JP7420683B2 - Surface layer gas hydrate recovery method and surface layer gas hydrate recovery system - Google Patents

Description

The present invention relates to a surface layer gas hydrate recovery method and a surface layer gas hydrate recovery system.

Gas hydrate is a hydrate of gases such as methane, and is expected to be used as a fuel, but it cannot exist stably as a hydrate unless it is in a low-temperature, high-pressure environment, so its natural location is the ocean floor. It is limited to areas where there is aquatic bottoms such as lake beds and permafrost layers.
There is also sand-layer gas hydrate that exists in sand layers on the ocean floor, but in order to recover it, it is necessary to excavate several hundred to several thousand meters from the ocean floor. Surface-type gas hydrate, which exists in lumps in the area, is attracting attention.
On the other hand, excavated gas hydrate is collected by being sucked into a recovery pipe together with water, but during excavation the recovery pipe is filled with saturated water with dissolved methane, so methane decomposition/hydration is slowed down. is in equilibrium. Therefore, there is a risk that methane gas generated by decomposition of gas hydrate during excavation will become hydrate in the recovery pipe and adhere to the wall surface, causing blockage.
On the other hand, in Patent Document 1, during excavation of surface gas hydrate, methane-unsaturated seawater is sucked in from a different location away from the excavation point with a hose and drawn into the recovery pipe, thereby removing gas hydrate that has adhered to the wall surface. It is removed by decomposing the methane into methane and dissolving it in seawater.

Japanese Patent Application Publication No. 2016-108774

The technique described in Patent Document 1 is useful in that it can prevent clogging of recovery pipes due to rehydration during excavation of surface gas hydrate.
On the other hand, the technique disclosed in Patent Document 1 requires a hose and a pump to draw methane-unsaturated water into the recovery pipe, and there is room for improvement in terms of weight and cost. Also, it cannot be applied to existing drilling equipment that does not have a hose or pump for pulling in. Therefore, it is necessary to create a non-equilibrium state inside the recovery tube by controlling the temperature and pressure inside the recovery tube or by injecting additives, or to mechanically remove the deposits by inserting a pig into the recovery tube, which increases cost and costs. There is also room for improvement in terms of cost.
The present invention has been made in view of the above problems, and provides a surface layer gas hydrate recovery method that can prevent clogging of recovery pipes by gas hydrate without increasing the weight or cost, regardless of the structure of the device. The purpose is to provide.

One aspect of the present invention is a method for recovering surface-type gas hydrate that exists in lumps within 100 m below the water bottom, in which the water bottom containing gas hydrate is excavated and brought close to the excavation surface. A lifting and recovery step in which the gas hydrate is recovered by suctioning the excavated materials together with water through the suction port of the lifting and recovery pipe, and a lifting and recovery step in which excavation is stopped and the suction port is pumped into the By moving underwater to the excavation point, the water on the moving path having a lower gas saturation rate than the water in the recovery pipe during excavation is inhaled, and the gas hydrate adhering to the inner wall of the recovery pipe is dissolved. a deposit removing step of removing the deposits by using a gas hydrate, and a deposit amount detection step of detecting the amount of the gas hydrate deposited on the inner wall of the lifting and collecting tube, performing the adhesion amount detection step during and/or after the completion of the lifting and retrieval step and before the adhesion removal step, and stopping the excavation in the retrieval step based on the detected amount of gas hydrate adhesion; and/or selecting the moving conditions for the deposit removal step .

Another aspect of the present invention is an excavator for excavating an underwater bottom containing surface gas hydrate present in a lump within a range of 100 m below the underwater bottom surface, and a lifting and collecting system installed in the excavator for sucking excavated materials. An excavation rig including a suction mechanism connected to a pipe and the lifting and recovery pipe to generate a suction force, a movement mechanism for moving the excavation rig, and a control unit for controlling the excavation machine, the suction mechanism, and the movement mechanism. A surface layer gas hydrate recovery system comprising: a detection section for detecting an amount of gas hydrate attached to an inner wall of the recovery pipe; and a control section for driving the excavator. excavate the bottom surface of the water containing gas hydrate, drive the suction mechanism to suck the excavated materials together with water from the lifting and collection pipe to recover the gas hydrate, and when the recovery is completed, the excavator By stopping the drive and driving the moving mechanism while continuing to suck water to move the drilling equipment underwater to the next drilling point, the gas saturation rate is lower than that of the water in the lifting and recovery pipe during drilling. Water on the route is sucked in to dissolve and remove the gas hydrate adhering to the inner wall of the recovery pipe , and the gas hydrate is removed during excavation and recovery of the gas hydrate, and/or the recovery pipe of the excavation equipment. Detecting the amount of gas hydrate attached to the inner wall of the recovery pipe during movement of the suction port and/or after completion of recovery of the gas hydrate and before starting movement of the drilling equipment. The method is characterized in that the excavation of the gas hydrate is stopped and/or the movement conditions of the excavation device are selected based on the detected amount of the gas hydrate attached .

In this configuration, after the completion of excavation at a certain excavation point, the suction port of the recovery pipe is moved to the next excavation point while continuing to inhale water, thereby inhaling water with a low gas saturation rate on the moving route. Dissolves gas hydrate attached to the inner wall of the recovery tube.
Therefore, there is no need to separately install a hose or pump for drawing in water with a low gas saturation rate, so it is possible to prevent clogging of the recovery pipe by gas hydrate without increasing weight or cost, regardless of the structure of the device.
In addition, with this configuration, gas hydrate attached to the inner wall of the recovery pipe can be removed by simply inhaling water during movement to the next excavation point, so there is no need to set up a separate work process for removal, reducing man-hours. It is also possible to suppress the cost increase due to the increase in the amount of electricity.

According to the present invention, it is possible to provide a surface layer gas hydrate recovery method that can prevent clogging of recovery pipes by gas hydrate without increasing weight or cost, regardless of the structure of the device.

FIG. 1 is a side view showing an overview of a recovery system used in the surface layer gas hydrate recovery method according to the present embodiment. FIG. 2 is an enlarged view of region R in FIG. 1, in which (a) shows methane hydrate being excavated, and (b) shows moving to the next excavation point after completion of the excavation at the excavation point in (a). FIG. 2 is a functional block diagram of the collection system of FIG. 1. FIG. FIG. 2 is a flow diagram showing an example of a method for recovering surface layer gas hydrate.

Hereinafter, preferred embodiments of the present invention will be described in detail based on the drawings.
First, a schematic configuration of a recovery system 1 used in the surface layer gas hydrate recovery method according to the present embodiment will be described with reference to FIGS. 1 to 3.
Here, the system is installed on a drilling ship 100 as the recovery system 1, and is a system that excavates a methane hydrate layer 203 that exists in a lump within a range of 100 m below the bottom surface of the seabed 201 to collect methane hydrate 207 ( A system for collecting MH) is illustrated.
As shown in FIGS. 1 to 3, the recovery system 1 includes an excavation device 3, a moving mechanism 5, and a control section 7.

The excavation device 3 is a device that excavates the methane hydrate layer 203 and recovers the methane hydrate 207, and includes an excavation device 9, a recovery pipe 11, a pump 13, and a detection unit 15.
The excavator 9 is a cylindrical rotary drill that excavates the methane hydrate layer 203. The excavator 9 has protrusions and cutters for excavation protruding from the bottom surface of the cylinder, and the bottom surface is brought into contact with the surface layer of the seabed 201 in which the methane hydrate layer 203 is buried, and the excavator 9 is moved around the axis of the cylinder as shown in FIG. 2(a). The methane hydrate layer 203 is excavated by lowering it while rotating in the A direction.

FIG. 2A shows a drill bit 9a as an example of a protrusion for drilling. The drill bit 9a is a drill having a smaller diameter than the excavator 9, and is rotatably attached to the excavator 9, but may be fixed to the excavator 9 so as not to rotate relative to the excavator 9.

The power for rotating the excavator 9 can be, for example, the power of a main engine or a generator inside the excavator 100. In this case, a rotation mechanism utilizing this power may be provided on the exposed deck of the drilling ship 100, and a power transmission shaft (not shown) may be provided in the hoisting and collecting pipe 11 to transmit the power to the excavator 9.

The recovery pipe 11 is a pipe that collects methane hydrate 207 from the methane hydrate layer 203 by inhaling the excavated material excavated by the excavator 9 together with seawater, as shown by the white arrow in FIG. 2(a). 9. More specifically, as shown in FIG. 2(a), a suction port 11a, which is the tip of the hoisting and collecting pipe 11 and which sucks in excavated material, is arranged inside the cylinder of the excavator 9.
The lifting and collecting pipe 11 has an inner diameter that corresponds to the required lifting amount of excavated materials, has physical properties that will not be damaged or corroded even if excavated materials or seawater come into contact with the inner wall, and is strong enough to not be deformed by ocean currents. Any known riser pipe can be used. Note that the methane hydrate layer 203 is a geological layer containing methane hydrate 207, but as shown in FIG. Both methane hydrate 207.

The pump 13 shown in FIG. 3 is a fluid machine that serves as a suction mechanism that generates suction force to lift the excavated material and seawater excavated by the excavator 9 above the excavation point, here to the drilling ship 100. 11. Since the methane hydrate 207 has a lower density than other substances such as seawater and mud sucked into the recovery pipe 11, it moves above the excavation point by buoyancy without applying an external force, but in this embodiment, seawater A pump 13 is provided because there is a case where only the water is inhaled.
As the pump 13, any known pump can be used as long as it can suck in the excavated material and seawater at a desired flow rate; for example, a fluid pump installed underwater can be used. However, since the suction mechanism only needs to be able to suck in excavated materials and seawater, a gas lift type device that injects gas into the recovery pipe 11 to suck in excavated materials and seawater may be used as the suction mechanism.

The detection unit 15 is a device that detects methane hydrate 207a attached to the inner wall of the recovery pipe 11, and is provided in the recovery pipe 11 as necessary. The reason for providing the detection section 15 is as follows.
The excavator 9 excavates methane hydrate 207 in the methane hydrate layer 203 together with the surface mud 205, and the recovery pipe 11 sucks in seawater along with these excavated materials. Therefore, the inside of the recovery pipe 11 during excavation is filled with methane hydrate 207, mud 205, and seawater at the excavation point.
Furthermore, in the methane hydrate layer 203, not only methane hydrate 207 but also methane gas is present. Furthermore, since methane hydrate 207 cannot stably exist as a hydrate unless in a low temperature, high pressure environment, it decomposes into methane gas depending on the environment during excavation. Since these methane gases dissolve in seawater, the seawater in the recovery pipe 11 becomes saturated water in which methane is dissolved, resulting in a reaction in which methane hydrate decomposes to produce methane, and methane becomes hydrated to form methane hydrate. The reaction becomes equilibrium within the recovery tube 11. In this state, if methane is generated within the recovery pipe 11 during excavation, an equilibrium state will be reached, and the methane may become hydrated within the recovery pipe 11 and adhere to the wall surface, potentially clogging the recovery pipe 11.
Therefore, it is preferable that the detection unit 15 detects the position and dimensions of the methane hydrate 207a attached to the inner wall.

The structure of the detection unit 15 can be selected as appropriate as long as it can detect the position and dimensions of the methane hydrate 207a attached to the inner wall.
For example, in FIG. 2A, an ultrasonic inspection device 15a provided on the outer wall of the lifting and collecting pipe 11 is illustrated as the detection unit 15. With this structure, ultrasonic waves are irradiated from the outer wall side to the inner wall side of the recovery tube 11, and the adhesion position of the methane hydrate 207a and the length of the deposit in the radial direction of the recovery tube 11 can be detected from the reflected waves.
When the detection unit 15 is an ultrasonic inspection device 15a, it may be fixed in advance to a location where methane hydrate 207a is likely to adhere. Alternatively, without fixing the detection part 15, use an actuator or the like (not shown) to move the outer wall of the hoisting tube 11 in the axial direction of the hoisting tube 11, which is B1 and B2 in FIG. 2(a), and in the radial direction, which is B3. It may be configured to be movable in the direction.

As the detection unit 15, an imaging device such as the camera 15b shown in FIG. 1 can also be exemplified. In this case, a lens of an imaging device may be placed inside the recovery tube 11 to image the inner wall, and the adhesion position and radial length of the methane hydrate 207a may be detected by image analysis or the like.

The moving mechanism 5 is a mechanism that moves the drilling rig 3 horizontally and vertically in the sea. In FIG. 1, the recovery system 1 is mounted on the drilling ship 100, so the mechanism for horizontal movement can be exemplified by a propeller or a main engine for navigating the drilling ship 100. When the lifting and collecting pipe 11 is a riser pipe, the vertical movement mechanism includes a pull-in winch that winds up the riser pipe. However, since the moving mechanism 5 only needs to be able to move the suction port 11a of the recovery pipe 11 horizontally and vertically, it does not necessarily have to be configured to move the entire drilling rig 3 and drilling ship 100.

The control unit 7 is a computer that controls the driving of the excavator 9, the pump 13, and the moving mechanism 5, and FIG. 1 illustrates a computer installed in the deck room of the excavator 9. In FIG. 1, the propeller and main engine for navigating the drilling ship 100 are illustrated as the moving mechanism 5, so the control unit 7 in FIG. computer.

The control unit 7 drives the excavator 9 to excavate the water bottom surface containing methane hydrate 207 as shown in FIG. methane hydrate 207 is recovered. This process is also called the harvesting process.

When the recovery of methane hydrate 207 is completed, such as by excavating the excavation point to a predetermined depth or by elapse of a predetermined time from the start of excavation, the control unit 7 stops driving the excavator 9. , the drilling rig 3 is moved underwater to the next drilling point.
At this time, as shown by the white arrow in FIG. 2(b), the control unit 7 drives the moving mechanism 5 while continuing to suck seawater from the suction port 11a to move the excavation rig 3 in the Z direction, which is the vertical direction. Raise the water to a height several meters above the level of the water bottom before excavation. Further, the excavation device 3 is moved by a predetermined distance in the horizontal X and Y directions to above the next excavation point. The excavator 3 is further lowered in the Z direction and placed at the next excavation point. During the movement, the suction port 11a also moves, so the seawater on the moving path, which has a lower gas saturation rate than the seawater in the recovery pipe 11 during excavation, is sucked in through the intake port 11a and the seawater in the recovery pipe 11 is removed. to a methane-unsaturated state. This brings the inside of the lifting and collecting pipe 11 into a non-equilibrium state. In this state, the methane hydrate 207a adhering to the inner wall attempts to reach an equilibrium state, decomposes into methane, and dissolves in the methane-unsaturated seawater. The control unit 7 removes the methane hydrate 207a attached to the inner wall due to this reaction. This process is also called a deposit removal process.

In this way, the recovery system 1 moves the suction port 11a of the recovery pipe 11 to the next excavation point while continuing to inhale seawater after the completion of excavation, thereby inhaling seawater with a low gas saturation rate on the movement route. , the methane hydrate 207a adhering to the inner wall of the recovery pipe 11 is dissolved.
In other words, instead of drawing seawater into the recovery pipe 11 with a hose from a place where the gas saturation rate is low, the suction port 11a of the recovery pipe 11 is moved to a place where seawater with a low gas saturation rate is present, and the seawater is sucked in. .

In this configuration, as shown in FIG. 2(a), seawater is drawn into the lifting and recovery pipe 11 by the suction port 11a and the pump 13 that draw in excavated material during excavation, and by the hose and pump that draw in seawater with a low gas saturation rate. There is no need to place it separately. Therefore, even in the conventional recovery system 1 without a hose or pump for drawing in seawater, the methane hydrate 207a attached to the inner wall of the recovery pipe 11 can be dissolved by simply changing the program of the control unit 7 to the same one as in this embodiment. It will be done. Therefore, regardless of the structure of the device, clogging of the recovery pipe 11 by the methane hydrate 207a can be prevented without increasing weight or cost.

In addition, with this configuration, the methane hydrate 207a attached to the inner wall of the recovery pipe 11 can be removed by simply inhaling seawater during movement to the next excavation point, so there is no need to provide a separate work process for removal. Cost increases due to increased man-hours can also be suppressed.

The control unit 7 may change the excavation conditions based on the adhesion amount of methane hydrate 207a detected by the detection unit 15.
For example, during excavation, the detection unit 15 detects the amount of methane hydrate 207a adhered to the excavated material while it is being collected in the collection pipe 11, and when the amount of adhesion exceeds a predetermined upper limit, the excavation is stopped and the excavated material is retrieved. The suction port 11a of the pipe 11 may be moved to the next excavation point.
The predetermined upper limit means that, among the dimensions of the methane hydrate 207a, the radial dimension of the recovery pipe 11 is such that if the excavation continues as it is, the recovery pipe 11 will be blocked before the amount of excavation reaches the target excavation amount. An example can be given of an amount where there is a certain degree of fear.

In this configuration, when the amount of methane hydrate 207a adhering to the inner wall of the recovery pipe 11 during excavation exceeds the upper limit, the excavation is stopped and the excavation is moved to the next excavation point. As a result, seawater with a low gas saturation rate on the moving path is sucked in, and the methane hydrate 207a attached to the inner wall of the recovery pipe 11 is dissolved.
Therefore, it is possible to prevent the recovery pipe 11 from being blocked by the methane hydrate 207a during excavation.

In addition, when stopping excavation and moving to the next excavation point because the amount of methane hydrate 207a adhering to the inner wall of the recovery pipe 11 during excavation has exceeded the upper limit, the "Next The "excavation point" may be the same point as the excavation point where excavation was stopped. Specifically, after stopping excavation, the excavator moves one end away from the excavation point and inhales seawater with a low gas saturation rate along the movement path, thereby dissolving the methane hydrate 207a attached to the inner wall of the recovery pipe 11. You may also return to the point where you stopped digging. This is because the excavation point where the excavation has been stopped has not been excavated to the target depth, so the excavation point is to be excavated again to the target excavation depth.

The control unit 7 may change the movement conditions based on the amount of methane hydrate 207a deposited by the detection unit 15 while inhaling seawater during movement to the next excavation point.
For example, the control unit 7 drives the detection unit 15 to detect the amount of methane hydrate 207a attached to the inner wall of the recovery pipe 11 while the suction port 11a of the recovery pipe 11 is moving. The moving conditions of the suction port 11a are changed so that as the detected amount of attached methane hydrate 207a increases, the amount of dissolved methane hydrate 207a increases. More specifically, when the detected amount of attached methane hydrate 207a is equal to or greater than a predetermined upper limit amount of attached during movement, the moving conditions of the suction port 11a are changed so that the amount of dissolved methane hydrate 207a increases. "Upper limit adhesion amount during movement" means that if the next excavation point is reached and excavation is started under the current movement conditions, there is a possibility that the lifting pipe 11 will be blocked before the excavation amount reaches the target excavation amount. There is a certain adhesion amount.

In this way, the moving conditions may be changed so that the amount of methane hydrate 207a that adheres to the inner wall of the recovery pipe 11 increases, the more the amount of methane hydrate 207a that dissolves increases.
With this configuration, it is possible to prevent the recovery pipe 11 from reaching the next excavation point with insufficient removal of the methane hydrate 207a attached to the inner wall.
Examples of movement conditions include the following.

First, moving speed can be exemplified as a moving condition.
Specifically, the greater the amount of methane hydrate 207a attached, the slower the moving speed of the suction port 11a, and the smaller the amount, the faster the moving speed.
By slowing down the movement speed as the amount of methane hydrate 207a attached increases, it is possible to increase the amount of methane-unsaturated seawater sucked into the recovery pipe 11 before reaching the next excavation point. can. As a result, the amount of methane hydrate 207a dissolved in seawater can be increased. Therefore, it is possible to prevent the recovery pipe 11 from reaching the next excavation point with insufficient removal of the methane hydrate 207a attached to the inner wall.
Note that the moving speed does not always need to be constant. For example, if the moving speed is to be slowed down, the average speed may be reduced by temporarily stopping on the moving route or by waiting without starting digging immediately after arriving at the next digging point.

The flow rate of seawater sucked into the recovery pipe 11 can also be exemplified as a movement condition.
Specifically, the flow rate of seawater sucked into the recovery pipe 11 may be increased as the amount of methane hydrate 207a adhered increases, and the flow speed may be decreased as the amount of adhered methane hydrate 207a decreases.
In this way, by increasing the flow rate of the seawater sucked in as the amount of methane hydrate 207a attached increases, the amount of methane-unsaturated seawater sucked into the recovery pipe 11 before reaching the next excavation point can be reduced. can be increased. As a result, the amount of methane hydrate 207a dissolved in seawater can be increased.

A moving route can also be exemplified as a moving condition.
Specifically, the movement path of the inlet 11a is set so that the larger the amount of methane hydrate 207a attached, the longer the route to the next excavation point, and the smaller the amount, the shorter the path to the next excavation point. All you have to do is change.
As a specific method of lengthening the route to the next excavation point, the route to the next excavation point may be set to a detour rather than the shortest distance. The route to be changed may be horizontal or vertical, or both. Alternatively, if there are multiple candidates for the next excavation point, the next excavation point may be changed to another excavation point that is farther away than the planned excavation point.
In this way, as the amount of methane hydrate 207a attached increases, the movement route becomes longer and the time required for movement increases, thereby increasing the amount of seawater sucked into the recovery pipe 11 before reaching the next excavation point. can be increased. This makes it possible to increase the amount of methane hydrate 207a dissolved in seawater during movement.

As for the movement conditions, any one of movement speed, flow rate, and movement route may be selected by considering the advantages of each, or a plurality of movement conditions may be implemented simultaneously.
For example, a configuration in which the moving speed is changed does not require changing the intake amount of seawater or the moving route of the recovery pipe 11, and is therefore suitable for devices in which it is difficult to change these changes.
Since the configuration in which the flow rate is changed does not change the travel time or the travel route, it is suitable when it is desired to promote dissolution of the methane hydrate 207a without changing the working time during excavation.
Since the configuration for changing the moving route does not require changing the moving speed or the suction speed, it is suitable for devices in which it is difficult to change these while moving.
The above are examples of movement conditions.

The detection unit 15 detects the amount of methane hydrate 207a attached to the inner wall of the recovery pipe 11 not only during excavation or movement.
For example, the detection unit 15 may detect the amount of methane hydrate 207a attached after the end of excavation at a certain point and before moving to the next excavation point. In this case, based on the detected amount of adhesion, the next excavation point and movement conditions may be selected so that the amount of adhesion becomes less than a predetermined amount by the time the next excavation point is reached. For example, as the amount of methane hydrate 207a attached increases, a more distant excavation point may be selected as the next excavation point, or the moving speed of the recovery pipe 11 may be made slower. With this configuration, the amount of methane hydrate 207a attached can be reduced to less than a predetermined amount without changing the excavation conditions or movement conditions during excavation or movement. Note that the predetermined amount here means, similar to the upper limit adhesion amount during movement, when the amount of excavation reaches the target amount of excavation if the next excavation point is reached and excavation is started under the current movement conditions. This is the amount of adhesion that may cause the recovery pipe 11 to become clogged before it is removed.

Note that the recovery system 1 is also provided with a device for separating methane hydrate 207 from the excavated material containing mud 205 and a device for storing the separated methane hydrate 207, but known devices may be used for these. Illustrations and detailed explanations will be omitted.
The above is an explanation of the configuration of the recovery system 1 used in the method for recovering methane hydrate 207 according to the present embodiment.

Next, a specific example of the method for recovering methane hydrate 207a according to this embodiment will be described with reference to FIG. 4.
First, the control unit 7 moves the drilling rig 3 along with the drilling ship 100 in the horizontal direction by moving the propulsion device of the drilling ship 100 as the moving mechanism 5, and moves the inlet 11a of the recovery pipe 11 directly above the excavation point. Place it in
Next, the control unit 7 drives the pull-in winch serving as the moving mechanism 5, etc. to pay out the recovery pipe 11 toward the seabed 201, and brings the bottom surface of the excavator 9 into contact with the excavation surface at the excavation point. This brings the suction port 11a closer to the excavation surface.

Next, as shown in FIG. 2(a), the control unit 7 lowers the excavator 9 while rotating, and starts excavating the water bottom surface, which is the methane hydrate layer 203 containing methane hydrate 207a, with the drill bit 9a. At the same time, the control unit 7 drives the pump 13 to suck in the excavated material together with seawater from the suction port 11a of the recovery pipe 11 brought close to the excavated surface, and recovers the methane hydrate 207a (S0 in FIG. 4). , recovery process).

Next, the control unit 7 drives the detection unit 15 to detect the amount of methane hydrate 207a adhering to the inner wall of the recovery pipe 11 during the recovery process (S1 in FIG. 4, adhesion amount detection step during recovery). ).
Next, the control unit 7 determines whether the amount of attached methane hydrate 207a detected in S1 is less than the upper limit. If it is less than the upper limit, the process proceeds to S3, and if it is not less than the upper limit, the process proceeds to S2-2 (S2 in FIG. 4).
If the amount of adhesion is not less than the upper limit in S2, that is, if it is more than the upper limit, there is a risk that the recovery pipe 11 will be blocked if the excavation continues, so the excavation at the excavation point is stopped and the process proceeds to S4 (Figure 4 S2-2).

If the adhesion amount is less than the upper limit in S2, the control unit 7 determines whether the amount of excavation at the excavation point during excavation is equal to or greater than the target excavation amount based on the excavation time, excavation depth, etc., and if it is equal to or greater than the target excavation amount. The process proceeds to S4, and if the amount of excavation is not equal to or greater than the target excavation amount, excavation is continued and the process returns to S1 (S3 in FIG. 4).
If the amount of adhesion is equal to or greater than the upper limit in S2, and if the amount of excavation is equal to or greater than the target amount of excavation in S3, the control unit 7 stops driving the excavator 9 to stop excavation (S4 in FIG. 4). However, the pump 13 continues to suck seawater.

Next, the control section 7 drives the detection section 15 to detect the amount of methane hydrate 207a attached to the inner wall of the recovery pipe 11 after the completion of the recovery process and before the attachment removal process (FIG. 4 (S5, pre-movement adhesion amount detection step).
Based on the adhesion amount of methane hydrate 207a detected in S5, the control unit 7 sets the next excavation point or movement conditions so that the adhesion amount of methane hydrate 207a becomes less than a predetermined amount by the time the next excavation point is reached. Select (S6 in FIG. 4, selection step).

Next, the control unit 7 drives the moving mechanism 5 to move the suction port 11a of the recovery pipe 11 to the next excavation point while continuing to suck seawater by the pump 13. As a result, as shown in FIG. 2(b), seawater on the movement path with a lower gas saturation rate than the seawater in the recovery pipe 11 during excavation is inhaled, and methane hydride adheres to the inner wall of the recovery pipe 11. The rate 207a is dissolved in the inhaled seawater and removed (S7 in FIG. 4, deposit removal step).

Next, the control unit 7 drives the detection unit 15 to detect the amount of methane hydrate 207a attached to the inner wall of the recovery pipe 11 while the suction port 11a of the recovery pipe 11 is moving (S8 in FIG. 4). , transfer amount detection process).
Next, the control unit 7 determines whether the amount of methane hydrate 207a adhered detected in S8 is less than the upper limit amount of adhered methane hydrate 207a during movement. If the amount of adhesion during movement is less than the upper limit, the process proceeds to S10, and if it is not less than the upper limit amount of adhesion during movement, the process proceeds to S11 (S9 in FIG. 4).
If the adhesion amount of methane hydrate 207a detected in S9 is less than the upper limit adhesion amount during movement, the control unit 7 moves to the next excavation point and returns without changing the movement conditions of the suction port 11a of the recovery pipe 11. (S10 in FIG. 4).

If the adhesion amount of methane hydrate 207a detected in S9 is not less than the upper limit adhesion amount during movement, that is, if it is greater than or equal to the upper limit adhesion amount during movement, the control unit 7 controls the recovery pipe so that the amount of methane hydrate 207a dissolved increases. The moving conditions of the suction port 11a of No. 11 are changed. Furthermore, the machine moves to the next excavation point under the changed movement conditions and returns (S11 in FIG. 4, movement condition changing step). Specifically, one or more of the moving speed, the flow rate of the seawater inhaled, and the moving route is changed.

When changing the moving speed, the moving speed of the suction port 11a is slowed down. When changing the flow rate of inhaled seawater, increase the flow rate of inhaled seawater. When changing the moving route, the moving route of the suction port 11a is changed so that the route to the next excavation point becomes longer.
The above is a description of a specific example of the surface layer gas hydrate recovery method according to the present embodiment.

As described above, in the recovery method of this embodiment, the bottom surface of the water containing methane hydrate 207 is excavated and the water is sucked in together with seawater. Carry out the deposit removal process by moving to the point.
In this configuration, after the completion of excavation at a certain excavation point, the suction port 11a of the recovery pipe 11 is moved to the next excavation point while continuing to inhale seawater, thereby inhaling seawater with a low gas saturation rate on the moving route. As a result, the methane hydrate 207a attached to the inner wall of the recovery pipe 11 is dissolved.
Therefore, there is no need to separately install a hose or pump to draw in seawater with a low gas saturation rate, thereby preventing clogging of the recovery pipe 11 by methane hydrate 207a without increasing weight or cost, regardless of the structure of the device. can.

Although the present invention has been described above with reference to the embodiments, the present invention is not limited to the embodiments. It is natural for those skilled in the art to come up with various modifications and improvements within the scope of the technical idea of the present invention, and these are also included in the present invention.

For example, in this embodiment, the gas hydrate recovery method is carried out by controlling the operations of the excavation rig 3 and the moving mechanism 5 by the control unit 7, but these operations are not controlled by the control unit 7 but by the worker manually. May be controlled.

Furthermore, in the present embodiment, the movement conditions and the next excavation point are selected based on the amount of methane hydrate 207a attached by the detection unit 15, but the movement conditions and the next excavation point are selected without detecting the amount of methane hydrate 207a attached by the detection unit 15. Excavation points may be selected. For example, the relationship between the movement conditions of the drilling rig 3, the excavation conditions, and the amount of methane hydrate deposited is determined through experiments, and by referring to this relationship, the amount of methane hydrate is reduced to the extent that the recovery pipe 11 is not blocked during excavation. Excavation conditions and moving conditions may be selected so that the amount of adhesion is maintained.

Further, in this embodiment, the method for recovering methane hydrate 207 existing on the seabed 201 has been described as an example, but this embodiment can also be applied to recovering gas hydrate existing on the bottom of a lake. For example, if the lake is a salt lake, salt water with a low gas saturation rate is sucked into the collection pipe 11 to remove gas hydrates attached to the inner wall, and if the lake is a freshwater lake, fresh water with a low gas saturation ratio is sucked into the collection pipe 11. 11 removes gas hydrate adhering to the inner wall by inhaling.

1: Recovery system 3: Drilling equipment 5: Movement mechanism 7: Control unit 9: Excavator 9a: Drill bit 11: Lifting and collecting pipe 11a: Suction port 13: Pump 15: Detection unit 15a: Ultrasonic inspection device 15b: Camera 100 : Drilling ship 201 : Seabed 203 : Methane hydrate layer 205 : Mud 207, 207a : Methane hydrate

Claims (8)

A method for recovering surface type gas hydrate that exists in a lump within a range of 100 m below the water bottom surface, the method comprising:
a lifting step of collecting the gas hydrate by excavating the bottom surface of the water containing gas hydrate and sucking the excavated material together with water through the suction port of a lifting pipe brought close to the excavation surface;
By stopping the excavation and moving the suction port underwater to the next excavation point while continuing to inhale water, the water on the moving path that has a lower gas saturation rate than the water in the recovery pipe during excavation is inhaled. a deposit removal step of dissolving and removing the gas hydrate deposited on the inner wall of the recovery pipe;
carrying out an adhesion amount detection step of detecting the adhesion amount of the gas hydrate adhering to the inner wall of the recovery pipe ;
During the lifting and collecting process, and/or during the deposit removing process, and/or after the completion of the lifting and collecting process and before the deposit removing process, the deposit amount detection process is performed, and the detected gas hydrate is A method for recovering surface layer gas hydrate , characterized by stopping excavation in the lifting and recovery step and/or selecting moving conditions in the deposit removal step based on the amount of deposited matter . carrying out a step of detecting the amount of gas hydrate attached to the inner wall of the lifting and collecting pipe during the lifting and collecting step;
The deposit removal step includes:
A step of stopping the excavation when the amount of gas hydrate adhesion detected in the adhesion amount detection step during lifting and recovery exceeds a predetermined upper limit, and moving the suction port of the recovery pipe to the next excavation point. The method for recovering surface layer gas hydrate according to claim 1. The deposit removal step includes:
a step of detecting the adhesion amount of the gas hydrate adhering to the inner wall of the recovery pipe while the suction port is moving;
a moving condition changing step of changing the moving conditions of the suction port so that the larger the amount of gas hydrate adhered detected in the moving amount detecting step, the more the dissolved amount of the gas hydrate during moving; ,
The method for recovering surface layer gas hydrate according to claim 1 or 2, wherein the method comprises: The movement condition changing step includes:
4. The step according to claim 3, wherein the moving speed of the suction port is decreased as the amount of gas hydrate adhered increases, and the speed of movement of the suction port is increased as the amount of adhered gas hydrate detected in the moving amount detection step increases. Method for recovering surface gas hydrate. The movement condition changing step includes:
According to claim 3 or 4, the step is to increase the flow rate of the water sucked into the recovery pipe as the amount of the gas hydrate adhesion detected in the moving adhesion amount detection step increases, and to decrease the flow speed as the amount decreases. A method for recovering surface gas hydrate. The movement condition changing step includes:
The suction port is configured such that the larger the amount of gas hydrate adhesion detected in the moving adhesion amount detection step, the longer the route to the next excavation point, and the shorter the path to the next excavation point. The method for recovering surface layer gas hydrate according to any one of claims 3 to 5, which is a step of changing the movement route of the gas hydrate. a pre-movement adhesion amount detection step of detecting the amount of gas hydrate adhering to the inner wall of the lifting and collecting pipe after the end of the lifting and collecting step and before the adhesion removal step;
Based on the adhesion amount of gas hydrate detected in the pre-movement adhesion amount detection step, the next step is carried out so that the amount of gas hydrate adhesion becomes less than a predetermined amount by the time the next excavation point is reached. 7. The surface layer gas hydrate recovery method according to claim 1, further comprising a selection step of selecting an excavation point and movement conditions. An excavator that excavates the water bottom containing superficial gas hydrate that exists in lumps within 100 m below the water bottom surface, a lifting pipe installed in the excavating machine to suck in the excavated material, and a connection to the lifting pipe. A surface gas hydrate recovery system comprising: an excavation rig including a suction mechanism that generates a suction force; a movement mechanism that moves the excavation rig; and a control unit that controls the excavation rig, the suction mechanism, and the movement mechanism. A system,
The lifting and collecting pipe has a detection part that detects the amount of the gas hydrate attached to the inner wall thereof,
The control unit includes:
Driving the excavator to excavate a water bottom surface containing gas hydrate, driving the suction mechanism to suck the excavated material together with water from the recovery pipe to recover the gas hydrate;
When the recovery is completed, the driving of the excavator is stopped, and the moving mechanism is driven to move the excavator underwater to the next excavation point while continuing to suck water, thereby removing the water in the recovery pipe during excavation. The gas hydrate attached to the inner wall of the recovery pipe is dissolved and removed by inhaling water on the movement route with a gas saturation rate lower than that of the gas hydrate, and/or during excavation and recovery of the gas hydrate. During the movement of the suction port of the recovery pipe of the drilling rig, and/or after the recovery of the gas hydrate is completed and before starting the movement of the drilling rig, the A surface layer characterized in that an amount of gas hydrate attached is detected, and based on the detected amount of attached gas hydrate, drilling of the gas hydrate is stopped and/or movement conditions of the drilling equipment are selected. Type gas hydrate recovery system.

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