JP2011209200A - Seabed observation system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To understand deformation of a foundation of a seabed to be observed in two-dimension or three-dimension with a simple system configuration.SOLUTION: The seabed observation system includes a plurality of sensor means for detecting displacement of the foundation of a seabed, a signal line which connects the plurality of sensor means in series, and a terminal station device which receives sensor signals detected by the plurality of sensor means. The plurality of sensor means are arranged in bellows form by the signal line.

Description

  The present invention relates to a seafloor observation system that monitors sensor signals from sensors disposed on the seabed in order to monitor changes in slope of the seabed and underground structures.

2. Description of the Related Art In recent years, seafloor observation technology that detects physical phenomena occurring on the seabed, such as vibrations caused by earthquakes occurring on the seafloor, changes in water pressure, magnetic changes, etc., and sends signals to the ground has attracted attention.
In particular, a technique for accurately and promptly detecting ground displacement, crustal movement, that is, seabed slope change and underground structure change has recently attracted attention.
This is because, for example, these technologies are applied in the fields of earthquake, tsunami breaking system, exploration of underground resources, or storage of carbon dioxide in submarine formations, which are still in the research stage.
The earthquake and tsunami breaking system is an important technology because it can quickly and accurately perform earthquake and tsunami breaking if the ground displacement can be detected accurately.
In the exploration of underground resources (oil, methane hydrate, gas, groundwater, minerals, etc.) and the underground storage of carbon dioxide, it is possible to prevent gas leakage and collapse accidents if the ground displacement can be detected accurately. This is an essential technology for ensuring safety.
In the storage of carbon dioxide in the seafloor formation, it is necessary to grasp how carbon dioxide diffuses by confirming changes in the underground structure on the sea floor and to promote the storage of carbon dioxide. Detecting the displacement of the ground is a basic technique for storing carbon dioxide in the seabed.
In particular, the state and extent of underground resources in the strata (where the subsurface resources are distributed and in what thickness and how they spread), and when storing carbon dioxide in the seabed, Confirmation of changes in the subsurface structure such as how carbon dioxide injected into the formation diffuses, and underground structure has not changed due to underground resource mining and carbon dioxide storage In order to confirm this, monitoring of changes in the slope of the seafloor surface, such as uplift and depression of the seafloor surface layer, to detect underground abnormalities at an early stage, it is necessary to avoid and take measures against gas leaks and sinking accidents. It has been.

As a technology for exploring underground resources and confirming changes in the geological structure beneath the sea floor, a technique called reflection seismic exploration is used to observe the reflected waves using an artificial seismic wave and grasp the underground structure. . In reflection seismic exploration, a pulsed artificial seismic wave is transmitted, the reflected wave reflected and returned at the underground interface is observed with a vibration sensor, and the boundary is reached at the time the reflected wave arrives from the first vibration (direct wave). Know the position of the surface (stratum surface). Hydrophones, speedometers, accelerometers and the like are used as sensors.
In addition, bubble-type inclinometers and accelerometers are used to observe changes in the slope of the seafloor surface layer, such as uplift and depression of the seafloor surface layer.
Examples of techniques for detecting the displacement of the ground and the fluctuation of the crust include the techniques of Patent Document 1, Patent Document 2, and Patent Document 3.

  The undersea stratum observation device of Patent Document 1 is a penetration cylinder that is built in the observation device casing and has a drill blade around a central hole at the lower end and can be moved up and down while rotating around a vertical axis. A sensor shaft having a cap that can be lifted and lowered coaxially, and a cap that can be opened and closed at the lower end, and a formation displacement sensor that is attached to the lower end of the sensor shaft and protrudes downward from the center hole when lowered. By penetrating the displacement sensor, changes in the seabed or crust are detected. The device described in Patent Document 1 is a device in which a single formation displacement sensor is inserted into a formation on the seabed to observe changes in the seabed and crust.

  In the ground deformation observation system using optical fiber sensor of Patent Document 2, in the construction on the seabed ground such as landfill, the amount of subsidence of the ground in the landfill sea area is measured from the stage where the landfill upper surface is below the sea level. In order to solve the problem that the measurement of settlement with a large number of subsidence plates hinders construction work and becomes a problem because there are many complicated ship carriers and earthlifts, A pair of optical fiber sensors arranged vertically in a grid around the inside and inside of it, and the subsidence / uplift of the ground at that position is discriminated based on the difference in strain between the top and bottom at any point in the ground for a predetermined time Each has a configuration and means for creating and displaying a two-dimensional distribution of subsidence / lift. In other words, an optical fiber sensor is used as a sensor, a light pulse is incident on the optical fiber sensor, and the reflected light is analyzed to detect distortion. Strain data can be obtained from this optical fiber sensor.

The displacement monitoring method for the ground and the like using the acceleration sensor of Patent Document 3 obtains the correct displacement by integrating the acceleration measurement value twice without requiring a fixed point, and the ground or the artificial structure or the like with high accuracy. To enable displacement monitoring, a sensor unit that includes an acceleration sensor, a data recording unit that digitally converts the acceleration sensor output and continuously records data, and data that performs necessary processing on the recorded data A method is described in which a displacement is obtained by integrating a measured value of an acceleration sensor twice by using a three-component servo acceleration sensor provided with a processing unit. In the evaluation of ground displacement during landslides and excavation work, the displacement of landslides and submarine ground is calculated and monitored using an acceleration sensor fixed to the ground or an artificial structure.

JP-A-5-213268 Japanese Patent Laid-Open No. 2003-232631 JP 2006-194822 A

With the exploration of underground resources (oil, methane hydrate, gas, groundwater, minerals, etc.) and storage of carbon dioxide in the formation, the state and extent of the underground resources in the formation (where and where the underground resources are in the formation) How the carbon dioxide is distributed in the seafloor formation, and how the carbon dioxide injected into the seabed formation diffuses when storing carbon dioxide in the seafloor formation. By monitoring changes in the slope of the seafloor surface, such as changes in the surface structure of the seabed, such as uplift and depression of the seafloor surface, it is possible to avoid and take measures against gas leaks and sinking accidents, etc., by catching underground abnormalities at an early stage. It is demanded.
In addition, sensitivity errors in the measurement results (sensitivity changes due to environmental temperature changes, etc.), sensitivity drift, environmental noise (electromagnetic noise, high frequency of power supply and circuit riding on sensor signal line, earthquake, tide, wave, ship navigation noise, There is a need for an accurate measurement system that avoids the effects of vibration noise during offshore construction, etc., and reduces errors in observation data.
On the other hand, as described in the above-mentioned patent document, sensing of submarine ground displacement, such as used in civil engineering construction work, excavation work, etc., that is, a technique for monitoring seabed slope change and underground structure Has been proposed,
The thing of patent document 1 is a proposal regarding a single formation displacement sensor, and the technique of patent document 2 measures the distortion which arose in the optical fiber, and discriminates the subsidence / lift of the ground. / It does not measure uplift.

  The present invention is intended to solve these problems, and changes in inclination within the observation area of the sea bottom and changes in the underground structure of the sea bottom area in a planar or three-dimensional manner. The purpose is to provide a simple system configuration that can be monitored.

The seafloor observation system according to the present invention includes a plurality of sensor means for monitoring a surface condition of an underground structure and a seabed, a seabed cable connecting the plurality of sensor means in series, the seabed cable, and the plurality of sensors. A substation device for receiving each sensor signal detected by the means, and the submarine cable connecting the sensor means in series is arranged so that the sensor arrangement position is specified in the observation area of the seabed. It is laid so as to have a surface configuration or a line configuration.
The sensor means is composed of a triaxial accelerometer.

Further, the present invention provides a sensor means comprising a plurality of triaxial accelerometers for monitoring the surface structure of the underground structure and the sea bottom, a submarine cable connecting the plurality of sensor means in series, and the submarine cable. And a terminal device that receives each sensor signal detected by the plurality of sensor means.
Further, the submarine cable connecting the sensor means in series is laid so as to have a surface configuration or a line configuration in such a manner that the sensor arrangement position is specified in the observation region on the sea bottom.

The present invention can simultaneously monitor changes in the geological structure under the seabed and the slope of the seafloor surface layer by using an accelerometer as a sensor to monitor the surface structure of the underground structure and the seabed. Therefore, the observation system can be configured with a simple configuration.
In addition, by connecting multiple sensors with cables and arranging them in a series length in the longitudinal direction, by placing the sensors in the observation area on the sea floor, the error of each sensor can be averaged, and the sensitivity error of the measurement results, Accurate measurement can be performed by removing influences such as sensitivity drift and environmental noise.
In addition, by arranging the sensor position so that the sensor position can be specified with respect to the seafloor observation area, it is possible to grasp the measurement location as a plane or line with multiple sensors instead of a single point, so the seafloor tilt observation can be made finer. This can be done, and it is possible to avoid and take measures against gas leaks and cave-in accidents by ascertaining underground abnormalities at an early stage.
In this way, it is possible to observe how changes in the formation affect the bottom of the sea by observing changes in the subsurface structure by reflection seismic surveys and observing changes in the surface of the sea bottom as slopes. For example, with carbon dioxide storage, carbon dioxide that should be stored in the formation leaks and rises near the bottom of the sea, so it is possible to observe changes in the slope of the sea floor that could not be obtained simply by observing changes in the underground structure. can get.

As described in Patent Documents 1-3, in the observation of the displacement of the sea floor used in civil engineering construction work and excavation work as in the prior art, it is necessary to observe the displacement of the sea floor uplift and descent. It can be said that it is effective, but it is not easy to find the displacement in the deep sea area.
On the other hand, the present invention is based on the observation start time, can observe how many tilted each sensor from there, and can confirm changes in the stratum structure under the sea floor, Multiple sensors are placed on the sea floor at appropriate positions within a given area, and the trend of displacement of the surface or line placed from these slope data can be ascertained. Trends and changes in the stratum structure beneath the ocean floor can be observed accurately.
In addition, it is possible to observe the underground structure and the inclination of the seafloor surface in combination with sensors other than accelerometers, but since two different systems are used for observation, two systems are used. It is necessary to prepare (each including a power feeding system and a transmission system), and the cost becomes high. However, the present invention can observe the inclination of the underground structure and the seabed surface by one system. .

1 is an overall configuration diagram of the present invention. It is the figure which showed the detail of arrangement | positioning of a sensor. Illustration of sensor operation

  Hereinafter, embodiments for carrying out the present invention will be described with reference to FIGS. 1, 2, and 3.

  FIG. 1 is a configuration diagram of a seabed observation system, and FIG. 2 is a diagram in which a sensor 11 and a repeater 12 are arranged on a seabed cable 20. The seabed observation system 1 includes a terminal device 10, a plurality of sensors 11 and repeaters 12 arranged at predetermined intervals on the seabed cable 20, and these are connected by the seabed cable 20. The sensors 11 are connected in series by the submarine cable which is a signal line for each sensor 11 at predetermined intervals, and are arranged so that the installation position of the sensor 11 is specified in the observation area 30 on the sea bottom as a whole. Yes.

  For example, in the example of FIG. 1, the submarine cable 20 in which the sensors 11 are arranged at intervals of 50 m on an offshore seabed of several tens of kilometers is shown in FIG. 1 as a row interval of about 250 m, a row length of 1000 m, and a row number of 5 rows. Assuming a series of installations, the area 30 (observation area, hereinafter referred to as “monitoring area”) that can be monitored is 1 square km of 1000 m × 1000 m. 100 sensors 11 are arranged.

  The submarine cable can be laid out at several tens of meters to several hundred meters depending on the condition of the bottom surface of the monitoring region 30 and the required accuracy of monitoring. The interval, the column length, and the number of columns can be changed as appropriate. Moreover, in the example of FIG. 1, although the submarine cable is arrange | positioned in the monitoring area | region 30 in the bellows shape, what is arrange | positioned planarly so that the position of each sensor 11 may comprise a matrix, The arrangement of the sensor 11 is not limited to this, and any of a linear shape, a circumferential shape, a polygonal shape, a crossing shape, and the like can be changed depending on the required accuracy of monitoring as long as the position of the sensor 11 can be specified. .

The sensor 11 is an accelerometer fixed to three orthogonal axes that simultaneously detect displacement in the X-axis direction, the Y-axis direction, and the Z-axis direction on a three-dimensional axis. Using the accelerometer 11 (hereinafter referred to as “sensor 11”) fixed to three axes, measuring the gravity vector and observing the inclination of the bottom of the sea to obtain the change in the bottom of the sea bottom over time. Can do.
The accelerometer 11 is not only a servo type (which changes the magnitude of the current obtained by controlling the pendulum to be moved by acceleration into an electric signal), but also a MEMS type (pushing the pendulum due to acceleration to “distortion”). It is also possible to use an “electrical signal” as the “size”.

  FIG. 2 is a diagram showing details of the arrangement of the sensor 11 including the repeater 12. Repeaters 12 are arranged at regular intervals of the sensor 11. The repeater 12 relays the signal detected by the sensor 11.

The seafloor observation system 1 according to the present embodiment includes a terminal device 10 (not shown, but includes a workstation, an optical transmission / reception device, a GPS time generator, a power feeding device, etc.), a submarine cable 20 and a submarine cable 20. Sensor 11 (three-component servo-type accelerometer) connected to the sensor 11 and a transmission unit (not shown) of the sensor 11, and the sensor 11 is arranged on the sea bottom of a predetermined monitoring region 30. The observation data transmitted from the sensor 11 is recorded by the terminal device 10 installed on land or on the ship.
The terminal device 10 identifies which sensor 11 the transmitted signal is emitted from, and records and analyzes the signal for each sensor 11 to detect changes in the structure and inclination of the ground. It is. The clock signal transmitted from the terminal device 10 is supplied to the transmission unit of the sensor 11 through the submarine cable 20. A transmission unit (not shown) of the sensor 11 digitizes the signal from the sensor 11 (A / D conversion) according to the timing of this clock, and transmits it to the terminal device 10 through the submarine cable 20. The terminal device 10 records the data sent from the transmission unit of the sensor 11 based on this clock signal.

  With reference to FIG. 3, how the sensor 11 detects the fluctuation of the crust 13 will be described. The upper diagram in FIG. 3 shows a state where the sensor 11 is installed on the crust 13. This is called the initial installation state. The sensor 11 observes the gravity acceleration vector in the initial installation state.

  The lower diagram shows a case where the crust has collapsed after the sensor 11 is installed. The inclination of the sensor 11 changes from the initial installation state due to the depression. When the gravitational acceleration vector is measured in this state, a change in inclination from the initial installation state can be observed. By capturing these in a plane and line, the change in the inclination of the entire crust 13 can be grasped in detail.

  In this way, the change in the inclination of the crust 13 on which the sensor 11 is placed can be detected at the same time, and the crustal movement in the range where the sensor 11 is placed can be grasped planarly and three-dimensionally.

  For example, a submarine cable in which a plurality of sensors 11 are arranged in a predetermined region on the bottom of the sea in order to determine how carbon dioxide injected below the bottom of the sea is diffused when carbon dioxide is stored in the seabed. 20 are connected in series and expanded, and an observation region 30 (for example, a submarine cable provided with sensors 11 arranged at a predetermined interval is laid at a predetermined column length, the number of columns, and the column interval. ) Continuously monitoring and observing changes in the slopes of the underground structure and the seabed, the terminal device is configured to perform the predetermined determination based on the data transmitted from each sensor 11. It is possible to observe ground changes in the area.

  When observing the underground structure under the seabed, the sensor 11 is used for observation by the reflection method. A predetermined method (not shown) causes an earthquake in the sea surface or in the sea, and the seismic wave propagates from the sea to the bottom of the sea. The propagated seismic wave is reflected at the boundary of the stratum and is observed by the sensor 11 disposed on the sea floor. At this time, the geological boundary is identified from the time of the earthquake and the time when the reflected wave is observed, and the underground structure is observed. Here, the reflected wave obtained by the reflection method exploration is vibration, and this is observed by the sensor 11 (accelerometer). Since the reflected wave is composed of a longitudinal wave and a transverse wave, the sensor 11 is combined with three axes (upper and lower directions and two horizontal directions) and observed. When the reflected wave reaches the sensor 11, the reflected wave vibrates the sensor 11. The sensor 11 observes the acceleration of the reflected wave.

  When observing changes in the inclination of the sea floor, the gravitational acceleration of the earth is measured by a sensor 11 installed on the sea floor. In this state, the gravitational acceleration vector obtained from the acceleration of each of the three axes of the sensor 11 indicates the direction of the center of the earth. Therefore, the respective inclinations of the three axes are obtained from the gravitational acceleration vectors obtained from the respective accelerations of the three axes. Thus, the change in the gravitational acceleration vector can be observed.

1 Submarine observation system, 10 Terminal equipment, 11 Sensor, 12 Repeater, 13 Crust, 20 Submarine cable

Claims (4)

A plurality of sensor means for monitoring the surface structure of the underground structure and the sea floor;
A submarine cable connecting the plurality of sensor means in series;
A terminal device connected to the submarine cable and receiving each sensor signal detected by the plurality of sensor means;
With
The submarine cable connecting the sensor means in series is laid so as to have a surface configuration or a line configuration by being arranged so that the sensor arrangement position is specified in an observation region on the bottom of the sea. Undersea observation system.   The seafloor observation system according to claim 1, wherein the sensor means includes a three-axis accelerometer. Sensor means comprising a plurality of three-axis accelerometers for monitoring the underground structure and the surface condition of the sea floor;
A submarine cable connecting the plurality of sensor means in series;
A terminal device connected to the submarine cable and receiving each sensor signal detected by the plurality of sensor means;
A seafloor observation system characterized by The submarine cable connecting the sensor means in series is laid so as to have a surface configuration or a line configuration by being arranged so that the sensor arrangement position is specified in an observation region on the bottom of the sea. The seabed observation system according to claim 3.

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