JP2022037988A - Surface layer type gas hydrate recovery method and surface layer type gas hydrate recovery system - Google Patents

Abstract

To provide a surface layer type gas hydrate recovery method that can prevent blockage of a pickup pipe due to gas hydrate without increasing the weight and cost regardless of a structure of a device.SOLUTION: A method for recovering surface layer type gas hydrate that exists in a mass within a range of 100 m below a bottom of the water from a bottom of the sea 201 comprises a picking up step of recovering methane hydrate 207 by sucking excavated material together with seawater and picking up it from a suction port 11a of a picking pipe 11 that excavates the bottom of the water containing methane hydrate 207 and brings it closer to the excavation surface, and a removing deposits step of sucking in seawater on a movement path having a lower gas saturation rate than seawater in the picking pipe 11 at the time of excavation to dissolve and remove methane hydrate 207a adhering to an inner wall of the picking pipe 11 by stopping excavation and moving the suction port 11a to the next excavation point while continuing to inhale seawater.SELECTED DRAWING: Figure 4

Description

The present invention relates to a method for recovering surface-type gas hydrate and a recovery system for surface-type gas hydrate.

Gas hydrate is a hydrate of gas 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 and high pressure environment, so its natural location is on the seabed. It is limited to areas where there is a water bottom such as the bottom of a lake or a permanent frozen soil layer.
There is also a sand layer type gas hydrate that exists in the sand layer of the seabed, but since it is necessary to excavate from the seabed to nearly several hundred to several thousand meters for recovery, it is within 100 m below the seabed. Attention is being paid to surface-type gas hydrates that exist in a mass in the range.
On the other hand, the excavated gas hydrate is collected by sucking it into the unloading pipe together with water, but since the inside of the unloading pipe during excavation is filled with saturated water in which methane is dissolved, methane is decomposed / hydrated. It is in equilibrium. Therefore, there is a risk that methane gas generated by decomposition of gas hydrate during excavation will hydrate in the pickup pipe and adhere to the wall surface to block it.
On the other hand, in Patent Document 1, gas hydrate adhering to the wall surface is obtained by sucking methane-unsaturated seawater with a hose from another place away from the excavation point and drawing it into the collection pipe during excavation of the surface-type gas hydrate. The rate is decomposed into methane and dissolved in seawater for removal.

Japanese Unexamined Patent Publication No. 2016-108774

The technique described in Patent Document 1 is useful in that it can prevent blockage of the pickup pipe due to rehydration during excavation of the surface layer type gas hydrate.
On the other hand, the technique of Patent Document 1 requires a hose or a pump for drawing methane-unsaturated water into the pickup pipe, and there is room for improvement in terms of weight and cost. It is also not applicable to existing drilling rigs that do not have pull-in hoses or pumps. Therefore, it is necessary to control the temperature and pressure inside the pickup pipe and inject additives to make the inside of the lift pipe into a non-equilibrium state, or to put a pig in the lift pipe to mechanically remove the deposits, which is costly. There is room for improvement in terms of cost.
The present invention has been made in view of the above problems, and a method for recovering a surface layer type gas hydrate that can prevent blockage of a pumping pipe due to gas hydrate without increasing the weight and cost regardless of the structure of the device is provided. The purpose is to provide.

One aspect of the present invention is a method for recovering a surface layer type gas hydrate that exists in a mass within a range of 100 m below the bottom of the water from the bottom of the water, and the bottom of the water containing the gas hydrate is excavated and brought closer to the excavated surface. The collection process of recovering the gas hydrate by sucking the excavated material together with water from the suction port of the collection pipe and collecting the gas hydrate, and the next suction port while stopping the excavation and continuing the suction of water. By moving underwater to the excavation point, water on a movement path having a lower gas saturation rate than water in the uplift pipe at the time of excavation is sucked in to dissolve the gas hydrate adhering to the inner wall of the uplift pipe. It is characterized by carrying out a step of removing deposits to be removed.

Another aspect of the present invention is an excavator for excavating a water bottom containing a surface-type gas hydrate existing in a lump within a range of 100 m below the water bottom from the water bottom, and an excavator provided in the excavator for sucking excavated material. An excavator including a pipe and a suction mechanism connected to the lift pipe to generate suction input, a moving mechanism for moving the excavator, and a control unit for controlling the excavator, the suction mechanism, and the moving mechanism. A surface layer type gas hydrate recovery system, the control unit drives the excavator to excavate the bottom of the water containing the gas hydrate, and drives the suction mechanism to excavate from the lift pipe. The gas hydrate is recovered by sucking an object together with water, and when the recovery is completed, the drive of the excavator is stopped, and the moving mechanism is driven while continuing the suction of water to move the excavator to the next excavation point. By moving in water, water on a movement path having a lower gas saturation rate than water in the collection pipe at the time of excavation is sucked in to dissolve and remove the gas hydrate adhering to the inner wall of the collection pipe. It is characterized by that.

In this configuration, after the excavation at one excavation point is completed, water with a low gas saturation rate on the movement path is sucked in by moving the suction port of the pickup pipe to the next excavation point while continuing to suck in water. Dissolve the gas hydrate adhering to the inner wall of the pickup pipe.
Therefore, since it is not necessary to separately install a hose or a pump for drawing in water having a low gas saturation rate, it is possible to prevent the lift pipe from being blocked by gas hydrate without increasing the weight and cost regardless of the structure of the apparatus.
In addition, with this configuration, the gas hydrate adhering to the inner wall of the pickup pipe can be removed simply by sucking water while moving to the next excavation point, so there is no need to separately provide a work process for removal, and the man-hours are required. The cost increase due to the increase can also be suppressed.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide a method for recovering a surface layer type gas hydrate that can prevent obstruction of a pickup pipe due to gas hydrate without increasing the weight and cost regardless of the structure of the apparatus.

It is a side view which shows the outline of the recovery system used in the recovery method of the surface layer type gas hydrate which concerns on this embodiment. In the enlarged view of the region R of FIG. 1, (a) shows the excavation of methane hydrate, and (b) shows the excavation point of (a) moving to the next excavation point after the excavation is completed. It is a functional block diagram of the recovery system of FIG. It is a flow chart which shows an example of the recovery method of the surface layer type gas hydrate.

Hereinafter, embodiments suitable for the present invention will be described in detail with reference to the drawings.
First, the schematic configuration of the recovery system 1 used in the recovery method of the surface layer type gas hydrate according to the present embodiment will be described with reference to FIGS. 1 to 3.
Here, it is a system mounted on the drillship 100 as the recovery system 1, and the methane hydrate layer 203 existing in a mass within a range within 100 m below the water bottom of the seabed 201 is excavated and the methane hydrate 207 ( An example is a system for recovering MH).
As shown in FIGS. 1 to 3, the recovery system 1 includes an excavation device 3, a moving mechanism 5, and a control unit 7.

The excavation device 3 is a device for excavating the methane hydrate layer 203 to recover the methane hydrate 207, and includes an excavator 9, a lift 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. In the excavator 9, a protrusion or a cutter for excavation is projected 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 embedded, and FIG. 2 (a) is centered on the axis of the cylinder. The methane hydrate layer 203 is excavated by lowering it while rotating it in the A direction.

FIG. 2A illustrates a drill bit 9a as an example of a protrusion for excavation. 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 with respect to the excavator 9.

As the power for rotating the excavator 9, for example, the power of the main engine or the generator in the drillship 100 can be used. In this case, a rotation mechanism using this power may be provided on the exposed deck of the drillship 100, and a power transmission shaft (not shown) may be provided in the lift pipe 11 to transmit the power to the drillship 9.

As shown by the white arrow in FIG. 2A, the unloading pipe 11 is a pipe that sucks the excavated material excavated by the excavator 9 together with seawater and recovers the methane hydrate 207 from the methane hydrate layer 203. It is provided in 9. More specifically, as shown in FIG. 2A, the suction port 11a, which is the tip of the lift pipe 11 and sucks the excavated material, is arranged inside the cylinder of the excavator 9.
The unloading pipe 11 has an inner diameter dimension corresponding to the required unloading yield of the excavated material, and has physical properties that do not damage or corrode even if the excavated material or seawater comes into contact with the inner wall, and has strength to the extent that it is not deformed by ocean currents. Any known riser tube can be used. The methane hydrate layer 203 is a layer containing the methane hydrate 207, but as shown in FIG. 2A, the methane hydrate 207 exists in a state of being buried in the mud 205, so that the excavated material is the mud 205. Both methane hydrate 207.

The pump 13 shown in FIG. 3 is a fluid machine as a suction mechanism for generating a suction input for pulling excavated objects and seawater excavated by the excavator 9 above the excavation point, here, to the drillship 100, and is a pickup pipe. Connected to 11. Since methane hydrate 207 has a lower density than substances sucked by other collection pipes 11 such as seawater and mud, it moves above the excavation point by buoyancy without applying external force, but in this embodiment, seawater A pump 13 is provided because only may be inhaled.
As the pump 13, a known pump can be used as long as it can suck excavated objects and seawater at a desired flow rate, and for example, a fluid pump installed in water can be exemplified. However, since the suction mechanism only needs to be able to suck the excavated material and seawater, a gas lift type device that injects gas into the pickup pipe 11 and sucks the excavated material and seawater may be used as the suction mechanism.

The detection unit 15 is a device for detecting the methane hydrate 207a adhering to the inner wall of the lift pipe 11, and is provided in the lift pipe 11 as needed. The reason for providing the detection unit 15 is as follows.
The excavator 9 excavates the methane hydrate 207 in the methane hydrate layer 203 together with the mud 205 in the surface layer, and the lift pipe 11 sucks seawater together with these excavated materials. Therefore, the inside of the lift pipe 11 during excavation is filled with methane hydrate 207, mud 205, and seawater at the excavation point.
Further, not only methane hydrate 207 but also methane gas is present in the methane hydrate layer 203. Further, since methane hydrate 207 cannot exist stably as hydrate unless it is in a low temperature and high pressure environment, it decomposes into methane gas depending on the environment at the time of excavation. Since these methane gases are dissolved in seawater, the seawater in the pickup pipe 11 becomes saturated water in which methane is dissolved, and the reaction in which methane hydrate is decomposed to produce methane and methane is hydrated to methane hydrate. The reaction becomes an equilibrium state in the pumping pipe 11. In this state, if methane is generated in the lift pipe 11 during excavation, the methane may hydrate in the lift pipe 11 and adhere to the wall surface to block the lift pipe 11 in an equilibrium state.
Therefore, it is preferable that the detection unit 15 detects the position and size of the methane hydrate 207a adhering to the inner wall.

If the detection unit 15 can detect the position and dimensions of the methane hydrate 207a adhering to the inner wall, the structure can be appropriately selected.
For example, in FIG. 2A, the ultrasonic inspection device 15a provided on the outer wall of the pickup pipe 11 is illustrated as the detection unit 15. With this structure, ultrasonic waves are radiated from the outer wall side to the inner wall side of the lift pipe 11 to detect the adhesion position of methane hydrate 207a and the radial length of the lift pipe 11 of the deposit from the reflected wave.
When the detection unit 15 is an ultrasonic inspection device 15a, it may be fixed in advance to a place where methane hydrate 207a is likely to adhere. Alternatively, without fixing the detection unit 15, the outer wall of the lift pipe 11 is attached to the outer wall of the lift pipe 11 by an actuator or the like (not shown), and the orientations of B1 and B2 in FIG. It may be configured to be movable in the direction.

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

The moving mechanism 5 is a mechanism for horizontally and vertically moving the excavator 3 in the sea. In FIG. 1, since the recovery system 1 is mounted on the drillship 100, the mechanism for horizontally moving the drillship 100 can be exemplified as a propeller or a main engine for navigating the drillship 100. When the lift pipe 11 is a riser pipe, a pull-in winch that winds up the riser pipe can be mentioned as a mechanism for vertically moving the riser pipe. However, since the moving mechanism 5 only needs to be able to move horizontally and vertically to the suction port 11a of the lift pipe 11, it does not necessarily have to be configured to move the entire drilling device 3 and the drillship 100.

The control unit 7 is a computer that controls the drive of the excavator 9, the pump 13, and the moving mechanism 5, and FIG. 1 illustrates a computer provided in the deck chamber of the excavator 9. Since FIG. 1 illustrates a propeller and a main engine that navigate the drillship 100 as the moving mechanism 5, the control unit 7 in FIG. 1 is also a computer that controls the navigation of the drillship 100, but is different from the computer that controls the navigation. It may be a computer.

The control unit 7 drives the excavator 9 to drive the pump 13 while excavating the bottom surface of the water containing methane hydrate 207 as shown in FIG. 2A, and sucks the excavated material from the pickup pipe 11 together with seawater. Then, the methane hydrate 207 is recovered. This process is also called a collection process.

When the recovery of methane hydrate 207 is completed by excavating an excavation point by 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 excavator 3 is moved underwater to the next excavation point.
At this time, as shown by the white arrow in FIG. 2B, the control unit 7 drives the moving mechanism 5 while continuing to suck seawater from the suction port 11a, and drives the excavator 3 in the vertical Z direction. Raise it to a height several meters above the height of the bottom of the water before excavation. Further, the excavator 3 is moved to the upper part of the next excavation point by moving a predetermined distance in the X direction and the Y direction which are horizontal directions. Further lowering in the Z direction, the excavator 3 is placed at the next excavation point. Since the suction port 11a also moves during the movement, the seawater on the movement path having a lower gas saturation rate than the seawater in the lift pipe 11 at the time of excavation is sucked from the suction port 11a and the seawater in the lift pipe 11 is sucked. Is methane unsaturated. As a result, the inside of the pickup pipe 11 is brought into a non-equilibrium state. In this state, the methane hydrate 207a adhering to the inner wall decomposes into methane in an attempt to reach an equilibrium state and dissolves in methane unsaturated seawater. The control unit 7 removes the methane hydrate 207a adhering to the inner wall by this reaction. This step is also referred to as a deposit removing step.

In this way, the recovery system 1 moves the suction port 11a of the pickup pipe 11 to the next excavation point while continuing to suck in seawater after the excavation is completed, thereby sucking in seawater having a low gas saturation rate on the movement path. , Methane hydrate 207a adhering to the inner wall of the pickup pipe 11 is dissolved.
That is, instead of drawing seawater into the pickup pipe 11 with a hose from a place having a low gas saturation rate, the suction port 11a of the lift pipe 11 is moved to a place where there is seawater having a low gas saturation rate to suck in the seawater. ..

In this configuration, as shown in FIG. 2A, it is the suction port 11a and the pump 13 that draw in the excavated material during excavation, and the hose and pump that draw in the seawater with a low gas saturation rate are drawn into the pumping pipe 11. There is no need to separate it. Therefore, even in the conventional recovery system 1 without a hose or a pump for drawing in seawater, the methane hydrate 207a adhering to the inner wall of the pickup pipe 11 is dissolved only by changing the program of the control unit 7 to the same as that of the present embodiment. Be done. Therefore, regardless of the structure of the device, it is possible to prevent the lift pipe 11 from being blocked by the methane hydrate 207a without increasing the weight and cost.

Further, in this configuration, the methane hydrate 207a adhering to the inner wall of the pickup pipe 11 can be removed only by sucking seawater while moving to the next excavation point, so that there is no need to separately provide a work process for removal. The cost increase due to the increase in man-hours can also be suppressed.

The control unit 7 may change the excavation conditions based on the amount of methane hydrate 207a adhered to the detection unit 15.
For example, during excavation, while the excavated material is being collected in the lift pipe 11, the detection unit 15 is made to detect the amount of methane hydrate adhered, and when the amount of adhesion exceeds a predetermined upper limit, excavation is stopped and the excavated material is collected. The suction port 11a of the pipe 11 may be moved to the next excavation point.
The predetermined upper limit is the radial dimension of the methane hydrate 207a, and if the excavation is continued as it is, the excavation pipe 11 is blocked before the excavation amount reaches the target excavation amount. It is possible to exemplify the amount of fear to have a certain size.

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

If the excavation is stopped and the excavation point is moved to the next excavation point because the amount of methane hydrate 207a adhering to the inner wall of the lift pipe 11 during excavation exceeds the upper limit in this way, The “excavation point” may be the same point as the excavation point where excavation was stopped. Specifically, after stopping excavation, it moves away from the excavation point and sucks in seawater with a low gas saturation rate on the movement path to dissolve the methane hydrate 207a adhering to the inner wall of the pickup pipe 11. It may be allowed to return to the point where excavation was stopped. This is because the excavation point where the excavation was stopped has not been excavated to the target depth, and therefore the excavation is performed again to the target excavation depth.

The control unit 7 may change the movement conditions based on the amount of methane hydrate 207a adhering to the detection unit 15 while sucking seawater during the 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 adhering to the inner wall of the unloading pipe 11 while the suction port 11a of the unloading pipe 11 is moving. The movement condition of the suction port 11a is changed so that the amount of the detected methane hydrate 207a adhered increases and the amount of the detected methane hydrate 207a dissolved increases. More specifically, when the detected adhered amount of methane hydrate 207a is equal to or greater than the predetermined upper limit adhered amount during movement, the moving conditions of the suction port 11a are changed so that the dissolved amount of methane hydrate 207a increases. The "upper limit adhesion amount during movement" means that if the excavation is started after reaching the next excavation point under the current movement conditions, the lift pipe 11 may be blocked before the excavation amount reaches the target excavation amount. There is a certain amount of adhesion.

The movement conditions may be changed so that the amount of methane hydrate 207a adhering to the inner wall of the pickup pipe 11 increases, and the amount of methane hydrate 207a dissolved increases.
With this configuration, it is possible to prevent the lift pipe 11 from reaching the next excavation point in a state where the methane hydrate 207a adhering to the inner wall is not sufficiently removed.
The following can be exemplified as the movement conditions.

First, the moving speed can be exemplified as a moving condition.
Specifically, the larger 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 may be.
By slowing the movement speed as the amount of methane hydrate 207a adhered increases in this way, it is possible to increase the amount of methane unsaturated seawater sucked into the pickup pipe 11 by the time it reaches 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 lift pipe 11 from reaching the next excavation point in a state where the methane hydrate 207a adhering to the inner wall is not sufficiently removed.
The moving speed does not have to be constant at all times. For example, when the moving speed is slowed down, the average speed may be slowed down by temporarily stopping on the moving path or by waiting without immediately starting the excavation after arriving at the next excavation point.

The flow velocity of the seawater sucked by the pickup pipe 11 can also be exemplified as a movement condition.
Specifically, the larger the amount of methane hydrate 207a attached, the faster the flow velocity of the seawater sucked by the pickup pipe 11, and the smaller the amount, the slower the flow velocity.
By increasing the flow velocity of the seawater sucked in as the amount of methane hydrate 207a adhered increases in this way, the amount of methane unsaturated seawater sucked into the pickup 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.

The movement route can also be exemplified as a movement condition.
Specifically, the movement route of the suction port 11a is such that the larger the amount of methane hydrate 207a adhered, the longer the route to the next excavation point, and the smaller the amount, the shorter the route to the next excavation point. Should be changed.
As a specific method of lengthening the route to the next excavation point, the route to move to the next excavation point may be a detour rather than the shortest distance. The route to be changed may be horizontal, 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 farther than the excavation point to be moved.
By lengthening the movement path and lengthening the time required for movement as the amount of methane hydrate 207a adhered increases in this way, the amount of seawater sucked into the pickup pipe 11 before reaching the next excavation point. Can be increased. This makes it possible to increase the amount of methane hydrate 207a that dissolves in seawater during movement.

As the movement condition, any one of the movement speed, the flow velocity, and the movement path may be selected in consideration of the advantages of each, or a plurality of movement conditions may be carried out at the same time.
For example, a configuration for changing the moving speed is suitable for an apparatus in which it is difficult to change the suction amount of seawater or the moving route of the pickup pipe 11.
Since the configuration for changing the flow velocity does not change the moving time or the moving path, it is suitable when it is desired to promote the dissolution of the methane hydrate 207a without changing the working time at the time of excavation.
Since it is not necessary to change the moving speed or the suction speed in the configuration of changing the moving path, it is suitable for a device in which it is difficult to change these while moving.
The above is an example of the movement conditions.

The detection unit 15 is not limited to detecting the amount of methane hydrate 207a adhering to the inner wall of the pickup pipe 11 during excavation or movement.
For example, the detection unit 15 may detect the amount of methane hydrate adhered after the excavation at a certain point is completed and before the movement to the next excavation point. In this case, the next excavation point and movement conditions may be selected so that the adhesion amount becomes less than a predetermined predetermined amount by the time the next excavation point is reached, based on the detected adhesion amount. For example, as the amount of methane hydrate 207a adhered to the methane hydrate increases, a distant excavation point may be selected as the next excavation point, or the moving speed of the lift pipe 11 may be slowed down. In this configuration, the amount of methane hydrate 207a adhered can be less than a predetermined amount without changing the excavation conditions or the movement conditions during excavation or movement. In addition, the predetermined predetermined amount referred to here is the same as the upper limit adhesion amount during movement, when the excavation amount reaches the target excavation amount when the excavation is started after reaching the next excavation point under the current movement conditions. This is the amount of adhesion that may cause the lift pipe 11 to be blocked before the work.

The recovery system 1 is also provided with a device for separating methane hydrate 207 from excavated materials containing mud 205 and a device for storing the separated methane hydrate 207. However, known devices may be used for these. Illustrations and detailed explanations are omitted.
The above is the description of the configuration of the recovery system 1 used in the recovery method of methane hydrate 207 according to the present embodiment.

Next, a specific example of the method for recovering methane hydrate 207a according to the present embodiment will be described with reference to FIG.
First, the control unit 7 moves the drilling device 3 in the horizontal direction together with the drillship 100 by moving the propulsion device of the drillship 100 as the moving mechanism 5, and the suction port 11a of the lift pipe 11 is directly above the drilling point. Place in.
Next, the control unit 7 drives the pull-in winch as the moving mechanism 5 to feed the lift 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. As a result, the suction port 11a is brought closer to the excavated surface.

Next, as shown in FIG. 2A, the control unit 7 lowers the excavator 9 while rotating it, and starts excavating the bottom of the water, which is the methane hydrate layer 203 containing the methane hydrate 207a, with the drill bit 9a. At the same time, the control unit 7 recovers the methane hydrate 207a by sucking the excavated material together with seawater from the suction port 11a of the unloading pipe 11 brought close to the excavation surface by driving the pump 13 and unloading it (S0 in FIG. 4). , Collection 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 unloading pipe 11 during the unloading step (S1 in FIG. 4, step of detecting the amount of methane hydrate adhered during unloading). ).
Next, the control unit 7 determines whether or not the adhered amount of the 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, the excavation pipe 11 may be blocked if the excavation is continued. Therefore, the excavation at the excavation point during excavation is stopped and the process proceeds to S4 (FIG. 4). S2-2).

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

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 unloading pipe 11 after the unloading step is completed and before the deposit removing step (FIG. 4). S5, adhesion amount detection step before movement).
Based on the amount of methane hydrate 207a adhered detected in S5, the control unit 7 sets the next excavation point or movement condition so that the amount of methane hydrate 207a adhered is less than the predetermined amount by the time it reaches the next excavation point. Select (S6 in FIG. 4, selection process).

Next, the control unit 7 drives the moving mechanism 5 while continuing to suck in seawater by the pump 13, and moves the suction port 11a of the pickup pipe 11 to the next excavation point. As a result, as shown in FIG. 2B, the methane hydrate adhering to the inner wall of the unloading pipe 11 is sucked in the seawater on the movement path having a lower gas saturation rate than the seawater in the unloading pipe 11 at the time of excavation. The rate 207a is dissolved in inhaled seawater and removed (S7 in FIG. 4, step of removing deposits).

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 lift pipe 11 while the suction port 11a of the lift pipe 11 is moving (S8 in FIG. 4). , Adhesion amount detection step during movement).
Next, the control unit 7 determines whether or not the adhesion amount of the methane hydrate 207a detected in S8 is less than the upper limit adhesion amount during movement. If it is less than the upper limit adhesion amount during movement, the process proceeds to S10, and if it is not less than the upper limit adhesion amount during movement, the process proceeds to S11 (S9 in FIG. 4).
When the adhered amount of methane hydrate 207a detected in S9 is less than the upper limit adhered amount during movement, the control unit 7 moves to the next excavation point and returns without changing the moving condition of the suction port 11a of the pickup pipe 11. (S10 in FIG. 4).

When the adhered amount of methane hydrate 207a detected in S9 is not less than the upper limit adhered amount during movement, that is, when it is equal to or more than the upper limit adhered amount during movement, the control unit 7 raises and collects the methane hydrate 207a so as to increase the dissolved amount. The movement condition of the suction port 11a of 11 is changed. Further, it moves to the next excavation point under the changed moving conditions and returns (S11 in FIG. 4, the moving condition changing step). Specifically, one or more of the moving speed, the flow velocity of the seawater to be inhaled, and the moving path are changed.

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

As described above, in the recovery method of the present embodiment, the bottom of the water containing methane hydrate 207 is excavated and sucked together with the seawater, and the excavation is stopped and the suction port 11a is next excavated while continuing the inhalation of the seawater. Carry out a deposit removal process that moves to the point.
In this configuration, seawater having a low gas saturation rate on the movement path is sucked by moving the suction port 11a of the lift pipe 11 to the next drilling point while continuing to suck seawater after the drilling at one drilling point is completed. Then, the methane hydrate 207a adhering to the inner wall of the pickup pipe 11 is dissolved.
Therefore, since it is not necessary to separately install a hose or a pump for drawing in seawater having a low gas saturation rate, it is possible to prevent the methane hydrate 207a from blocking the pickup pipe 11 regardless of the structure of the device without increasing the weight and cost. 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 a person 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 the present embodiment, the control unit 7 controls the operations of the excavation device 3 and the moving mechanism 5, thereby implementing a gas hydrate recovery method. However, these operations are manually performed by a worker instead of the control unit 7. You may control it.

Further, in the present embodiment, the movement condition and the next excavation point are selected based on the adhesion amount of the methane hydrate 207a detected by the detection unit 15, but the movement condition and the next excavation point are selected without the detection unit 15 detecting the adhesion amount. The excavation point may be selected. For example, the relationship between the movement condition of the excavator 3 and the excavation condition and the amount of methane hydrate adhered is obtained by an experiment or the like, and the methane hydrate is adjusted to the extent that the methane hydrate does not block during excavation with reference to this relationship. Excavation conditions and movement conditions may be selected so that the amount of adhesion is maintained.

Further, in the present embodiment, the method of recovering the methane hydrate 207 existing on the seabed 201 has been described as an example, but the present embodiment can also be applied to the recovery of the gas hydrate existing on the lake bottom. For example, if the lake is a salt lake, the pumping pipe 11 sucks in salt water with a low gas saturation rate to remove the gas hydrate adhering to the inner wall, and if the lake is a freshwater lake, the freshwater with a low gas saturation rate is picked up. 11 removes the gas hydrate adhering to the inner wall by inhaling.

1: Recovery system 3: Excavation device 5: Moving mechanism 7: Control unit 9: Excavator 9a: Drill bit 11: Lifting pipe 11a: Suction port 13: Pump 15: Detection unit 15a: Ultrasonography device 15b: Camera 100 : Excavator 201: Seabed 203: Methane hydrate layer 205: Mud 207, 207a: Methane hydrate

Claims (8)

It is a method for recovering surface-type gas hydrate that exists in a mass within a range of 100 m below the bottom of the water from the bottom of the water.
A unloading process in which the gas hydrate is recovered by digging the bottom of the water containing the gas hydrate and sucking the excavated material together with water from the suction port of the unloading pipe brought close to the excavated surface.
By stopping excavation and moving the suction port underwater to the next excavation point while continuing to inhale water, water on a movement path having a lower gas saturation rate than the water in the collection pipe at the time of excavation is sucked. Then, the deposit removing step of dissolving and removing the gas hydrate adhering to the inner wall of the pick-up pipe, and
A method for recovering surface-type gas hydrate, which is characterized by carrying out. A step of detecting the amount of the gas hydrate adhering to the inner wall of the unloading pipe during the unloading step was carried out.
The deposit removing step is
A step of stopping excavation and moving the suction port of the collection pipe to the next excavation point when the adhesion amount of the gas hydrate detected in the adhesion amount detection step during collection exceeds a predetermined upper limit. The method for recovering a surface layer type gas hydrate according to claim 1. The deposit removing step is
A moving adhesion amount detection step of detecting the adhesion amount of the gas hydrate adhering to the inner wall of the lift pipe while the suction port is moving, and a step of detecting the adhesion amount during movement.
A moving condition changing step of changing the moving conditions of the suction port so that the larger the amount of the gas hydrate adhered detected in the moving amount detection step, the larger the amount of the gas hydrate dissolved during the movement. ,
The method for recovering a surface layer type gas hydrate according to claim 1 or 2. The movement condition changing step is
The third aspect of claim 3, which is a step of slowing the moving speed of the suction port as the amount of the gas hydrate adhered detected in the moving adhesion amount detecting step increases, and increasing the moving speed of the suction port as the amount decreases. A method for recovering surface-type gas hydrate. The movement condition changing step is
The step according to claim 3 or 4, which is a step of increasing the flow velocity of the water sucked by the pickup pipe as the amount of the gas hydrate adhered detected in the moving adhesion amount detecting step increases, and decreasing the flow rate as the amount decreases. How to recover surface-type gas hydrate. The movement condition changing step is
The suction port is such that the larger the amount of the gas hydrate adhered in the moving adhesion detection step, the longer the route to the next excavation point, and the smaller the amount, the shorter the route to the next excavation point. The method for recovering a surface layer type gas hydrate according to any one of claims 3 to 5, which is a step of changing the movement route of the above. A pre-movement adhesion amount detection step of detecting the adhesion amount of the gas hydrate adhering to the inner wall of the unloading pipe after the completion of the unloading step and before the deposit removing step.
Based on the adhesion amount of the gas hydrate detected in the pre-movement adhesion amount detection step, the following is such that the adhesion amount of the gas hydrate becomes less than a predetermined predetermined amount by the time the next excavation point is reached. The method for recovering a surface layer type gas hydrate according to any one of claims 1 to 6, wherein a selection process for selecting an excavation point and a movement condition is carried out. An excavator that excavates the bottom of the water containing a surface-type gas hydrate that exists in a mass within a range of 100 m below the bottom of the water from the bottom of the water, and a lift pipe that is installed in the excavator and sucks excavated materials and is connected to the lift pipe. Recovery of surface gas hydrate having an excavator with a suction mechanism to generate a suction input, a moving mechanism to move the excavator, and a control unit to control the excavator, the suction mechanism, and the moving mechanism. It ’s a system,
The control unit
The excavator is driven to excavate the bottom of the water containing the gas hydrate, and the suction mechanism is driven to suck the excavated material together with water from the collection pipe to recover the gas hydrate.
When the collection is completed, the drive of the excavator is stopped, the moving mechanism is driven while continuing to suck water, and the excavator is moved underwater to the next excavation point, so that the water in the pumping pipe at the time of excavation is collected. A surface layer type gas hydrate recovery system, characterized in that water on a moving path having a lower gas saturation rate is sucked in to dissolve and remove the gas hydrate adhering to the inner wall of the pick-up pipe.

Images