WO2019112035A1

WO2019112035A1 - Method for exploring ocean floor subterranean layers

Info

Publication number: WO2019112035A1
Application number: PCT/JP2018/045078
Authority: WO
Inventors: 栄一淺川; 文俊村上; 均塚原; 秀太郎齊藤
Original assignee: 株式会社地球科学総合研究所
Priority date: 2017-12-08
Filing date: 2018-12-07
Publication date: 2019-06-13
Also published as: JPWO2019112035A1

Abstract

In this method for exploring ocean floor subterranean layers, a hydrophone array comprising a plurality of hydrophones is used to generate sound waves above and/or below the hydrophone array while keeping the plurality of hydrophones arrayed underwater at intervals in the vertical direction, and information including reflected wave amplitude, the direction from which the reflected waves arrive, and time delay following the generation of the sound waves is detected by each of the plurality of hydrophones.

Description

Submarine basement exploration method

The present invention relates to a method of searching a submarine basement layer.
This application claims the benefit of U.S. Provisional Patent Application No. 10 / 9,067, filed Dec. 8, 2017, which is filed in the United States. Priority is claimed under 62/2 596,116, the contents of which are incorporated herein by reference.

Conventional submarine resources include petroleum and natural gas. In the exploration of oil and natural gas under the sea floor, using hydrophone arrays with multiple hydrophones, the long side direction of the hydrophone array is aligned along the direction (horizontal direction) parallel to the water surface in the sea A method is used in which a hydrophone array is towed by an exploration boat, a reflection wave of seismic waves generated from an energy source is detected, and a submarine topography and a submarine formation are identified (see Patent Document 1).

In recent years, the seafloor hydrothermal deposit has attracted attention as one of the seabed resources.
The seafloor hydrothermal deposit is a deposit formed by the process in which the hydrothermal fluid containing various metals ejected on the seabed is cooled by the surrounding seawater, and is expected as a seabed resource. In the vicinity of the active seafloor hydrothermal deposit, unique topography such as chimney chimneys and mounds where they are broken are formed. Therefore, it was considered to identify and mine the seabed topography. However, there is a problem that the temperature is high around the active seafloor hydrothermal deposit, making it difficult to extract resources.

On the other hand, if it is a hydrothermal deposit where hydrothermal activity on the seabed has stopped, the time has passed since it was formed, and there is a possibility that the temperature is low and resources can be collected. However, in this case, the hydrothermal deposit is buried in the sediment of the seabed, and it is difficult to locate the hydrothermal deposit from the topography of the seabed.
Therefore, after identifying the submarine topography such as the chimney group and the mound where they collapsed, a method of boring in the vicinity and identifying the formation configuration under the submarine has been adopted. However, this method is not efficient because boring is performed while the formation structure under the seabed is unknown.

U.S. Pat. No. 3,943,484

Petroleum, which has been attracting attention as a submarine resource in the past, is contained in a sand layer having a thickness of several hundreds of meters 2 to 3 km below the sea floor. On the other hand, the seafloor hydrothermal deposit is formed at a shallow position several tens m to about 100 m below the sea floor and has a thickness of at most about several tens m.
The present inventors towed hydrophone arrays with a exploration boat so that a plurality of hydrophones used for oil exploration under the seabed are aligned in a direction parallel to the water surface (horizontal direction) in the sea, An attempt was made to identify the position of the seafloor hydrothermal deposit by a method of detecting the reflected wave of the sound wave generated from the hypocenter (Patent Document 1). However, in this method, the hydrophone receives the reflected waves from all directions without distinction, so there is much noise such as the reflected waves from the side, and the resolution of the information to be acquired is low. Therefore, it has been difficult to obtain information on a thin submarine hydrothermal deposit having a thickness of a few tens of meters to 100 meters below the sea floor.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a method of searching a submarine base layer which can analyze the formation of a subseabed shallow position such as a submarine hydrothermal deposit.

The method of searching a submarine basement layer according to the present invention uses a hydrophone array having a plurality of hydrophones, and while maintaining a state in which the plurality of hydrophones are vertically spaced from each other in seawater, the hydrophones A sound wave is generated at least one of the upper side and the lower side of the array, and information including the swing width of the reflected wave, the arrival direction of the reflected wave, and the time delay from the generation of the sound wave is detected by each of the plurality of hydrophones. It is characterized by

In the method of searching a submarine base layer according to the present invention, since a plurality of hydrophones are arranged at intervals in the vertical direction (vertical direction) in the hydrophone array, the reflected wave from the submarine base layer immediately below the hydrophone array is There is a difference in time to reach each hydrophone. Therefore, the detection information of each hydrophone can be processed in consideration of the time difference in which the reflected waves reach the respective hydrophones. In addition, since a plurality of hydrophones are arranged at intervals in the vertical direction, when detecting a reflected wave from the seabed foundation layer directly under the hydrophone array, the horizontal position of each hydrophone is the same position It becomes possible to

In the method of searching a seabed bed according to the present invention, a reflected wave from the seabed bed is extracted from the information detected by each of the plurality of hydrophones, and the reflected waves from the seabed bed extracted are overlapped. Is preferred.

In the method of searching a submarine base layer according to the present invention, the horizontal position of each hydrophone at the time of detecting the reflected wave is the same position, and the reflected wave from the submarine base layer directly under the hydrophone array is each hydrophone The time difference to arrive at can be specified in advance by the distance between each hydrophone.
That is, in the present invention, a plurality of hydrophones are arranged at intervals in the vertical direction (vertical direction) in the hydrophone array. It can be extracted in consideration of the distance between hydrophones and the velocity of acoustic waves in the sea.
Thus, when extracting information of a specific reflected wave from the submarine foundation immediately below each hydrophone array from the arrival time difference of sound waves in each hydrophone, the information acquired by each hydrophone is lateral. Although information on reflected waves and reflected waves from other directions is also included, it is only information on reflected waves from the seabed foundation layer directly under the hydrophone array that overlaps in information detected by each hydrophone. Therefore, if the information detected by each hydrophone is extracted and superimposed corresponding to the arrival time difference of the sound wave in each hydrophone, the side reflection wave which each detection information has or the reflected wave from other direction Since the information in the above does not overlap, the information of the side reflection wave and the reflection wave from the other direction is not emphasized when the information is superimposed, and can be excluded.

In the method of searching a submarine basement layer according to the present invention, the hydrophone array is maintained at a constant water depth from the sea level, and the sound waves are generated plural times at intervals in time while being moved in a certain direction, It is preferable that each time the sound wave is generated, information including the swing width of the reflected wave, the arrival direction of the reflected wave, and the time delay from the generation of the sound wave is detected by each of the plurality of hydrophones.
According to the method of searching the submarine basement layer, it is possible to search the formation of the submarine underground layer in a wide area.

In the method of searching a submarine basement layer according to the present invention, a deep sea movement search device or a deep sea towing body is connected to one end of a cable to which the plurality of hydrophones are attached, and the deep sea movement search device is a remote control type It is an unmanned underwater vehicle (ROV: Remotely operated vehicle) or an autonomous unmanned underwater vehicle (AUV: autonomous underwater vehicle), and the acoustic positioning device attached to the hydrophone array It is preferable to measure the position in water.

According to the deep sea movement search device or the deep sea towing body connected to one end of the cable to which the plurality of hydrophones are attached, a reflected wave from the sea floor immediately below the hydrophone array while moving the hydrophone array in a certain direction Can be detected. Further, according to the acoustic positioning device, since the underwater position of the hydrophone array is specified, it becomes possible to move the hydrophone array closer to the bottom of the sea floor to detect a reflected wave, and the accuracy of the detected information is improves.

It is preferable that the water depth of the said deep-sea movement survey device is constant in the exploration method of the seabed foundation of the present invention.

In the method of searching a submarine basement layer according to the present invention, when the depth of the deep sea movement surveying apparatus is constant, the sea floor topography and the like are taken into consideration, and the depth of the horizontal movement of the hydrophone array is hardly inhibited by the topography of the sea floor. It is good to do. In this case, the search can be performed without mounting a camera or the like on the deep sea movement search device.

It is preferable to measure the height of the said deep-sea movement survey device from the seabed with the altitude measurement device attached to the said hydrophone array in the exploration method of the seabed foundation layer of this invention.

In the method of the present invention, when measuring the height of the deep sea movement surveying apparatus from the seabed with the altimetry apparatus, the height of the hydrophone array from the seabed can be maintained constant. The information of the reflected wave from the seabed immediately below the hydrophone array can be easily processed.

It is preferable that the said hydrophones are arranged in series and the said hydrophone array is comprised in the exploration method of the seabed foundation layer of this invention.
When the plurality of hydrophones are arranged in series, it is easy to prepare a hydrophone array.

It is preferable that the said hydrophones are arranged in parallel and the said hydrophone array is comprised in the exploration method of the seabed foundation layer of this invention.
When the plurality of hydrophones are arranged in parallel, a failed hydrophone can be easily identified and replacement of the failed hydrophone is easy. In addition, it is possible to change the hydrophone interval according to the search target.

According to the method of exploration of a seabed bed according to the present invention, it is possible to provide a method of searching a seabed bed capable of analyzing the formation of a bed located at a shallow position on the seabed such as a hydrothermal deposit.

It is a schematic diagram which shows the exploration method of the seabed foundation layer performed by suspending a hydrophone array so that the length direction of the hydrophone array used by this embodiment may become perpendicular to the seabed. It is a schematic diagram which shows the exploration method of the seabed foundation layer performed by floating a hydrophone array so that the length direction of the hydrophone array used by this embodiment may become perpendicular to the seabed. It is a schematic diagram which shows an example which installs the high frequency hypocenter in the deep sea towing body, and receives the sound wave oscillated in the sea and the sound wave oscillated in the sea by the hydrophone array of this embodiment. It is a schematic diagram showing an example which installs a high frequency hypocenter in a remote control type unmanned underwater vehicle, and receives a sound wave oscillated in the sea and a sound wave oscillated in the sea by the hydrophone array of this embodiment. It is an example of the two-dimensional imaging of the seabed underlayer obtained by the exploration method of the seabed underlayer shown in the conventional example. It is an example of the two-dimensional imaging of the seabed underlayer obtained by the exploration method of the seabed underlayer shown in the present embodiment. It is a schematic diagram which shows an example of the hydrophone array used by this embodiment.

Hereinafter, although an example of an embodiment of the present invention is explained in detail with reference to figures, the present invention is not interpreted as limiting to these embodiments.

First Embodiment
In the method of searching the seabed underlayer according to the first embodiment described with reference to FIGS. 1, 3 and 4, first, a receiver using a hydrophone array 11 is prepared. In the present embodiment, a hydrophone array 11 in which a plurality of hydrophones 12 are connected in series is used. Specifically, a plurality of hydrophones 12 are installed at regular intervals in the pipe, and the hydrophones 11 are prepared by wiring between them to prepare the hydrophone array 11. Here, about 16 to 32 hydrophones can be used as the plurality of hydrophones. The distance between adjacent hydrophones is not limited, but it is preferable to set the hydrophones at intervals of about 1 to 10 m. One end of the hydrophone array 11 is connected to a data logger 13 to record information obtained by each hydrophone 12.

Next, the main cable 15 having the weight 14 attached to the tip is connected to the exploration boat 21 and the main cable 15 is vertically suspended in the sea. In the main cable 15, the hydrophone array 11 is fixed so that the plurality of hydrophones 12 are arranged along a direction parallel to the length direction of the main cable 15.
Although the weight 14 is not particularly limited, it is possible to suspend the main cable 15 vertically to the seabed, and for example, a weight 14 of 1 ton can be used.
Although not shown, when the main cable 15 is suspended vertically, a deep sea tow body (Deep tow) 22 or a deep sea movement search device is connected to the exploration boat 21 and the hydrophone array 11 is connected from the deep sea tow body 22 or the deep sea movement search device. The fixed main cable 15 may be hung vertically.

When the hydrophone array 11 is fixed to the main cable 15, the data recording device 13 for recording the received information of the hydrophone 12 may be disposed at the upper end or the lower end of the hydrophone array 11.
The data recording device 13 can simultaneously record information of a plurality of hydrophones 12 simultaneously, and the information detected by the plurality of hydrophones 12 is stored in a recording medium in the data recording device 13.

As an epicenter to generate sound waves used for exploration of the submarine underground layer, an air gun 23 or a parka used on the sea, or a deep sea towing body 22 shown in FIG. 3 or a deep sea movement surveying apparatus shown in FIG. A high frequency hypocenter (SBP: Sub bottom profiler) mounted on a submersible vehicle (ROV: Remotely operated vehicle) 32 or an autonomous underwater vehicle (AUV) can be used.
An air gun emits compressed air into water to generate an acoustic wave, and a parker generates an acoustic wave by electric spark discharge. The high frequency hypocenter oscillates an acoustic pulse toward the lower part. Sound waves are generated by one or more types of hypocenters selected from an air gun, a parker, and a high frequency hypocenter. Also, the sound waves may be generated at least one of the upper side and the lower side of the hydrophone array 11. The upper side of the hydrophone array 11 may be directly above, and the lower side may be directly below.

In the method of searching the submarine basement layer according to the present embodiment, the hydrophone array 11 is maintained suspended vertically to the bottom of the sea floor, and the search boat 21 or the deep-sea tow body 22 is used at a constant water depth from the sea level. While moving the hydrophone array 11 in a certain direction, sound waves are generated a plurality of times at intervals in time by the above-mentioned earthquake source. Here, the certain direction may be horizontal.
At this time, the horizontal movement speed of the hydrophone array 11 is a speed at which the hydrophone array 11 can be maintained suspended vertically to the seabed. For example, the moving speed of the hydrophone array 11 in the horizontal direction may be set to about 1 to 2 km / hour.
When moving at such a speed that the hydrophone array 11 can be maintained suspended vertically relative to the seabed, the oscillation point of the sound wave generated at least one of the upper side and the lower side (directly above and directly below) of the hydrophone array 11 And the receiving point for receiving the reflected wave from the seabed foundation layer by the hydrophone array 11 at substantially the same position in the horizontal direction. For example, in the case of searching a submarine basement layer of 1000 to 1500 m, assuming that the horizontal movement speed of the hydrophone array 11 is about 1 km / hour, the oscillation of the sound wave immediately above and / or just below the hydrophone array 11 The point and the sound wave receiving point are approximately at the same position (zero offset) in the horizontal direction. Further, even when the oscillation point of the sound wave and the reception point of the sound wave are shifted in the horizontal direction, the distance is very small, and it is difficult to affect the information to be detected.
In FIGS. 3 and 4, although the arrangement position of the air gun 23, the arrangement position of the deep sea towing body 22 equipped with the high frequency hypocenter or the deep sea movement search device 32 is not directly above and / or just below the hydrophone array 11, An air gun 23, a deep sea towing body 22 equipped with a high frequency hypocenter, or a deep sea movement survey device 32 is disposed approximately directly above and / or just below the hydrophone array 11, which is a schematic diagram in which the reflection state of sound waves is made easy to understand.

The plurality of hydrophones 12 can detect information including the amplitude of the reflected wave of the sound wave from the submarine underlayer, the arrival direction of the reflected wave, and the time delay from the generation of the reflected wave.
In the present embodiment, the plurality of hydrophones 12 are arranged at intervals in the vertical direction (vertical direction) with respect to the seabed. Therefore, if the distance between adjacent hydrophones 12 is specified beforehand and made to correspond to the velocity of the sound wave in the sea, the reflected wave from the seabed foundation layer directly below the hydrophone array 11 is received by the hydrophone 12 at the lower end of the hydrophone array 11 After that, it is possible to specify the time for which each hydrophone 12 receives a signal.

The information by the reflected wave from immediately below the hydrophone array 11 is extracted according to the time difference of the reflected wave reaching each hydrophone 12. That is, when the information taking into consideration the arrival time difference of the sound wave in each hydrophone 12 is extracted from the acquired information and the information is superimposed, only the information of the reflected wave from immediately below the hydrophone array 11 is emphasized and clear information You can get
Specifically, the time difference of arrival time of sound waves per interval of adjacent hydrophones 12 is calculated from the speed of sound in water, and the time when a specific reflected wave reaches each hydrophone 12 is determined, according to the time difference Extracted data.
Thus, when extracting information of a specific reflected wave from the submarine foundation layer immediately below each hydrophone array 11 from the arrival time difference of sound waves in each hydrophone 12, it is possible to use information acquired by each hydrophone 12 Although the information of the side reflection wave and the reflection wave from other directions are also included, the information detected by each hydrophone 12 overlaps is the reflection wave from the seabed foundation layer directly under the hydrophone array 11 It is information only.
Therefore, if the information detected by each hydrophone 12 is extracted and superimposed in consideration of the arrival time difference of the sound wave in each hydrophone 12, the side reflection wave that each detected information has or from other direction Since the information of the reflected waves does not overlap, the information of the side reflected waves and the reflected waves from other directions is not emphasized when overlapping the information, and can be excluded.

According to the sound waves generated from the epicenter, not only the reflected wave from the seabed foundation layer but also the reflected wave from the sea surface is generated.
The reflected wave from the seabed foundation layer is an upward traveling wave, and the reflected wave from the sea surface is a downward traveling wave. In the present embodiment, the interval between adjacent hydrophones 12 is specified in advance, and information indicating the arrival time difference of the sound wave from the lower end side of the hydrophone array 11 and the arrival time difference of the sound wave from the upper end side of the hydrophone array 11 It is easy to separate information.
Therefore, in consideration of the arrival time difference of the sound wave in each hydrophone 12, before extracting and superposing the information detected by each hydrophone 12, data pre-processing to separate the information by the reflected wave from the sea surface is performed be able to.

Second Embodiment
In the second embodiment, a hydrophone array 11 in which a plurality of hydrophones 12 similar to those in the first embodiment are connected in series is prepared, and a float 31 for the hydrophone array 11 to float vertically in the sea is It is installed at one end of the phone array 11. Further, a data recording device 13 is connected to one end of the hydrophone array 11.
In FIG. 2, the data recording device 13 and the float 31 are connected to the upper end side of the hydrophone array 11, and the data recording device 13 is disposed between the float 31 and the hydrophone array 11. However, the arrangement position of the data recording device 13 is not limited, and the data recording device 13 may be arranged on the lower end side of the hydrophone array 11.
As the data recording device 13, the same one as that of the first embodiment can be used.

In the second embodiment, a remotely operated unmanned underwater vehicle (ROV: Remotely operated vehicle) 32 or an autonomous underwater vehicle (AUV: autonomous underwater vehicle), which is a deep sea movement search device, is prepared. The remote control type unmanned submersible vehicle 32 may be connected to the exploration boat 21.
Next, one end of the hydrophone array 11 to which the float 31 is not connected is connected to the remote-controlled unmanned underwater vehicle 32 or the autonomous unmanned underwater vehicle.
According to the above configuration, the hydrophone array 11 connected to the remote-controlled unmanned underwater vehicle 32 or the unmanned unmanned underwater vehicle under the sea will be in a vertically floating state by the float 31.

As a seismic source for generating a sound wave used for the exploration of the submarine basement, as in the first embodiment, an air gun or a parka used on the sea, or a high frequency wave mounted on a remote control type unmanned submersible unit 32 or an unmanned type unmanned submersible A hypocenter (SBP: Sub bottom profiler) or the like can be used.
The method and position of generating the sound wave are the same as in the first embodiment.

In the method of searching the seabed bed according to the present embodiment, the floating state of the hydrophone array 11 is maintained in the vertical direction by the floats 31 of the hydrophone array 11, and the unmanned underwater vehicle 32 of remote control type or the unmanned unmanned type unmanned While moving the hydrophone array 11 in a certain direction using a submersible machine, sound waves are generated plural times at intervals in time by the above-mentioned earthquake source. Here, the certain direction may be horizontal.
At this time, the moving speed of the hydrophone array 11 in the horizontal direction is the same as that of the first embodiment.

The plurality of hydrophones 12 can detect information including the amplitude of the reflected wave of the sound wave from the submarine underlayer, the arrival direction of the reflected wave, and the time delay from the generation of the reflected wave.
In the present embodiment, the plurality of hydrophones 12 are arranged at intervals in the vertical direction (vertical direction) with respect to the seabed. Therefore, if the distance between adjacent hydrophones 12 is specified in advance and made to correspond to the velocity of the sound wave in the sea, the reflected wave from the seabed foundation layer immediately below the hydrophone array 11 is received by the hydrophone 12 at the lower end of the hydrophone array 11 After that, it is possible to specify the time for which each hydrophone 12 receives a signal.
The method of extracting the information by the reflected wave from immediately below the hydrophone array 11 is the same as that of the first embodiment.

As described above, in the first and second embodiments, a hydrophone array in which a plurality of hydrophones are connected in series from the data recording device 13 is used, but a plurality of hydrophones are connected in parallel. You may use Specifically, as shown in FIG. 7, a plurality of cables 41 having different lengths are connected in parallel to the data recording device 13, and the hydrophone 12 is attached to the tip of each cable 41. Next, the cables 41 to which the hydrophones 12 are attached are respectively fixed to the linear central member (rope) 42 connected to the data recording device 13 so that the intervals of the plurality of hydrophones 12 become constant. , Hydrophone array 43 is configured. Thus, in the hydrophone array 43 in which a plurality of hydrophones 12 are connected in parallel, when any one of the hydrophones 12 fails, only the cable 41 attached with one hydrophone 12 is replaced. You can do repairs with In addition, there is an advantage that it is easy to check which hydrophone 12 in the hydrophone array 43 is broken.

In the first and second embodiments, the hydrophones are arranged at regular intervals, but the regular intervals may be regular or irregular.

The hydrophon array 11, the deep sea tow body 22 used in the first embodiment, and the remote control type unmanned underwater vehicle 32 or the autonomous unmanned underwater vehicle used in the second embodiment have the acoustic positioning device (SSBL) : Super Short Baseline method may be attached. The position of the hydrophone array is calculated by the acoustic positioning device, and the bottom position, depth, moving direction, etc. of the hydrophone array can be determined from the position of the hydrophone array obtained.
When the water depth of the hydrophone array is constant, it is preferable that the water depth at the upper end of the hydrophone array is such that the horizontal movement of the hydrophone array is not easily inhibited by the topography of the seabed in consideration of the seabed topography and the like. For example, when the deep sea tow body 22 is used, it is preferable to set the seabed height at the lower end of the hydrophone array to 100 m to 200 m.
In the case of using the remote control type unmanned spacecraft 32, the seabed height of the hydrophone array is preferably maintained such that the lower end height of the hydrophone array is 5 m to 10 m. In this case, observation of the seabed condition around the hydrophone array can be simultaneously performed to avoid the inhibitor.

The hydrophone array used in the first and second embodiments may be provided with at least one of an inclinometer and a compass. When at least one of the inclinometer and the compass is installed on the hydrophone array, the hydrophone array is suspended vertically in the sea, or the hydrophone array is vertically floated. It can be confirmed.

In the first embodiment and the second embodiment, the sound waves are generated by one or more types of hypocenters selected from an air gun, a parker, and a high frequency hypocenter (SBP), but the sound waves generated from the air gun are 10 to At 300 Hz, the sound wave generated from the spring is 20 to 1 kHz, and the sound wave generated from the high frequency seismic source (SBP) is 500 to 2.5 kHz. That is, the energy of the sound wave from the high frequency seismic source (SBP) which generates the sound wave near the seabed is smaller than the sound wave from the air gun or the spoter used on the sea. Therefore, when combining an air gun with a high frequency hypocenter (SBP), or when combining a parker with a high frequency hypocenter (SBP), the cross correlation method is used to obtain information on sound waves from ocean sources and sound waves generated near the seabed. It is good to separate from the information of

In the first embodiment and the second embodiment, the hydrophone array is suspended vertically (or floats vertically) with respect to the seabed by a search boat, a deep sea tow body, a deep sea movement search device, or floating. Tow, and the method of detecting the information of the reflected wave was shown.
According to the method of the present embodiment, the information of the reflected wave immediately below the hydrophone array is extracted by excluding the information of the side reflected wave and the reflected wave from other directions in each hydrophone constituting the hydrophone array. It is possible to obtain clear two-dimensional imaging of the seabed underlayer.

By identifying the submarine topography such as the chimney group and the mound where they collapsed and boring the area thereabout, a method of searching a conventional submarine basement layer and the present invention for the submarine region where the submarine hydrothermal deposit is confirmed We applied the method of exploration of the seabed and confirmed the difference in the obtained data.

(1) Conventional Example A hydrophone array in which 16 hydrophones are arranged in series at intervals of 5 m is prepared, and the long side direction of the hydrophone array is parallel to the water surface in a deep sea tow body (Deep tow). It was towed at about 1 m / sec to maintain the following condition (horizontal direction). At this time, the seabed height of the hydrophone array was about 100 m. The seabed height was measured indirectly from the difference between the hydrophone depth and the seabed depth.
Next, a sound wave of about 20 to 1 kHz was oscillated every 5 seconds from the sea using a parker, and the hydrophones received the reflected waves from the seabed and the seabed foundation layer.
The information of the reflected wave detected by each hydrophone was recorded and analyzed by a data recorder connected to one end of the hydrophone array. The data recording device is capable of simultaneously recording information of a plurality of hydrophones simultaneously, using a sampling rate of 10 kHz, time stamped by an atomic clock (CSAC), and the detected information is in the data recording device. Was stored on a recording medium.
A two-dimensional imaging diagram of the seabed underlayer obtained from the analyzed data is shown in FIG.

In the conventional method, in order to maintain the state (horizontal direction) in which the long side direction of the hydrophone array is parallel to the water surface, it is necessary to set the towing speed of the hydrophone array to about 1 m / sec. Therefore, the position of the hydrophone array at the time of emitting the sound wave using the hypocenter and the position of the hydrophone array at the time of receiving the reflected wave from the seabed foundation layer are largely shifted. That is, it was necessary to analyze data at different points. In addition, it is difficult to increase the towing speed of the hydrophone array and increase the resolution (number of observation points) in the observation range, and as shown in FIG. Could not be analyzed in detail.
Furthermore, in this method, it is difficult to remove the reflected wave from the lateral direction of the hydrophone array, and there is a tendency that the detected information has a lot of noise and the resolution of the information is low.

(2) Invention Example A hydrophone array was prepared in which 16 hydrophones were arranged at intervals of 5 m in the vertical direction (vertical direction). The hydrophone array was fixed along the length direction of the main cable with the weight attached to the tip, and the main cable was suspended vertically from the sea bottom from the deep sea towing body submerged in the sea.
Next, the hydrophone array was towed at a speed of about 1 km / hour (0.28 m / sec) so that the hydrophone array was suspended vertically to the seabed. At this time, the height of the bottom of the hydrophone array was 100 m. The seabed height was measured indirectly from the difference between the hydrophone depth and the seabed depth.

Next, a sound wave of about 20 to 1 kHz is oscillated approximately immediately above the hydrophone array every 5 seconds using a parker mounted on the exploration boat, and each hydrophone receives the reflected waves from the seabed and the seabed foundation layer. did.
The information of the reflected wave detected by each hydrophone was recorded and analyzed by the same data recording device as the conventional example connected to one end of the hydrophone array.
A two-dimensional imaging diagram of the seabed underlayer obtained from the analyzed data is shown in FIG. The two-dimensional imaging diagram of the seabed underlayer shown in FIG. 6 is a portion surrounded by a broken line in FIG.

In the method of the present invention, the towing speed of the hydrophone array is about 1 km / hour (0.28 m / sec) in order to maintain the hydrophone array suspended vertically to the seabed. Therefore, in consideration of the speed of sound in the sea, the point of oscillation of the sound wave by the parka placed almost directly above the hydrophone array and the point of reception of the reflected wave from the seabed underground layer in the hydrophone array are almost the same. It is a position. Therefore, it is possible to increase the accuracy of the reception of the reflected wave corresponding to the oscillated sound wave.
In addition, the towing speed of the hydrophone array is slower compared to the conventional example, and the resolution (number of observation points) in the observation range can be increased, and as shown in FIG. We were able to analyze in detail the stratum at the position of.

The sound wave oscillated toward the submarine foundation layer is reflected at a location where the composition of the formation changes (eg, between the mud layer and the gravel layer).
In the method of the present invention, 16 hydrophones are arranged at intervals of 5 m in the vertical direction (vertical direction), and the time difference for the reflected waves to arrive from the seabed directly below the hydrophone array is calculated in advance to each hydrophone From the information of the reflected wave obtained by each hydrophone, the information according to this time difference was extracted, and the information of 16 hydrophones was superimposed.
According to this method, only the reflected waves from the bottom of the hydrophone array overlap, and it is possible to remove the information of the reflected waves in the lateral direction and the reflected waves from other directions. Therefore, it was possible to obtain highly accurate information on the seabed foundation layer.
When the information detected by the present inventors was analyzed by the above method, as shown in FIG. 6, there was no reflection under the hydrothermal deposit 60 and no formation was confirmed. In FIG. 6, the hydrothermal deposit 60 is a portion surrounded by the upper boundary and the lower boundary, and there is no reflection of the formation indicated by the shade of dark gray and light gray immediately below it.
From the example of the present invention described above, it has been confirmed that according to the method of the present invention, it is possible to easily identify the position of the hydrothermal deposit by two-dimensional imaging.

According to the method of exploration of a seabed bed according to the present invention, it is possible to provide a method of searching a seabed bed capable of analyzing the formation of a bed located at a shallow position on the seabed such as a hydrothermal deposit. Moreover, the exploration method of the seabed foundation layer of the present invention is also applicable to the exploration of seabed resources such as methane hydrate.

11 Hydrophone array 12 Hydrophone 13 Data recorder 14 Weight 15 Main cable 21 Exploration boat 22 Deep-sea tow body

Claims

A method of searching a submarine basement layer,
Using a hydrophone array having a plurality of hydrophones,
Under seawater, the plurality of hydrophones are arranged at intervals in the vertical direction, and sound waves are generated at least one of the upper side and the lower side of the hydrophone array,
A method of searching a seabed foundation layer, wherein information including a swing width of a reflected wave, an arrival direction of the reflected wave, and a time delay from generation of the sound wave is detected by each of the plurality of hydrophones.
The method of searching a seabed bed according to claim 1, wherein
The reflected wave from the seabed foundation layer is extracted from the information detected by each of the plurality of hydrophones,
A method of searching a seabed underlayer characterized by superimposing reflected waves from the extracted seabed underlayer.
The method of searching a seabed bed according to claim 2,
The hydrophone array is maintained at a constant depth from the surface of the sea and, while being moved in a certain direction, the sound waves are generated plural times at intervals in time.
Each time the sound wave is generated, information including the swing width of the reflected wave, the arrival direction of the reflected wave, and the time delay from the generation of the sound wave is detected by each of the plurality of hydrophones. Submarine basement exploration method.
The method of searching a seabed bed layer according to any one of claims 1 to 3,
A deep sea mobile search device or a deep sea tow body is connected to one end of a cable to which the plurality of hydrophones are attached, and the deep sea mobile search device is a remotely operated unmanned underwater vehicle (ROV: Remotely operated vehicle) or an autonomous type It is an unmanned underwater vehicle (AUV: autonomous underwater vehicle),
A method of searching a seabed underlayer, comprising measuring an underwater position of the deep-sea mobile search device or the deep-sea towed body by an acoustic positioning device attached to the hydrophone array.
The method of searching a seabed bed according to claim 4,
A method of searching a submarine basement layer, wherein the water depth of the deep sea movement search device is constant.
The method of searching a seabed bed according to claim 4,
A method of searching a seabed underlayer, comprising measuring the height of the deep sea movement surveying apparatus from the seabed with an altimetry apparatus attached to the hydrophone array.
The method of searching a seabed bed according to claim 1, wherein the plurality of hydrophones are arranged in series to constitute the hydrophone array.
The method of searching a seabed bed according to claim 1, wherein the plurality of hydrophones are arranged in parallel to constitute the hydrophone array.