A method for measuring gas holdup rate in liquid plug area of ​​horizontal oil-gas-water slug flow

Abstract

The invention relates to a method for measuring gas holdup in a liquid plug area of ​​a horizontal oil-gas-water slug flow. After obtaining response signals of a distributed ultrasonic sensor and a conductivity grid sensor, the following data processing is performed on the liquid plug area of ​​the oil-gas-water slug flow: an amplitude-frequency joint analysis of a pulse peak sequence of a receiver A is performed to obtain a pulse peak sequence of the receiver A with the influence of oil droplets eliminated; radial cross-section imaging of a pipeline of an oil-gas-water three-phase slug flow is realized by measuring the response signal with a conductivity grid sensor, and gas holdup and bubble radius in regions I, II and III are extracted; an average bubble radius in region I and its normalized value are calculated, and a relationship between the normalized value and the gas holdup in region I is described; a modified MCBL model based on the size of three-phase flow bubbles is established; the gas holdup in region I measured by the receiver A is obtained; the gas holdups in regions II and III measured by the receivers B and C are obtained respectively; and the gas holdup in the liquid plug area of ​​the oil-gas-water slug flow on the entire radial cross-section of the pipeline is measured.

Description

Technical Field

[0001] The present invention relates to a method for measuring gas holdup rate in liquid plug area of ​​horizontal oil-gas-water plug flow based on distributed ultrasonic sensors. Background Art

[0002] The phenomenon of horizontal oil-gas-water three-phase flow is widely present in important industrial production processes such as petroleum and chemical industry. Due to the complex interaction between gas-liquid and liquid-liquid interfaces, horizontal oil-gas-water three-phase flow usually presents multi-scale flow structure characteristics, among which oil-gas-water slug flow is the most common complex flow pattern in horizontal pipes. Horizontal oil-gas-water slug flow presents quasi-periodic motion with alternating liquid film zone and liquid slug zone. Water is the continuous phase in the liquid slug zone, which is filled with non-uniformly distributed bubbles and oil droplets. The measurement of the phase holdup ratio between the liquid slug zone and the horizontal oil-gas-water slug flow is of great significance for understanding the laws of heat transfer / mass transfer between phases and revealing the mechanism of flow pattern conversion.

[0003] As a non-invasive measurement technology, ultrasonic measurement technology has almost no interference to the fluid, is not affected by the corrosion and mineralization of the measured fluid, can work in extreme environments, and has the advantages of high precision and high speed; single-mode ultrasonic sensing strategy is difficult to meet the measurement of flow parameters of complex flow patterns of horizontal oil, gas and water three-phase flow. Scholars mostly use multi-modal combined sensing systems to measure the phase holdup, velocity and flow rate of horizontal oil, gas and water three-phase flow (IEEE Transactions on Instrumentation and Measurement, vol. 70, pp. 1-9, 2021; Chemical Engineering Journal, vol. 427, pp. 131982, 2022); previous scholars' measurement of three-phase flow parameters generally targets specific and simple flow structures, such as stratified wavy flow, and there is still a lack of effective measurement methods for oil, gas and water slug flow parameters; considering the complex sound propagation characteristics in oil, gas and water three-phase flow, how to construct a new ultrasonic sensing structure and how to analyze the response signal of the ultrasonic sensor are issues worth considering; Summary of the invention

[0004] The purpose of the present invention is to propose a method for measuring the gas holdup rate in the liquid plug area of ​​a horizontal oil-gas-water slug flow based on a distributed ultrasonic sensor; the distributed ultrasonic sensor adopts two modes, transmission and scattering, to achieve gas holdup rate measurement in different areas of the radial cross section of the pipeline, thereby effectively improving the measurement accuracy of the gas holdup rate in the liquid plug area of ​​the oil-gas-water three-phase slug flow. The technical solution is as follows:

[0005] A method for measuring gas holdup rate in a liquid plug area of ​​a horizontal oil-gas-water plug flow. The measuring device used comprises a host computer, a distributed ultrasonic sensor measurement system and a conductivity grid sensor system. The two systems respectively comprise two groups of sensor parts distributed on the same pipeline. One group of sensor parts adopts a distributed ultrasonic sensor, including four ultrasonic probes A, B, C, and D distributed on the pipe wall, wherein D is a transmitting probe used for transmitting pulsed ultrasonic waves, and probes A, B, and C are used for receiving ultrasonic signals, which are called receivers; the transmitting probe D is located at the bottom of the pipeline, facing the receiver A, and the receivers B and C are located on both sides of the receiver A; the digital signals collected by the distributed ultrasonic sensor measurement system and the conductivity grid sensor system are transmitted to the host computer;

[0006] The radial cross section of the pipeline is divided into a main lobe area and a side lobe area according to the ultrasonic propagation path; the main lobe area is area I, and the side lobe areas are distributed on both sides of the main lobe area, namely areas II and III. The boundary between area I and areas II and III is determined by the line connecting the edge of the transmitter D and the midpoint of the arc between the receivers A and B, and the receivers A and C;

[0007] The other sensing part uses a conductive grid sensor, including an excitation electrode T i With receiving electrode R j , each excitation electrode is parallel to each other and is located in the same radial section of the pipeline, while each receiving electrode is arranged parallel to each other on another radial section of the pipeline, and the excitation electrode and the measuring electrode form a cross point in the pipeline; by sequentially exciting the excitation electrodes T i , obtain a frame of data from the conductivity grid sensor, which reflects the phase distribution information at all intersections on the radial section of the pipeline; to mark the excitation signal V for the excitation electrode E The excitation sequence is: Assume that the conductivity grid sensor outputs a marker signal V Mark , the marker signal is the same as the excitation signal V E The data obtained by the conductivity grid sensor with the same period of square wave are transmitted to the host computer;

[0008] A horizontal oil-gas-water three-phase flow experiment was carried out to obtain the response signals of the distributed ultrasonic sensor and the conductivity grid sensor; the following data processing was performed for the liquid plug area of ​​the oil-gas-water slug flow:

[0009] S1, perform an amplitude-frequency joint analysis of the pulse peak sequence of receiver A, obtain the decomposed IMF components representing different frequencies through the empirical mode decomposition (EMD) method, perform amplitude threshold processing on the high-frequency components, and obtain the pulse peak sequence of receiver A with the oil drop effect eliminated by subtracting the processed high-frequency components from the pulse peak sequence of receiver A;

[0010] S2, using the conductivity grid sensor to measure the response signal to realize radial cross-section imaging of the oil-gas-water three-phase slug flow pipeline, and extracting the gas holdup and bubble radius in regions Ⅰ, Ⅱ and Ⅲ;

[0011] S3, calculate the average bubble radius in area I and its normalized value Where D is the inner diameter of the pipe,

[0012] Establish Gas holdup in zone I measured with conductivity grid sensor The relationship between Gas holdup rate in region I relationship;

[0013] S4, according to step S3, establish a modified MCBL model based on the bubble size of the three-phase flow to describe the ultrasonic transmission wave attenuation coefficient α and the gas holdup rate in region I relationship;

[0014] S5, calculate the attenuation coefficient α of the ultrasonic transmission wave received by receiver A, and bring the calculated α into the modified MCBL model to obtain the gas holdup rate of region I measured by receiver A

[0015] S6, based on the statistical model established by the Chapman function, the gas holdup rates of regions II and III measured by receivers B and C are obtained and

[0016] S7 According to the area of ​​regions I, II and III, and The weighted average of the three is used to achieve the gas holding rate of the liquid plug area in the entire pipeline radial section. measurement.

[0017] Furthermore, the method of step S1 is as follows:

[0018] S11, using the empirical mode decomposition (EMD) method to decompose the pulse peak sequence VAmp of the receiver A into a series of intrinsic mode functions (IMFs) and the linear superposition of the remaining parts; by gradually extracting the scale components of the original signal from high frequency to low frequency, the decomposed mode functions are arranged in order from high frequency to low frequency, IMFi is the decomposed signal component representing different frequencies, and fast Fourier transform is performed on different IMF components to obtain the corresponding spectrum;

[0019] S12, preset threshold The high-frequency component IMF1 is subjected to amplitude threshold processing. The signals in IMF1 with amplitudes higher than the threshold are set to 0; the signals in IMF1 with amplitudes lower than the threshold are retained to obtain the processed IMF1 component. By subtracting the processed IMF1 component from the pulse peak sequence of receiver A, the pulse peak sequence of receiver A with the oil droplet effect eliminated can be obtained.

[0020] Furthermore, the method of step S2 is as follows:

[0021] S21, radial cross-section imaging of oil-gas-water three-phase slug flow pipeline, calculation of instantaneous water holdup matrix Will Convert to a two-dimensional visualization image;

[0022] S22, remove the oil phase distribution in the pipeline radial cross-section imaging results, retain the water phase and gas phase distribution, regard the area with a roundness lower than the threshold θ as a coherent oil droplet, and treat it as a water phase; set the area with a position lower than the height limit value as the water phase, and obtain the instantaneous water holdup matrix after removing the oil phase

[0023] S23, matrix-based Calculate the bubble radius for the radial section of the pipe.

[0024] Furthermore, the method of S21 is as follows:

[0025] Read the flag signal V Mark , and extract its rising edge. The i-th rising edge indicates that the current excitation signal is applied to the excitation electrode T i ; For the kth frame data, when the excitation electrode T i In the excitation state, calculate the receiving electrode R j The extreme difference is denoted as V m (i,j,k), for V m(i,j,k) Perform normalization to obtain the normalized matrix V N (i,j,k):

[0026]

[0027] Where V w (i,j) and V o (i, j) are the calibration data when the pipeline is filled with water and oil respectively, V N (i, j, k) is approximately linearly related to the local water holding capacity at each intersection;

[0028] The cubic spline interpolation method with a step size of h is used to interpolate V N (i,j,k) is interpolated to obtain the interpolation matrix V ip(x,y,k), where x and y represent the horizontal and vertical coordinates of the matrix, respectively, and the interpolation matrix V ip (x,y,k) is considered as the instantaneous water holdup matrix Will Converted into a two-dimensional visualization image.

[0029] Further, the method of step S23 is as follows:

[0030] S231, calculate instantaneous gas holdup rate

[0031]

[0032] S232, the instantaneous gas holding rate The location where the local maximum of appears is defined as the bubble center;

[0033] S233, identifying bubbles;

[0034] S234, the bubble is regarded as a standard circle, and the bubble radius R is calculated by calculating the area s occupied by the bubble, that is:

[0035]

[0036] Among them, Δx, Δy represent the instantaneous holdup rate matrix The horizontal and vertical distances between elements in .

[0037] Furthermore, the method of identifying bubbles in step S233 is as follows:

[0038] S2331, the gas holding rate at the center of each bubble is expressed as Y gcore Indicates that the adaptive threshold ξ=β·Y is introduced gcore , used to determine the boundary of each bubble, where β is the adaptive threshold factor;

[0039] S2332, establish a bubble identification matrix Sign(x,y) and a bubble counter BCount, and set all elements in the bubble identification matrix Sign(x,y) and BCount to 0;

[0040] S2333, for the first bubble center found, BCount is increased by 1, and the corresponding element in Sign(x,y) is marked as the current value of BCount, that is, marked as 1; the eight adjacent elements around the bubble center point are checked one by one; the elements that are greater than the above-mentioned adaptive threshold ξ and have not been marked will be marked with the same value, and the corresponding elements in Sign(x,y) are updated to 1; the adjacent elements around each marked element are continuously checked until the entire bubble area is marked; when a bubble is completely marked, the search for the next bubble center continues; after finding another bubble, BCount is increased by 1, and the corresponding Sign(x,y) element is marked as the current value of BCount; this process continues until all bubbles are identified.

[0041] Furthermore, the modified MCBL model based on the three-phase flow bubble size established in step S3 is as follows:

[0042]

[0043] Where k1 is the ultrasonic longitudinal wave number in the water phase, Y g is the air holding rate; A0 and A1 are the longitudinal wave coefficients A n The first two items, B n The solution is obtained by the first kind Bessel function j n (x), the second kind of Bessel function n n (x) and the three particle size coefficients are obtained.

[0044] Furthermore, in step S5, the formula for calculating the attenuation coefficient α of the ultrasonic transmission wave received by the receiver A is as follows:

[0045]

[0046] in, represents the average value of the pulse peak sequence of receiver A obtained by step S1 after eliminating the influence of oil droplets, represents the average value of the pulse peak train at receiver A under full water conditions.

[0047] Further, the method of step S6 is as follows:

[0048] The normalized forms of the signals measured by receivers B and C are and It is expressed as:

[0049]

[0050] in, are the average values ​​of the ultrasonic pulse peak sequences of receivers B and C for each liquid plug, and They are and The maximum value of

[0051] Establish Gas holdup rates in regions II and III measured with conductivity grid sensors Relationship, using Chapman function to describe and and The relationship between them is as follows:

[0052]

[0053] Among them, ε Ⅱ ,υ Ⅱ , σ Ⅱ and ε Ⅲ ,υ Ⅲ , σ Ⅲ represents the undetermined coefficient in the Chapman function; the gas holding rates of regions II and III measured by receivers B and C are obtained using the statistical model and

[0054] Furthermore, the distributed ultrasonic sensor measurement system includes the excitation module, signal conditioning module, FPGA module, signal acquisition and data transmission module containing the distributed ultrasonic sensor. The excitation module generates an excitation pulse under the action of the FPGA control signal, and the transmitting probe D generates a pulsed ultrasonic wave under the action of the excitation signal; after being transmitted and scattered by the horizontal oil, gas and water three-phase flow fluid in the pipeline, the ultrasonic wave is received by probes A, B and C and converted into three weak electrical signals. After amplitude amplification and bandpass filtering by the signal conditioning module, it is converted into a digital signal through the data acquisition module. After preprocessing in the FPGA, it is uploaded to the host computer through the data transmission module.

[0055] The present invention adopts the above technical solution, which has the following advantages:

[0056] (1) The present invention uses an ultrasonic method to measure the oil-gas-water three-phase slug flow, which can achieve non-invasive detection and can measure opaque pipelines.

[0057] (2) The bubble size in the liquid plug area of ​​the oil-gas-water three-phase slug flow was detected using a conductivity grid sensor, and the MCBL model was modified, which effectively improved the measurement accuracy of the gas holdup rate in the central area of ​​the radial cross-section of the pipeline.

[0058] (3) The ultrasonic sensor of the present invention adopts a distributed structure and can simultaneously obtain ultrasonic transmission and scattering dual-mode information, thereby achieving accurate measurement of the gas holdup rate in different areas of the radial cross section of the pipeline. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Figure 1 Schematic diagram of horizontal oil-gas-water slug flow structure: (a) oil droplet dispersion slug flow; (b) oil droplet emulsification slug flow

[0060] Figure 2 Distributed ultrasonic sensor structure

[0061] Figure 3 Distributed Ultrasonic Sensor Measurement System

[0062] Figure 4 Schematic diagram of pipeline radial section partition

[0063] Figure 5 Conductivity grid sensor and its measurement system

[0064] Figure 6 The distributed ultrasonic sensor response signal (U sg =0.737m / s, U sl =0.59m / s)

[0065] Figure 7 The pulse peak sequence (U sg =0.737m / s)

[0066] Figure 8 The pulse peak sequence (U sg =0.442m / s): (a) Receiver B; (b) Receiver C

[0067] Fig. 9 The measurement response signal of the conductivity grid sensor (U sg =1.917m / s, U sl =0.737m / s)

[0068] Fig.10 Flow chart of gas holdup rate measurement in liquid plug area of ​​horizontal oil-gas-water slug flow

[0069] Fig.11 EMD decomposition and FFT analysis of the pulse peak sequence of receiver A: (a) U sg =0.147m / s, U sl =0.074m / s; (b)U sg =1.917m / s, U sl =0.737m / s

[0070] Fig.12Flow chart of using conductivity grid sensor to measure response to visualize fluid structure, measure gas holdup and bubble radius in different regions

[0071] Fig.13 Visualization results of the liquid plug area of ​​oil-gas-water slug flow by conductivity grid sensor (U sg =1.032m / s,U sl =0.442m / s): (a)t=1.474s; (b)t=1.532s; (c)t=1.615s; (d)t=1.665s

[0072] Fig.14 Visualization results of the liquid plug area of ​​the oil-gas-water slug flow after removing the oil phase distribution (U sg =1.032m / s,U sl =0.442m / s): (a)t=1.474s; (b)t=1.532s; (c)t=1.615s; (d)t=1.665s

[0073] Fig.15 Relationship between the normalized value of the average bubble radius in region I and the gas holdup rate measured by the conductivity grid sensor

[0074] Fig.16 The ultrasonic transmission wave attenuation coefficient α and the gas holdup rate in region I described by the modified MCBL model Relationship Fig.17 Relationship between the normalized values ​​of the response signals of receivers B and C and the gas holdup rates in regions II and III: (a) receiver B; (b) receiver C

[0075] Fig.18 Measurement results of gas holdup in the liquid plug region of horizontal oil-gas-water three-phase slug flow using distributed ultrasonic sensors DETAILED DESCRIPTION

[0076] The present invention proposes a method for measuring the gas holdup rate in the plug area of ​​a horizontal oil-gas-water plug flow based on a distributed ultrasonic sensor. The sensor consists of four ultrasonic probes distributed on the pipe wall, one of which is a probe D and an ultrasonic transmitter, and the other three probes A, B, and C are ultrasonic receivers. Receiver A can obtain most of the energy transmitted by the multiphase flow fluid, and the side receivers B and C receive the energy scattered from the sound beam. By carrying out a horizontal oil-gas-water three-phase flow dynamic experiment, the measurement responses of the distributed ultrasonic sensor and the conductivity grid sensor under different flow patterns are obtained simultaneously. The conductivity grid sensor is used to establish the relationship between the normalized value of the average bubble radius and the gas holdup rate in the central area of ​​the pipeline, so as to correct the MCBL model (IEEE Transactions on Instrumentation and Measurement, vol. 70, no. 9502613, pp. 1-13, 2020), and the gas holdup rate in the central area of ​​the pipeline is measured based on the corrected MCBL model and the response signal of receiver A. In addition, a statistical model is established using the response signals of receivers B and C to achieve the measurement of the gas holdup rate in the side area of ​​the pipeline. Compared with the measurement results of conductivity grid sensors, distributed ultrasonic sensing has higher measurement accuracy for the gas holdup rate in the liquid plug zone of oil-gas-water three-phase slug flow.

[0077] The present invention is described in detail below in conjunction with the accompanying drawings and embodiments. The present invention includes:

[0078] To achieve Figure 1 The gas holdup rate measurement of the liquid plug area of ​​the horizontal oil-gas-water plug flow shown in the figure is designed as follows Figure 2 The distributed ultrasonic sensor shown in the figure consists of four ultrasonic probes distributed on the pipe wall. Among them, probe D is used to transmit pulsed ultrasonic waves, and probes A, B and C are used to receive ultrasonic signals. Transmitter probe D is located at the bottom of the pipe, facing receiver A, and receivers B and C are located on both sides of A, with an angle of 60 degrees. The distributed ultrasonic sensor measurement system is shown in Figure 1. Figure 3 As shown, it includes an excitation module, a signal conditioning module, an FPGA module, and a signal acquisition and data transmission module. The excitation module generates an excitation pulse under the control signal of the FPGA, and the transmitting probe D generates a pulsed ultrasonic wave under the action of the excitation signal. The ultrasonic pulse repetition frequency is f prf After being transmitted and scattered by the horizontal oil, gas and water three-phase flow in the pipeline, the ultrasonic wave is received by probes A, B and C and converted into three weak electrical signals. After being amplified and band-pass filtered by the signal conditioning module, it is converted into a digital signal by the data acquisition module. After being pre-processed in the FPGA, it is uploaded to the host computer through the data transmission module.

[0079] according to Figure 4The radial section of the pipeline is divided into two parts as shown in the figure. Ultrasonic propagation has obvious directivity, and the radial section of the pipeline can be divided into the main lobe area and the side lobe area according to its propagation path. The main lobe area, that is, area I, is also the area where the ultrasonic energy is mainly concentrated. Among them, the boundary between area I and areas II and III is determined by the line connecting the edge of the transmitter D and the midpoint of the arc between the receivers A and B, and the receivers A and C.

[0080] Design as Figure 5 The conductivity grid sensor system shown in Figure 1 is composed of excitation electrodes (T1 to T 10 ) and the receiving electrode (R1 to R 10 ). Each excitation electrode is parallel to each other and located in the same radial section of the pipeline, while each receiving electrode is arranged parallel to each other on another radial section of the pipeline. The excitation electrode and the measuring electrode form 10×10 intersections in the pipeline. The analog switch is controlled by a single chip to realize T1 to T 10 Cyclic excitation. In a specific time period, only one excitation electrode T i , i=1,2,…,10 and the excitation signal V E The signal conditioning module receives the current signals (I1, I2, ..., I 10 ) is converted into a voltage signal (V m,1 ,V m,2 ,…,V m,10 ). Voltage signal V m,1 To V m,10 The data is transmitted to the host computer by the data acquisition module. 10 Electrodes can obtain a frame of data from the conductivity grid sensor, which can reflect the phase distribution information at all intersections on the radial section of the pipeline. In order to mark the excitation order of each excitation electrode, the microcontroller outputs a marking signal V Mark , the marker signal is the same as the excitation signal V E The square wave with the same period is transmitted to the host computer by the data acquisition module.

[0081] Horizontal oil-gas-water three-phase flow experiments were carried out to obtain the response signals of distributed ultrasonic sensors and conductivity grid sensors.

[0082] Figure 6 shows the gas phase superficial velocity U sg =0.737m / s, liquid superficial velocity U sl= 0.59m / s, the response signal of the distributed ultrasonic sensor. At this time, the flow pattern in the pipeline is oil droplet dispersion slug flow. It can be seen that within the sampling time of 40μs, all three receivers can detect the complete pulse signal. Due to the directivity of the ultrasonic wave, the pulse peak value received by receiver A is significantly higher than that of receivers B and C. For the response signals of receivers A, B and C, each pulse peak value is extracted to obtain the pulse peak sequence of receivers A, B and C, as shown in Figure 7 and Figure 8 shown.

[0083] Fig. 9 The signal amplitude of the receiving electrode of the conductivity grid sensing system in the oil droplet emulsion slug flow pattern is shown, showing the alternation of the liquid film region and the liquid plug region.

[0084] according to Fig.10 The process shown is used to measure the gas holdup rate in the liquid plug area of ​​the oil-gas-water slug flow.

[0085] ① For the liquid plug area of ​​the oil-gas-water slug flow, the amplitude-frequency joint analysis of the pulse peak sequence of receiver A is performed to eliminate the influence of the oil phase on the response signal of receiver A.

[0086] a) Use the empirical mode decomposition (EMD) method to decompose the pulse peak sequence of receiver A into a series of intrinsic mode functions (IMFs) and the linear superposition of the remaining parts. By gradually extracting the scale components of the original signal from high frequency to low frequency, the decomposed mode functions are arranged in order from high to low frequency:

[0087]

[0088] Where V Amp represents the pulse peak sequence of receiver A, IMFi is the decomposed signal component representing different frequencies, and r represents the residual component.

[0089] Fig.11 The results of EMD decomposition of the pulse peak sequence of receiver A are shown, and fast Fourier transform is performed on different IMF components to obtain the corresponding spectrum.

[0090] b) Perform amplitude threshold processing on the high frequency components. The amplitude is caused by bubbles and is set to 0; the amplitude below the threshold in IMF1 The amplitude of is caused by the oil droplets and its value is retained. By subtracting the processed IMF1 component from the pulse peak sequence of receiver A, the pulse peak sequence of receiver A with the oil droplet effect eliminated can be obtained.

[0091] ② Press Fig.12The process shown in the figure uses the conductivity grid sensor to measure the response signal to realize the radial cross-section imaging of the oil-gas-water three-phase slug flow pipeline, and simultaneously extracts the gas holdup rate and bubble radius in regions Ⅰ, Ⅱ and Ⅲ.

[0092] a) Realize radial cross-section imaging of oil-gas-water three-phase slug flow pipeline. First, read the marker signal V Mark , and extract its rising edge. The i-th rising edge indicates that the current excitation signal is applied to the i-th excitation electrode. For the k-th frame data, when the i-th excitation electrode is in the excitation state, calculate the range of the j-th receiving electrode signal, recorded as V m (i,j,k), where i,j=1,2,…,10; k=1,2,…,N. m(i,j,k) Perform normalization to obtain the normalized matrix V N (i,j,k):

[0093]

[0094] Where V w (i,j) and V o (i, j) are the calibration data when the pipeline is filled with water and oil respectively. N (i, j, k) and the local water holding capacity at each intersection can be approximated as a linear relationship. Subsequently, the cubic spline interpolation method with a step size of h is used to interpolate V N (i,j,k) is interpolated to obtain the interpolation matrix V ip (x,y,k), where x and y represent the horizontal and vertical coordinates of the matrix respectively. Interpolation matrix V ip (x,y,k) can be regarded as the instantaneous water holdup matrix Will The phase distribution in the radial section of the pipeline can be shown by converting it into a two-dimensional visualization image. Fig.13 As shown, the darker parts represent the areas where bubbles or oil droplets exist.

[0095] b) Remove the oil phase distribution in the pipeline radial cross-section imaging results, and retain the water phase and gas phase distribution. In order to avoid misidentifying the aggregated and adhered oil droplets as bubbles, the concept of roundness is introduced, and the area with a roundness lower than the threshold value θ is regarded as adhered oil droplets and treated as the water phase; considering the difference in the distribution position of bubbles and oil droplets, the area below the height limit value (set as 1 / 3 of the inner diameter of the pipeline in this embodiment) is set as the water phase area. Through the above operations, the instantaneous water holdup matrix after removing the oil phase is obtained. The corresponding water phase and gas phase distribution are as follows Fig.14 shown.

[0096] c) Matrix-based Follow these steps to calculate the bubble radius in the radial section (two-dimensional plane) of the pipeline:

[0097] (a) First calculate the instantaneous gas holdup rate

[0098]

[0099] (b) In a frame of data, the gas holding rates of bubbles of different sizes are different. The location where the local maximum of the gas holding rate appears is defined as the bubble center, and the gas holding rate of each bubble center is expressed as Y gcore Introducing adaptive threshold ξ=β·Y gcore , which is used to determine the boundary of each bubble, where β is the adaptive threshold factor.

[0100] (c) Establish the bubble identification matrix Sign(x,y) and the bubble counter BCount, and set all elements in the bubble identification matrix Sign(x,y) and BCount to 0. After finding the center of the first bubble, BCount increases by 1, and the corresponding element in Sign(x,y) is marked as 1 (that is, the current value of BCount). Then, check the eight adjacent elements around the center of the bubble one by one. Elements that are greater than the above adaptive threshold ξ and have not been marked will be marked, and the corresponding elements in Sign(x,y) will be updated to 1. Continue to check the adjacent elements around each marked element until the entire bubble area is marked. When a bubble is completely marked, continue to search for the next bubble center. After finding another bubble, BCount increases by 1, and the corresponding Sign(x,y) element is marked as the current value of BCount. This process continues until all bubbles on the two-dimensional plane are identified.

[0101] (d) Assuming that the two-dimensional plane bubble is a standard circle, the radius R of the bubble is calculated by calculating the area s occupied by the bubble, that is:

[0102]

[0103] Among them, Δx, Δy represent the instantaneous holdup rate matrix The horizontal and vertical distances between the elements in the 2D plane are calculated using formula (4).

[0104] ③Calculate the average bubble radius in area I and its normalized value Where D is the inner diameter of the pipe. Gas holdup in zone I measured with conductivity grid sensor relationship, such as Fig.15 As shown in the figure, each point in the figure comes from a frame of data from the conductivity grid sensor. The SLogistic function is used to describe Gas holdup rate in region I Relationship:

[0105]

[0106] Among them, λ A , B and λ C Represents the undetermined coefficients in the SLogistic function.

[0107] ④ Substitute formula (5) into the MCBL model and establish a modified MCBL model based on the bubble size of three-phase flow:

[0108]

[0109] Where k1 is the ultrasonic longitudinal wave number in the water phase, Y g is the air holding rate. A0 and A1 are the longitudinal wave coefficients A n The first two items, B n The solution can be obtained by the first kind Bessel function j n (x), the second kind of Bessel function n n (x) and three particle size coefficients are obtained. The ultrasonic transmission wave attenuation coefficient α described by the modified MCBL model and the gas holdup rate in region I The relationship is as Fig.16 shown.

[0110] ⑤ Calculate the attenuation coefficient α of the ultrasonic transmission wave received by receiver A:

[0111]

[0112] in, represents the average value of the pulse peak sequence of receiver A obtained by step ① to eliminate the influence of oil droplets, represents the average value of the pulse peak sequence of receiver A under full water conditions. Substituting α calculated by formula (7) into formula (6), the gas holdup rate of area I measured by receiver A can be obtained:

[0113] ⑥ Receivers B and C measure the normalized form of the signal, and It can be expressed as:

[0114]

[0115] in, are the average values ​​of the ultrasonic pulse peak sequences of receivers B and C for each liquid plug, and They are and The maximum value of .

[0116] Then, create Gas holdup rates in regions II and III measured with conductivity grid sensors Relationships, such as Fig.17 As shown. The Chapman function is used to describe and and The relationship between them is as follows:

[0117]

[0118] Among them, ε Ⅱ ,υ Ⅱ , σ Ⅱ and ε Ⅲ ,υ Ⅲ , σ Ⅲ represents the undetermined coefficient in the Chapman function. Using formula (9), we can obtain the gas holdup rates of regions II and III measured by receivers B and C respectively: and

[0119] ⑦ According to the area of ​​regions I, II and III, and The weighted average of the three can realize the gas holding rate of the liquid plug area of ​​the oil-gas-water segment plug flow on the entire pipeline radial section. measurement.

[0120] Experimental verification and results:

[0121] A horizontal oil-gas-water three-phase flow experiment was carried out in the Multiphase Flow Laboratory of Tianjin University to obtain the measurement responses of distributed ultrasonic sensors and conductivity grid sensors to oil-gas-water slug flow.

[0122] The conductivity grid sensor is used to visualize the phase distribution in the radial section of the pipeline. After removing the oil phase distribution, the average bubble radius in area I is calculated based on the gas and water phase distributions. and its normalized value Establish Gas holdup in zone I measured with conductivity grid sensor The relationship between the two is described by the SLogistic function. Gas holdup rate in region I Relationship:

[0123]

[0124] Substituting formula (10) into the modified MCBL model, we obtain the modified MCBL model based on the bubble size of three-phase flow:

[0125]

[0126] Where k1 = 8377,

[0127] By performing amplitude-frequency joint processing on the pulse peak sequence of receiver A, the measured value of the attenuation coefficient α of the ultrasonic transmission wave can be obtained. Substituting the measured value of the attenuation coefficient α into formula (11), the gas holdup rate of region I measured by receiver A is solved by an iterative method.

[0128] Normalize the measurement signals of receivers B and C to obtain normalized values and

[0129] Then, according to Gas holdup rates in regions II and III measured with conductivity grid sensors The relationship between the two is obtained as follows:

[0130]

[0131] The above statistical model can be used to obtain the gas holdup rates of regions II and III measured by receivers B and C: and

[0132] According to the area of ​​regions I, II and III, and The weighted average of the three can realize the gas holding rate of the liquid plug area of ​​the oil-gas-water segment plug flow on the entire pipeline radial section. The measurement results are as follows Fig.18 It can be seen that compared with the measurement results of the conductivity grid sensor, the distributed ultrasonic sensor has a higher measurement accuracy for the gas holdup rate in the liquid plug area of ​​the oil-gas-water three-phase slug flow.

Claims

1. A method for measuring gas holdup in a liquid plug area of ​​a horizontal oil-gas-water plug flow. The measuring device used comprises a host computer, a distributed ultrasonic sensor measurement system and a conductivity grid sensor system. The two systems respectively comprise two sets of sensor parts distributed on the same pipeline. One set of sensor parts adopts a distributed ultrasonic sensor, including four ultrasonic probes A, B, C, and D distributed on the pipe wall. D is a transmitting probe, used to transmit pulsed ultrasonic waves, and probes A, B and C are used to receive ultrasonic signals, called receivers; the transmitting probe D is located at the bottom of the pipeline, facing the receiver A, and receivers B and C are located on both sides of the receiver A; the digital signals collected by the distributed ultrasonic sensor measurement system and the conductivity grid sensor system are transmitted to the host computer; The radial cross section of the pipeline is divided into a main lobe area and a side lobe area according to the ultrasonic propagation path; the main lobe area is area I, and the side lobe areas are distributed on both sides of the main lobe area, namely areas II and III. The boundary between area I and areas II and III is determined by the line connecting the edge of the transmitting probe D and the midpoint of the arc between the receivers A and B, and the receivers A and C; The other sensing part uses a conductive grid sensor, including an excitation electrode T i With receiving electrode R j , each excitation electrode is parallel to each other and is located in the same radial section of the pipeline, while each receiving electrode is arranged parallel to each other on another radial section of the pipeline, and the excitation electrode and the measuring electrode form a cross point in the pipeline; by sequentially exciting the excitation electrodes T i , a frame of data from the conductivity grid sensor is obtained, and the data reflects the phase distribution information at all intersections on the radial cross section of the pipeline; the data obtained by the conductivity grid sensor is transmitted to the host computer; After obtaining the response signals of the distributed ultrasonic sensor and the conductivity grid sensor, the following data processing is performed for the oil-gas-water slug flow liquid plug area: S1, perform an amplitude-frequency joint analysis of the pulse peak sequence of receiver A, obtain the decomposed IMF components representing different frequencies through the empirical mode decomposition (EMD) method, perform amplitude threshold processing on the high-frequency components, and obtain the pulse peak sequence of receiver A with the oil drop effect eliminated by subtracting the processed high-frequency components from the pulse peak sequence of receiver A; S2, using the conductivity grid sensor to measure the response signal to realize radial cross-section imaging of the oil-gas-water three-phase slug flow pipeline, and extracting the gas holdup and bubble radius in regions Ⅰ, Ⅱ and Ⅲ; S3, calculate the average bubble radius and its normalized value in region I, and establish the bubble normalized value and the gas holding rate of region I measured by the conductivity grid sensor The SLogistic function is used to describe the relationship between the bubble normalization value and the gas holding rate in area I. relationship; S4, according to step S3, establish a modified MCBL model based on the bubble size of the three-phase flow to describe the ultrasonic transmission wave attenuation coefficient α and the gas holdup rate in region I relationship; S5, calculate the attenuation coefficient α of the ultrasonic transmission wave received by receiver A, and bring the calculated α into the modified MCBL model to obtain the gas holdup rate of region I measured by receiver A S6, based on the statistical model established by the Chapman function, obtain the gas holdup Y of regions II and III measured by receivers B and C respectively g Ⅱ,B and Y g Ⅲ,C ; S7 According to the area of ​​regions I, II and III, Y g Ⅱ,B and Y g Ⅲ,C The weighted average of the three is used to measure the gas holdup rate of the liquid plug area of ​​the oil-gas-water plug flow in the entire pipeline radial cross section.

2. The gas holdup rate measurement method according to claim 1, characterized in that: The method of step S1 is as follows: S11, using the empirical mode decomposition (EMD) method to decompose the pulse peak sequence VAmp of the receiver A into a series of intrinsic mode functions (IMFs) and the linear superposition of the remaining parts; by gradually extracting the scale components of the original signal from high frequency to low frequency, the decomposed mode functions are arranged in order from high frequency to low frequency, IMFi is the decomposed signal component representing different frequencies, and fast Fourier transform is performed on different IMF components to obtain the corresponding spectrum; S12, preset threshold The high-frequency component IMF1 is subjected to amplitude threshold processing. Signals in IMF1 with amplitudes higher than the threshold are set to 0. Signals in IMF1 with amplitudes lower than the threshold are retained to obtain the processed IMF1 component. The pulse peak sequence of receiver A with the influence of oil droplets eliminated can be obtained by subtracting the processed IMF1 component from the pulse peak sequence of receiver A.

3. The gas holdup rate measurement method according to claim 1, characterized in that: The method of step S2 is as follows: S21, radial cross-section imaging of oil-gas-water three-phase slug flow pipeline, calculation of instantaneous water holdup matrix Will Convert to a two-dimensional visualization image; S22, remove the oil phase distribution in the pipeline radial cross-section imaging results, retain the water phase and gas phase distribution, regard the area with a roundness lower than the threshold θ as a coherent oil droplet, and treat it as a water phase; set the area with a position lower than the height limit value as the water phase, and obtain the instantaneous water holdup matrix after removing the oil phase S23, matrix-based Calculate the bubble radius for the radial section of the pipe.

4. The method for measuring gas holdup rate according to claim 3, characterized in that: The S21 method is as follows: is the excitation signal V for the excitation electrode E The excitation sequence is: Assume that the conductivity grid sensor outputs a marker signal V Mark , read the mark signal V Mark , and extract its rising edge. The i-th rising edge indicates that the current excitation signal is applied to the excitation electrode T i ; For the kth frame data, when the excitation electrode T i In the excitation state, calculate the receiving electrode R j The extreme difference is denoted as V m (i,j,k), for V m(i,j,k) Perform normalization to obtain the normalized matrix V N (i,j,k): Where V w (i,j) and V o (i, j) are the calibration data when the pipeline is filled with water and oil respectively, V N (i, j, k) is approximately linearly related to the local water holding capacity at each intersection; The cubic spline interpolation method with a step size of h is used to interpolate V N (i,j,k) is interpolated to obtain the interpolation matrix V ip (x,y,k), where x and y represent the horizontal and vertical coordinates of the matrix, respectively, and the interpolation matrix V ip (x,y,k) is considered as the instantaneous water holdup matrix Will Converted into a two-dimensional visualization image.

5. The method for measuring gas holdup rate according to claim 3, characterized in that: The method of step S23 is as follows: S231, calculate instantaneous gas holdup rate S232, the instantaneous gas holding rate The location where the local maximum of appears is defined as the bubble center; S233, identifying bubbles; S234, the bubble is regarded as a standard circle, and the bubble radius R is calculated by calculating the area s occupied by the bubble, that is: R=(π -1 (s) 1 / 2 =[π -1 ΔxΔy∑Y g WMS (x,y,k)] 1 / 2 Among them, Δx, Δy represent the instantaneous holdup rate matrix Y g WMS The horizontal and vertical distances between elements in (x,y).

6. The method for measuring gas holdup rate according to claim 5, characterized in that: The method of identifying bubbles in step S233 is as follows: S2331, the gas holding rate at the center of each bubble is expressed as Y gcore Indicates that the adaptive threshold ξ=β·Y is introduced gcore , used to determine the boundary of each bubble, where β is the adaptive threshold factor; S2332, establish a bubble identification matrix Sign(x,y) and a bubble counter BCount, and set all elements in the bubble identification matrix Sign(x,y) and BCount to 0; S2333, for the first bubble center found, BCount is increased by 1, and the corresponding element in Sign(x,y) is marked as the current value of BCount, that is, marked as 1; the eight adjacent elements around the bubble center are checked one by one; the elements that are greater than the above adaptive threshold ξ and have not been marked will be marked with the same value, and the corresponding elements in Sign(x,y) are updated to 1; the adjacent elements around each marked element are continuously checked until the entire bubble area is marked; After completely marking a bubble, continue searching for the next bubble center; after finding another bubble, BCount increases by 1, and the corresponding Sign(x,y) element is marked as the current value of BCount; this process continues until all bubbles are identified.

7. The method for measuring gas holdup rate according to claim 1, characterized in that: The modified MCBL model based on the three-phase flow bubble size established in step S3 is as follows: Where k1 is the ultrasonic longitudinal wave number in the water phase; A0 and A1 are the longitudinal wave coefficients A n The first two items, B n The solution is obtained by the first kind Bessel function j n (x), the second kind Bessel function n n (x) and the three particle size coefficients are obtained.

8. The method for measuring gas holdup rate according to claim 1, characterized in that: In step S5, the formula for calculating the attenuation coefficient α of the ultrasonic transmission wave received by the receiver A is as follows: in, represents the average value of the pulse peak sequence of receiver A obtained by step S1 after eliminating the influence of oil droplets, represents the average value of the pulse peak sequence of receiver A under full water conditions, and D represents the inner diameter of the pipe.

9. The method for measuring gas holdup rate according to claim 1, characterized in that: The method of step S6 is as follows: the normalized forms of the measurement signals of receivers B and C are respectively and It is expressed as: in, are the average values ​​of the ultrasonic pulse peak sequences of receivers B and C for each liquid plug, and They are and The maximum value of Establish Gas holding rate Y in regions II and III measured with conductivity grid sensor g ΙΙ,WMS , Y g ΙIΙ,WMS Relationship, using Chapman function to describe With Y g ΙΙ,WMS , With Y g ΙIΙ,WMS The relationship between them is as follows: Among them, ε Ⅱ ,υ Ⅱ , σ Ⅱ and ε Ⅲ ,υ Ⅲ , σ Ⅲ represents the undetermined coefficient in the Chapman function; the gas holding rate Y of regions II and III measured by receivers B and C respectively is obtained by using the statistical model g Ⅱ,B and Y g Ⅲ,C .

10. The gas holdup rate measurement method according to any one of claims 1 to 9, characterized in that: The distributed ultrasonic sensor measurement system includes an excitation module containing a distributed ultrasonic sensor, a signal conditioning module, an FPGA module, and a signal acquisition and data transmission module; the excitation module generates an excitation pulse under the action of the FPGA control signal, and the transmitting probe D generates a pulsed ultrasonic wave under the action of the excitation signal; after being transmitted and scattered by the horizontal oil-gas-water three-phase flow fluid in the pipeline, the ultrasonic wave is received by probes A, B and C and converted into three weak electrical signals; after being amplified and band-pass filtered by the signal conditioning module, it is converted into a digital signal through the signal acquisition module; after being pre-processed in the FPGA, it is uploaded to the host computer through the data transmission module.

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