JP2003120167A - Gas hydrate investigation system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas hydrate investigation system capable of improving the investigation accuracy and investigation efficiency of gas hydrate present in the seabed. SOLUTION: This system for investigating a hydrate layer H present in the seabed ground G by boring comprises a research ship 10 floating on the water; a boring device 41 for boring the seabed ground G to collect the gas hydrate; a riser pipe for connecting the research ship 10 to the boring device 41; and a jacket foundation 32 integrated to the boring device 41 and buried in the seabed ground G to fix the boring device 41 to the seabed ground G.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an investigation system for investigating gas hydrate existing in the ground of water bottom such as sea bottom.

[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 there will be a large amount in the seabed of the sea near Japan, and exploration or surveys are about to be carried out sequentially.

In order to discover the hydrate layer existing on the sea floor such as the sea floor, first, the size and depth of the hydrate layer are roughly grasped by physical exploration using elastic waves and the like, and then core sampling is carried out by boring or the like. It is common to conduct this to investigate this hydrate layer. In other words, the investigation of the hydrate layer means that a boring device is hung from the exploration boat above the water to the bottom of the water, and the ground of the bottom of the water is excavated by this boring device to collect a core (columnar material), which is pulled up to the top of the research boat for analysis. It is carried out to determine whether or not the hydrate layer actually exists, and if so, the depth or layer thickness of the hydrate layer.

[0005]

In order to perform such an investigation with high accuracy and high efficiency, it is necessary to firmly fix the boring device on the ground of the seabed, but the influence of wave height, ocean current, etc. Therefore, the research ship or the boring device may be subjected to a moving force. When that happens,
The undersea boring device was not stable, and it was difficult to secure high positioning accuracy during sampling and high excavation accuracy. Also, unlike petroleum, gas hydrate cannot exist at room temperature and pressure, so it may be decomposed (gasified) by friction heat during excavation, but it is necessary to accurately understand the excavation situation from the sea. Is difficult,
Therefore, it has been difficult to effectively suppress such decomposition and conduct a highly efficient survey. Furthermore, when pulling the collected gas hydrate core from the seabed under low temperature and high pressure conditions to the sea under normal temperature and pressure conditions,
Depending on the temperature and pressure conditions, the gas hydrate may deteriorate. There is also a problem that if the quality changes, it becomes difficult to accurately grasp the depth and layer thickness of the hydrate layer. For these reasons, a survey system with improved survey accuracy and survey efficiency has been desired.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a gas hydrate investigation system capable of improving the investigation accuracy and the investigation efficiency of the gas hydrate existing at the bottom of the water.

[0007]

The invention according to claim 1 is a system for investigating a gas hydrate existing in the ground of the bottom of the water by boring, wherein a floating structure floating on the water and the bottom of the water. A boring device for boring the ground to collect the gas hydrate, a pipe connecting the above-water structure and the boring device, integrated with the boring device, and embedded in the ground at the bottom of the water. A water bottom foundation for fixing the boring device to the ground of the water bottom.

As described above, since the water bottom foundation is embedded in the water bottom ground, the boring device can be firmly fixed on the water bottom ground.

The invention according to claim 2 is the gas hydrate investigation system according to claim 1, further comprising a float having buoyancy adjusting means for imparting buoyancy to the pipe and adjusting the buoyancy. It is characterized by

As described above, since the float having the buoyancy adjusting means imparts the buoyancy to the pipe and holds at least a part of the weight of the pipe and the boring device, even if the ground of the water bottom is soft. , It is possible to hold the boring device in place while suppressing the possibility of the boring device being buried in the seabed.

A third aspect of the present invention is the gas hydrate investigation system according to the second aspect, which is characterized by comprising a measuring device for measuring the load and the vertical displacement of the pipe.

As described above, since the measuring device for measuring the load and the vertical displacement of the pipe is provided,
The buoyancy of the float can be adjusted based on the measurement data from this measuring device.

The invention according to claim 4 is the gas hydrate investigation system according to any one of claims 1 to 3, wherein a temperature sensor for detecting the ambient temperature is provided near the tip of the boring device. It is characterized by having. Also,
The invention according to claim 5 is the gas hydrate investigation system according to any one of claims 1 to 4, wherein a pressure sensor for detecting an ambient temperature is provided in the vicinity of the tip of the boring device. Is characterized by.

As described above, since the temperature sensor or the pressure sensor is provided to detect the temperature or the pressure around the tip of the boring device, it is necessary to accurately grasp the decomposition of the gas hydrate during excavation. You can

The invention according to claim 6 is the gas hydrate investigation system according to any one of claims 1 to 5, wherein a heating device for heating the surroundings is provided near the tip of the boring device. It is characterized by

As described above, since the heating device around the tip portion of the boring device is provided, the gas hydrate around the tip portion of the boring device can be heated and decomposed, and the gas can be formed with a simple structure. The existence of hydrate can be accurately grasped.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a gas hydrate investigation system according to the present invention will be described below with reference to FIGS.
Will be explained.

[First Embodiment] First, the first embodiment will be described with reference to FIG. This gas hydrate survey system (hereinafter, may be simply referred to as “survey system”) excavates a hydrate layer (gas hydrate) H formed in a seabed (submersible ground) G by boring. It is for exploration, and is provided with a research vessel (water structure) 10, a riser pipe (pipe) 20, and a seabed rig 30. Further, the seabed rig 30 includes a burst prevention device 31, a boring device 41 for boring the seabed ground G, and a jacket foundation (waterbed foundation) 32 protruding downward from the periphery of the boring equipment 41 and embedded in the seabed soil G. , And are integrally formed.

The research ship 10 floats above the sea and is a submarine rig 3
0 is remotely controlled, and a plurality of thrusters (not shown) are provided for selection so that the position of the ship can be kept constant and boring can be performed without being swept by wind or tidal current. In addition, GPS (Gro
The bal positioning system (not shown) enables the position of the ship to be recognized and held with high accuracy even in the open sea.

The riser pipe 20 is a flexible pipe that connects the research vessel 10 and the submarine rig 30. The riser pipe 20 has a function as a transport pipe capable of transporting various measuring instruments and materials between them. It also has a function as a mud pipe for feeding and draining mud necessary for boring. That is, the riser pipe 20 and the boring device 41 are directly connected to each other via the outburst prevention device 31, and muddy water can be circulated between the research ship 10 and the seabed rig 30. The temperature and concentration of the muddy water are managed collectively on the research ship 10.

Inside the riser pipe 20, a drill pipe (not shown) rotatably inserted into the riser pipe 20 is provided. This drill pipe is rotationally driven by a motor (not shown) on the research ship 10, and this rotational driving force is transmitted to the boring device 41 via the outburst prevention device 31. That is, the boring bit 42 at the tip of the shaft 43, which will be described later, can be rotated to excavate the excavation hole B. Although a mechanism for transmitting the rotational drive force to the shaft 43 from above the research ship 10 is used here, a rotary drive system may be installed on the bottom of the sea such as inside the explosion prevention device 31.

The violence prevention device 31 is composed of a large number of safety valves, and is installed on the seabed G so as to close the hole of the excavation hole B in order to control the pressure in the excavation hole B. ing. When the gas hydrate decomposes during excavation of the hydrate layer H, or when the pressure in the drill hole B rises due to hitting the free gas layer, the safety valve operates and the drill hole B
The internal pressure can be released into the sea, and it is possible to accurately prevent the natural gas or the like from exploding or spurting out.

The jacket foundation 32 is the boring device 4
1 is integrally provided on the outburst prevention device 31 so as to surround 1 from the outer peripheral side, and can be expanded and contracted from the outburst prevention device 31. The jacket foundation 32 is in a state of being housed on the side of the outburst prevention device 31 when degenerated,
At the time of extension, it projects downward from the explosion prevention device 31 and is embedded in the seabed ground G to firmly fix the seabed rig 30 to the seabed ground G. The jacket base 32 may have a cylindrical shape and surround the boring device 41 from the outer peripheral side, or may have a plurality of rod shapes and surround the boring device 41 from the outer peripheral side.

As shown in FIG. 3, the boring device 41 includes a boring bit 42 for excavating the seabed G and a shaft 43 for rotatably supporting the boring bit 42.
And casing pipes 44a and 44b that are inserted stepwise according to the excavation depth.

The boring bit 42 is provided at the tip of the shaft 43, and is rotationally driven by a motor on the research ship 10 to excavate the seabed G, and core sampling of gas hydrate from the hydrate layer H is performed. It is something to do. The shaft 43 is added in sequence according to the excavation depth of the boring bit 42 so that the length can be adjusted.

The casing pipe 44 is for preventing the excavation hole B from collapsing, and the pipe is inserted stepwise according to the excavation depth. In the example of FIG. 3, the first pipe portion (casing pipe) 44a located inside
And a second pipe portion (casing pipe) located outside
44b and 44b are fixed by cement (not shown), that is, a two-stage state.
As the excavation further progresses, the pipe portions can be sequentially provided outside the second pipe portion 44b to have three or more stages.

In the survey method using such a survey system, the previously assembled submarine rig 30 is carried by the survey ship 10 to the survey point, and the submarine rig 30 is settled toward the seabed. And submarine rig 3
When 0 lands on the seabed, the jacket foundation 32 is extended to project downward from the explosion prevention device 31. By doing so, the jacket foundation 32 has a relatively soft seabed ground G.
Embedded in the seabed, the seabed rig 30 is firmly fixed to the seabed,
The boring device 41 can stably excavate the seabed G. Then, the core of the gas hydrate collected from the hydrate layer H is pulled up from the boring device 41 to the research ship 10 by the riser pipe 20.

In the gas hydrate survey system according to the present embodiment, the seabed rig 30 having the boring device 41 is provided with the jacket foundation 32 embedded in the seabed ground G and fixing the seabed rig 30 to the seabed ground G. I am trying. Therefore, the seabed rig 30 including the boring device 41 can be firmly fixed on the seabed ground G, and even if the research ship 10 and the seabed rig 30 try to move due to the influence of wave height, wind, or ocean current, the boring device 41 moves. Can be prevented. As a result, the survey accuracy can be significantly improved.

[Second Embodiment] Next, a second embodiment of the present invention will be described with reference to FIG. The gas hydrate investigation system in this embodiment is the same as that in the first embodiment, except that it is equipped with the floats 10A and 10B. Therefore, the same components as those in the first and second embodiments are designated by the same reference numerals, and detailed description thereof will be omitted.

The floats 11A and 11B float on the sea together with the research ship 10 and are connected to the riser pipe 20 via a wire 23. At least a part of the weight of the riser pipe 20 and the submarine rig 30 is attached to the floats 11A and 11B. Hold. The floats 11A and 11B are provided with water supply / drainage pumps (buoyancy adjusting means) 12a and 12b capable of supplying and discharging seawater into the floats 11A and 11B, respectively. These water supply / drainage pumps 12a, 12b can adjust the buoyancy of the floats 11A, 11B by increasing / decreasing the amount of water in the floats 11A, 11B by remote control from the research ship 10.

The riser pipe 20 has a measuring device 24 for measuring the load and the vertical displacement of the riser pipe 20.
Is provided. The measuring device 24 is connected to the research vessel 10 on the sea, and the measurement data on the load and the displacement in the vertical direction detected by the measuring device 24 are sent to the research vessel 10 on the sea. When the measurement data from the measuring device 24 is sent to the research ship 10, the water supply / drainage pump 1 is manually or automatically controlled by the research ship 10.
Float 11A, 11B by operating 2a, 12b appropriately
Adjust the buoyancy of the riser pipe 20 and seabed rig 3
Hold 0 in place.

In the gas hydrate investigation system according to this embodiment, the water supply / drainage pump 12 for adjusting the buoyancy is used.
The floats 11A and 11B which have a and 12b and give buoyancy to the riser pipe 20 are provided.
Therefore, at least a part of the own weight of the riser pipe 20 and the seabed rig 30 can be held, and for example, even when the seabed ground G is soft, it is possible to suppress the possibility that the boring device 41 is buried in the seabed, and thus the boring device. 41 can be held in place.

A measuring device 24 for measuring the load and vertical displacement of the riser pipe 20 is provided so that the buoyancy of the floats 11A and 11B can be adjusted based on the measured value. for that reason,
The buoyancy can be adjusted according to the undulation state of the seabed ground G, the wave height, and the state of the ocean current, and the seabed rig 30 can be held at a fixed position, and the drilling by the boring device 41 can be stabilized to minimize the drilling error. It is possible to suppress and improve the survey accuracy and survey efficiency.

In the present embodiment, the case where the float is floated above the sea has been described, but the present invention is not limited to this, and the float may be used while being submerged in the sea. Alternatively, the riser pipe may be directly provided without using a wire.

[Third Embodiment] Next, a third embodiment of the present invention will be described with reference to FIG. In addition, in this gas hydrate investigation system, except that a temperature / pressure sensor (temperature sensor, pressure sensor) 51 is provided near the tip of the boring device,
And the same as in the second embodiment. for that reason,
The same components as those in the first and second embodiments are designated by the same reference numerals, and detailed description thereof will be omitted.

Boring bit 4 of the boring device 41
A temperature / pressure sensor (temperature sensor, pressure sensor) 51 that detects the temperature and the pressure around it is provided at a position near two. The temperature / pressure sensor 51 is connected to the research vessel 10 on the sea, and the temperature and pressure data detected by the temperature / pressure sensor 51 is sent to the research vessel 10 on the sea.

The boring bit 42 is the hydrate layer H.
When the gas hydrate is reached and the gas hydrate is excavated, there is a possibility that the gas hydrate near the tip of the boring device 41 may be decomposed due to frictional heat generated during the excavation. If the decomposition proceeds excessively, a large amount of natural gas will be generated and released from the explosion prevention device 31 into the sea,
It may not be possible to effectively recover energy resources, and may hinder core sampling.

Since the reaction in which the gas hydrate decomposes to produce water and natural gas is an endothermic reaction, when the gas hydrate decomposes, the ambient heat is removed and the temperature drops sharply. As long as the normal earth and sand in the seabed G is excavated, the phenomenon that the temperature decreases is unlikely to occur. Therefore, when the temperature detected by the temperature / pressure sensor 51 suddenly decreases, the gas hydrate is reduced. It can be determined that it is disassembled.

Further, as described above, when the gas hydrate decomposes, a large amount of natural gas is released as a gas, and the pressure in the drilled hole B rapidly rises. Even when the pressure detected by the temperature / pressure sensor 51 suddenly rises, it can be determined that the gas hydrate is decomposed.

As described above, when the temperature / pressure data from the temperature / pressure sensor 51 is sent to the research ship 10 and it is judged from the data that the gas hydrate is decomposed,
By manual control or automatic control from the research vessel 10,
Adjust the excavation speed, the temperature and concentration of the mud water. That is, the rotation speed of the boring bit 42 is reduced, and the temperature, concentration, etc. of the muddy water are adjusted to the excavation speed to prevent excessive decomposition of the gas hydrate.

In the gas hydrate survey system according to this embodiment, the position near the boring bit 42,
That is, a temperature / pressure sensor 51 for detecting the ambient temperature and pressure is provided near the tip of the boring device 40. Therefore, the decomposition of the gas hydrate at the time of excavation can be accurately grasped, and the gasification can be promptly dealt with so that the investigation accuracy and the investigation efficiency can be improved.

[Fourth Embodiment] FIG. 5 shows the fourth embodiment of the gas hydrate investigation system according to the present invention.
Will be explained. The gas hydrate investigation system is the same as that in the third embodiment except that the temperature sensor additional heating device (heating device) 52 is provided in the vicinity of the boring bit 42. Therefore, the same components as those in the third embodiment will be designated by the same reference numerals and detailed description thereof will be omitted.

Boring bit 4 of boring device 41
A temperature sensor additional heating device (heating device) 52 that heats the surroundings and detects the temperature is provided at a position in the vicinity of 2. The temperature sensor additional heat device 52 is a device in which a temperature sensor that detects the ambient temperature and a heating device that heats the surroundings are integrated, and is connected to the research vessel 10 on the sea. That is, it can be heated by remote control from the research vessel 10 on the sea, and the detected temperature data is sent to the research vessel 10 on the sea. Although the temperature sensor and the heating device are integrally provided here, the temperature sensor and the heating device may be separately provided as separate devices.

Since the gas hydrate is solid like ordinary earth and sand in the seabed G, even if the boring bit 42 reaches the hydrate layer H and starts excavating the gas hydrate, the research vessel 10 on the sea surface is not affected. Therefore, it may be difficult to accurately grasp the situation. In such a case, the boring device 41 is heated by the sensor-added heat device 52.
It is possible to know whether or not the hydrate layer H is being excavated by heating the seabed ground G in the vicinity of the tip end of the above and monitoring the temperature change thereof.

With ordinary earth and sand, there is almost no change even when heated, and the ambient temperature only rises as it is heated. On the other hand, in the case of gas hydrate, decomposition starts when it is heated to a predetermined temperature. As described above, when the gas hydrate is decomposed, ambient heat is taken away, so that the temperature in the vicinity of the tip of the boring device 41 once rises due to heating, but then sharply decreases.

That is, if the transition of the temperature detected by the sensor-added heat device 52 increases with heating, it can be determined that the boring bit 42 is excavating ordinary earth and sand or the like. it can. On the other hand, if there is a tendency that the temperature drops sharply after the elapse of a certain time, it can be determined that the boring bit 42 is excavating the hydrate layer H. In addition, in order to determine whether or not the hydrate layer H is being drilled, the boring device 41 is used.
It is sufficient to decompose only a small amount of the gas hydrate existing in the vicinity of the tip of the. That is, the heating here does not mean that a large amount of heat is applied to decompose all the gas hydrate in the hydrate layer H.

In the gas hydrate investigation system according to the present embodiment, the ambient temperature can be heated by the sensor-added heating device 52. Therefore, the gas hydrate near the tip of the boring device 41 can be forcibly decomposed, and the depth and layer thickness of the hydrate layer H can be accurately investigated without necessarily collecting the core. The survey accuracy and survey efficiency can be improved.

[0048]

As described above, in the gas hydrate investigation system according to the present invention, since the above-mentioned structure is adopted, the investigation accuracy and the investigation efficiency of the gas hydrate existing at the bottom of the water are improved. It is possible to provide a gas hydrate survey system that can be operated.

[0049]

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing a first embodiment of a gas hydrate investigation system according to the present invention.

FIG. 2 is a schematic configuration diagram showing a second embodiment of a gas hydrate investigation system according to the present invention.

FIG. 3 is a partially enlarged view showing the boring device in FIG. 1 in an enlarged manner.

FIG. 4 is a schematic configuration diagram showing a third embodiment of a gas hydrate investigation system according to the present invention.

FIG. 5 is a schematic configuration diagram showing a fourth embodiment of a gas hydrate investigation system according to the present invention.

[Explanation of symbols]

10 Survey vessels (floating structures) 11A, 11B float 12a, 12b Water supply / drainage pump (buoyancy adjusting means) 20 Riser pipe (pipe) 24 Measuring device 30 subsea rigs 31 Explosion prevention device 32 Jacket foundation (water bottom foundation) 41 Boring device 42 bowling bit 44a 1st pipe part (casing pipe) 44b Second pipe part (casing pipe) 51 Temperature / pressure sensor (temperature sensor, pressure sensor) 52 Temperature sensor with heater (heating device) G Seabed (waterbed ground) H hydrate layer (gas hydrate)

Claims (6)

[Claims] 1. A system for investigating a gas hydrate existing in the ground of a water bottom by boring, wherein a floating structure above the water and the ground of the water bottom are drilled to collect the gas hydrate. A boring device, a pipe connecting the above-water structure and the boring device, an integral part of the boring device, and a water bottom foundation that is embedded in the ground of the water bottom to fix the boring device to the ground of the water bottom. A gas hydrate survey system characterized by comprising: 2. The gas hydrate survey system according to claim 1, further comprising a float having buoyancy adjusting means for adjusting the buoyancy while applying buoyancy to the pipe. 3. A measuring device for measuring a load and a vertical displacement of the pipe is provided.
Gas hydrate survey system described in. 4. The vicinity of the tip of the boring device,
The gas hydrate investigation system according to any one of claims 1 to 3, further comprising a temperature sensor that detects an ambient temperature. 5. The vicinity of the tip of the boring device,
The gas hydrate investigation system according to any one of claims 1 to 4, further comprising a pressure sensor that detects a surrounding pressure. 6. In the vicinity of the tip of the boring device,
The gas hydrate investigation system according to any one of claims 1 to 5, further comprising a heating device for heating the surroundings.