Method for measuring carbon dioxide storage status

Abstract

This invention provides a method for measuring carbon dioxide storage conditions that does not require an artificial seismic source and allows for continuous monitoring. [Solution] A method for measuring the storage status of carbon dioxide stored underground 11, characterized in that a vibration receiver 20 installed in advance on the surface (seabed 13) where the carbon dioxide storage area 12 exists is used to measure the micro-tremors of the ground caused by vibrations when a wind power generation facility 40 installed near the storage area 12 is in operation, thereby measuring the storage status of carbon dioxide stored underground 11.

Description

Technical Field

[0001] The present disclosure relates to a measurement method for a carbon dioxide storage state.

Background Art

[0002] In recent years, CCS (Carbon Capture and Storage) projects for storing carbon dioxide underground have been planned. In this CCS project, it is necessary to monitor the spread and behavior of carbon dioxide injected underground, as well as whether there is any leakage to the ground surface after injection.

[0003] Non-Patent Document 1 discloses a monitoring technique by four-dimensional seismic survey. This technique performs monitoring by repeatedly conducting three-dimensional seismic surveys using an artificial seismic source. However, since this technique uses an artificial seismic source for each survey, seismic excitation work and costs are incurred each time, and measurements are performed only about once every 1 to 2 years. In addition, the analysis takes 2 to 3 months. Therefore, there are problems that immediate monitoring cannot be achieved and the cost is high.

[0004] Non-Patent Document 2 discloses a monitoring technique using a permanent OBC (Ocean Bottom Cable). In this technique, a digital seabed cable connected to seismometers is laid on the seabed to receive elastic waves. However, this technique has a cable length of several hundred meters and a limit of several tens of seismometers, so it can only be used in offshore and shallow sea areas with a water depth of 100 m or less. In addition, since this technique uses an artificial seismic source during surveys, there is a problem that seismic excitation work and costs are incurred.

[0005] Non-Patent Document 3 discloses a monitoring technique by microtremor survey. This technique obtains the underground elastic wave velocity structure using artificial ground microtremors (minute vibrations imperceptible to humans) originating from nature such as pulsations and waves, and human activities such as traffic and factories. However, this technique has a problem that continuous monitoring cannot be performed because there are not always significant microtremors necessary for monitoring around the monitoring target. [Prior art documents] [Non-patent literature]

[0006] [Non-Patent Document 1] Petroleum Mining Handbook, Japan Petroleum Institute, 2013, p. 141 (upper right column) [Non-Patent Document 2] Petroleum Mining Handbook, Japan Petroleum Institute, 2013, p. 161 (upper right column) [Non-Patent Document 3] Handbook of Geophysical Exploration, Japan Society of Exploration Geophysicists, Chapter 4: Microtremors and Vibrations, pp. 203-210. [Overview of the project] [Problems that the invention aims to solve]

[0007] The objective of this disclosure is to provide a method for measuring carbon dioxide storage conditions that does not require an artificial seismic source and allows for continuous monitoring. [Means for solving the problem]

[0008] The carbon dioxide storage status measurement method according to the present invention is a carbon dioxide storage status measurement method for measuring the storage status of carbon dioxide stored underground, characterized in that a vibration receiver installed in advance on the ground surface where the carbon dioxide storage area exists is used to measure the micro-movements of the ground surface caused by vibrations during the operation of a wind power generation facility installed near the storage area, thereby measuring the storage status of carbon dioxide stored underground.

[0009] According to the present invention, since it utilizes the micro-tremors of the Earth's surface caused by vibrations during the operation of wind power generation facilities, it eliminates the need for artificial seismic sources and reduces the effort and cost of seismic generation work. Furthermore, because it utilizes micro-tremors of the Earth's surface caused by vibrations from wind power generation facilities, monitoring can be performed continuously. Note that "Earth's surface" refers to the surface of the Earth's crust and includes the seabed.

[0010] In the method for measuring the carbon dioxide storage status according to the present invention, it is preferable that the vibration receiver is positioned in a region where the carbon dioxide storage area and the propagation area of ​​the micro-tremors during the operation of the wind power generation facility overlap in a plan view.

[0011] According to the present invention, it is possible to appropriately measure micro-vibrations of the ground surface caused by vibrations of wind power generation facilities in a carbon dioxide storage area.

[0012] In the method for measuring carbon dioxide storage status according to the present invention, it is preferable that the vibration receiver is one or more of either an optical fiber sensor or a geophone.

[0013] According to the present invention, it is possible to appropriately measure micro-vibrations of the ground surface caused by vibrations of wind power generation facilities in a carbon dioxide storage area. Furthermore, by using optical fiber sensors, vibrations can be measured simultaneously at hundreds of points over tens of kilometers of cable. Also, by using optical fiber sensors, stable operation with minimal failures over the long term can be expected, without the need for electronic equipment that was previously essential for sensor modules. Additionally, by using optical fiber sensors in conjunction with geophones, data from both can be used to calibrate the data.

[0014] The method for measuring carbon dioxide storage conditions according to the present invention preferably involves measuring microtremors on the Earth's surface by microtremor array exploration.

[0015] According to the present invention, it is possible to appropriately measure micro-vibrations of the ground surface caused by vibrations of wind power generation facilities in a carbon dioxide storage area. [Effects of the Invention]

[0016] The carbon dioxide storage status measurement method according to the present invention does not require an artificial seismic source, thus reducing the time and cost of seismic generation work. Furthermore, monitoring can be performed continuously. [Brief explanation of the drawing]

[0017] [Figure 1]This is a perspective view showing the configuration of equipment for performing the method for measuring the carbon dioxide storage state in the embodiment. [Figure 2] This is a plan view for explaining the method for measuring the carbon dioxide storage state in the embodiment. [Figure 3] This is a side view for explaining the method for measuring the carbon dioxide storage state in the embodiment. [Figure 4] This is a flowchart showing the procedure for performing the method for measuring the carbon dioxide storage state in the embodiment. [Modes for Carrying Out the Invention]

[0018] Hereinafter, embodiments of the present invention will be described in detail, but the embodiments of the present invention are not limited to the embodiments described below. In addition, the dimensions, materials, shapes, relative arrangements, and the like of the components described in the embodiments are not intended to limit the scope of the present invention thereto unless otherwise specifically specified, and are merely illustrative. Note that the sizes, positional relationships, and the like of members shown in each drawing may be exaggerated or simplified for clarity of explanation. In addition, illustration of some elements may be omitted to avoid excessively complicated drawings.

[0019] The method for measuring a carbon dioxide storage state according to the embodiment is a method for measuring the storage state of carbon dioxide stored in the ground of a sea area. The method for measuring the carbon dioxide storage state uses a geophone pre-installed on the seabed where the carbon dioxide storage area exists. Specifically, microtremors on the ground surface generated by receiving vibrations during operation of a wind power generation facility installed in the vicinity of the storage area are measured by the geophone. Thereby, the storage state of the carbon dioxide stored in the ground is measured.

[0020] First, the outline of the embodiment will be described with reference to FIGS. 1 to 3. As shown in Figs. 1 to 3, on the seabed 13 where the carbon dioxide (CO₂) storage region 12 stored in the underground 11 of the sea area 10 exists, an optical fiber sensor 21 and a geophone 22 which is a seismometer are laid as the geophones 20. The optical fiber sensor 21 is connected to a computer 30. Note that an electric cable separate from the optical fiber sensor 21 may be arranged along the optical fiber sensor 21, and the geophone 22 may be connected to the computer 30 via this electric cable. In the present embodiment, the seabed 13 where the storage region 12 exists refers to the region of the seabed 13 that overlaps with the carbon dioxide storage region 12 and the region where carbon dioxide may leak (leakage region 14) in plan view. That is, in the present embodiment, the geophones 20 are installed on the seabed 13 above the carbon dioxide storage region 12, and the geophones 20 are also installed on the seabed 13 above the carbon dioxide leakage region 14.

[0021] Then, the geophones 20 measure microtremors of the ground surface (the seabed 13 in the present embodiment) generated by receiving vibrations during operation of the wind power generation facility 40 installed in the vicinity of the storage region 12, thereby measuring the storage state of the carbon dioxide stored in the underground 11. Note that the vicinity of the storage region 12 refers to a range where the geophones 20 can detect the microtremors of the ground surface caused by the wind power generation facility 40. The geophones 20 measure and analyze the microtremors of the ground surface, and these data are sent to the computer 30 via the optical fiber sensor 21 for constant monitoring. Note that these data may be sent to the computer 30 via an electric cable connected to the geophone 22 and separate from the optical fiber sensor 21, so that constant monitoring is performed.

[0022] As shown in Figs. 2 and 3, the geophones 20 are preferably arranged in a region where the carbon dioxide storage region 12 and the microtremor propagation region 41 during operation of the wind power generation facility 40 overlap in plan view. Thereby, the microtremors of the ground surface caused by the vibration of the wind power generation facility 40 can be appropriately measured for the carbon dioxide storage region 12. Note that a part of the geophones 20 may be arranged outside the overlapping region. In addition, the illustration of the geophone 22 and the leakage region 14 is omitted in Figs. 2 and 3.

[0023] In this embodiment, the vibration receiver 20 continuously measures and analyzes microtremors on the ground surface caused by the operation of the wind power generation facility 40 to capture changes in the physical properties of the ground 11 and monitor carbon dioxide in the ground 11 (monitoring of the carbon dioxide storage area). Carbon dioxide stored in the storage area 12 leaks out, for example, by traveling along faults 15 in the ground 11. As the carbon dioxide stored in the storage area 12 spreads and moves in the ground 11, changes occur in the elastic wave velocity and density of the geological layer. Since microtremor exploration like this embodiment can detect the elastic wave velocity of the geological layer, the area where carbon dioxide exists can be identified by detecting changes in the elastic wave velocity and density of the geological layer.

[0024] The preferred method for measuring carbon dioxide storage conditions is to measure surface microtremors using a microtremor array survey. Microtremor array survey is a survey method that estimates the S-wave structure of the ground by inversely analyzing the phase velocity of the obtained surface waves. This allows for the appropriate measurement of surface microtremors caused by vibrations from the wind power generation facility 40 in the carbon dioxide storage area 12.

[0025] The wind power generation facility 40 operates 24 / 7 throughout the year, generating micro-tremors on the ground surface during operation. By using these micro-tremors for monitoring, the need for artificial earthquake generation is eliminated. Furthermore, by permanently installing the receiver 20 on the seabed 13, real-time observations that cannot be performed by seismic reflection surveys can be conducted, enabling rapid detection of carbon dioxide leaks.

[0026] The storage area 12 for carbon dioxide stored underground 11 in the sea area 10 is selected not only based on the suitability of the underground 11 for storage but also on the convenience of injection facilities and transportation, being located at a depth of approximately 300m or less from the seabed 13 and within a few kilometers of the coast. Furthermore, offshore wind power generation facilities are often constructed in multiple units in coastal areas with favorable wind conditions at a water depth of 100m, and there are many cases where wind power generation facilities 40 are installed in groups near the carbon dioxide storage area 12. In such cases, long-term continuous monitoring becomes possible by using the constant micro-tremors of the ground surface caused by the operation of the wind power generation facilities 40.

[0027] To gain a detailed understanding of the behavior of carbon dioxide underground 11 and to detect leaks early, it is desirable that the monitoring interval be as short as possible, and ideally in real time. Furthermore, the monitoring period is long-term, exceeding 20 years. According to the carbon dioxide storage status measurement method of this embodiment, since it uses micro-tremors on the ground surface caused by vibrations from the continuously operating wind power generation facility 40, monitoring can be performed continuously over a long period.

[0028] Next, referring to Figure 4, the procedure for measuring the carbon dioxide storage status in the embodiment will be described. The procedure from geological survey to monitoring will be carried out in the following steps.

[0029] 1. Geological survey (Process S1) Geological surveys of the seabed, including geophysical exploration and drilling, will be used to identify potential areas for carbon dioxide storage on the seabed. Furthermore, within these candidate areas, areas where carbon dioxide may leak when injected will be identified.

[0030] 2. Identification of the fine adjustment range (Process S2) This embodiment utilizes micro-vibrations of the ground surface caused by the operation of wind power generation facilities, and therefore identifies the range of micro-vibrations of the ground surface caused by the operation of wind power generation facilities. The range of micro-vibrations is identified by placing a vibration detector in the candidate area for carbon dioxide storage and the area where carbon dioxide may leak when carbon dioxide is injected, and measuring the micro-vibrations of the ground surface caused by the operation of wind power generation facilities.

[0031] 3. Determining the monitoring range (Process S3) The monitoring range for carbon dioxide will be the overlapping area between the candidate carbon dioxide storage area identified in step S1 and the area of ​​micro-tremors on the ground caused by the operation of the wind power generation facility identified in step S2.

[0032] 4. Determination of the placement position of the vibration receiver (Process S4) The vibration receiver will be positioned within the monitoring range determined in process S3, and within the area where carbon dioxide leakage is possible, as identified in process S1.

[0033] 5. Placement of the vibration receiver (Process S5) The receiver is placed on the seabed at the receiver placement location determined in step S4. Preferably, the receiver is one or more of either an optical fiber sensor or a geophone. This allows for the appropriate measurement of micro-vibrations on the ground caused by the vibrations of the wind power generation facility in the carbon dioxide storage area.

[0034] The vibration receiver can be either an optical fiber sensor or a geophone, but an optical fiber sensor can simultaneously measure vibrations at hundreds of points using a cable tens of kilometers long, which is longer than installing numerous seismometers. Therefore, optical fiber sensors enable monitoring over a wide area, such as measuring further offshore. Furthermore, by using the optical fiber itself as the sensor, it is possible to expect stable operation with fewer failures over the long term without using any electronic equipment that was essential for sensor modules. For this reason, it is preferable to use an optical fiber sensor as the vibration receiver.

[0035] Furthermore, it is possible to use optical fiber sensors and geophones in combination. In this case, geophones are placed at predetermined intervals near the cable housing the optical fiber sensors. This has the advantage of allowing calibration using data from both devices. In addition, it is preferable that the optical fiber sensors be arranged in a meandering pattern, like drawing a single line, at the receiver placement location. That is, it is preferable to arrange a single optical fiber sensor in a meandering pattern on the seabed where carbon dioxide reservoirs exist. This has the advantage of allowing monitoring with a single optical fiber sensor.

[0036] 6. Monitoring (Process S6) Injection wells are constructed to inject carbon dioxide into candidate storage areas. Before injecting carbon dioxide from the injection wells, the velocity of the geological formation is determined as a reference value by performing microtremor analysis using a vibration detector. Subsequently, by comparing the change in the velocity of the geological formation caused by the injection of carbon dioxide from the injection wells with the reference value, it is possible to identify the injection points of carbon dioxide. Furthermore, since the velocity of the geological formation changes if carbon dioxide leaks out, it is also possible to identify the location of carbon dioxide leakage.

[0037] As explained above, the carbon dioxide storage status measurement method of this embodiment uses micro-tremors on the ground caused by vibrations during the operation of wind power generation facilities, thus eliminating the need for artificial seismic sources and reducing the effort and cost of seismic generation work. Furthermore, because it uses micro-tremors on the ground caused by vibrations from wind power generation facilities, monitoring can be performed continuously.

[0038] Although the embodiments for carrying out the invention have been described in more detail above, the spirit of the present invention is not limited to these descriptions and must be interpreted broadly based on the claims. Furthermore, various modifications and alterations based on these descriptions are also included in the spirit of the present invention. For example, the receiver is specified to use one or more of either an optical fiber sensor or a geophone, but other types of receivers may also be used. Furthermore, while the optical fiber sensor is specified to use one optical fiber sensor, multiple optical fiber sensors may be arranged in multiple columns or rows at the receiver's location, or they may be arranged in a grid pattern. [Explanation of symbols]

[0039] 10 sea area 11 underground 12 Reservoirs 13 Undersea 14 Leakage Area 15 Faults 20 Geophone 21 Fiber Optic Sensor 22 Geophone 30 Computers 40 Wind power generation facilities 41 Propagation Region

Claims

1. A method for measuring the carbon dioxide storage status, which measures the storage status of carbon dioxide stored in the ground, Using a vibration receiver pre-installed on the ground surface where the aforementioned carbon dioxide storage area exists, A method for measuring the storage status of carbon dioxide, characterized by having a vibration receiver measure the micro-tremors of the ground surface caused by vibrations during the operation of a wind power generation facility installed near the storage area, thereby measuring the storage status of carbon dioxide stored in the ground.

2. The method for measuring the carbon dioxide storage status according to claim 1, characterized in that the vibration receiver is positioned in a region where the carbon dioxide storage area and the region where the micro-tremors are propagated during the operation of the wind power generation facility overlap in a plan view.

3. The method for measuring carbon dioxide storage status according to claim 1 or 2, characterized in that the vibration receiver is one or more of an optical fiber sensor and a geophone.

4. A method for measuring the carbon dioxide storage status according to claim 1 or 2, characterized in that microtremors on the ground surface are measured by microtremor array exploration.

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