Optical fiber monitoring method and device for pipeline flow evolution in hydrate exploitation process

Abstract

The invention belongs to the technical field of hydrate exploitation engineering experiments, and discloses an optical fiber monitoring method and device for pipeline flow evolution in the hydrate exploitation process, and the device comprises a simulation pipeline, a gas-liquid supply and separation module, a data acquisition module and a PC; the simulation pipeline is a closed-loop pipeline and comprises a fluid inlet section, a middle section, an ascending section and a backflow section; the data acquisition module comprises an optical fiber sensor assembly, a pressure detection assembly, a gas flow detection assembly, a liquid flow detection assembly and a camera assembly, and multiple data acquisition modes are adopted to realize dynamic real-time monitoring of flow velocity, flow and flow distance of different fluids in the pipeline and omnibearing monitoring of gas and liquid flowing through the pipeline; therefore, the purpose of simultaneously and effectively monitoring multiple parameters for a long time in a complex gas-liquid flowing environment is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of hydrate mining engineering experiments, and in particular relates to an optical fiber monitoring method and device for pipeline flow evolution during hydrate mining. Background Art

[0002] Natural gas hydrates are ice-like solid compounds formed by natural gas (mainly methane) and water under high pressure and low temperature conditions. Hydrate deposits are widely distributed in terrestrial permafrost environments and deepwater formations such as oceans and lakes. As an alternative new energy source, natural gas hydrates have high energy density, large reserves, huge resource potential, and broad development prospects. my country has abundant marine hydrate resources, and the efficient development of marine hydrate resources plays an important role in ensuring national energy security and achieving carbon neutrality goals. In 2020, my country successfully implemented the second round of hydrate pilot production, with an average daily gas production of more than 2.87×104m3, which effectively promoted the industrialization of marine hydrates, but also encountered many theoretical and technical bottlenecks.

[0003] How to detect wellbore flow risks and ensure wellbore flow safety throughout the entire cycle is the key to achieving efficient development of hydrates. In an objective environment that is abnormal to conventional marine oil and gas production, how to accurately understand the complex hydrate phase change and gas-liquid multiphase flow process in the wellbore after gas and liquid production in the marine hydrate reservoir is the key to developing core technologies such as full-cycle wellbore flow risk monitoring and wellbore flow risk response. However, the wellbore and reservoir are a thermal-fluid coupled system. Hydrate decomposition and gas-liquid production in the reservoir will affect the gas-liquid flow state and temperature-pressure distribution in the wellbore, and the gas-liquid flow state in the wellbore is related to the temperature and pressure changes in the wellbore, which in turn affects the thermal flow evolution, hydrate decomposition, and gas-liquid migration and production in the reservoir. Changes in the flow state of multiphase fluids in the wellbore bring many potential hazards to hydrate production trials. For example, the transition process from slug flow to annular mist flow during lifting will seriously affect the gas lift efficiency, and changes in fluid flow state will directly affect the working efficiency of the pump, etc. Therefore, real-time monitoring of the fluid flow state in the wellbore is of great significance to ensure efficient hydrate production and safe production.

[0004] Conventional flow state monitoring methods (including high-speed photography, ray attenuation, capacitance tomography, acoustic wave measurement, etc.) can only achieve single-point or multi-point monitoring, with high monitoring costs, poor real-time performance, and low accuracy, and cannot meet the needs of full-well section and full-life cycle monitoring. In addition to not having the above-mentioned shortcomings, the fiber optic sensing technology that has emerged in recent years can further enhance its durability and adaptability as well as the diversity of monitoring objects by encapsulating optical fibers, so as to achieve the purpose of long-term and effective monitoring of multiple parameters simultaneously in a complex gas-liquid flow environment, and realize real-time, continuous, and permanent monitoring along the wellbore.

[0005] In order to realize real-time monitoring of the fluid flow status in the wellbore and ensure the efficient exploitation and safe production of hydrates, a series of simulation experiments are carried out to verify and improve key technologies and methods such as full-cycle detection of wellbore flow risks and ensuring wellbore flow safety. This will undoubtedly provide a large amount of detailed and reliable data for the rapid improvement of hydrate exploitation and accelerate the industrialization process. Summary of the invention

[0006] In view of the deficiencies in the prior art, the present invention provides an optical fiber monitoring method and device for pipeline flow evolution during hydrate extraction, which can realize dynamic real-time monitoring of flow rates and flow distances of different fluids in the pipeline, as well as all-round monitoring of the gas and liquid flowing through the pipeline, including flow state monitoring at the fluid inlet, middle section, and ascending section, so as to achieve the purpose of simultaneously and effectively monitoring multiple parameters for a long time in a complex gas-liquid flow environment.

[0007] Fiber Bragg Grating (FBG) is a fiber optic sensing technology that can sense the strain, temperature and other parameters of external objects. Its principle is to use the photosensitivity of the fiber material to form a periodic change of the refractive index in the fiber, so that the propagation behavior of light changes. It is extremely sensitive to changes in the surrounding strain and temperature, which will cause the central wavelength λ of the Bragg reflected light to change. B changes.

[0008] Working principle of the present invention:

[0009] During the hydrate mining process, the fluid transported in the mining wellbore includes water and gas decomposed from hydrates. When the flow of water and gas in the pipeline changes, the central wavelength of the fiber optic sensor (FGB) in the pipeline changes. This change is received by the fiber optic Bragg grating demodulator, and the data is analyzed and processed by a computer to convert the wavelength signal into the flow of water and gas. Multiple visible self-assembled optical fiber tubes are arranged at different positions in the pipeline, several of which are horizontal and one is vertical, simulating the state of horizontal wells and vertical wells. At the same time, a high-speed camera can be used to see the flow state of gas and liquid fluids in the pipeline in real time without obstacles, and the FGB sensor in the visible self-assembled optical fiber tube can be used to detect the flow changes of water and gas at different positions in the pipeline in real time.

[0010] On the one hand, the present invention provides a method for optical fiber monitoring of pipeline flow evolution during hydrate production, comprising the following steps:

[0011] S1. Laying simulated pipeline: The pipeline is set as a closed-loop pipeline, including a fluid inlet section, a middle section, an ascending section and a reflux section. Four visible self-assembled optical fiber tubes are laid in the pipeline, three of which are horizontally set to simulate the state of a horizontal well and are located in the fluid inlet section and the middle section, and one is vertically set to simulate the state of a vertical well and is located in the ascending section;

[0012] S2. Arrangement and testing of FBG sensors: Calibrate the central wavelength of the FBG sensor; set an FBG sensor perpendicular to the pipeline direction in each visible integrated optical fiber tube, set the strain sensing sensitivity coefficient corresponding to the FBG sensor, start the optical fiber data test, and monitor the optical fiber Bragg grating wavelength data;

[0013] The calibration method of the central wavelength of the FBG sensor is as follows: When the relationship between the change of the fiber Bragg grating wavelength and the change of temperature and strain is:

[0014] Δλ B =(α+ξ)λ B ΔT+(1-ρ e ) B Δε=K T ΔT+K ε Δε

[0015] Where: When axial uniform strain and temperature act on the fiber Bragg grating simultaneously, there is no interaction between temperature and strain parameters, and the linear thermal expansion coefficient α, thermo-optic coefficient ξ and effective elastic coefficient ρ e is a constant; where Δλ B is the wavelength displacement, ΔT is the temperature change, Δε is the strain change, K T is the temperature sensitivity coefficient of the sensor, K ε is the strain sensitivity coefficient of the sensor;

[0016] S3, continuously injecting water at a predetermined flow rate into the pipeline;

[0017] S4, after the water flow rate is stable, methane gas at a pressure of 1 MPa is continuously injected into the pipeline, and the water and methane gas are fully mixed through the gas-liquid mixer;

[0018] S5. Turn on the pressure transmitter and the gas and liquid flow meters to monitor the changes in the pressure and fluid flow in the pipeline;

[0019] S6, turning on the high-speed camera to observe the fluid state in the visible assembled optical fiber tube in real time, and monitoring the fluid flow video image;

[0020] S7, changing the flow of water and gas, repeating steps S3-S6, wherein the pressure transmitter and gas and liquid flow meter arranged on the pipeline display the real-time flow of water and gas at different positions, when the flow of water and gas in the pipeline changes, the central wavelength of the FBG sensor changes, and this change is received by the fiber grating demodulator, and the fiber grating demodulator outputs the received signal to the PC, and the PC analyzes and processes the data to convert the wavelength signal into the flow of water and gas;

[0021] S8. The wavelength signal pairs of the FBG sensor obtained by the test are used for different flow modes, and the visual images and FBG test data are combined and analyzed by a PC to obtain the wavelength response characteristics of the fiber Bragg grating at different positions, different flow states and different gas-liquid flow rates;

[0022] The data obtained from the above test steps include FBG sensor test data during the flow of water and gas in the pipeline, monitoring data from pressure transmitters and gas and liquid flow meters, and fluid flow video data recorded by high-speed cameras.

[0023] Further, the PC integrated analysis in step S8 includes: the PC analyzes and processes data to convert the wavelength signal into the flow rate of water and gas, and the PC analyzes and processes data to convert the visual image into the flow state of water and gas;

[0024] Among them, the PC analyzes and processes the data to convert the wavelength signal into the flow rate of water and gas as follows:

[0025] When the pipeline fluid flows at different flow rates, the inertial force and shear force of the fluid impact the sensor, causing vibration and strain. When the flow rate and flow rate are known, the strain data of the FBG sensor (3) is recorded and a mathematical model between the flow rate and strain is established. The flow rate of the fluid is related to the flow rate and the cross-sectional area of ​​the pipeline, so the real-time gas and water flow rates are calculated.

[0026] The PC analyzes and processes the data to convert the visual images into the flow state of water and gas. Specifically, the high-speed camera obtains video images under different gas-liquid ratios and flow rates. The bubble generation and merging in the pipeline, the gas-liquid interface fluctuations, and the gas and liquid distribution are obtained through analysis of the video images. The corresponding flow pattern evolution is analyzed, and the flow patterns include bubbly flow, bubbly flow, laminar flow, etc.

[0027] Furthermore, the mathematical model between flow velocity and strain is:

[0028] ε=α 1 V liquid +α 2 V gas ,

[0029] Where, ε is the strain value obtained by FBG test;

[0030] V liquid and V gas are the flow rates of the liquid and gas phases, respectively;

[0031] α 1 and α 2 It is an empirical constant that reflects the relationship between flow rate and strain and is obtained by fitting experimental test data.

[0032] Furthermore, one FBG sensor has one measuring point, and each FBG sensor needs to have its strain sensitivity coefficient calibrated individually.

[0033] Furthermore, the FBG sensor test data is the sensor strain change caused by the change of gas-liquid fluid flow rate.

[0034] On the other hand, the present invention also proposes an optical fiber monitoring device for pipeline flow evolution during hydrate extraction, comprising a simulated pipeline, a gas-liquid supply and separation module, a data acquisition module, and a PC; the simulated pipeline is connected to the gas-liquid supply and separation module, the gas-liquid supply and separation module is used to transport gas and liquid into the simulated pipeline, and to separate the mixed gas and liquid, the data acquisition module is installed on the simulated pipeline, and the data acquisition module is electrically connected to the PC;

[0035] The simulation pipeline is configured as a closed-loop pipeline, including a fluid inlet section, a middle section, a rising section, and a reflux section;

[0036] The data acquisition module includes an optical fiber sensor component, a pressure detection component, a gas flow detection component, a liquid flow detection component, and a camera component;

[0037] The optical fiber sensor assembly includes an FBG sensor, a visible assembled optical fiber tube and a grating optical fiber demodulator. The FBG sensor is inserted into the visible assembled optical fiber tube through a reserved hole in a PC visual tube in a direction perpendicular to the pipeline; the grating optical fiber demodulator is connected to the FBG sensor and the PC respectively.

[0038] Furthermore, the simulated pipeline is mainly assembled and connected by a steel pipe and a PC visual tube. The steel pipe is connected to the visual self-assembled optical fiber tube through a flange, and the inner diameters of the steel pipe and the visual self-assembled optical fiber tube are consistent. The flange connection end is sealed by an O-ring.

[0039] Furthermore, there are four visible self-assembled optical fiber tubes, three of which are horizontally arranged to simulate the horizontal well state and are located in the fluid inlet section and the middle section, and one is vertically arranged to simulate the vertical shaft state and is located in the ascending section; an FBG sensor is arranged in each visible self-assembled optical fiber tube in a direction perpendicular to the pipeline.

[0040] Furthermore, the camera assembly includes a high-speed camera and a camera bracket, which can be disassembled and transferred to monitor the gas-liquid flow state in the visually assembled optical fiber tube at different positions of the pipeline.

[0041] Furthermore, the gas-liquid supply and separation module includes a high-pressure pipeline pump, a methane cylinder, a gas-liquid mixer, and a gas-liquid separation tank. The fluid inlet section injects water into the simulated pipeline through the high-pressure pipeline pump, injects methane gas into the pipeline through the methane cylinder, mixes water and methane gas through the gas-liquid mixer, and separates the gas and liquid in the pipeline through the gas-liquid separation tank at the tail of the reflux section, so that the water is injected into the high-pressure pipeline pump again.

[0042] Compared with the prior art, the advantages of the present invention are as follows:

[0043] 1. The fiber optic monitoring method and device for pipeline flow evolution during hydrate extraction of the present invention uses a fiber Bragg grating (FBG) sensor to monitor the fluid state and flow rate in real time, which can achieve high-precision and fast-response measurements; the application of this monitoring method and experimental device enables effective monitoring of gas-liquid flow states under high pressure and low temperature environments. This method can effectively monitor for a long time in a complex gas-liquid flow environment, has strong adaptability, and can perform real-time dynamic monitoring of various flow states, such as changes in laminar flow and turbulent flow. The device not only monitors the flow changes of gas and liquid, but also records various parameters such as pressure and flow rate in real time, and combines with high-speed cameras for visual monitoring to provide comprehensive data support.

[0044] 2. Compared with the prior art, the present invention not only monitors the dynamic changes of gas-liquid flow based on FBG sensors, but also combines multiple monitoring methods, deploys fluid flow meters and pressure rheometers, and simultaneously obtains fluid flow video image data, and jointly interprets the evolution characteristics of gas-liquid flow, thereby improving the accuracy of the data.

[0045] The optical fiber deforms differently when the flow rate of the fluid to be measured is different, which results in different output optical signals to detect the flow rate of the fluid. The detection accuracy and sensitivity are extremely high. At the same time, the integrated optical fiber tube that can be set horizontally or vertically simulates the wellbore flow monitoring in horizontal wells or vertical wells.

[0046] 3. The device proposed in the present invention for measuring the evolution of gas-liquid flow in the wellbore during hydrate extraction based on fiber Bragg grating (FGB) technology not only monitors the flow changes of gas and liquid, but also can record various parameters such as pressure and flow rate in real time, and combines with high-speed cameras for visual monitoring, providing comprehensive data support, realizing rapid, accurate and long-term testing of in-situ conditions, and has the advantages of small size and high precision.

[0047] 4. The distributed optical fiber sensor layout proposed in the present invention can monitor the gas-liquid flow status at different locations at the same time. This distributed layout improves the comprehensiveness and accuracy of monitoring, can better evaluate the dynamic changes of the fluid in the pipeline, and realize the precise measurement of the gas-liquid flow in the wellbore during the hydrate extraction process, thereby correctly evaluating the gas-liquid flow status and flow in the wellbore.

[0048] 5. The device proposed in the present invention realizes the full mixing and separation of gas and water in the hydrate mining process, detects the gas-liquid flow state in the pipeline in situ, and has a simple structure and convenient operation.

[0049] In summary, the present invention monitors the evolution characteristics of gas-liquid flow in the pipeline during hydrate extraction based on fiber Bragg grating (FGB) technology, effectively solving the need for real-time monitoring of fluid flow in the wellbore, and real-time acquisition of flow velocity, flow rate and flow state at multiple points in the pipeline, thereby realizing dynamic monitoring of the entire pipeline. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 It is a schematic structural diagram of an optical fiber monitoring device for gas-liquid flow evolution characteristics in a pipeline during hydrate production according to an embodiment of the present invention;

[0051] Figure 2 FIG. 4 is a schematic diagram of a FBG sensor according to an embodiment of the present invention.

[0052] Among them, 1. Steel pipe; 2. Visually assembled optical fiber tube; 3. FBG sensor; 4. Pressure transmitter; 5. Gas-liquid homogenizer; 6. Needle valve; 7. Gas-liquid separation tank; 8. Gas flow meter; 9. Ball valve; 10. Fluid flow meter; 11. Gas injection pipeline; 12. High-pressure pipeline pump; 13. Gas-liquid mixer; 14. Computer; 15. Optical fiber demodulator; 16. Methane cylinder; 17. High-speed camera. DETAILED DESCRIPTION

[0053] To facilitate those skilled in the art to understand the present invention, specific implementations of the present invention are described below with reference to the accompanying drawings.

[0054] like Figures 1-2 As shown, the present invention discloses an optical fiber monitoring device for pipeline flow evolution in a hydrate mining process, comprising a simulated pipeline, a gas-liquid supply and separation module, a data acquisition module, and a PC. The simulated pipeline is connected to the gas-liquid supply and separation module, the gas-liquid supply and separation module is used to transport gas and liquid into the simulated pipeline, and to separate the mixed gas and liquid, the data acquisition module is installed on the simulated pipeline, and the data acquisition module is electrically connected to the PC.

[0055] The simulated pipeline is set as a closed-loop pipeline, including the fluid inlet section, middle section, rising section and reflux section. Figure 1 As shown, the fluid inlet section and the middle section are arranged horizontally, the ascending section is arranged vertically, and the reflux section is located between the ascending section and the fluid inlet section. The simulated pipeline is mainly assembled and connected by a steel pipe 1 and a PC sight tube. The steel pipe 1 is made of stainless steel.

[0056] The data acquisition module includes an optical fiber sensor component, a pressure detection component, a gas flow detection component, a liquid flow detection component, and a camera component.

[0057] Specifically, the optical fiber sensor assembly includes an FBG sensor 3, a visual self-assembled optical fiber tube 2, and a grating optical fiber demodulator 15. The FBG sensor 3 is inserted into the visual self-assembled optical fiber tube 2 through a reserved hole of a PC visual tube in a direction perpendicular to the pipeline. The grating optical fiber demodulator 15 is connected to the FBG sensor 3 and the PC, respectively.

[0058] The steel pipe 1 is connected to the visible self-assembled optical fiber tube 2 through a flange, and the inner diameters of the steel pipe 1 and the visible self-assembled optical fiber tube 2 are consistent, and the flange connection end is sealed by an O-ring.

[0059] In this embodiment, there are four visible self-contained optical fiber tubes 2, three of which are horizontally arranged to simulate the horizontal well state and are located in the fluid inlet section and the middle section, and one is vertically arranged to simulate the vertical shaft state and is located in the ascending section; each visible self-contained optical fiber tube 2 is arranged with an FBG sensor 3 perpendicular to the pipeline direction.

[0060] The camera assembly includes a high-speed camera 17 and a camera bracket, which are used to monitor the gas-liquid flow state in the visually assembled optical fiber tube 2 at different positions of the pipeline.

[0061] The gas-liquid supply and separation module includes a high-pressure pipeline pump 12, a methane cylinder 16, a gas-liquid mixer 13, and a gas-liquid separation tank 7. The fluid inlet section injects water into the simulated pipeline through the high-pressure pipeline pump 12, injects methane gas into the pipeline through the methane cylinder 16, and mixes water and methane gas through the gas-liquid mixer 13. At the tail of the reflux section, the gas and liquid in the pipeline are separated by the gas-liquid separation tank 7, and the water is injected into the high-pressure pipeline pump 12 again.

[0062] like Figure 1 As shown, a needle valve 6 and a ball valve 9 are also installed on the steel pipe 1; a hole is reserved on the steel pipe 1 to connect the pressure transmitter 4, the fluid flow meter 10 and the gas-liquid homogenizer 5; and a hole is reserved on the visible integrated optical fiber tube 2 to insert the optical fiber sensor.

[0063] refer to Figure 2 , FBG sensor 3, all sensors have different lengths and there is only one measuring point on each sensor.

[0064] According to the above device, the experimental operation is as follows: turn on the high-pressure pipeline pump 12 to inject water at a predetermined flow rate into the pipeline; turn on the methane cylinder 16 to inject methane gas into the pipeline, and fully mix the water and methane gas through the gas-liquid mixer 13; turn on the high-speed camera 17 to monitor the flow state of the gas-liquid fluid in the visible assembled optical fiber tube 2 in real time; turn on the PC to collect data from the FBG sensor 3, the pressure transmitter 4, the gas flow meter 8 and the fluid flow meter 10 in real time.

[0065] The present invention also proposes a method for optical fiber monitoring of pipeline flow evolution during hydrate production, comprising the following steps:

[0066] Step 1. Laying a simulated pipeline: The pipeline is set as a closed-loop pipeline, including a fluid inlet section, a middle section, a rising section and a reflux section. Four visible self-assembled optical fiber tubes 2 are laid in the pipeline, three of which are horizontally set to simulate the horizontal well state and are located in the fluid inlet section and the middle section, and one is vertically set to simulate the vertical shaft state and is located in the rising section.

[0067] Step 2, arrangement and testing of FBG sensor 3: calibration of the central wavelength of FBG sensor 3; setting an FBG sensor 3 perpendicular to the pipeline direction in each visible self-assembled optical fiber tube 2, setting the strain sensing sensitivity coefficient corresponding to FBG sensor 3, starting optical fiber data testing, and monitoring the optical fiber Bragg grating wavelength data.

[0068] Step 3: Continuously inject water at a predetermined flow rate into the pipeline.

[0069] Step 4: After the water flow rate becomes stable, methane gas at a pressure of 1 MPa is continuously injected into the pipeline, and the water and methane gas are fully mixed through the gas-liquid mixer 13 .

[0070] Step 5: The pressure transmitter and gas and liquid flow meters installed on the pipeline display the real-time flow of water and gas at different locations. Turn on the pressure transmitter and gas and liquid flow meters to monitor the changes in pressure and fluid flow in the pipeline.

[0071] Step 6: Turn on the high-speed camera 17 to observe the fluid state in the visible assembled optical fiber tube 2 in real time and monitor the fluid flow video image.

[0072] Step 7, change the flow rate of water and gas, repeat steps S3 to S6, when the flow rate of water and gas in the pipeline changes, the central wavelength of the FBG sensor 3 changes, this change is received by the fiber grating demodulator, and the fiber grating demodulator outputs the received signal to the PC.

[0073] Step 8: The wavelength signal of the FBG sensor obtained by the test corresponds to different flow modes. The video image, FBG test data, and gas and liquid flow meter data are integrated and analyzed by a PC to obtain the wavelength response characteristics of the fiber Bragg grating under different flow states and different gas and liquid flow rates.

[0074] The data obtained in the above steps include the test data of the FBG sensor 3 during the flow of water and gas in the pipeline, the monitoring data of the pressure transmitter and the gas and liquid flow meters, and the fluid flow video data recorded by the high-speed camera 17.

[0075] Among them, PC integrated analysis includes: PC analysis and processing data to convert wavelength signals into water and gas flow rates, PC analysis and processing data to convert video images into flow states of water and gas.

[0076] Specifically, the PC analyzes and processes the data to convert the wavelength signal into the flow rate of water and gas as follows:

[0077] When the pipeline fluid flows at different flow rates, the inertial force and shear force of the fluid impact the sensor, causing vibration and strain. When the flow rate and flow rate are known, the strain data of FBG sensor 3 is recorded and a mathematical model between flow rate and strain is established:

[0078] ε=α 1 V liquid +α 2 V gas ,

[0079] Where ε is the strain value obtained by FBG test; V liquid and V gas are the flow rates of the liquid phase and the gas phase respectively; α 1 and α 2 It is an empirical constant, reflecting the relationship between flow velocity and strain, obtained by fitting experimental test data;

[0080] The flow rate of the fluid is related to the flow velocity and the cross-sectional area of ​​the pipe, so the real-time gas and water flow rates can be calculated.

[0081] Specifically, the PC analyzes and processes data to convert video images into the flow state of water and gas: the high-speed camera obtains images under different gas-liquid ratios and different flow rates. By analyzing the images, the bubble generation and merging in the pipeline, the gas-liquid interface fluctuations and the gas and liquid distribution are obtained. The corresponding flow pattern evolution is analyzed, and the flow patterns include bubbly flow, bubbly flow, laminar flow, etc.

[0082] One FBG sensor 3 has one measuring point, and each FBG sensor 3 needs to be calibrated individually for the strain sensitivity coefficient.

[0083] The test data of FBG sensor 3 is the sensor strain change caused by the change of gas-liquid fluid flow rate.

[0084] Through the monitoring method described above in this embodiment, the present invention can achieve real-time monitoring of the gas-liquid flow evolution characteristics in the pipeline during hydrate production and obtain the flow changes of gas and liquid in the pipeline; the experimental operation is simple and the test can be repeated.

[0085] The above-described embodiments of the present invention do not constitute a limitation on the protection scope of the present invention. Any modification, equivalent substitution and improvement made within the spirit and principle of the present invention shall be included in the protection scope of the claims of the present invention.

Claims

1. A fiber optic monitoring method for pipeline flow evolution during hydrate production, characterized in that: The following steps are involved: S1. Laying a simulated pipeline: The pipeline is set as a closed-loop pipeline, including a fluid inlet section, a middle section, an ascending section and a reflux section. Four visible self-contained optical fiber tubes (2) are laid in the pipeline, three of which are horizontally arranged to simulate a horizontal well state and are located in the fluid inlet section and the middle section, and one is vertically arranged to simulate a vertical well state and is located in the ascending section; S2. Arrangement and testing of FBG sensors (3): calibration of the central wavelength of the FBG sensors (3); setting an FBG sensor (3) perpendicular to the pipeline direction in each visible integrated optical fiber tube (2), setting the strain sensing sensitivity coefficient corresponding to the FBG sensor (3), starting optical fiber data testing, and monitoring the optical fiber Bragg grating wavelength data; S3, continuously injecting water at a predetermined flow rate into the pipeline; S4, after the water flow rate stabilizes, methane gas at a pressure of 1 MPa is continuously injected into the pipeline, and the water and methane gas are fully mixed through the gas-liquid mixer (13); S5. Turn on the pressure transmitter and the gas and liquid flow meters to monitor the changes in the pressure and fluid flow in the pipeline; S6, turning on the high-speed camera (17) to observe the state of the fluid in the visible assembled optical fiber tube (2) in real time, and monitoring the video image of the fluid flow; S7, changing the flow rate of water and gas, repeating steps S3 to S6, wherein when the flow rate of water and gas in the pipeline changes, the central wavelength of the FBG sensor (3) changes, and this change is received by the fiber grating demodulator, and the fiber grating demodulator outputs the received signal to the PC; S8. The wavelength signal of the FBG sensor obtained by the test corresponds to different flow modes. The video image, FBG test data and gas and liquid flow meter data are integrated and analyzed by a PC to obtain the wavelength response characteristics of the fiber Bragg grating under different flow states and different gas and liquid flow rates; The data obtained in the above steps include the test data of the FBG sensor (3) during the flow of water and gas in the pipeline, the monitoring data of the pressure transmitter and the gas and liquid flow meters, and the fluid flow video data recorded by the high-speed camera (17).

2. The optical fiber monitoring method according to claim 1, characterized in that: The PC integrated analysis in step S8 includes: the PC analyzes and processes data to convert the wavelength signal into the flow rate of water and gas, and the PC analyzes and processes data to convert the video image into the flow state of water and gas; Among them, the PC analyzes and processes the data to convert the wavelength signal into the flow rate of water and gas as follows: When the pipeline fluid flows at different flow rates, the inertial force and shear force of the fluid impact the sensor, causing vibration and strain. When the flow rate and flow rate are known, the strain data of the FBG sensor (3) is recorded and a mathematical model between the flow rate and strain is established. The flow rate of the fluid is related to the flow rate and the cross-sectional area of ​​the pipeline, so the real-time gas and water flow rates are calculated. The PC analyzes and processes the data to convert the video images into the flow state of water and gas. Specifically, the high-speed camera obtains images with different gas-liquid ratios and flow rates. The bubble generation and merging in the pipeline, the gas-liquid interface fluctuations, and the gas and liquid distribution are obtained through image analysis. The corresponding flow pattern evolution is analyzed, and the flow patterns include bubbly flow, bubbly flow, and laminar flow.

3. The optical fiber monitoring method according to claim 2, characterized in that: The mathematical model between flow velocity and strain is: ε=α1V liquid +α2V gas , Where, ε is the strain value obtained by FBG test; V liquid and V gas are the flow rates of the liquid and gas phases, respectively; α1 and α2 are empirical constants that reflect the relationship between flow rate and strain and are obtained by fitting experimental test data.

4. The optical fiber monitoring method according to claim 1, characterized in that: One FBG sensor (3) has one measuring point, and each FBG sensor (3) needs to have its strain sensitivity coefficient calibrated individually.

5. The optical fiber monitoring method according to claim 1, characterized in that: The test data of the FBG sensor (3) is the sensor strain change caused by the change of gas-liquid fluid flow rate.

6. An optical fiber monitoring device for gas-liquid flow evolution characteristics in a pipeline during hydrate extraction, based on the optical fiber monitoring method according to any one of claims 1 to 5, characterized in that: It comprises a simulation pipeline, a gas-liquid supply and separation module, a data acquisition module, and a PC; the simulation pipeline is connected to the gas-liquid supply and separation module, the gas-liquid supply and separation module is used to transport gas and liquid into the simulation pipeline and separate the mixed gas and liquid, the data acquisition module is installed on the simulation pipeline, and the data acquisition module is electrically connected to the PC; The simulation pipeline is configured as a closed-loop pipeline, including a fluid inlet section, a middle section, a rising section, and a reflux section; The data acquisition module includes an optical fiber sensor component, a pressure detection component, a gas flow detection component, a liquid flow detection component, and a camera component; The optical fiber sensor assembly comprises an FBG sensor (3), a visual self-assembled optical fiber tube (2) and a grating optical fiber demodulator (15); the FBG sensor (3) is inserted into the visual self-assembled optical fiber tube (2) in a direction perpendicular to the pipeline through a reserved hole of a PC visual tube; the grating optical fiber demodulator (15) is respectively connected to the FBG sensor (3) and a PC.

7. The optical fiber monitoring device according to claim 6, characterized in that: The simulated pipeline is mainly assembled and connected by a steel pipe (1) and a PC visual tube. The steel pipe (1) and the visual self-assembled optical fiber tube (2) are connected by a flange, and the inner diameters of the steel pipe (1) and the visual self-assembled optical fiber tube (2) are consistent. The flange connection end is sealed by an O-ring.

8. The optical fiber monitoring device according to claim 6, characterized in that: There are four visible self-contained optical fiber tubes (2), three of which are horizontally arranged to simulate the state of a horizontal well and are located at the fluid inlet section and the middle section, and one is vertically arranged to simulate the state of a vertical well and is located at the ascending section; each visible self-contained optical fiber tube (2) is provided with an FBG sensor (3) in a direction perpendicular to the pipeline.

9. The optical fiber monitoring device according to claim 6, characterized in that: The camera assembly comprises a high-speed camera (17) and a camera bracket, and is used to monitor the gas-liquid flow state in the visually assembled optical fiber tube (2) at different positions of the pipeline.

10. The optical fiber monitoring device according to claim 6, characterized in that: The gas-liquid supply and separation module comprises a high-pressure pipeline pump (12), a methane cylinder (16), a gas-liquid mixer (13), and a gas-liquid separation tank (7). The fluid inlet section injects water into the simulated pipeline through the high-pressure pipeline pump (12), injects methane gas into the pipeline through the methane cylinder (16), mixes water and methane gas through the gas-liquid mixer (13), separates gas and liquid in the pipeline through the gas-liquid separation tank (7) at the tail of the reflux section, and injects water into the high-pressure pipeline pump (12) again.

Images