Deep sea bottom gas leakage flux in-situ monitoring device and measuring method

Abstract

The invention relates to the technical field of ocean engineering observation equipment, in particular to a deep sea seabed gas leakage flux in-situ monitoring device and a measuring method.The deep sea seabed gas leakage flux in-situ monitoring device comprises a fixed cavity, a mounting frame and a balance weight seat, the upper end and the lower end of the fixed cavity are provided with a gas release port and a gas inlet respectively, electromagnetic valves are installed at the upper end and the lower end of the fixed cavity respectively, and a gas measuring device is arranged in the fixed cavity; the top of the mounting frame is fixedly connected with the upper portion of the fixing cavity through a sealing plate, the bottom of the mounting frame is connected with the balance weight seat through an acoustic releaser, a containing cavity is formed between the sealing plate and the balance weight seat in the mounting frame through a floating block, the mounting frame is connected with a pressure-resistant bin and a battery bin in the containing cavity, a controller is arranged in the pressure-resistant bin, and a lithium battery pack is arranged in the battery bin. The controller is electrically connected with the two electromagnetic valves and the acoustic releaser through cables, and an underwater acoustic communication system which is electrically connected with the controller and can transmit data with the outside is further installed in the containing cavity of the installation frame. High-precision deep sea seabed gas leakage flux is realized based on the fiber bragg grating, and continuous real-time long-term observation can be realized.

Description

Technical Field

[0001] The present invention relates to the technical field of marine engineering geological observation equipment, and particularly relates to an in-situ monitoring device and measurement method for deep-sea submarine gas leakage flux. Background Art

[0002] Submarine gas leakage refers to a process in which gas in the seabed is released into seawater, which is the result of various chemical, biological, geological, and physical processes occurring within the seabed and is widely distributed and diverse throughout the continental margin. In addition to the geomorphic manifestations of submarine gas leakage (e.g., pitted seabed surface, authigenic carbonate crusts on deep-water corals and submarine mounds), its fluid conduit characteristics (such as landslides, faults, mud volcanoes, etc.) also play an important role in facilitating gas escape. It is difficult to determine the scale of submarine gas leakage because the leakage characteristics, including bubble size, velocity, and concentration, usually show significant temporal variations on time scales ranging from a few seconds to several decades. Therefore, in-situ observation of submarine gas leakage flux can provide information about submarine geological changes and understand potential submarine geological disasters that may occur.

[0003] Currently, there are two methods for measuring submarine gas leakage flux: one is acoustic detection inversion, and the other is direct submarine observation. The method of acoustic detection inversion (such as Chinese Patent Application for Invention CN108931777A, CN113624639B, and Chinese Patent Application for Utility Model CN214334779U) can only perform single detection and cannot obtain the long-term changes in submarine gas leakage. Moreover, the error of the submarine gas leakage flux obtained by acoustic detection inversion is relatively large, so it has great limitations. In contrast, the method of direct submarine observation can obtain the changes in the time series of submarine gas leakage flux and has greater advantages. Currently, among the similar devices that have been disclosed, Chinese Patent Application for Invention CN102012246B determines the average rate of in-situ flow of natural gas leakage from submarine cold seeps by the quantitative volume evacuation method (the number of times of measuring a quantitative volume of gas), and can also determine the total amount of natural gas leaking upward from the seabed. However, this device takes a long time for one measurement, and its observation method is actually not continuous, so the time resolution of the measured data is relatively low. For short-term rapid gas eruptions, it is difficult to determine the gas release pattern. Chinese Patent Application for Invention CN113624639B adopts a method of quickly capturing and obtaining the gas volume to calculate the instantaneous flux, but it needs to be used in conjunction with an underwater robot and cannot perform continuous in-situ observation, so its actual use is very limited. Obviously, for the goal of accurately obtaining the long-term changes in submarine gas leakage flux, the current related technical methods and measurement devices still have defects and cannot meet the existing practical application requirements, which is an urgent problem to be solved at present. Summary of the Invention

[0004] The present invention provides an in-situ continuous real-time long-term observation device for deep-sea gas leakage flux based on fiber Bragg grating, which is used to overcome the deficiencies of the prior art.

[0005] The present invention is realized through the following technical solutions: Provide an in-situ monitoring device for deep-sea gas leakage flux, including a fixed cavity, a mounting frame connected with floating blocks on the circumferential surface, and a counterweight seat provided with a gas channel.

[0006] The upper end of the fixed cavity is provided with a gas release port, and the lower end is provided with a gas inlet facing the gas channel. Solenoid valves are respectively installed at the gas release port and the inlet. A gas measurement device for measuring the gas leakage flux is arranged in the fixed cavity.

[0007] The top of the mounting frame is fixedly connected with the upper part of the fixed cavity through a sealing plate. The bottom of the mounting frame is detachably connected with the counterweight seat through an acoustic releaser. A receiving cavity is formed between the sealing plate and the counterweight seat in the mounting frame through the floating blocks. A pressure-resistant chamber and a battery chamber are connected in the receiving cavity of the mounting frame. A controller is arranged in the pressure-resistant chamber, and a high-density lithium battery pack is arranged in the battery chamber. The controller is respectively electrically connected with the two solenoid valves and the acoustic releaser through cables. A underwater acoustic communication system electrically connected with the controller and capable of transmitting data to the outside is also installed in the receiving cavity of the mounting frame.

[0008] Furthermore, a horn-shaped collecting cover is connected at the gas inlet at the bottom of the fixed cavity.

[0009] By setting the horn-shaped collecting cover, it is convenient to collect the seabed gas and make it concentrate and enter the fixed cavity.

[0010] Furthermore, the gas measurement device includes a pressure-resistant outer shell. An LED light source emitter, a photodiode, and a multi-channel fiber Bragg grating demodulator are respectively arranged inside the pressure-resistant outer shell, and a high-density lithium battery pack for supplying power to the three is also provided. The photodiode and the multi-channel fiber Bragg grating demodulator are respectively connected to a combined socket at the top of the pressure-resistant outer shell through optical fibers. It also includes a plurality of fiber Bragg grating gas sensing devices located at the bottom of the pressure-resistant outer shell. Each fiber Bragg grating gas sensing device includes a multi-stage coupling prism and transmission optical fibers respectively connected to both ends of the multi-stage coupling prism. The transmission optical fiber at the upper end of each multi-stage coupling prism is connected to the LED light source emitter inside the pressure-resistant outer shell through an optoelectronic watertight connector. The end of the transmission optical fiber at the lower end of each multi-stage coupling prism is connected to a sensor assembly. Each sensor assembly is plugged into the combined socket at the top of the pressure-resistant outer shell through a double-headed cable assembly and is respectively connected to the photodiode and the multi-channel fiber Bragg grating demodulator.

[0011] The multi-stage coupled prism serves as the sensing section. Two gratings are inscribed on the transmission optical fiber of the fiber Bragg grating gas sensing device. One is used to measure temperature, and the other is used to measure pressure. The temperature sensor is used to correct the measurement value of the pressure sensor, thereby ensuring the accuracy of the pressure data. The fiber Bragg grating utilizes the reflection characteristics of light. As the temperature and pressure change, the spectral characteristics of the grating change. By comparing the wavelength shift of the reflected light of the grating, the changes in temperature and pressure can be accurately measured. The LED light source emitter is used to emit a light beam into the optical fiber system to excite the reflected light of the grating in the optical fiber. The light beam emitted by the LED light source emitter is transmitted through the transmission optical fiber to the multi-stage coupled prism serving as the measurement section; the photodiode is used to receive the optical signal reflected back by the multi-stage coupled prism. The photodiode can convert the received optical signal into an electrical signal, which is further analyzed by the signal processing system; the transmission optical fiber connects the LED light source emitter and the photodiode, transmitting the excitation light and the reflected light. The split design enables the optical signal to be distributed through different paths, allowing the light passing through the multi-stage coupled prism to be transmitted to the multi-channel fiber demodulator and the photodiode respectively. This ensures the transmission of the signal and the accuracy of the measurement; the multi-stage coupled prism is the key sensing section in the system, and its main function is to reflect the optical signal through the change in refractive index. When the multi-stage coupled prism is in the gas, due to the low refractive index of the gas, the light undergoes total internal reflection in the prism and returns to the photodiode. When the multi-stage coupled prism comes into contact with seawater, since the refractive index of seawater is different from that of the gas, the total internal reflection of light is disrupted, and part of the light passes through the prism and enters the seawater, resulting in a decrease in the intensity of the reflected light. By monitoring the change in the intensity of the returned light, the volume change of the gas can be deduced, and thus the leakage flux of the gas can be calculated; the function of the multi-channel fiber demodulator is to demodulate the change in the light wave. It can determine the temperature, pressure, and light intensity changes by measuring the wavelength shift of the light beam, and further deduce the volume and leakage flux of the gas.

[0012] The overall working process is as follows: When the device starts to work, the LED light source emitter emits laser light into the transmission optical fiber. The laser light propagates through the transmission optical fiber and reaches the multi-stage coupled prism. When the multi-stage coupled prism is in the gas, due to the low refractive index of the gas, the light undergoes total internal reflection in the prism and returns to the photodiode. The optical signal received by the photodiode is transmitted through the optical fiber to the multi-channel fiber demodulator. The demodulator obtains the data related to the gas volume and pressure by analyzing the change in light intensity and the wavelength shift.

[0013] When the multi-stage coupled prism comes into contact with seawater, due to the different refractive index of seawater, part of the light passes through the prism and enters the seawater, and the light intensity received by the photodiode weakens. According to the change in light intensity, the amount of gas released can be deduced. In addition, the temperature and pressure sensors in the system will simultaneously monitor the environmental conditions to ensure the accuracy of the measurement by correcting the temperature and pressure data.

[0014] In this way, the optical fiber measurement system can capture the volume change of the gas in real time and continuously, and calculate the gas leakage flux. The measurement data can be transmitted to the surface buoy through the underwater acoustic communication system, and further transmitted to the laboratory for real-time analysis.

[0015] Furthermore, it also includes a coupled communication buoy. The coupled communication buoy transmits data with the underwater acoustic communication system through wireless communication. The coupled communication buoy is connected to the surface buoy through a cable, and the surface buoy transmits data with the land laboratory through satellite communication.

[0016] By setting the coupled communication buoy to cooperate with the satellite communication of the surface buoy, the real-time data monitored by the monitoring device can be transmitted to the land laboratory.

[0017] Furthermore, a sensor interface for reading the data stored in the gas measurement device is provided on the sealing plate.

[0018] The sensor interface can be connected to the internal sensors to measure indicators such as the temperature, pressure, salinity, methane concentration, and carbon dioxide concentration of the seawater affected by the undersea gas release, and further judge the situation of gas release. Furthermore, it provides data support for the monitoring of undersea geological disasters.

[0019] Furthermore, a guardrail is installed on the sealing plate.

[0020] By setting the guardrail, on the one hand, it can play a protective role, and on the other hand, it can be used for the manipulator of the ROV robot to grab during deployment.

[0021] An observation method using an in-situ monitoring device for undersea gas leakage flux includes the following steps: S1. Deployment: The manipulator of the underwater robot ROV grabs the guardrail of the device and drives the device to descend. During deployment, the upper solenoid valve and the lower solenoid valve are opened. The ROV determines the accurate position of the undersea gas leakage through the underwater camera, and then covers the device above the leakage point. The manipulator detaches from the device to complete the undersea fixed-point deployment.

[0022] S2. Measurement: The lower solenoid valve is opened and the upper solenoid valve is closed. The gas and seawater enter the fixed cavity through the gas channel via the collection hood. When there is no gas in the fixed cavity, the light intensity received by the photodiode is the weakest. As the amount of captured gas gradually increases, the light intensity received by the photodiode gradually increases.

[0023] By calculating the gas volume change based on the change in light intensity, the temperature of the gas T and pressure P are measured. The gas volume change can be calculated according to the ideal gas equation: ; Where:V is the volume of the gas, n is the number of moles of the gas, R is the ideal gas constant, T is the temperature of the gas, P is the pressure of the gas.

[0024] According to the change in the volume of the gas, the flux formula is used to calculate the leakage flux of the gas: ; where: Q is the gas flux, Δ V is the change in gas volume per unit time, A is the area for gas flux measurement, Δ t is the time interval.

[0025] During the measurement process, the change in gas volume Δ V can be calculated through the real-time monitoring data of temperature and pressure. By accumulating multiple measurement cycles, the long-term change in gas flux Q can be obtained.

[0026] S3. Transmission: An underwater acoustic communication system is installed on the monitoring device and is combined with a coupled communication buoy. The controller sends the measurement data to the receiving end of the coupled communication buoy through the underwater acoustic communication system. The receiving end of the coupled communication buoy transmits the data upward along the cable to the surface buoy, and the buoy transmits the data to the land laboratory via satellite communication.

[0027] S4. Recovery: The upper solenoid valve and the lower solenoid valve are opened, and the acoustic releaser is controlled to separate the mounting frame and the counterweight seat. Through the buoyancy of the floating block on the mounting frame, the whole can be driven to float upward. The controller sends distance data in real time during the upward floating process until it floats to the sea surface to complete the recovery.

[0028] Furthermore, before the measurement in step S2, in-situ zero drift correction is performed: Open the upper solenoid valve to allow the gas in the fixed cavity to overflow, then close the lower solenoid valve to prevent the gas released from the seabed from entering the fixed cavity, and then close the upper solenoid valve to seal the fixed cavity to stabilize the internal temperature and pressure, and use this as a reference to correct the sensor measurement value.

[0029] Furthermore, after the in-situ zero drift correction, the output signals of the fiber Bragg grating gas sensing devices for measuring temperature and pressure are calibrated respectively.

[0030] Temperature calibration: The wavelength shift of the fiber Bragg grating is used to measure the temperature. The reflected wavelength λ of the fiber Bragg grating will shift with the change in temperature and can be expressed by a linear relationship: ; Wherein: Δλ is the change in the reflection wavelength of the fiber grating, α is the temperature sensitivity coefficient, which is a constant obtained through a calibration experiment, representing the wavelength change caused by a unit temperature change; Δ T is the temperature change.

[0031] Under known temperature conditions, record the reflection wavelength of the fiber grating gas sensing device; fit multiple sets of temperature and reflection wavelength data to obtain the relationship between temperature and wavelength change; use this relationship for online calculation of temperature to inversely deduce the real-time temperature.

[0032] Pressure calibration: Since the pressure change will affect the refractive index of the optical fiber, thus changing the reflection wavelength: ; Wherein: Δλ is the change in the reflection wavelength; β is the pressure sensitivity coefficient, which is a constant obtained through experimental calibration, Δ P is the pressure change.

[0033] Use known pressure conditions to calibrate the fiber grating gas sensing device, record the fiber grating reflection wavelengths under different pressures; fit the measured pressure and the reflection wavelength change to obtain the linear relationship between pressure and wavelength change, and use this relationship to calculate the pressure online.

[0034] Furthermore, if the temperature and pressure change simultaneously, the fiber grating gas sensing device will be affected by both temperature and pressure simultaneously. The effects of temperature and pressure can be calibrated separately and corrected by combining the two effects. The output wavelength change of the fiber grating gas sensing device can be expressed as a function of the combined action of temperature and pressure: ; Δ T and Δ P represent the changes in temperature and pressure respectively; α and β are the temperature and pressure sensitivity coefficients obtained through experiments; under known temperature and pressure conditions, conduct a combined calibration experiment, record the reflection wavelength under each set of conditions, and use multiple linear regression or other fitting methods to determine the contributions of temperature and pressure to the wavelength change. The obtained calibration coefficients α and β can be used to calculate the temperature and pressure in real time during actual measurement.

[0035] Advantages of the present invention: First, the present invention can conduct long-term real-time in-situ observation of the seabed gas leakage flux. Compared with existing technical equipment, it significantly improves the time resolution and data real-time performance of the seabed gas leakage flux, and plays an important role in the monitoring and early warning of seabed geological disasters.

[0036] II. The quasi-distributed measurement of the submarine gas leakage flux is realized based on the fiber Bragg grating gas sensing device. Compared with the traditional method, an accurate mathematical relationship is established between the output signal of the fiber Bragg grating sensor and the actual physical quantities (such as temperature and pressure), thereby making the measurement of the gas leakage flux more accurate and reliable. In the deep-sea environment, due to its excellent corrosion resistance, electromagnetic interference resistance, and stability, this sensor can perform long-term and accurate monitoring, significantly improving the measurement accuracy of the submarine gas leakage flux.

[0037] III. Based on the quasi-distributed fiber Bragg grating sensor array, it has the advantages of anti-electromagnetic and atomic radiation interference, thin diameter, soft texture, light weight mechanical properties, insulation, non-inductive electrical properties, water resistance, high temperature resistance, corrosion resistance chemical properties, etc. For the in-situ long-term monitoring of high pressure and high corrosion in the deep-sea seabed, the advantages are very prominent.

[0038] IV. By the method of regularly connecting to the external seawater, the in-situ zero drift correction of the sensor is realized, enhancing the stability of the sensor for long-term in-situ measurement, improving the quality of the observed data, and indirectly improving the measurement accuracy of the sensor.

[0039] V. The quasi-distributed fiber Bragg grating sensor array is arranged inside the observation device, less affected by the external environment, and has high stability.

[0040] VI. The structure is simple, with fewer moving parts, high overall stability, high reliability, and can balance the reliability of the structure and the use efficiency of the sensor. The device is recovered by self-floating after being thrown, and the bottom counterweight can be discarded, so it can achieve rapid recovery without relying on underwater robots and only requires ROV assistance to be deployed to the release point during deployment. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 It is a schematic diagram of the overall structure of the present invention.

[0042] Figure 2 is Figure 1 a side view of

[0043] Figure 3 It is a schematic diagram of the internal vertical section of the mounting rack in the present invention.

[0044] Figure 4 It is a schematic diagram of the vertical section of the fixed cavity in the present invention.

[0045] Figure 5 It is a top view of the present invention.

[0046] Figure 6 It is a top perspective view of the present invention.

[0047] Figure 7 It is a bottom view of the present invention.

[0048] Figure 8 Schematic diagram of the internal structure in the fixed cavity of the present invention.

[0049] Figure 9 Schematic diagram of the structure of the gas measurement device in the present invention.

[0050] Figure 10 Schematic diagram of the measurement principle in the present invention.

[0051] Figure 11 Schematic diagram when the gas measurement device in the present invention is measuring.

[0052] Figure 12 Schematic diagram of in-situ correction of zero drift in the present invention.

[0053] Figure 13 Schematic diagram of the deployment and data transmission structure of the present invention on the seabed.

[0054] As shown in the figure: 1. Fixed cavity, 2. Floating block, 3. Counterweight seat, 4. Gas release port, 5. Guardrail, 6. Sensor interface, 7. Pressure-resistant chamber, 8. Battery chamber, 9. Gas inlet, 10. Mounting frame, 11. Free-state gas methane sensor, 12. Accommodation cavity, 13. Collection hood, 14. Lower electromagnetic valve, 15. Upper electromagnetic valve, 16. Fiber Bragg grating gas sensing device, 17. LED light source emitter, 18. Transmission optical fiber, 19. Multistage coupling prism, 20. Multichannel fiber optic demodulator, 21. Photodiode, 22. Sealing plate, 23. High-density lithium battery pack, 24. Buoy, 25. Satellite, 26. Onshore laboratory, 27. Coupling communication buoy, 28. Underwater robot ROV, 29. Pressure-resistant housing, 30. Combination socket, 31. Sensor end assembly, 32. Double-headed cable assembly, 33. Photoelectric watertight connection component. Specific implementation manners

[0055] To clearly illustrate the technical features of this solution, the following elaborates on this solution through specific implementation manners.

[0056] Embodiment 1: As Figures 1-9 shown, a deep-sea seabed gas leakage flux in-situ monitoring device includes a fixed cavity 1, a mounting frame 10 connected to a floating block 2 on the circumferential surface, and a counterweight seat 3 provided with a gas channel. In this embodiment, the fixed cavity 1 is a cylindrical cavity.

[0057] The upper end of the fixed chamber 1 is provided with a gas release port 4 and the lower end is provided with a gas inlet 9 facing the gas passage. A free-state gas methane sensor 11 is also installed in the fixed chamber 1 for detecting free-state methane gas. A horn-shaped collection cover 13 is connected to the bottom of the fixed chamber 1 at the gas inlet 9. Solenoid valves are respectively installed at the gas release port 4 and the inlet 9, that is, an upper solenoid valve 15 is installed at the gas release port 4 and a lower solenoid valve 14 is installed at the gas inlet 9. A gas measuring device for measuring the flux is arranged in the fixed chamber 1.

[0058] The top of the mounting frame 10 is fixedly connected to the upper part of the fixed chamber 1 through a sealing plate 22. A guardrail 5 is installed on the sealing plate 22, and a sensor interface 6 for reading the internal data of the gas measuring device is arranged on the sealing plate 22. The bottom of the mounting frame 10 is detachably connected to the counterweight base 3 through an acoustic release device. An accommodation chamber 12 is formed between the sealing plate 22 and the counterweight base 3 in the mounting frame 10 by a floating block 2. A pressure-resistant chamber 7 and a battery chamber 8 are connected in the accommodation chamber 12 of the mounting frame 10. A controller is arranged in the pressure-resistant chamber 7, and a high-density lithium battery pack is arranged in the battery chamber 8. The controller is electrically connected to the two solenoid valves and the acoustic release device through cables respectively. A underwater acoustic communication system electrically connected to the controller and capable of transmitting data to the outside is also installed in the accommodation chamber 12 of the mounting frame 10.

[0059] The gas measuring device includes a pressure-resistant outer shell 29 made of 316L stainless steel. An LED light source emitter 17, a photodiode 21 and a multi-channel fiber Bragg grating demodulator 20 are respectively arranged inside the pressure-resistant outer shell 29, and a high-density lithium battery pack 23 for supplying power to the three respectively. The photodiode 21 and the multi-channel fiber Bragg grating demodulator 20 are respectively connected to a combined socket 30 at the top of the pressure-resistant outer shell 29 through transmission optical fibers 18; it also includes a plurality of fiber Bragg grating gas sensing devices 16 located at the bottom of the pressure-resistant outer shell 29. Each fiber Bragg grating gas sensing device 16 includes a multi-stage coupling prism 19 and transmission optical fibers 18 respectively connected to both ends of the multi-stage coupling prism 19. The transmission optical fiber 18 at the upper end of each multi-stage coupling prism 19 is connected to the LED light source emitter 17 inside the pressure-resistant outer shell 29 through an optoelectronic watertight connector 33. The end of the transmission optical fiber 18 at the lower end of each multi-stage coupling prism 19 is connected to a sensor assembly 31. Each sensor assembly 31 is plugged into the combined socket 30 at the top of the pressure-resistant outer shell 29 through a double-headed cable assembly 32 and is respectively connected to the photodiode 21 and the multi-channel fiber Bragg grating demodulator 20.

[0060] In this embodiment, as Figure 9As shown in the figure, the gas measurement device includes six fiber Bragg grating gas sensing devices 16. Two gratings for measuring temperature and pressure respectively are engraved on each transmission optical fiber. The multi-stage coupling prism 19 serves as the sensing section. The multi-channel fiber optic demodulator 20 can demodulate the wavelength change of light and further calculate the synchronous temperature and pressure changes. The photodiode 21 can sense the light intensity change and further calculate the synchronous volume change of the calculated gas. If only the photodiode 21 is used to sense the light intensity change to infer the gas volume change, there will be errors because the influence of temperature and pressure on the gas volume is not considered at this time, and only relying on the laboratory calibration function to infer, the error is relatively large. The laboratory calibration function comes from the empirical linear fitting values at room temperature and pressure obtained by measuring different gas positions multiple times. Therefore, through the multi-channel fiber optic demodulator 20, the wavelength change of light can be demodulated, and the synchronous temperature and pressure changes can be further calculated. Using the temperature and pressure data to correct the calculation result of the gas volume can significantly improve the measurement accuracy.

[0061] Since the spatial resolution of the entire measurement system depends on the number of stages of the multi-stage coupling prism 19, and the number of stages of the multi-stage coupling prism 19 can reach the millimeter level, compared with the existing technical means, the measurement accuracy and resolution of this application are greatly improved. The measurement results of the sensors of the six fiber Bragg grating gas sensing devices 16 can be mutually verified, or the average value can be taken to reduce data errors and improve data quality.

[0062] As Figure 12 shown in the figure, it also includes a coupled communication buoy 27. The coupled communication buoy 27 transmits data with the underwater acoustic communication system through wireless communication. The coupled communication buoy 27 is connected to the surface buoy through a cable, and the surface buoy 24 transmits data with the land laboratory 26 through satellite 25 communication.

[0063] Embodiment 2: An observation method using an in-situ monitoring device for deep-sea submarine gas leakage flux includes the following steps: S1. Deployment: The manipulator of the underwater robot ROV28 grabs the guardrail 5 of the device and drives the device to descend. When deploying, the upper solenoid valve 15 and the lower solenoid valve 14 are opened. The ROV28 determines the accurate position of the submarine gas leakage through the underwater camera, and then covers the device above the leakage point. The manipulator detaches from the device to complete the submarine fixed-point deployment.

[0064] S2. Measurement: The lower solenoid valve 14 is opened, and the upper solenoid valve 15 is closed. The gas and seawater enter the fixed cavity 1 through the gas channel via the collection hood. When there is no gas in the fixed cavity 1, the light intensity received by the photodiode 21 is the weakest. As the amount of captured gas gradually increases, the light intensity received by the photodiode 21 gradually increases.

[0065] AsFigure 11 As shown, before measurement, in-situ zero drift correction is carried out: open the upper electromagnetic valve 15 to allow the gas in the fixed chamber 1 to overflow, then close the lower electromagnetic valve 14 to prevent the gas released from the seabed from entering the fixed chamber 1, and then close the upper electromagnetic valve 15 to seal the fixed chamber 1 so that the internal temperature and pressure are stable, and use this as a reference to correct the sensor measurement value.

[0066] After in-situ zero drift correction, the output signals of the fiber Bragg grating gas sensing devices for measuring temperature and pressure are calibrated respectively.

[0067] Temperature calibration: The wavelength shift of the fiber Bragg grating is used to measure temperature. The reflected wavelength λ of the fiber Bragg grating will shift with the change of temperature, and it can be expressed by a linear relationship: ; where: Δλ is the change in the reflected wavelength of the fiber Bragg grating, α is the temperature sensitivity coefficient, which is a constant obtained through calibration experiments and represents the wavelength change caused by a unit temperature change; Δ T is the temperature change.

[0068] Under known temperature conditions, record the reflected wavelength of the fiber Bragg grating gas sensing device; fit multiple groups of temperature and reflected wavelength data to obtain the relationship between temperature and wavelength change; use this relationship for online calculation of temperature to reverse infer the real-time temperature.

[0069] Pressure calibration: Since pressure change will affect the refractive index of the optical fiber, thus changing the reflected wavelength: ; where: Δλ is the change in the reflected wavelength; β is the pressure sensitivity coefficient, which is a constant obtained through experimental calibration, Δ P is the pressure change.

[0070] Use known pressure conditions to calibrate the fiber Bragg grating gas sensing device, record the reflected wavelengths of the fiber Bragg grating under different pressures; fit the measured pressure and the change in the reflected wavelength to obtain the linear relationship between pressure and wavelength change, and use this relationship for online calculation of pressure.

[0071] If the temperature and pressure change simultaneously, the fiber Bragg grating gas sensing device will be affected by both temperature and pressure. The effects of temperature and pressure can be calibrated separately and corrected by combining the two effects. The change in the output wavelength of the fiber Bragg grating gas sensing device can be expressed as a function of the combined action of temperature and pressure: ; Δ T and Δ Prespectively represent the changes in temperature and pressure; α and β are the temperature and pressure sensitivity coefficients obtained through experiments; under known temperature and pressure conditions, a joint calibration experiment is carried out, the reflected wavelength under each group of conditions is recorded, and multiple linear regression or other fitting methods are used to determine the contributions of temperature and pressure to the wavelength change, and the calibration coefficients α and β can be used to calculate the temperature and pressure in real time during actual measurement.

[0072] By calculating the change in gas volume from the change in light intensity, the temperature T and pressure P of the gas are measured, and the change in gas volume can be calculated according to the ideal gas equation: ; where: V is the volume of the gas, n is the number of moles of the gas, R is the ideal gas constant, T is the temperature of the gas, P is the pressure of the gas.

[0073] According to the change in gas volume, the leakage flux of the gas is calculated using the flux formula: ; where: Q is the gas flux, Δ V is the change in gas volume per unit time, A is the area for gas flux measurement, Δ t is the time interval.

[0074] During the measurement process, the change in gas volume Δ V can be calculated from the real-time monitoring data of temperature and pressure. By accumulating over multiple measurement cycles, the long-term change in gas flux Q can be obtained.

[0075] S3. Transmission: An underwater acoustic communication system is installed on the monitoring device and is combined with the coupled communication buoy 27. The controller sends the measurement data to the receiving end of the coupled communication buoy 27 through the underwater acoustic communication system. The receiving end of the coupled communication buoy 27 transmits the data upward along the cable to the surface buoy 24, and the buoy 24 transmits the data to the land laboratory 26 through satellite 25 communication.

[0076] S4. Recovery: The upper solenoid valve 15 and the lower solenoid valve 14 are opened, and the acoustic release is controlled to separate the mounting frame 10 and the counterweight seat 3. Through the buoyancy of the floating block 2 on the mounting frame 10, the whole can be driven to float upward. The controller sends distance data in real time during the upward floating process until it floats to the sea surface to complete the recovery.

[0077] To more clearly illustrate the working process of the gas measurement device, the following is a calculation case based on fiber Bragg grating temperature and pressure sensors. The volume change of the gas is measured by optical fiber, and the gas flux is calculated using the calibration formula.

[0078] Sensor data: Fiber Bragg grating gas sensing device: Measured wavelength change Δλ T = 0.25 nm, Fiber Bragg grating pressure sensor: Measured wavelength change Δλ P = 1.50 nm, Temperature change Δ T = 5°C; Pressure change Δ P = 1000 Pa.

[0079] Calibration coefficient: Temperature sensitivity coefficient: α = 0.05 nm / °C; Pressure sensitivity coefficient: β = 0.002 nm / Pa.

[0080] Measurement area of gas leakage: A = 0.1 m 2 (assuming the sensing section area of the sensor is 0.1 m 2 ), Observation time interval: Δ t= 1 s.

[0081] Conversion of temperature and pressure. According to the calibration formula of the fiber Bragg grating, the changes in temperature and pressure are calculated first.

[0082] Temperature change: Δλ т = α·Δ T ; 0.25 nm = 0.05 nm / °C·Δ T ; Δ T = 0.25 nm / 0.05 nm / °C = 5°C.

[0083] This result shows that a temperature change of 5°C is consistent with the measured wavelength change of 0.25 nm.

[0084] Pressure change: Δλ P = β ·Δ P ; 1.50 nm = 0.002 nm / Pa·Δ P ; Δ P = 1.50 nm / 0.002 nm / Pa = 750 Pa.

[0085] This result indicates that a pressure change of 750 Pa is consistent with a measured wavelength change of 1.50 nm.

[0086] Calculate the change in gas volume: According to the ideal gas equation (assuming the gas is an ideal gas), we can calculate the change in gas volume. The change in gas volume is related to the temperature and pressure changes: ; For simplicity, assume the number of moles of the gas n remains constant, and use experimentally calibrated data to estimate the volume change. For the estimation of the volume change, we adopt the empirical relationship between the wavelength change and the volume change: ; where, k is a constant obtained through calibration, and Δλ is the change in the fiber reflection wavelength. The constant k = 0.1 m 3 / nm, then: ΔV T = 0.1 m 3 / nm·0.25 nm = 0.025 m 3 ; ΔV P = 0.1 m 3 / nm·1.50 nm = 0.15 m 3 .

[0087] Calculate the gas flux: The gas flux Q is calculated by the formula: ; where: Δ V is the change in gas volume per unit time, A is the area for gas flux measurement, Δ t is the time interval; in this embodiment, A = 0.1 m 2 , and the time interval is 1 s, then: Q T = 0.025 m 3 / 0.1 m 2 ·1 s = 0.25 m 3 / s; Q P = 0.15 m 3 / 0.1 m 2 ·1 s = 1.5 m 3 / s.

[0088] Finally, by synthesizing the effects of temperature and pressure changes on the gas volume, the total gas flux can be obtained: Q total = Q T +Q p =0.25 m 3 / s + 1.5 m 3 / s = 1.75 m 3 / s.

[0089] The workflow is summarized as follows: 1. Data acquisition: The temperature and pressure sensors monitor the gas volume change in real time through fiber Bragg gratings.

[0090] The change in the reflection wavelength is correlated with the temperature and pressure changes of the gas through the photodiode and LED light source transmitter system.

[0091] 2. Data calibration: Use the calibration coefficients α and β to convert the measured wavelength change into the actual temperature and pressure changes.

[0092] 3. Volume calculation: Estimate the gas volume change Δ V .

[0093] Use the empirical constant k to correlate the wavelength change with the gas volume change.

[0094] 4. Gas flux calculation: Based on the measured volume change and time interval, calculate the gas flux Q .

[0095] Synthesize the contributions of different influencing factors (such as temperature and pressure changes) to the volume change.

[0096] Through the above calculations, the working process of the gas measurement device is demonstrated. In practical applications, this process can be used to continuously monitor the gas leakage flux on the deep - sea floor and provide support for the monitoring of submarine geological disasters through real - time data transmission.

[0097] Certainly, the above description is not limited to the above examples. The technical features not described in the present invention can be realized by or adopted from the prior art, and will not be elaborated here. The above embodiments and the accompanying drawings are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. The present invention has been described in detail with reference to the preferred embodiments. Those of ordinary skill in the art should understand that any changes, modifications, additions or substitutions made by those of ordinary skill in the technical field within the scope of the essence of the present invention do not depart from the purpose of the present invention and should also fall within the scope of protection of the claims of the present invention.

Claims

1. A deep seabed gas leakage flux in-situ monitoring device, characterized by: It includes a fixed cavity, a mounting frame with a floating block connected to the circumference, and a counterweight seat with a gas channel. A gas release port is arranged at the upper end of the fixed cavity, and a gas inlet port opposite to the gas channel is arranged at the lower end. Electromagnetic valves are installed at the gas release port and the inlet port respectively. A gas measuring device for measuring gas leakage flux is arranged in the fixed cavity. The top of the mounting frame is fixedly connected to the upper part of the fixed cavity through a sealing plate, and the bottom of the mounting frame is detachably connected to the counterweight seat through an acoustic releaser. A accommodating cavity is formed between the sealing plate and the counterweight seat through the floating block in the mounting frame. The mounting frame is connected to a pressure-resistant chamber and a battery chamber in the accommodating cavity. A controller is arranged in the pressure-resistant chamber, and a high-density lithium battery pack is arranged in the battery chamber. The controller is electrically connected to two electromagnetic valves and the acoustic releaser through cables respectively. An underwater acoustic communication system that is electrically connected to the controller and can transmit data to the outside is also installed in the accommodating cavity of the mounting frame.

2. The deep seabed gas leakage flux in-situ monitoring device according to claim 1 is characterized by: The bottom of the fixed cavity is connected with a trumpet-shaped collecting cover at the gas inlet.

3. The deep seabed gas leakage flux in-situ monitoring device according to claim 1 is characterized by: The gas measuring device comprises a pressure-resistant shell, inside which are arranged an LED light source transmitter, a photodiode and a multi-channel fiber Bragg grating demodulator, and a high-density lithium battery pack for powering the three respectively, the photodiode and the multi-channel fiber Bragg grating demodulator are respectively connected to the combination socket on the top of the pressure-resistant shell through optical fibers; the gas measuring device also comprises a plurality of fiber Bragg grating gas sensing devices located at the bottom of the pressure-resistant shell, each fiber Bragg grating gas sensing device comprises a multi-stage coupling prism and transmission optical fibers respectively connected to the two ends of the multi-stage coupling prism, the transmission optical fiber at the upper end of each multi-stage coupling prism is connected to the LED light source transmitter in the pressure-resistant shell through an optoelectronic water-tight connector, the end of the transmission optical fiber at the lower end of each multi-stage coupling prism is connected to a sensor assembly, and each sensor assembly is plugged into the combination socket on the top of the pressure-resistant shell through a double-headed cable assembly and is respectively connected to the photodiode and the multi-channel fiber Bragg grating demodulator.

4. The deep seabed gas leakage flux in-situ monitoring device according to claim 1 is characterized by: It also includes a coupled communication buoy, which transmits data with a hydroacoustic communication system via wireless communication. The coupled communication buoy is connected to a surface buoy via a cable, and the surface buoy transmits data with a land laboratory via satellite communication.

5. The deep seabed gas leakage flux in-situ monitoring device according to claim 1 is characterized by: The sealing plate is provided with a sensor interface which can read the data stored in the gas measuring device.

6. The deep seabed gas leakage flux in-situ monitoring device according to claim 1 is characterized by: A guardrail is installed on the sealing plate.

7. A measurement method using the deep seabed gas leakage flux in-situ monitoring device according to claim 1, characterized in that: The following steps are involved: S1. Deployment: The manipulator of the underwater robot ROV grabs the guardrail of the monitoring device and drives the monitoring device down. When deploying, the upper solenoid valve and the lower solenoid valve are opened. The ROV determines the exact location of the seabed gas leakage through the underwater camera, and then covers the monitoring device above the leakage point. The manipulator detaches from the device to complete the seabed fixed-point deployment; S2. Measurement: The lower solenoid valve is opened and the upper solenoid valve is closed. The gas and seawater enter the fixed cavity through the gas channel and the collection cover. When there is no gas in the fixed cavity, the light intensity received by the photodiode is the weakest. As the amount of captured gas gradually increases, the light intensity received by the photodiode gradually increases. The change in gas volume is calculated by the change in light intensity, and the temperature of the gas is measured T and pressure P , the change in gas volume can be calculated using the ideal gas equation: ； in: V is the volume of the gas, n is the number of moles of gas, R is the ideal gas constant, T is the temperature of the gas, P is the pressure of the gas; According to the change in gas volume, the gas leakage flux is calculated using the flux formula: ; in: Q is the gas flux, Δ V is the change in gas volume per unit time, A is the area over which the gas flux is measured, Δ t is the time interval; During the measurement, the gas volume changes Δ V The calculation can be performed based on the real-time monitoring data of temperature and pressure. By accumulating multiple measurement cycles, the gas flux can be obtained. Q Long-term changes in S3, transmission: the monitoring device is equipped with a hydroacoustic communication system, and in conjunction with a coupled communication buoy, the controller sends the measurement data to the receiving end of the coupled communication buoy through the hydroacoustic communication system, and the receiving end of the coupled communication buoy transmits the data upward along the cable to the surface buoy, and the buoy transmits the data to the land laboratory through satellite communication; S4. Recovery: The upper solenoid valve and the lower solenoid valve are opened to control the acoustic releaser to separate the mounting frame from the counterweight seat at the bottom. The buoyancy of the floating block on the mounting frame can drive the entire vessel to float upward. The controller sends distance data in real time during the floating process until it floats to the sea surface to complete the recovery.

8. The measurement method using the deep seabed gas leakage flux in-situ monitoring device according to claim 7 is characterized in that: Before measuring in step S2, an in-situ zero drift correction is performed: the upper solenoid valve is opened to allow the gas in the fixed cavity to overflow, and then the lower solenoid valve is closed to prevent the gas released from the seabed from entering the fixed cavity. The upper solenoid valve is then closed to seal the fixed cavity to stabilize the internal temperature and pressure, which is used as a reference to calibrate the gas measurement device.

9. The measurement method using the deep seabed gas leakage flux in-situ monitoring device according to claim 8 is characterized in that: After zero drift correction in situ, the output signals of the fiber Bragg grating gas sensing device used to measure temperature and pressure are calibrated respectively; Temperature calibration: The temperature is measured by using the wavelength shift of the fiber Bragg grating. The reflection wavelength λ of the fiber Bragg grating will shift with the change of temperature, which can be expressed by a linear relationship: ； Where: Δλ is the change in the reflected wavelength of the fiber Bragg grating, α is the temperature sensitivity coefficient, which is a constant obtained through calibration experiments and represents the wavelength change caused by a unit temperature change; Δ T is the temperature change; Under known temperature conditions, the reflected wavelength of the fiber Bragg grating gas sensing device is recorded; multiple sets of temperature and reflected wavelength data are fitted to obtain the relationship between temperature and wavelength changes; the relationship is used to calculate the temperature online and infer the real-time temperature; Pressure calibration: Since pressure changes affect the refractive index of the optical fiber, the reflected wavelength will change: ； Where: Δλ is the change in reflection wavelength; β is the pressure sensitivity coefficient, which is a constant obtained through experimental calibration, Δ P It is the pressure change; The fiber Bragg grating gas sensing device was calibrated using known pressure conditions, and the fiber Bragg grating reflection wavelength under different pressures was recorded. The measured pressure and reflection wavelength changes were fitted to obtain the linear relationship between pressure and wavelength changes, and the pressure was calculated online using this relationship.

10. The measurement method using the deep seabed gas leakage flux in-situ monitoring device according to claim 9 is characterized in that: If the temperature and pressure change at the same time, the fiber Bragg grating gas sensing device will be affected by both temperature and pressure. The effects of temperature and pressure can be calibrated separately and corrected by combining the effects of both. The output wavelength change of the fiber Bragg grating gas sensing device can be expressed as a function of the combined effects of temperature and pressure: ； Δ T and Δ P Represent the changes of temperature and pressure respectively; α and β It is the temperature and pressure sensitivity coefficient obtained through experiments; under known temperature and pressure conditions, a joint calibration experiment is carried out, the reflection wavelength under each set of conditions is recorded, and multiple linear regression or other fitting methods are used to determine the contribution of temperature and pressure to the wavelength change, and the calibration coefficient is obtained α and β It can be used to calculate temperature and pressure in real time during actual measurement.

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