A method for measuring water holding rate based on spiral annular microwave resonance sensor

Abstract

The application provides a spiral annular microwave resonance sensor and a water holdup rate measuring method based on the spiral annular microwave resonance sensor, and the method is as follows: coaxial feed lines of the spiral annular microwave resonance sensor are connected with an excitation port and a receiving port of a vector network analyzer respectively, an observation window is arranged on an inclined measuring pipe section, a high-speed camera for obtaining a flow pattern of the flowing oil-water two-phase flow is arranged at the observation window, and the spiral annular microwave resonance sensor is arranged downstream of the high-speed camera; a mixed dielectric constant model changing with the water holdup rate under different flow patterns is established, which is used for predicting the water holdup rate under the corresponding flow pattern according to the obtained mixed dielectric constant; the mixed dielectric constant is obtained based on the relationship between the resonance frequency and the mixed dielectric constant; and the water holdup rate is predicted according to the mixed dielectric constant model corresponding to the current flow pattern recognized by the high-speed camera and changing with the water holdup rate. The application can realize the water holdup rate measurement of the oil-water two-phase flow under a complex flow pattern.

Description

Technical Field

[0001] This invention relates to a method for measuring the water holding capacity of liquid-liquid two-phase flow using microwave sensors in the industrial field. Background Technology

[0002] Multiphase flow is widely present in complex industrial processes, particularly in oil extraction and transportation, where oil-water two-phase flow is common in oil wells. Accurate measurement of the water holdup in this two-phase flow is crucial for optimizing dynamic production characteristics and improving oil recovery. However, influenced by gravity, interfacial forces, and tilt angles, the local velocity and concentration of the oil-water two-phase flow undergo complex changes, resulting in complex flow structures such as rolling countercurrents, pseudo-slugs, and random flows, posing a challenge to measuring the water holdup in directional oil wells.

[0003] The measurement of water holdup in oil-water two-phase flow is significantly affected by the flow pattern. To date, many researchers at home and abroad have used observation, high-speed photography, and various sensor measurement techniques to study the flow patterns of vertically rising oil-water two-phase flow (inclination angle of 0°). The flow patterns in vertical pipes are mainly divided into: (1) water-in-oil fine bubble flow; (2) water-in-oil bubble flow; (3) water-in-oil slug flow; (4) transition flow; and (5) oil-in-water flow. Researchers' studies on inclined rising oil-water two-phase flow at large angles are based on the vertical foundation. Currently, the well-known oil-water two-phase flow in inclined rising pipes is mainly divided into 7 flow patterns, namely, water-in-oil dispersion flow with local countercurrent in the water layer (DO / W CT), water-in-oil dispersion flow with pseudo-slug flow in the water layer (DO / W PS), water-in-oil dispersion flow with unidirectional flow in the water layer (DO / W CC), and uniformly dispersed oil droplet flow (VFD O / W). The study covers water-in-oil (DW / O) and water-droplet uniformly dispersed (DW / O) flows, as well as transitional flows (CT) where oil is a continuous phase and water is intermittently distributed in both oil-in-water and water-in-oil phases. Accurate water holdup measurement in inclined oil-water two-phase flows relies on precise analysis of local flow characteristics. The interphase structure of inclined oil-water two-phase flows is complex and variable, with differences in flow structures across different flow patterns. For complex flow structures such as pseudo-slug flows and localized countercurrents, the requirements for designing water holdup measurement sensors are even more stringent. Therefore, optimizing the design of water holdup measurement sensors that are independent of flow pattern characteristics is crucial.

[0004] Based on the significant differences in physical properties such as conductivity, dielectric constant, and refractive index between oil and water fluids, various methods for measuring water holdup have been developed, including conductivity methods, capacitance methods, microwave methods, and optical methods. For electrical methods, traditional capacitance and conductivity sensors often measure water holdup based on the Maxell equation. While this equation offers high accuracy for homogeneous multiphase flows, it exhibits significant errors for complex, inclined oil-water two-phase flows. Furthermore, the aforementioned two types of sensors are limited by their operating principles and cannot measure water holdup in both water-in-oil and oil-in-water states. Microwaves, with their short wavelength, high frequency, and strong thermal effect, have found wide application in fields such as petroleum and coal mining, biomedicine, chemical materials, and soil and water resources. Microwave methods detect the water content in oil-water mixtures based on the difference in relative dielectric constants between oil and water, improving measurement accuracy compared to traditional low-frequency sensors. Microwave sensors primarily employ transmission and resonance methods. Transmission-based microwave sensors often rely on the phase shift in the transmission coefficient, which is directly related to the effective dielectric constant of the oil-water mixture, to achieve measurement. However, due to high losses, this type of sensor has low accuracy under high water content conditions. Due to its high sensitivity, microwave resonant sensors are increasingly used for full-range water content measurement. Currently, most microwave resonator-based sensors are non-planar, including various structures such as cavities, cylindrical fins, and transmission lines. However, these cavity-based sensors all have some drawbacks: complex cavity resonant antennas, interference from cylindrical fins on the measured fluid, and complex bypass design of transmission lines. Furthermore, current research on microwave resonant sensors for measuring oil-water flow mainly targets relatively uniformly distributed, velocity-independent bubbly, annular, and laminar flows. Reports on low-velocity, unevenly distributed dispersed phases and the influence of salinity are extremely rare. Therefore, to improve measurement accuracy, adapt to changes in oil-water flow patterns, optimize the design of microwave sensors, reduce the spatial sensitivity inhomogeneity of the sensor detection field, and ensure ideal stability and repeatability of the sensor response are crucial for high-resolution water content measurement. Summary of the Invention

[0005] This invention proposes a spiral-type ring microwave resonant sensor and a method for measuring water holdup based on this sensor. By measuring the resonant frequency change of the spiral-type ring microwave resonant sensor, the water holdup of oil-water two-phase flow under complex flow patterns can be measured. To achieve the above objective, the technical solution adopted by this invention is as follows: A spiral ring microwave resonant sensor includes a metal ring, a spiral emitting electrode, a spiral receiving electrode, a metal shielding shell, and a coaxial feed line. The metal ring is tightly fitted to the outer wall of a measuring pipe. The spiral emitting electrode and the spiral receiving electrode are located on the same circumferential surface outside the metal ring, and the circumferential surface is coaxial with the metal ring and has a coupling gap. The spiral emitting electrode and the spiral receiving electrode are respectively connected to the terminals of the coaxial feed line. The coaxial feed line connected to the spiral emitting electrode serves as the input terminal of the microwave excitation signal, and the coaxial feed line connected to the spiral receiving electrode serves as the output terminal of the microwave response signal. The shielding layer is placed on the outer periphery of the spiral emitting electrode and the spiral receiving electrode.

[0006] Furthermore, the geometric dimensions of the helical ring microwave resonant sensor were optimized using finite element analysis software. The optimal geometric parameters of the helical ring microwave resonant sensor were determined by calculating the sensitivity of the resonant frequency output of the helical ring microwave resonant sensor to the change of the mixed dielectric constant under different pitches and coupling gaps.

[0007] Furthermore, the geometric parameters of the spiral ring microwave resonant sensor are as follows: the pitch of the spiral emitting electrode and the spiral receiving electrode. L= 94 mm, helix angle 360°, length of metal ring L =94 mm, the coupling distance between the metal ring and the spiral emitting and receiving electrodes. d =0.5 mm.

[0008] Furthermore, the inner and outer radii of the measuring pipe on which the helical ring microwave resonant sensor is installed are respectively r =10mm, R =15 mm; other geometric parameters are as follows: the angle between the spiral emitting electrode and the spiral receiving electrode is 120°, and the thickness is 0.2 mm; the length and thickness of the metal ring are equal to the pitch and thickness of the spiral emitting electrode and the spiral receiving electrode.

[0009] Furthermore, the coupling gap is filled with a transparent silicone insulating material; the shielding layer is isolated from the spiral emitting electrode and the spiral receiving electrode by the transparent silicone insulating material.

[0010] Furthermore, the measuring pipe is a glass pipe.

[0011] This invention also provides a water-holding capacity measurement method based on the aforementioned spiral ring microwave resonant sensor, used for measuring the water-holding capacity of oil-water two-phase flow. The spiral ring microwave resonant sensor is connected to a vector network analyzer for both its microwave excitation signal input and microwave response signal output. The measurement method is as follows: An observation window is made on the measuring pipe, and a high-speed camera is installed at the observation window to acquire the flow pattern of the oil-water two-phase flow. A spiral ring microwave resonant sensor is installed downstream of the observation window. A vector network analyzer is used to obtain the microwave resonant frequency fluctuation signal after the oil-water two-phase flow passes through the spiral ring microwave resonant sensor, thereby obtaining the transmission parameter S. 21 The amplitude-frequency characteristic curves are obtained, and the resonant frequencies in each curve are extracted. Different water holding capacities correspond to different resonant frequency shifts. A mixed dielectric constant model for different flow patterns as a function of water holding capacity was established, which was used to predict the water holding capacity under the corresponding flow patterns based on the obtained mixed dielectric constant. The mixed dielectric constant is obtained based on the relationship between the resonant frequency and the mixed dielectric constant. Based on the mixed dielectric constant model corresponding to the current flow pattern identified by the high-speed camera, the water holding capacity is predicted.

[0012] Furthermore, the measuring pipe is installed on an inclined pipeline for measuring the water holdup of the oil-water two-phase flow in the inclined pipeline.

[0013] Furthermore, the measurement methods specifically include: S1. Fix the prepared spiral ring microwave resonant sensor to the measuring pipe, connect it to the vector network analyzer through a coaxial line, and connect the vector network analyzer to the host computer for online data acquisition. S2. A dynamic experimental system for oil-water two-phase flow was constructed. A vector network analyzer was used to collect the amplitude-frequency response curves of a spiral ring microwave resonant sensor under different operating conditions in real time. The collected data was recorded by a host computer, and the resonant frequency output under each operating condition was obtained through data processing. The mixed dielectric constant was calculated based on the relationship between the resonant frequency and the mixed dielectric constant. (1) In the formula, c At the speed of light, It is a mixed dielectric constant. Permeability, The resonant wavelength, f It is the resonant frequency.

[0014] S3. Using the oil-water two-phase flow dynamic experimental system built in step S2, experiments were conducted under different flow patterns and operating conditions. A mixed dielectric constant model varying with water holdup under different flow patterns was established. This model was used to predict the water holdup under the corresponding flow pattern based on the obtained mixed dielectric constant. Specifically, the established mixed dielectric constant models varying with water holdup under different flow patterns are as follows: (2) In the formula, Y w This is the predicted water holding capacity.A and B The coefficients are related to different flow patterns. ε w The dielectric constant of water is ε o Let be the permittivity of the oil phase, and let... k = AY w + B , k By using experimental data from fast-closing valves to determine the parameters to be measured under different flow patterns, a mixed dielectric constant model that varies with water holding capacity can be obtained for different flow patterns.

[0015] S4. During the oil-water two-phase flow measurement process, the oil-water two-phase flow image of the measurement pipeline acquired by the high-speed camera is sent to the host computer. The host computer obtains the output of the resonant frequency under the current operating condition based on the data acquired by the vector network analyzer, and calculates the mixed dielectric constant based on the relationship between the resonant frequency and the mixed dielectric constant. The current flow pattern is identified based on the image acquired by the high-speed camera. The water holding capacity is predicted using the mixed dielectric constant model that varies with the water holding capacity under the current flow pattern.

[0016] The present invention has the following advantages due to the adoption of the above technical solutions: (1) Based on the principle of microwave resonance, this invention measures the water holding capacity of inclined oil-water two-phase flow under complex flow patterns. In the dynamic experiment, within the excitation frequency range of 1 GHz to 1.3 GHz, the resonant frequency of the spiral ring microwave resonant sensor has a good response to the change in water holding capacity in the pipe, reflecting the high sensitivity of the spiral ring microwave resonant sensor.

[0017] (2) The spiral structure designed in this invention can effectively reduce the limitations of measurement in different directions and achieve stable measurement of water holding capacity. The coupling design of the spiral emitting electrode and the spiral receiving electrode with the metal ring can effectively improve the capture efficiency of the resonant frequency. The overall sensor structure design makes the electric field distribution excited in the pipeline more uniform, which not only improves the measurement accuracy, but also plays a role in suppressing the flow pattern to a certain extent, thereby realizing the detection of water holding capacity when the flow structure of the inclined oil-water two-phase flow changes in time and space.

[0018] (3) A hybrid dielectric constant model was constructed using the shunt method to solve for the water holding capacity and compared with the data from the fast-closing valve. The results show that the designed spiral-shaped microwave resonant sensor for water holding capacity can measure the water holding capacity at various tilt angles, and the hybrid dielectric constant model established by the shunt method has good water holding capacity prediction accuracy. Attached Figure Description

[0019] Figure 1 This is a three-dimensional schematic diagram of a spiral ring microwave resonant sensor.

[0020] Figure 2 This is a schematic diagram of the cross-section of a spiral ring microwave resonant sensor.

[0021] Figure 3 It is a simulation model for optimizing the size of a spiral ring microwave resonant sensor.

[0022] Figure 4 The sensitive field distribution of the spiral ring microwave resonant sensor is: (a) three-dimensional field distribution; (a) two-dimensional field distribution.

[0023] Figure 5 These are the response curves of a spiral ring microwave resonant sensor as the dielectric constant of the mixed fluid changes: (a) Response of the spiral ring microwave resonant sensor under different dielectric constants; (b) Relationship between resonant frequency and mixed dielectric constant.

[0024] Figure 6 It is a curve showing the resonant frequency of a spiral ring microwave resonant sensor as a function of water holding capacity under DO / W CC flow pattern; Figure 7 It is a curve showing the resonant frequency of a spiral ring microwave resonant sensor as a function of water holding capacity under VFD O / W flow pattern; Figure 8 This is a curve showing the resonant frequency of a spiral ring microwave resonant sensor as a function of water holding capacity under a DO / W CT flow pattern. Figure 9 It is a curve showing the change of resonant frequency of a spiral ring microwave resonant sensor with water holding capacity under DO / W PS flow pattern; Figure 10 It is a curve showing the resonant frequency of a spiral ring microwave resonant sensor under TF flow pattern as a function of water holding capacity; Figure 11 It is a dynamic experimental device for oil-water two-phase flow tilted at 45 degrees.

[0025] Figure 12 These are high-speed camera images of flow patterns in dynamic experiments: (a) DO / W CC; (b) VFD O / W; (c) DO / WCT; (d) DO / W PS; (e) TF; (f) DW / O.

[0026] Figure 13 The resonant frequency of an oil-water two-phase flow tilted at 45 degrees. f r With moisture content K w and flow rate U m The relationship.

[0027] Figure 14 It is a graph showing the resonant frequency response under the experimental conditions of inclined oil-water two-phase flow.

[0028] Figure 15 The result is the predicted water holdup of the oil-water two-phase flow at a 45-degree inclination.

[0029] Appendix Figure 1 Label Explanation: 1. Microwave sensor spiral emitting electrode plate; 2. Microwave sensor spiral receiving electrode plate; 3. Metal ring; 4. Coaxial feeder terminal; 5. Shielding layer; 6. Acrylic glass measuring tube; L Pitch; L 1. Length of shielding layer.

[0030] Appendix Figure 2 Label Explanation: α , the angle between the plates; R Pipe outer radius; r Pipe inner radius; d The coupling distance between the metal ring and the spiral receiving electrode of the microwave sensor; d 1. The distance between the shielding layer and the spiral receiving electrode of the microwave sensor. Detailed Implementation

[0031] This invention aims to design a microwave spiral ring resonant sensor for measuring the water holdup in oil-water two-phase flow. By detecting the resonant frequency of the microwaves, the water holdup information under dynamic experimental conditions can be obtained. The specific implementation process is described below with reference to the accompanying drawings: (1) The structure diagram of the spiral ring microwave resonant sensor is as follows: Figure 1 and Figure 2 As shown, this spiral ring microwave resonant sensor consists of a spiral emitting electrode 1, a spiral receiving electrode 2, a metal ring 3, a coaxial feed line 4, a metal shielding shell 5, and an acrylic glass tube 6. Electrode 1 is used for microwave signal excitation, and electrode 2 is used for microwave signal reception. The metal ring is tightly fitted to the outer wall of the glass tube along a direction parallel to the tube wall. The spiral emitting electrode and the spiral receiving electrode are separated from the metal ring by insulating material, with a certain coupling gap. d This structure is commonly found in planar microring structures. There is a certain coupling gap between the electrode and the ring. When microwaves are injected into the helical transmitting electrode via a coaxial line, they are coupled into the ring through the coupling gap, and then coupled out of the ring again into the helical receiving electrode. This process conforms to coupling theory, and the microwave transmission between the two ports exhibits two-port network characteristics. The existence of this coupling structure has a "filtering" effect, making S... 21The curve exhibits a significant resonance effect at the resonant frequency, demonstrating a narrow 3dB bandwidth, which improves the quality factor and facilitates accurate resonant frequency acquisition. The spiral emitting and receiving electrodes are connected to the core of the coaxial feeder, with one end connected to the microwave excitation signal input and the other end serving as the microwave response signal output, connected to a vector network analyzer. A shielding layer is placed outside the spiral emitting and receiving electrodes, separated from them by insulating material. This shielding layer is connected to the outer shell of the coaxial feeder, forming a floor to prevent electromagnetic field leakage within the conduit and to shield against external electromagnetic interference. The inner and outer radii of the conduit are respectively... r =10 mm, R =15 mm. The distance between the spiral emitting electrode and the spiral receiving electrode and the metal ring. d The diameter is 0.5 mm. This spiral ring microwave resonant sensor is placed close to the outer wall of the tube. When the fluid being measured flows through the glass tube, the spiral ring microwave resonant sensor can achieve non-contact measurement. As the dielectric constant of the fluid changes, the resonant frequency shifts.

[0032] (2) To ensure the high sensitivity of the helical ring resonant microwave sensor and its adaptability to various complex flow patterns in inclined pipes, its geometry was optimized using the finite element analysis software HFSS (High Frequency Structure Simulator). The optimized model of the helical ring microwave resonant sensor is as follows: Figure 3 As shown. By analyzing the sensitivity response of the oil bubble at five different cross-sections in the pipeline, the following key parameters were identified: the pitch of the spiral emitting electrode and the spiral receiving electrode. L= 94 mm, helix angle 360°, length of metal ring L =94 mm, the coupling distance between the metal ring and the spiral emitting and receiving electrodes. d =0.5 mm. Finally, the optimized geometric parameters of the spiral ring microwave resonant sensor are as follows: the pitch of the spiral emitting electrode and the spiral receiving electrode... L= The spiral ring has a diameter of 94 mm, an angle of 120°, a thickness of 0.2 mm, a helix angle of 360°, and is made of brass. The length of the metal ring is equal to the pitch of the spiral emitting and receiving plates, also 94 mm, with a thickness of 0.2 mm, and is also made of brass. The insulating material used in the spiral ring microwave resonant sensor is transparent silicone. The coupling distance between the metal ring and the spiral emitting and receiving plates is... d =0.5 mm, the spacing between the spiral emitting electrode and the spiral receiving electrode and the shielding layer d 1 = 6 mm, the shielding layer material is brass, length L1 = 134 mm, thickness is 0.2 mm.

[0033] The optimal size of the spiral ring microwave resonant sensor has the following sensitive field distribution: Figure 4 As shown, this spiral ring microwave resonant sensor exhibits a uniform and strong sensitive field distribution, with an average sensitivity of 0.839411.

[0034] (3) To further investigate the resonant frequency shift of the spiral ring microwave resonant sensor under different mixed dielectric constants, an optimized spiral ring microwave resonant sensor model was established, and the amplitude-frequency characteristic curves of the spiral ring microwave resonant sensor under different mixed dielectric constants were obtained as follows: Figure 5 As shown in (a). The dielectric constant ranges from 3.2 to 78, corresponding to a water holding capacity of 0-100%. Figure 5 It can be seen that this spiral-shaped ring microwave resonant sensor exhibits good resonant frequency response to changes in the mixed dielectric constant; the resonant frequency gradually increases as the mixed dielectric constant decreases. The resonant frequencies corresponding to each mixed dielectric constant are extracted, and the curves showing the relationship between the resonant frequency and the mixed dielectric constant are obtained as follows. Figure 5 As shown in (b), the resonant frequency decreases non-linearly with increasing dielectric constant, and the measurement sensitivity is low in the low dielectric constant region. As the dielectric constant increases, the rate of change of the curve gradually increases, and the measurement sensitivity of the response increases. When the mixed dielectric constant is greater than 40, the resonant frequency and dielectric constant are almost linearly related. The formula for obtaining the mixed dielectric constant based on the relationship between the resonant frequency and the mixed dielectric constant is as follows: (1) In the formula c At the speed of light, , It is a mixed dielectric constant. ρ is the permeability; typically, the permeability of a non-magnetic medium is about 1. This is the resonant wavelength.

[0035] (4) For inclined oil-water two-phase flow, the flow pattern distribution is not uniform, which affects the measurement of the helical ring microwave resonant sensor. Therefore, the resonant frequency output response of the designed helical ring microwave resonant sensor under different flow patterns involved in the dynamic experiment of inclined oil-water two-phase flow was further investigated. The results are as follows: Figures 6-10 As shown. The measurement sensitivity of the spiral ring microwave resonant sensor is defined here. δ For output variables ( f ) with input variables ( Y w The quantity that changes with the change of ) This is used to characterize the water holdup response sensitivity for different flow patterns. For the DO / WCC flow pattern, dynamic experiments show that it is mainly distributed in the high water cut region. The flow pattern is characterized by oil droplets distributed in the upper layer of the pipe, with pure water in the lower layer, and its water holdup varies from approximately 84% to 98%. Changing the diameter of the oil droplets can alter the water holdup. Figure 6 The diagram shows the variation of the resonant frequency of the DO / W CC flow pattern with water holding capacity. It indicates that for the CC flow pattern, the resonant frequency changes almost linearly with water holding capacity, and its sensitivity... δ The resonant frequency changes by 4.8 MHz / 1%, meaning that for every 1% change in water holdup, the resonant frequency changes by 4.8 MHz. The VFD O / W flow pattern also exists in high water-content regions. Its characteristics include relatively uniform oil droplet dispersion in the pipe, and a water holdup range of approximately 80%-98%. By changing the droplet size, the water holdup is altered, thus obtaining the resonant frequency response corresponding to different water holdup rates. Figure 7 As shown, for the VFD O / W flow pattern, when the water holdup is greater than 84%, the corresponding resonant frequency changes almost linearly with the water holdup. The change decreases when the water holdup is less than 84%, indicating a weakening of sensitivity. δ The sensitivity value is 7.847 MHz / 1%, indicating a higher sensitivity compared to the DO / W CC flow pattern. In the dynamic experiment, as the oil phase ratio increases, a DO / W CT flow pattern emerges. Oil droplets are distributed not only in the upper layer of the pipe but also intermittently in the lower layer, corresponding to a large range of water holdup. With a variation range of 75%-95%, the simulation results are as follows: Figure 8 As shown, similar to the VFD O / W flow pattern, when the water holdup is low (<80%), the rate of change of the resonant frequency with respect to the water holdup decreases. Within the water holdup variation range, the overall sensitivity is 5.82 MHz / 1%. In the dynamic experiment, the DO / W PS flow pattern is characterized by oil droplets carried by an oil plug distributed in the upper part of the pipe, with a water holdup variation range of approximately 60%-80%. Figure 9 The diagram shows the variation of the resonant frequency of the DO / W PS flow pattern with water holding capacity. It reveals that for the DO / W PS flow pattern, the resonant frequency exhibits a significant nonlinear trend with water holding capacity, and the rate of change decreases as the water holding capacity decreases. According to the formula... Its sensitivity can be calculated δ The value is 1.516 MHz / 1%. The main characteristic of the transitional flow pattern TF in the dynamic experiment is the separate continuous phases of oil and water. Therefore, a relatively ideal TF flow pattern simulation was established, with its water holdup variation range approximately 25%-40%. The corresponding resonant frequency varies with the water holdup as follows: Figure 10 As shown, its sensitivity δAt 0.22MHz / 1%, compared to other flow patterns, the response sensitivity of the spiral ring microwave resonant sensor is significantly lower. However, overall, the spiral ring microwave resonant sensor exhibits good water-holding capacity response under five typical inclined oil-water two-phase flow patterns.

[0036] Experimental verification and results: Based on the simulation results above, a helical ring microwave resonant sensor was designed, and a dynamic experiment of inclined oil-water two-phase flow was carried out. The experimental setup is as follows: Figure 11 As shown. The aqueous and oil phases are introduced into the inclined measuring tube section via peristaltic pumps from water and oil tanks respectively. After sufficient development in a 250 cm development tube section, the flow pattern is observed in real time using a high-speed camera. The two-phase flow then passes through a spiral ring microwave resonant sensor and finally enters a mixing tank for complete settling before being recycled. The spiral ring microwave resonant sensor is connected to a vector network analyzer to acquire output curves in real time, followed by data analysis on a host computer. The aqueous phase is room temperature tap water with a mineralization of 180 ppm and a dielectric constant of 78; the oil phase is No. 3 industrial white oil with a dielectric constant of 3.2. The experimental conditions are set as follows: Total flow rate... Q m 5 m 3 / d-15 m 3 / d, corresponding to the total flow velocity U m The velocity is 0.1840 m / s - 0.552 m / s, and the water content is... K w The range is 50%-98%, and it includes 176 sets of experimental conditions.

[0037] Five typical flow patterns were observed in the 45-degree inclined oil-water two-phase flow dynamic experiment: water-in-oil dispersion flow with local countercurrent in the water layer (DO / W CT), water-in-oil dispersion flow with pseudo-slug flow in the water layer (DO / W PS), water-in-oil dispersion flow with co-current in the water layer (DO / W CC), uniformly dispersed oil droplets flow (VFD O / W), oil-in-water dispersion flow with oil as the continuous phase (DW / O), and transitional flow pattern (TF), such as... Figure 12 As shown. When the water content is high (above 90%), due to the density difference between the oil and water phases, oil bubbles are mainly located in the top region of the pipe, while single-phase water occupies the bottom. The pipe is mainly a water-in-oil flow type. When the total flow velocity is high, the increase in the water phase flow rate in the pipe will break up the oil bubbles at the top of the pipe, forming a continuous oil bubble cluster, most of which are small and spherical. The oil bubbles are dispersed and flow in the upper region of the pipe, forming... Figure 12 (a) shows the DO / W CC. When both the total flow rate and water content are very high, the turbulent kinetic energy of the mixed fluid increases, causing the oil bubbles to be broken into very fine bubbles, which are relatively uniformly dispersed throughout the pipe, forming a structure like... Figure 12 (b) shows the VFD O / W. For example... Figure 12 (d) illustrates the DO / W PS flow pattern, which occurs under low total flow rate and low water content conditions. In this case, the turbulent kinetic energy of the fluid inside the pipe is relatively low. Oil droplets moving upwards at the top of the pipe aggregate into an oil plug, followed by oil bubbles of varying sizes at the tail of the plug. As the total flow velocity increases, the turbulent energy of the mixed fluid also increases accordingly. The oil plug moving upwards in the pipe is broken into continuously distributed oil bubbles of varying sizes, forming the DO / W CT flow pattern. Figure 12 (c)). The typical characteristic of this flow pattern is that oil bubbles at the top of the pipe are dispersed in the water and move upwards, while there is localized countercurrent in the water phase at the bottom of the pipe. This countercurrent indicates that the flow velocity of the water phase at the bottom of the pipe has reversed, and the oil droplets are carried along in a tumbling, upward motion. When the water content is low (between 40% and 50%), as the total flow velocity further increases, the flow pattern evolves towards a transitional flow pattern where oil is the continuous phase and the oil and water phases appear intermittently, such as... Figure 12 As shown in (e).

[0038] During the dynamic experiment, when using a vector network analyzer to obtain the resonant frequency output, the scanning frequency range was set to 1.02 GHz to 1.35 GHz based on the simulation results, the measurement data points were 1001, and the excitation signal power was set to automatic. The vector network analyzer was connected to the host computer via a network cable, and NetAssist was used to remotely control the vector network analyzer for signal acquisition. The sampling frequency was set to 100 ms, and the acquisition time was set to 20 s to fully reflect the changes in the fluid inside the pipe. Subsequently, the obtained 200 sets of data were used to plot microwave signal fluctuation curves to characterize the microwave resonant frequency response under various operating conditions. Figure 13The microwave resonant frequency fluctuation curves under typical flow patterns are shown. As can be seen from the figure, the spiral ring microwave resonant sensor exhibits good response to inclined oil-water flow. In the dynamic experiment, the resonant frequency gradually decreases with increasing water content, reaching its minimum in pure water. The resonant frequency fluctuation curve also reveals flow pattern information; different flow patterns exhibit different fluctuation characteristics. For the VFD O / W flow pattern, the resonant frequency is the lowest due to the uniform distribution of oil droplets, resulting in smaller signal fluctuations. When the flow pattern is DO / W CC, the water content decreases, and the resonant frequency increases relative to the VFD O / W flow pattern. Simultaneously, the oil bubbles are distributed in the upper layer, and the slight non-uniformity in the flow increases the signal fluctuation amplitude. When the flow pattern is DO / W PS, the oil content further increases, leading to a further increase in the resonant frequency output. The quasi-periodic oil plug causes the signal to exhibit quasi-periodic fluctuation characteristics. Furthermore, the dense oil droplet clusters at the tail of the oil plug cause short, sharp peaks within each fluctuation period. When the flow pattern is DO / WCT, the further increase in oil content leads to an increase in the resonant frequency, and the signal fluctuation exhibits reduced volatility accompanied by a non-periodic downward jump peak. This is considered to be related to the counterflow phenomenon. When counterflow occurs, the water phase at the bottom of the pipe is entrained and turbulent, leading to an increase in water content in some areas of the pipe, ultimately resulting in a downward jump signal. When the flow pattern is TF, the resonant frequency further increases with the further increase in oil content. At this time, the signal fluctuation weakens. This is because there is continuous oil in the upper layer and continuous water in the lower layer of the pipe, and the oil droplets are unevenly distributed in the middle region of the pipe. Under the influence of microwave averaging measurement, the oil-water change is small throughout the entire measurement pipe section, resulting in smaller fluctuations.

[0039] right Figure 13 The microwave signal was averaged to obtain a response chart of the resonant frequency of the oil-water two-phase flow tilted at 45° as a function of water cut and total flow velocity, as shown below. Figure 14 As shown. Observation Figure 14 When the total flow velocity is constant, the resonant frequency gradually increases as the water content decreases, which is consistent with theoretical derivation and simulation experiments. At low flow velocities, the resonant frequency changes with water content by 3.015 MHz / 1%, while at high flow velocities, the resonant frequency changes with water content by 4.586 MHz / 1%.

[0040] in accordance with Figure 14 The resonant frequency response of a spiral ring microwave resonant sensor is used to solve for the water holdup in an inclined oil-water two-phase flow. From formula (1), it can be seen that... λ g Related to the structure of the spiral ring microwave resonant sensor, when the medium in the pipe is pure water, the mixed dielectric constant is 78 and the magnetic permeability is 1. At this time, the resonant frequency of the spiral ring microwave resonant sensor is 1.062 GHz, which can be calculated. λ gWith a value of 0.032, the relationship between the resonant frequency and the mixed dielectric constant can be obtained as follows: ,in f 0 represents the resonant frequency. Substituting the measured resonant frequency value into this equation yields the mixed dielectric constant. Analysis shows that the flow structure changes with the water holdup in each flow pattern. Therefore, a mixed dielectric constant model varying with the water holdup is constructed: (2) In the formula Y w This is the predicted water holding capacity. A and B The coefficients are related to different flow patterns. ε w The dielectric constant of water is ε o Let be the permittivity of the oil phase, and let... k = AY w + B , k These are the parameters to be measured under different flow patterns.

[0041] Two fast-closing valves were connected downstream of a spiral-shaped toroidal microwave resonant sensor. Experimental data from these valves were used to determine the measured parameters under different flow regimes. Simultaneously, to compare the performance under various flow regimes... k The pattern of value changes is calculated here. k average Parameters corresponding to different flow patterns of oil-water two-phase flow A , B and The values ​​are shown in Table 1. Comparison of the values ​​corresponding to different flow patterns... The value indicates that as the degree of aggregation of oil droplets in the dispersed phase increases, As the value gradually increases, when the flow pattern is VFD O / W, the flow structure in the direction of the electric field is that oil droplets are randomly distributed in the pipe, making the model close to 1 / 3. When the value is minimum and the flow pattern is DO / W CC, the flow structure inside the pipe exhibits a common pattern of randomness and parallel connections in the direction of the electric field. As the value increases, when the flow pattern is DO / W CT, the flow structure exhibits parallel and series modes in the direction of the electric field, with the parallel mode being dominant. When the value is between 0.5 and 1, and the flow pattern is DO / WPS, the flow structure also exhibits parallel and series modes in the direction of the electric field, but the degree of oil droplet coalescence is further increased. When the value becomes large, and the flow pattern is TF, the flow structure inside the pipe becomes extremely complex. Various modes randomly combine along the electric field direction, leading to greater droplet coalescence. The value becomes the largest.

[0042] Table 1

[0043] Substituting the parameters from Table 1 into Equation (2), we obtain the predicted water holdup of the inclined oil-water two-phase flow, as follows: Figure 15 As shown. To quantitatively evaluate the water holdup prediction results of the spiral ring microwave resonant sensor for oil-water two-phase flow, the statistical indicators of absolute mean relative error (AAPD) and absolute mean error (AAD) are introduced: (3) (4) in, n The number of experimental conditions. For the first i Predicted water holding capacity under sub-condition For the first i The measured water holding capacity under this operating condition is also called the experimental value.

[0044] As shown in the figure, the water holding capacity prediction for each flow pattern achieved good results, with an AAD of 0.019 and an AAPD of 2.51%, and the overall error remained within ±5%.

Claims

1. A method for measuring water holding capacity based on a spiral ring microwave resonant sensor, wherein the spiral ring microwave resonant sensor comprises a metal ring, a spiral emitting electrode, a spiral receiving electrode, a metal shielding shell, and a coaxial feed line; wherein the metal ring is tightly fitted to the outer wall of the measuring pipe; the spiral emitting electrode and the spiral receiving electrode are located on the same circumferential surface outside the metal ring, the circumferential surface being coaxial with the metal ring and having a coupling gap; the spiral emitting electrode and the spiral receiving electrode are respectively connected to the terminals of the coaxial feed line, the coaxial feed line connected to the spiral emitting electrode serves as the input end of the microwave excitation signal, and the coaxial feed line connected to the spiral receiving electrode serves as the output end of the microwave response signal; the shielding layer is placed on the outer periphery of the spiral emitting electrode and the spiral receiving electrode; the spiral ring microwave resonant sensor is connected to a vector network analyzer for the microwave excitation signal input end and the microwave response signal output end; the measurement method is as follows: An observation window is made on the measuring pipe, and a high-speed camera is installed at the observation window to acquire the flow pattern of the oil-water two-phase flow. A spiral ring microwave resonant sensor is installed downstream of the observation window. A vector network analyzer is used to obtain the microwave resonant frequency fluctuation signal after the oil-water two-phase flow passes through the spiral ring microwave resonant sensor, thereby obtaining the transmission parameter S. 21 The amplitude-frequency characteristic curves are obtained, and the resonant frequencies in each curve are extracted. Different water holding capacities correspond to different resonant frequency shifts. A mixed dielectric constant model for different flow patterns as a function of water holding capacity was established, which was used to predict the water holding capacity under the corresponding flow patterns based on the obtained mixed dielectric constant. The mixed dielectric constant is obtained based on the relationship between the resonant frequency and the mixed dielectric constant. Based on the mixed dielectric constant model corresponding to the current flow pattern identified by the high-speed camera, which varies with the water-holding capacity, the water-holding capacity is predicted; the measuring pipe is installed on an inclined pipeline for measuring the water-holding capacity of the oil-water two-phase flow in the inclined pipeline; the measurement method specifically includes: S1. Fix the prepared spiral ring microwave resonant sensor to the measuring pipe, connect it to the vector network analyzer through a coaxial line, and connect the vector network analyzer to the host computer for online data acquisition. S2. A dynamic experimental system for oil-water two-phase flow was constructed. A vector network analyzer was used to collect the amplitude-frequency response curves of a spiral ring microwave resonant sensor under different operating conditions in real time. The collected data was recorded by a host computer, and the resonant frequency output under each operating condition was obtained through data processing. The mixed dielectric constant was calculated based on the relationship between the resonant frequency and the mixed dielectric constant. (1) In the formula, c At the speed of light, It is a mixed dielectric constant. Permeability, The resonant wavelength, f The resonant frequency; S3. Using the oil-water two-phase flow dynamic experimental system built in step S2, experiments were conducted under different flow patterns and operating conditions. A mixed dielectric constant model varying with water holdup under different flow patterns was established. This model was used to predict the water holdup under the corresponding flow pattern based on the obtained mixed dielectric constant. Specifically, the established mixed dielectric constant models varying with water holdup under different flow patterns are as follows: (2) In the formula, Y w This is the predicted water holding capacity. A and B The coefficients are related to different flow patterns. ε w The dielectric constant of water is ε o Let be the permittivity of the oil phase, and let... k = AY w + B , k To determine the parameters to be measured under different flow patterns, experimental data from quick-closing valves are used to obtain the mixed dielectric constant model that varies with water holding capacity under different flow patterns. S4. During the oil-water two-phase flow measurement process, the oil-water two-phase flow image of the measurement pipeline acquired by the high-speed camera is sent to the host computer. The host computer obtains the output of the resonant frequency under the current operating condition based on the data acquired by the vector network analyzer, and calculates the mixed dielectric constant based on the relationship between the resonant frequency and the mixed dielectric constant. The current flow pattern is identified based on the image acquired by the high-speed camera. The water holding capacity is predicted using the mixed dielectric constant model that varies with the water holding capacity under the current flow pattern.

2. The water holding capacity measurement method according to claim 1, characterized in that, The geometric dimensions of the helical ring microwave resonant sensor were optimized using finite element analysis software. The optimal geometric parameters of the helical ring microwave resonant sensor were determined by calculating the sensitivity of the resonant frequency output of the helical ring microwave resonant sensor to the change of the mixed dielectric constant under different pitches and coupling gaps.

3. The water holding capacity measurement method according to claim 1, characterized in that, The geometric parameters of the spiral ring microwave resonant sensor are as follows: the pitch of the spiral emitting electrode and the spiral receiving electrode is 94 mm, the spiral angle is 360°, the length of the metal ring along the axial direction of the measuring pipe is equal to the pitch of the spiral emitting electrode and the spiral receiving electrode, and the coupling distance between the metal ring and the spiral emitting electrode and the spiral receiving electrode is 0.5 mm.

4. The water holding capacity measurement method according to claim 1, characterized in that, The inner and outer radii of the measuring pipe on which the helical ring microwave resonant sensor is installed are respectively r =10 mm, R =15 mm; other geometric parameters are as follows: the angle between the spiral emitting electrode and the spiral receiving electrode is 120°, and the thickness is 0.2 mm; the length and thickness of the metal ring are equal to the pitch and thickness of the spiral emitting electrode and the spiral receiving electrode.

5. The water holding capacity measurement method according to claim 1, characterized in that, The coupling gap is filled with a transparent silicone insulating material; the shielding layer is isolated from the spiral emitting electrode and the spiral receiving electrode by a transparent silicone insulating material.

6. The water holding capacity measurement method according to claim 1, characterized in that, The measuring pipe is a glass pipe.

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