of such gas hydrate requires a technology which is significantly different from the oil excavation and recovery. That is, in the case of petroleum, it is generally known that it exists as a liquid at a specific place covered with hard rock as already known. Therefore, when excavating and recovering oil, there is a bedrock using a boring device.
A sampling hole may be drilled at a location and the marine structure may be sucked up from the sampling hole. On the other hand, the gas hydrate is a solid and does not always exist in the bedrock, but it often spreads laterally in the soft seabed. In addition, like petroleum, it is not always concentrated in a specific place, and it is often scattered in a plurality of layers. For this reason, oil drilling and recovery technology, such as picking up a sampling hole at one place on the seabed and sucking it up,
It is almost impossible to apply it directly to the excavation and recovery of gas hydrate.

As a method for excavating and recovering gas hydrate that has been proposed so far, natural water (gas) is obtained by injecting hot water or the like into the hydrate layer in the seabed to decompose the gas hydrate in the seabed. And was transported to the sea in this gas state. However, in such a method, a large amount of heat required for decomposing gas hydrate is generated.
After a long distance, it must continue to be sent to the cold seabed. It is very difficult to accurately transfer such heat, and it is difficult to decompose the gas hydrate at a position far away from the injection hole for hot water or the like, and it can be said that the recovery efficiency is good. There wasn't. Further, when the gas hydrate is decomposed into a gas state, there is a problem that the handling property is inferior as compared with the case of a solid state.
In addition, as described above, when gasified, the volume of natural gas (gas) becomes 170 times as large as that of the gas hydrate in the solid state, and there is a possibility that the gas will be blown up at the seabed. In the unlikely event of a sudden blow, not only the gas cannot be effectively recovered, but also various equipment installed on the seabed side may be damaged or damaged.Therefore, it is also necessary to take measures against the blowout, which is expensive and time-consuming to construct. It was For these reasons, the method of gasifying on the seabed is not preferable, and another method, that is, an excavation and recovery method capable of improving handling efficiency and recovery efficiency or transportation efficiency has been desired.

The present invention has been made in view of the above circumstances, and provides a method for excavating and recovering gas hydrate and a system for excavating and recovering gas hydrate, which can improve the handling property and the recovery efficiency and the transportation efficiency. With the goal.

[0007]

According to a first aspect of the present invention, there is provided a method of excavating a gas hydrate existing in the ground on the sea floor and recovering the gas hydrate to an offshore structure, the method comprising excavating the gas hydrate. At the same time, the seawater in the vicinity of the offshore structure is sent to the gas hydrate, and is pulled up to the offshore structure as a gas hydrate slurry that is a mixture of the gas hydrate and the seawater.

As described above, seawater is sent to a gas hydrate to form a mixture of gas hydrate and seawater, that is, a gas hydrate in the form of powder and a gas hydrate slurry dispersed in seawater, Since it is collected and collected as a liquid, the handling property of the gas hydrate can be remarkably improved. In addition, in order to make the gas hydrate into a granular form as described above, it is necessary to decompose a small amount, but seawater near the offshore structure, that is, warm seawater near the sea surface (warm seawater) By supplying water to the gas hydrate, the amount of heat for decomposition can be suitably supplied. Furthermore, in order to make the gas hydrate into a granular form, it is only necessary to decompose it in a small amount, and compared with the case of almost completely decomposing the gas hydrate, the required amount of heat can be significantly reduced, and the blast The fear can be suppressed. Furthermore, since the seawater is sent while excavating the gas hydrate on the seabed, and the gas hydrate is slurried and collected, the number of drill holes formed in the ground on the seabed is
It can be the minimum required.

The invention according to claim 2 is the method for excavating and recovering gas hydrate according to claim 1, wherein the sediment mixed in the gas hydrate slurry is separated at a position near the seabed, The gas hydrate slurry is pulled up to the offshore structure.

As described above, since the gas hydrate slurry is pulled up to the sea after separating the sediment near the seabed, it is not necessary to collect the heavy sediment, and it is necessary to discard it before pulling it up. It is possible to reduce the amount of cargo to be transported to the sea and reduce the energy required for transportation.

The invention according to claim 3 is the method for excavating and recovering gas hydrate according to claim 2, wherein the gas mixed in the gas hydrate slurry pulled up to the offshore structure is separated. Is characterized by.

As described above, since the gas mixed in the gas hydrate slurry is separated, it is possible to perform a post-treatment suitable for each of the gas hydrate slurry which is a liquid and the gas which is a gas. , Both can be effectively used as energy sources.

A fourth aspect of the present invention is the method for excavating and recovering gas hydrate according to the third aspect, wherein the gas hydrate slurry is dehydrated to remove the concentrated gas hydrate slurry or seawater. And gas hydrate.

As described above, since the gas hydrate slurry is dehydrated to obtain the concentrated gas hydrate slurry or the gas hydrate from which seawater has been removed, the seawater in the gas hydrate slurry is reduced or reduced. It is possible to reduce the volume when the material is removed and transported to the post-treatment side or transported to the land side or the like.

The fifth aspect of the present invention is the method for excavating and collecting gas hydrate according to the fourth aspect, wherein the gas hydrate slurry or the gas hydrate is washed with washing water.

As described above, since the gas hydrate slurry or the gas hydrate is washed, the highly corrosive seawater is washed away to suppress the occurrence of corrosion on the pipes and containers during transportation. You can

The invention according to claim 6 is the method for excavating and recovering gas hydrate according to claim 5, wherein the cleaning water is added to the gas hydrate obtained after the cleaning to obtain the gas hydrate. A gas hydrate slurry, which is a mixture with the washing water, is used.

As described above, since the mixture of gas hydrate and cleaning water, that is, the gas hydrate in the form of powder or granules, is made into the gas hydrate slurry to be dispersed in the cleaning water, the gas having low corrosiveness is used. It can be a hydrate slurry.

According to a seventh aspect of the present invention, there is provided a system for excavating and recovering gas hydrate existing in the ground on the sea floor, which comprises excavating an offshore structure, the ground on the sea floor and the gas hydrate. Along with, the seawater at a position near the offshore structure is sent to the gas hydrate, and an excavation and recovery device that recovers the gas hydrate slurry that is a mixture of the gas hydrate and the seawater, and the excavation and recovery device and the A pipe that is connected to an offshore structure and supplies seawater in the vicinity of the offshore structure to the excavation and recovery apparatus, and that transports the gas hydrate slurry to the offshore structure. And

By using the gas hydrate excavation and recovery system configured as described above, the gas hydrate excavation and recovery method according to the first aspect can be suitably implemented.

The invention according to claim 8 is the gas hydrate excavation and recovery system according to claim 7, wherein the pipe is a pipe having a double pipe structure composed of an outer pipe and an inner pipe. The gas hydrate slurry is caused to flow in the gap between the pipe and the inner pipe, and seawater in the vicinity of the offshore structure is caused to flow inside the inner pipe.

As described above, since the gas hydrate slurry is caused to flow through the gap between the outer pipe and the inner pipe and the warm seawater is caused to flow inside the inner pipe by using the double pipe structure pipe, It is possible to suitably suppress the heat of seawater from escaping into the sea. That is, since the warm seawater is surrounded by the gas hydrate slurry, even if the heat of the warm seawater tries to escape to the outside during the transfer, this heat is absorbed by the gas hydrate slurry being transferred, and the gas hydrate is Used to partially decompose, heat rarely escapes into the sea. Therefore, the heat once collected can be effectively used without being released to the outside.

A ninth aspect of the present invention is the gas hydrate excavation and recovery system according to the seventh or eighth aspect, wherein the gas hydrate excavation and recovery system is provided near the seabed and is mixed in the gas hydrate slurry. It is characterized by being provided with a sediment separating device for separating sediment.

Further, the invention according to claim 10 is the gas hydrate excavation and recovery system according to claim 9, wherein the earth and sand separating device is provided with the gas hydrate slurry introduced therein for a predetermined time. It is characterized by being a gravity sedimentation type sediment separating apparatus which sediments the sediment by allowing it to stay.

Further, the invention according to claim 11 is the gas hydrate excavation and recovery system according to claim 9, wherein the sediment separating device applies centrifugal force to the gas hydrate slurry introduced therein. It is characterized by being a centrifugal separation type earth and sand separating device which discharges the earth and sand to the outside by generating.

Further, the invention according to claim 12 is the gas hydrate excavation and recovery system according to any one of claims 9 to 11, which is provided on the offshore structure and is pulled up to the offshore structure. In addition, a gas-liquid separator for separating the gas mixed in the gas hydrate slurry is provided.

Further, the invention according to claim 13 is the gas hydrate excavation and recovery system according to claim 12, which is provided in the offshore structure and dehydrates and concentrates the gas hydrate slurry. It is characterized in that it is provided with a dehydrator for producing a gas hydrate slurry or a gas hydrate from which seawater has been removed.

Further, the invention according to claim 14 is the gas hydrate excavation and recovery system according to claim 12 or 13, wherein the gas hydrate slurry or the gas is provided on the offshore structure. A cleaning device for cleaning the hydrate with cleaning water is provided.

Further, the invention according to claim 15 is the gas hydrate excavation and recovery system according to claim 14, wherein the cleaning device has the gas hydrate slurry or the gas hydrate inside thereof. Introduce only a fixed amount, and after the predetermined amount of washing is completed, pay out to the outside,
It is characterized by being a batch cleaning type cleaning device.

Further, the invention according to claim 16 is the gas hydrate excavation and recovery system according to claim 14, wherein the cleaning device continuously contains the gas hydrate slurry or the gas hydrate therein. It is characterized in that it is a continuous cleaning type cleaning device which is continuously introduced while being continuously introduced, and is discharged to the outside in the order in which the cleaning is completed.

By using the gas hydrate excavation and recovery system configured as described above, the gas hydrate excavation and recovery method according to any one of claims 2 to 6 can be suitably implemented.

[0032]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a gas hydrate excavation and recovery method and an excavation and recovery system according to the present invention will be described below with reference to the drawings. Here, a case will be described as an example where the hydrate layer H formed in the seabed G with a substantially horizontal spread is excavated and the gas hydrate is collected and recovered as shown in FIG.

The gas hydrate excavation and recovery system shown in FIG. 1 (hereinafter may be simply referred to as "excavation and recovery system") excavates the hydrate layer H formed in the seabed G to form a gas hydrate. It is collected and recovered as a gas hydrate slurry that is a mixture with seawater, and has a sea structure 10 floating on the sea, a double pipe (pipe having a double pipe structure) 20, and an excavation provided on the seabed side. The recovery device 30 and the earth and sand separation device 40 provided integrally with the excavation recovery device 30 are provided.

The offshore structure 10 floats above the sea and remotely controls the excavation and recovery device 30 and the sediment separating device 40 on the seabed, and keeps its position constant without being swept by wind or tidal current. In order to perform the above, a plurality of thrusters (thrusters) (not shown) are provided. In addition, GPS (Global Positionin using an artificial satellite
g System (not shown) allows the user's position to be recognized and held with high accuracy even in the open ocean. The offshore structure 10 includes a gas-liquid separation device 11
A dehydrator 12 and a cleaning device 13. Further, a pump 22p for collecting seawater in the vicinity of the offshore structure 10, that is, warm seawater near the sea surface (warm seawater) and sending the collected water to the double pipe 20 is also provided.

The double pipe 20 is a flexible pipe that connects the offshore structure 10 and the sediment separating device 40, and has a function of transporting various measuring instruments and materials between the sea top side and the sea bottom side. At the same time, it has a function of sending the gas hydrate slurry from the seabed side to the seaside side, and a function of sending warm seawater from the seaside side to the seabed side. That is, the double pipe 20 and the excavation and recovery device 30 are connected via the earth and sand separating device 40.

The double pipe 20 has a double pipe structure consisting of an outer pipe 21 and an inner pipe 22. Outer tube 2
Gas hydrate slurry (described later) sent from the seabed side can be made to flow in the gap portion between the inner pipe 21 and the inner pipe 22, and warm seawater from the pump 22p can be made to flow inside the inner pipe 21. It is like this. Outer tube 2
1 is directly connected to the sediment separating device 40,
The inner pipe 22 bypasses the sediment separating device 40 and can directly feed warm seawater to the excavation and recovery device 30 (see FIGS. 3A and 3B).

The excavation recovery device 30 includes an excavation base portion 31 installed near the sea bottom GL, an excavation device portion 32 for excavating the seabed ground G and the hydrate layer H, and the excavation base portion 31 to the excavation device portion 32. And a shaft 33 that transmits the driving force to the. Then, the excavation hole formed between the excavation base portion 31 and the excavation device portion 32 has a double pipe portion 34.
Is covered by.

The excavation base 31 is installed on the sea bottom GL almost integrally with the sediment separating device 40, and has a function as a base on the sea bottom in excavation and gas hydrate recovery. As a specific function, the first
Further, according to the remote control from the offshore structure 10, the excavation speed, the excavation direction, etc. of the excavation device section 32 are operated using an actuator (not shown). Secondly, the shaft 33 and the double pipe portion 34 are extended along with the excavation of the excavation device portion 32. The shaft 33 and the double pipe portion 34 are each divided into a plurality of segments, and by sequentially adding these segments, the shaft 33 and the double pipe portion 34 can be extended along with the excavation. And thirdly, the warm seawater flowing through the inner pipe 22 of the double pipe 20 is taken in, and the taken warm seawater is passed through the double pipe portion 34 and the excavation device portion 32.
Send water to the side.

The excavation device section 32 is connected to the excavation base section 31 by a shaft 33. An excavation bit 32a is provided at the tip of the excavation bit 32a, and the rotational driving force from the excavation base 31 is transmitted via the shaft 33.
By the rotation of 2a, the seabed G and the hydrate layer H
You can dig in. In the excavation using the excavation device section 32, the excavation is started from the excavation base section 31 in a substantially vertical direction, and then the excavation direction is gradually changed. To be That is, when the hydrate layer H arrives, it is possible to excavate in a direction substantially parallel to the spreading direction.

At the tip of the excavation device 32,
For example, a pulse neutron sensor (not shown) or the like may be attached to perform logging of the seafloor ground G, the hydrate layer H, and other geological formations. This pulse neutron sensor emits neutrons toward the front formation and detects radiation emitted from the formation to obtain various data such as porosity, water saturation rate or rock quality of the formation.
If a communication device is connected to such a pulse neutron sensor and the obtained data can be transmitted to the offshore structure 10 etc. in real time, the excavation recovery device 30 can be controlled while grasping the progress of the excavation at any time. it can.

FIG. 2 shows a magnified view of the vicinity of the excavation tip. Note that FIG. 2 shows a state in which the excavation device section 32 is excavating the hydrate layer H. As shown in this figure,
The double pipe part 34 is composed of an outer pipe 34a and an inner pipe 34b which are arranged with a predetermined gap therebetween. The excavation device portion 32 and the rotary shaft 33 are provided inside the inner pipe 34b with a predetermined gap from the inner pipe 34b.

Seawater (warm seawater) Ws from the drilling base 31
Is the inside of the inner pipe 34b, that is, the excavation device portion 3
2 and the gap between the shaft 33 and the inner pipe 34b. Further, the leading end of the inner pipe 34b in the excavation direction projects a little longer than the leading end of the outer pipe 34a in the excavation direction.
34h that can discharge seawater Ws to the side of
Are formed. With such a configuration, the seawater Ws sent from the drilling base 31 is not
4b through the gap between the excavator unit 32 and the excavator unit 32, and is discharged to the front side in the excavating direction of the excavator unit 32, and the hole 34
It is also discharged to the side of the inner tube 34b through h. This makes it possible to increase the contact area between the gas hydrate and the seawater Ws and improve the contact efficiency.

As the digging device section 32 digs through the hydrate layer H, the gas hydrate is ground and the seawater Ws sent through the inner pipe 34b comes into contact with the gas hydrate. Then, the gas hydrate absorbs the heat in the seawater Ws and is decomposed to some extent. However, although the seawater Ws was originally warm seawater, the amount of heat possessed by the seabed is not so high, and only some of the gas hydrate is decomposed. The partially decomposed gas hydrate is dispersed in the seawater Ws in the form of a granular material, and is a mixture of the seawater Ws and the gas hydrate (see FIG. 2). The code Hs) is formed. The gas hydrate slurry Hs is caused to flow into the gap between the outer pipe 34a and the inner pipe 34b and sent to the excavation base 31 to collect the slurry gas hydrate in the excavation base 31.

At this time, if the gas hydrate cannot be sufficiently decomposed with the seawater Ws alone and the powder form of the preferred form cannot be obtained, the decomposition accelerator is added to the warm seawater in the marine structure 10. It is desirable to keep it. Examples of such decomposition accelerators include alcohols such as methanol or ethylene glycols such as monoethylene glycol, diethylene glycol and triethylene glycol.

As described above, when the gas hydrate becomes powdery, a part of it is decomposed into water and natural gas (gas), which are mixed in the gas hydrate slurry Hs. is doing. Moreover, the earth and sand in the seabed G or the hydrate layer H are inevitably mixed in the gas hydrate slurry Hs. That is, the recovered gas hydrate slurry Hs contains natural gas and earth and sand in addition to the gas hydrate.
The gas hydrate slurry Hs collected and collected in the excavation base 31 is sent from the excavation base 31 to the sediment separating device 40, where the sediment is separated from the gas hydrate slurry.

As a concrete example of the sediment separating apparatus 40, a gravity sedimentation type sediment separating apparatus (designated by reference numeral 40A) is shown in FIG.
FIG. 3 (b) shows a centrifugal type sediment separating apparatus (designated by reference numeral 40B) in FIG. 3 (a). First, the sediment separating device 4
0A will be described. This earth and sand separating device 40A has a cylindrical body tube 41 attached to the lower end side of the double pipe 20.
And an introduction pipe 41a for introducing the gas hydrate slurry (reference numeral Hs in FIG. 3) from the excavation base 31 into the barrel 41. Below the barrel 41, a discharge port 4 for discharging earth and sand (reference numeral D in FIG. 3) separated from the gas hydrate slurry Hs to the sea bottom GL.
1b is formed.

The gas hydrate slurry Hs containing the earth and sand D from the excavation and recovery apparatus 30 is introduced into the barrel 41 through the introduction pipe 41a and allowed to stay in the barrel 41 for a predetermined period of time. Has a lower specific gravity than seawater and therefore tries to rise toward the double pipe 20. On the other hand, since the specific gravity of the sediment D is heavier than that of seawater, the sediment D gradually settles due to gravity, is discharged from the opening 41b, and falls onto the sea floor GL. In this way, the earth and sand D mixed in the gas hydrate slurry Hs is separated.

As described above, the earth and sand separator 41A is a earth and sand separator of the type that performs gravity separation by utilizing the fact that the specific gravities of gas hydrate, seawater and earth and sand are different. If such a sediment separating device 41A is used, a special actuator or the like is not required, the device configuration can be simplified, and almost no energy required for separating the sediment can be required.

Next, the earth and sand separating device 40B will be described. This earth and sand separator 40B is the same as the earth and sand separator 4 described above.
0A is provided with a screw 42 and a motor (actuator) 43 that rotationally drives the screw 42. The screw 42 has a spiral blade 42a on its outer surface side, and is rotated at a high speed by a motor 43 to apply a centrifugal force to the gas hydrate slurry Hs introduced into the barrel 41, and It operates so as to send the hydrate slurry Hs to the upper double pipe 20 side. The screw 42 and the inner wall of the barrel 41 are arranged with a predetermined gap therebetween.

The gas hydrate slurry Hs containing the earth and sand D from the excavation and recovery device 30 is introduced into the barrel 41 and the screw 42 is rotated at high speed. This way
Centrifugal force is generated in the gas hydrate slurry Hs, and due to this centrifugal force, the earth and sand D having a high specific gravity is blown to the outside, and the gas hydrate having a low specific gravity is gathered to the inside. The earth and sand D that has been blown to the outside collides with the inner wall of the barrel 41, then settles through the gap between the barrel 41 and the screw 42 due to gravity, is discharged from the opening 41b, and is on the sea floor GL. It falls to. On the other hand, the gas hydrate collected inward has a specific gravity lighter than that of seawater and is sent upward by the screw 42, so that the gas hydrate rises toward the double pipe 20.

As described above, the sediment separating device 41B is a sediment separating device of the type that performs sediment separation by centrifugal separation by utilizing the fact that the specific gravities of gas hydrate, seawater and sediment are different from each other. By using such a sediment separating device 40B, the sediment D can be accurately separated in a short time, and the gas hydrate slurry Hs can be sent to the offshore structure 10 at high speed and with high efficiency.

The earth and sand D discharged to the sea bottom GL
If it is to be backfilled in the excavation hole again by using a sediment transporting device or the like, collapse of the seabed ground G can be effectively prevented, and thus backfilling is preferable.

The gas hydrate slurry Hs thus separated from the earth and sand is used as the outer pipe 21 of the double pipe 20.
It is pulled up to the floating structure 10 through the gap between the inner pipe 22 and the inner pipe 22. During this pulling up, part of the gas hydrate in the gas hydrate slurry may decompose. At this time, the heat of the warm seawater flowing inside the inner pipe 22 is preferably suppressed from escaping into the sea by the gas hydrate slurry flowing in the gap between the outer pipe 21 and the inner pipe 22. ing. That is, since the warm seawater is in a state of being surrounded by the gas hydrate slurry, even if the heat of the warm seawater tries to escape to the outside during transfer, this heat is absorbed by the gas hydrate slurry during transfer, Gas hydrate is used to partially decompose and heat seldom escapes into the sea. This is because the decomposition temperature of gas hydrate is lower than the temperature of seawater, so the gas hydrate slurry may remove heat from the sea or warm seawater, but it does not release it. , Heat transfer from warm seawater into the sea is blocked.

When the heat of the warm seawater escapes into the sea, the collected heat escapes to the outside of the excavation system, resulting in heat loss. However, it is absorbed by the gas hydrate slurry and decomposes the gas hydrate. If utilized, no heat loss will occur as the heat remains in the drilling system. This is because even if the gas hydrate is decomposed into natural gas, this natural gas is effectively recovered by the gas-liquid separator 11 described later. In other words, in the double pipe 20, the warm seawater and the gas hydrate slurry are countercurrent to each other and can exchange heat with each other. As described above, by using the double pipe 20, the heat once collected by collecting the warm seawater can be effectively used in the excavation and recovery system without being released to the outside.

The gas hydrate slurry pulled up to the water structure 10 is sent to the gas-liquid separator 11 shown in FIG. 1 to separate the mixed natural gas.

The gas-liquid separation device 11 performs gas-liquid separation by, for example, allowing the gas hydrate slurry to remain in the container for a predetermined time. The natural gas separated from the gas hydrate slurry by the gas-liquid separator 11 is sent to the land side through the pipeline P. Instead of using the pipeline P, the LNG (liquefied natural gas) ship or the like may be used to transport to the land side. Gas-liquid separation device 1
The gas hydrate slurry from which natural gas has been separated by 1 is sent to the dehydrator 12.

The dehydrator 12 dehydrates the gas hydrate slurry into a concentrated gas hydrate slurry or a solid gas hydrate from which seawater has been removed. The structure may be provided with a screen or the like for separating gas hydrate and seawater from each other, or may be one that is subjected to centrifugal force for dehydration. Here, in consideration of improving the handling property of the gas hydrate in the post-treatment,
Although a concentrated gas hydrate slurry is prepared, if it is not necessary to take handling properties into consideration, most of the seawater in the gas hydrate slurry may be removed to form a solid gas hydrate. The gas hydrate slurry concentrated by the dehydrator 12 is the cleaning device 1
Sent to 3.

The cleaning device 13 cleans the gas hydrate slurry with cleaning water to almost completely remove the seawater, and after removing the seawater, the gas hydrate slurry which is a mixture of the gas hydrate and the cleaning water. As a result, it is paid out to the outside of the cleaning device 13. The discharged gas hydrate slurry may be transported to the land side by the container ship C after being enclosed in a container, or may be transported to the land side by a pipeline. When it is sealed in a container as in the former case, it may be dehydrated immediately before sealing and transported as a solid gas hydrate.

Although the cleaning device 13 is designed to discharge the gas hydrate slurry using cleaning water in consideration of improving the handling property of the gas hydrate, the handling property is particularly good. If it is not necessary to consider it, it may be dispensed as a solid gas hydrate. Further, here, fresh water is used as the wash water, but it is also possible to use fresh water to which a chemical or the like that provides a high washing effect is added.

As a specific example of the cleaning device 13, a batch cleaning type cleaning device (reference numeral 13A) for cleaning each batch
4 (a) to 4 (d), and FIG. 5 shows a continuous cleaning type cleaning device (reference numeral 1) capable of continuous cleaning treatment.
3B to 13D) are shown in FIGS.

First, the batch cleaning type cleaning device 13A will be described. As shown in FIG. 4A, this cleaning device 13A includes a cleaning container 51, an inlet pipe 52 for introducing the gas hydrate slurry from the dehydrator 12 into the cleaning container 51, and a cleaned gas hydrate. A dispensing pipe 53 for dispensing to the outside of the cleaning container 51, and cleaning water (fresh water) is supplied into the cleaning container 51 and the cleaning water after cleaning is cleaned by the cleaning container 51.
A washing water supply / withdrawal pipe 54 for withdrawing outside and a washing water withdrawing pipe 55 for withdrawing the washing water after washing out of the washing container 51 are provided.

The cleaning container 51 is a pressure container having a substantially cylindrical shape, and a screen 51a is provided on the lid surface side (upper side) and a screen 51b is provided on the bottom surface side (lower side). There is. These screens 51a, 51b
Allows the permeation of seawater and cleaning water but prevents the permeation of particulate gas hydrate. That is, it has a function of filtering out the gas hydrate, and the gas hydrate introduced into the cleaning container 51 can move vertically only between the screens 51a and 51b. In addition, in order to prevent decomposition of the particulate gas hydrate, the cleaning container 51 is separately provided with a pressurizing means for pressurizing the inside of the cleaning container 51, a cooling means for cooling the inside of the cleaning container 51, and the like. May be.

The introducing pipe 52 has one end connected to the dehydrator 12 (not shown in FIG. 4) and the other end connected to the upper side of the cleaning container 51 and below the screen 51a. . In the middle of the conduit of the introduction pipe 52,
A control valve 52v is provided. Further, the discharge pipe 53 is on the lower side of the cleaning container 51 and on the screen 5
It is connected above 1b. A control valve 53v is provided in the middle of the pipe of the dispensing pipe 53.

The cleaning water supply / drain pipe 54 is connected to the bottom surface of the cleaning container 51, that is, below the screen 51b, and supplies the cleaning water Wf from the lower side of the cleaning container 51 and performs cleaning after cleaning. The water Wf can be discharged. In the middle of the conduit of the wash water supply / extraction pipe 54,
A control valve 54v is provided. The cleaning water drain pipe 55 is connected to the lid surface portion of the cleaning container 51, that is, above the screen 51a, so that the cleaning water Wf after cleaning can be extracted from the upper side of the cleaning container 51. . A control valve 55v is provided in the conduit of the wash water extraction pipe 55.
The control valves 52v, 53v, 54v, 5
The opening degree of 5v is controlled by a control means (not shown).

The cleaning of gas hydrate using this cleaning device 13A will be described below. First, FIG. 4 (a)
As shown in, the control valves 53v, 54v, 5
5v is closed and the control valve 52v is opened to remove the gas hydrate slurry Hs from the dehydrator 12.
Is introduced into the cleaning container 51 by a predetermined amount. Next in FIG.
As shown in (b), the control valve 52v is closed, the control valves 54v and 55v are opened, and the cleaning water Wf is passed from the lower side to the upper side of the cleaning container 51 for a predetermined time to clean the gas hydrate. To do.

After a predetermined time has passed, the control valves 54v and 55v are closed to stop the flow of the wash water Wf. Then, as shown in FIG. 4C, only the control valve 54v is opened again, and the cleaning water Wf in the cleaning container 51 is drained from the lower side of the cleaning container 51. At this time, a gas hydrate slurry, which is a mixture of gas hydrate and cleaning water Wf (reference numeral H in FIG. 4D described later).
The cleaning water Wf is allowed to remain in the linear container 51 to such an extent as to be f). If one cleaning is not enough, these operations are repeated a plurality of times to remove the seawater adhering to the gas hydrate until it is almost complete.

Finally, as shown in FIG. 4D, the control valve 54v is closed and the control valve 53v is closed.
Is opened, and the gas hydrate slurry Hf in the cleaning container 51 is discharged to the outside. Thus, the cleaning of the gas hydrate in the gas hydrate slurry Hs introduced by the predetermined amount, that is, the cleaning of one batch is completed. By repeating the above operation, the gas hydrate slurry H
The gas hydrate in s is sequentially washed to produce a gas hydrate slurry Hf which is a slurry of gas hydrate and washing water.

Such a batch cleaning type cleaning device 13
If A is used, the gas hydrate can be carefully washed for each batch.

Next, the continuous cleaning type cleaning device 13B will be described. As shown in FIG. 5A, the cleaning device 13B includes a cleaning container 61 and an introduction pipe 6 for introducing the gas hydrate slurry from the dehydrator 12 into the cleaning container 61.
2, a discharge pipe 63 for discharging the cleaned gas hydrate to the outside of the cleaning container 61, a cleaning water supply pipe 64 and a spray nozzle 64n for supplying and spraying cleaning water (fresh water) into the cleaning container 61, and after cleaning The washing water withdrawing pipe 65 for withdrawing the washing water of (1) to the outside of the washing container 61 and the screen 71 are provided.

The cleaning container 61 is a pressure container, and a screen 71 is attached inside thereof so as to be inclined from the lower side of the end of the introduction pipe 62 to the discharge pipe 63. This screen 71 allows the permeation of seawater and cleaning water but prevents the permeation of particulate gas hydrate, and has the function of filtering out gas hydrate. The cleaning container 61 includes a cleaning container 6 in order to prevent decomposition of particulate gas hydrate.
A pressurizing unit for pressurizing the inside of the cleaning container 1, a cooling unit for cooling the inside of the cleaning container 61, and the like may be separately provided.

The introduction pipe 62 has one end connected to the dehydrator 12 (not shown in FIG. 5) and the other end connected to the upper side of the cleaning container 61 and directly above the screen 71. That is, the gas hydrate slurry Hs can be introduced onto the screen 71. Further, the dispensing pipe 63 is connected to the lower side of the cleaning container 61.

The spray nozzle 64n is provided above the cleaning container 61 above the screen 71, and a cleaning water supply pipe 64 is connected to the spray nozzle 64n. That is, the cleaning water Wf can be sprayed onto the screen 71. Also, the wash water drain pipe 6
5 is connected to the lower side of the cleaning container 61 so that the cleaning water Wf that has passed through the screen 71 can be extracted to the outside of the cleaning container 61.

The cleaning of the gas hydrate using the cleaning device 13B is performed by continuously introducing the gas hydrate slurry Hs from the dehydrating device 12 into the cleaning container 61.
That is, while continuously introducing the gas hydrate slurry Hs from the introduction pipe 62 onto the screen 71, the cleaning water is continuously sprayed from the spray nozzle 64n. At this time, seawater in the gas hydrate slurry Hs drops below the screen 71, and the filtered gas hydrate is
Wash water Wf while sliding down in the inclined direction of the screen 71
Washed by. The washing water Wf after washing also drops below the screen 71 and is drawn out of the washing container 61 by the washing water drain pipe 65.

The washed gas hydrate is washed with water W.
It is slid down to the discharge pipe 63 in a state containing a little f, and is discharged to the outside of the cleaning container 61 as a gas hydrate slurry (reference symbol Hf) which is a mixture of gas hydrate and cleaning water Wf.

Next, the continuous cleaning type cleaning device 13C will be described. This cleaning device 13C is the same as the cleaning device 13 described above.
Compared to B, the screen 71 is replaced by a screen conveyor including a pair of rotary shafts 72, 72 and a screen belt 73, which is the only difference. Therefore, the same components as those in the cleaning device 13B are designated by the same reference numerals, and detailed description thereof will be omitted.

A screen belt 73, which is an endless belt, is stretched between the rotating shafts 72-72.
The screen belt 73 has the screen 71 in the form of an endless belt and allows seawater and cleaning water to pass therethrough, but prevents permeation of particulate gas hydrate. That is, the rotary shafts 72, 7
When 2 is rotated by an actuator (not shown), the screen belt 73 is moved in the direction of the arrow in the figure.

In the cleaning of gas hydrate using the cleaning device 13C, the gas hydrate slurry Hs from the introducing pipe 62 is continuously introduced onto the screen belt 73 while the screen belt 73 is moved in the direction of the arrow in the figure. The cleaning water is moved and the cleaning water is continuously sprayed from the spray nozzle 64n. At this time, the seawater in the gas hydrate slurry Hs falls below the screen belt 73, and the filtered gas hydrate is washed by the wash water Wf while being conveyed as the screen belt 73 moves.
The cleaning water Wf after cleaning also drops to the lower side of the screen belt 73, and is discharged to the outside of the cleaning container 61 by the cleaning water drain pipe 65.

The washed gas hydrate is washed with water W.
It is conveyed to a position just above the payout pipe 63 with some f included,
It is dropped toward the dispensing pipe 63. In this way, the gas hydrate slurry (reference symbol Hf), which is a mixture of the gas hydrate and the cleaning water Wf, is discharged to the outside of the cleaning container 61.

Next, the continuous cleaning type cleaning device 13D will be described. This cleaning device 13D is the same as the cleaning device 13 described above.
Compared with B, only a screen drum 74 and a motor 75 are provided instead of the screen 71. Therefore, the same components as those in the cleaning device 13B are designated by the same reference numerals, and detailed description thereof will be omitted.

The screen drum 73 has the screen 71 in the form of a drum having a substantially cylindrical shape, and allows seawater and cleaning water to pass therethrough, but prevents the particulate gas hydrate from passing therethrough. It is a thing. The rear side of the screen drum 73 is rotatably supported on the side portion of the cleaning container 61 so that the axis of the introduction pipe 62 and the rotation axis are substantially the same, and is indicated by an arrow in the figure by a motor 75. It is designed to rotate in the direction. In addition, the front side of the screen drum 73 is opened immediately above the payout pipe 63. A spiral screw blade 74a is provided inside the screen drum 74, and the gas hydrate inside the screen drum 74 can be conveyed from the rear side to the front side as the screen drum 74 rotates. You can do it.

In cleaning the gas hydrate using the cleaning device 13D, the gas hydrate slurry Hs from the introducing pipe 62 is continuously introduced into the screen drum 74 while the screen drum 74 is moved in the direction of the arrow in the figure. In addition, the cleaning water is continuously sprayed from the spray nozzle 64n. At this time, the gas hydrate slurry H
The seawater in s falls below the screen drum 74, and the filtered gas hydrate is washed by the wash water Wf while being transported to the front side as the screen drum 74 rotates. The washing water Wf after washing is also used for the screen drum 7.
4 to the lower side, and the washing water drain pipe 65 is used to wash the washing container 6
1 is pulled out.

The washed gas hydrate is washed with water W.
It is conveyed to a position just above the payout pipe 63 with some f included,
It is dropped toward the dispensing pipe 63. In this way, the gas hydrate slurry (reference symbol Hf), which is a mixture of the gas hydrate and the cleaning water Wf, is discharged to the outside of the cleaning container 61.

These continuous cleaning type cleaning devices 13B, 13
If C and 13D are used, it is possible to sequentially clean the gas hydrates that have been sent, so that the cleaning speed can be increased and the cleaning efficiency can be improved.

In the gas hydrate excavation and recovery method and the excavation and recovery system according to the present embodiment, the hydrate layer H is excavated by using the excavation and recovery device 30, and the double pipe 20 is used to detect the position near the seabed. Seawater is sent to the hydrate layer H to form a gas hydrate slurry that is a mixture of gas hydrate and seawater.
I try to raise it to zero. In this way, the gas hydrate is made into a granular form and is dispersed in seawater to form a gas hydrate slurry, which is collected and collected as a liquid, so that the handling property of the gas hydrate can be significantly improved. Therefore, the recovery efficiency and the transportation efficiency can be improved. Further, in order to make the gas hydrate into a granular form, it is necessary to decompose a small amount, but by sending warm seawater near the sea surface to the hydrate layer H, the amount of heat for decomposition is preferable. And the recovery efficiency can be further enhanced.

Further, by using the double pipe 20, the outer pipe 2
Since the gas hydrate slurry is caused to flow in the gap between the inner pipe 22 and the inner pipe 22 and the warm seawater is caused to flow inside the inner pipe 22, it is possible to suitably prevent the heat of the warm seawater from escaping into the sea. Therefore, the heat once collected can be effectively used without being released to the outside of the excavation and recovery system without generating heat loss. Therefore, the heat utilization efficiency in the excavation and recovery system can be improved.

Furthermore, in order to make the gas hydrate into a granular form, it is only necessary to decompose it in a small amount, and the required amount of heat can be significantly reduced compared to the case of almost complete decomposition. Since almost no heat transfer from the side to the seabed side is required, the device configuration can be simplified. Further, since it is possible to suppress the possibility of a sudden jet and to eliminate a certain measure against the jet, it is possible to reduce the apparatus cost and the construction cost.

Furthermore, since the seawater is sent while excavating the hydrate layer H on the seabed to make the gas hydrate into a slurry and to recover it, the number of drill holes formed in the seabed G should be the minimum required. It is possible to reduce the construction cost and improve the construction efficiency.

Further, after the earth and sand mixed in the gas hydrate slurry is separated at a position near the sea bottom by using the earth and sand separating device 40, the gas hydrate slurry is pulled up 10 to the offshore structure. Therefore, heavy soil that does not need to be collected can be discarded before being pulled up, the amount of cargo to the sea can be reduced, the energy required for transportation can be reduced, and collection efficiency can be further improved. You can

If the structure of the sediment separating device 40 used here is a gravity-sedimentation-type sediment separating device 40A, a special actuator or the like is not required and the structure of the device can be simplified and the sediment D can be separated. The energy required for can be almost eliminated. Further, if the centrifugal separation type sediment separating device 40B is used, the sediment D can be accurately separated in a short time, and the gas hydrate slurry Hs can be sent to the offshore structure 10 at high speed and with high efficiency.

Further, since the gas mixed with the gas hydrate slurry pulled up to the offshore structure 10 is separated by using the gas-liquid separator 11, the gas hydrate slurry which is a liquid and the gas are separated. Post-treatment suitable for each of certain gases can be performed, both can be effectively used as energy sources, and the utilization efficiency of the recovered gas hydrate can be improved.

Further, since the gas hydrate slurry is dehydrated by using the dehydrator 12 to obtain a concentrated gas hydrate slurry, the seawater in the gas hydrate slurry is reduced or removed to carry out the post-treatment. The volume at the time of transportation to the side or transportation to the land side can be reduced, and the transportation efficiency and the transportation efficiency can be improved.

Further, since the gas hydrate slurry is cleaned with the cleaning water Wf by using the cleaning device 13, highly corrosive seawater is washed away to cause corrosion of pipes and containers during transportation. Can be accurately suppressed, and the reliability and durability of various transportation devices can be improved.

Further, the cleaning water Wf is added to the gas hydrate obtained after the cleaning so that a mixture of the gas hydrate and the cleaning water, that is, a gas hydrate in the form of powder or granules is dispersed in the cleaning water. Since it is made into a slurry, it is possible to obtain a gas hydrate slurry having reduced corrosiveness while improving the handling property.

If the cleaning device 13 used here is a batch cleaning type cleaning device 13A, the gas hydrate can be carefully cleaned for each batch. In addition, continuous cleaning type cleaning devices 13B, 13C, 13
If D is set, it is possible to sequentially clean the gas hydrate that has been sent, so that the cleaning speed can be increased and the cleaning efficiency can be improved.

In the above-described embodiment, the gas hydrate slurry sent from the seabed side to the offshore structure is subjected to various treatments in the state of being a slurry. The gas hydrate may be decomposed at any place. In this case, since heat is absorbed with decomposition, such cold heat is
It is desirable to effectively use it for cooling or a cooling device on the offshore structure.

[0096]

As described above, in the gas hydrate excavation and recovery method and the excavation and recovery system according to the present invention, since the above-mentioned configuration is adopted, the handling property of the gas hydrate is improved and recovery is performed. It is possible to provide a method for excavating and collecting gas hydrate and a system for excavating and recovering gas, which can improve efficiency and transportation efficiency.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of a gas hydrate excavation and recovery system according to the present invention.

FIG. 2 is a partially enlarged view showing an enlarged part of FIG.

FIG. 3 is a side sectional view showing a specific example of a sediment separating apparatus used in the present invention, wherein (a) shows a gravity sedimentation type sediment separating apparatus, and (b) shows a centrifugal separation type sediment separating apparatus.

FIG. 4 is a side sectional view showing a batch cleaning type cleaning device as a specific example of the cleaning device used in the present invention.

FIG. 5 is a side sectional view showing a continuous cleaning type cleaning device as a specific example of the cleaning device used in the present invention.

[Explanation of symbols]

10 Offshore Structure 11 Gas-Liquid Separator 12 Dehydrator 13 Cleaning Device 13A Cleaning Device (Batch Cleaning Type Cleaning Device) 13B, 13C, 13D Cleaning Device (Continuous Cleaning Type Cleaning Device) 20 Double Pipe (Double Pipe Structure) Pipes 21 outer pipe 22 inner pipe 22p pump 30 excavation recovery device 40 sediment separation device 40A sediment separation device (gravity sedimentation type sediment separation device) 40B sediment separation device (centrifugal separation device) G seabed ground H hydrate layer (gas hydrate)

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Shojiro Iwasaki             1-1 1-1 Wadasaki-cho, Hyogo-ku, Kobe-shi, Hyogo             No. Mitsubishi Heavy Industries, Ltd.Kobe Shipyard (72) Inventor Yuichi Kondo             1-1 1-1 Wadasaki-cho, Hyogo-ku, Kobe-shi, Hyogo             No. Mitsubishi Heavy Industries, Ltd.Kobe Shipyard (72) Inventor Kozo Yoshikawa             2-1-1 Niihama, Arai-cho, Takasago, Hyogo Prefecture             Takasago Laboratory, Mitsubishi Heavy Industries, Ltd. (72) Inventor Hiromitsu Nagayasu             2-1-1 Niihama, Arai-cho, Takasago, Hyogo Prefecture             Takasago Laboratory, Mitsubishi Heavy Industries, Ltd. (72) Inventor Shoji Watanabe             2-1-1 Niihama, Arai-cho, Takasago, Hyogo Prefecture             Takasago Laboratory, Mitsubishi Heavy Industries, Ltd. F-term (reference) 2D065 FA23 FA31 FA35 GA00

Claims (16)

[Claims] 1. A method of excavating a gas hydrate existing in the ground on the sea floor and recovering the gas hydrate to an offshore structure, wherein the gas hydrate is excavated and seawater near a position of the offshore structure is A method for excavating and recovering gas hydrate, which comprises supplying water to a gas hydrate and raising it to the offshore structure as a gas hydrate slurry which is a mixture of the gas hydrate and the seawater. 2. The gas according to claim 1, wherein after the earth and sand mixed in the gas hydrate slurry is separated at a position near the seabed, the gas hydrate slurry is pulled up to the offshore structure. Hydrate excavation recovery method. 3. The method for excavating and collecting gas hydrate according to claim 2, wherein the gas mixed in the gas hydrate slurry pulled up to the offshore structure is separated. 4. The gas hydrate excavation and recovery method according to claim 3, wherein the gas hydrate slurry is dehydrated to obtain a concentrated gas hydrate slurry or a gas hydrate from which seawater has been removed. . 5. The method for excavating and collecting gas hydrate according to claim 4, wherein the gas hydrate slurry or the gas hydrate is washed with washing water. 6. A gas hydrate slurry obtained by adding the cleaning water to the gas hydrate obtained after the cleaning to form a gas hydrate slurry which is a mixture of the gas hydrate and the cleaning water. The gas hydrate excavation recovery method described. 7. A system for excavating and collecting gas hydrate existing in the ground of the sea floor, which comprises excavating the sea structure, the ground of the sea floor and the gas hydrate, and An excavation and recovery device that sends seawater in the vicinity to the gas hydrate and recovers it as a gas hydrate slurry that is a mixture of the gas hydrate and the seawater, and connects the excavation and recovery device and the offshore structure. A pipe for supplying seawater at a position in the vicinity of the offshore structure to the excavation and recovery device and for transporting the gas hydrate slurry to the offshore structure. system. 8. The pipe is a pipe having a double pipe structure including an outer pipe and an inner pipe, and the gas hydrate slurry is flowed in a gap portion between the outer pipe and the inner pipe to form a pipe of the inner pipe. The gas hydrate excavation and recovery system according to claim 7, wherein seawater at a position near the offshore structure is allowed to flow inside. 9. The gas hydrate according to claim 7 or 8, further comprising a sediment separating device which is provided in the vicinity of the seabed and separates sediment mixed in the gas hydrate slurry. Rate drilling recovery system. 10. The sediment separating apparatus is a gravity sedimentation type sediment separating apparatus that sediments the sediment by allowing the gas hydrate slurry introduced therein to stay for a predetermined time. Item 9. A gas hydrate excavation and recovery system according to Item 9. 11. The sediment separation device is a centrifugal separation type sand separation device that discharges the sediment to the outside by generating a centrifugal force in the gas hydrate slurry introduced therein. The gas hydrate excavation and recovery system according to claim 9. 12. A gas-liquid separator provided on the offshore structure for separating the gas mixed in the gas hydrate slurry pulled up by the offshore structure. 11. The gas hydrate excavation and recovery system according to any one of 11. 13. A dewatering device provided on the offshore structure for dehydrating the gas hydrate slurry to obtain a concentrated gas hydrate slurry or a gas hydrate from which seawater has been removed. The gas hydrate excavation and recovery system according to claim 12. 14. The gas according to claim 12 or 13, further comprising a cleaning device provided on the offshore structure for cleaning the gas hydrate slurry or the gas hydrate with cleaning water. Hydrate excavation recovery system. 15. The cleaning apparatus of the batch cleaning type, wherein the cleaning apparatus introduces a predetermined amount of the gas hydrate slurry or the gas hydrate into the inside thereof, and after the cleaning of the predetermined amount is finished, the cleaning apparatus is discharged to the outside. The gas hydrate excavation and recovery system according to claim 14, which is a device. 16. The cleaning device is a continuous cleaning type in which the gas hydrate slurry or the gas hydrate is continuously introduced into the cleaning device for continuous cleaning, and the cleaning is discharged to the outside in the order in which the cleaning is completed. 15. The gas hydrate excavation recovery system according to claim 14, wherein the gas hydrate excavation recovery system is a cleaning device.