Pulse wave ultrasonic Doppler oil-gas-water three-phase slug flow measurement method

Abstract

The invention provides an oil-gas-water three-phase slug flow measurement method based on pulse wave ultrasonic Doppler, which comprises the following steps of: obliquely mounting a pulse wave ultrasonic Doppler sensor at the bottom of a pipeline, and ensuring that an included angle between a sound wave and a fluid flowing direction is theta; based on the pulse echo intensity principle and the Doppler principle, echo intensity profile data reflecting phase interface distribution characteristics and flow velocity profile data reflecting flow field distribution characteristics are synchronously obtained through the pulse wave ultrasonic Doppler sensor; according to the dynamic response of the test data to the flow process, establishing a signal processing algorithm to realize unit structure division of the slug flow, and further extracting related information of proportions of different areas of the slug flow, liquid film thickness and flow velocity of a gas bomb area, gas content of the gas bomb area and flow velocity of a liquid bomb area; finally, various kinds of information are fused through a physical model, and measurement of the total volume flow is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of multiphase flow measurement, and relates to a method for measuring the total volume flow rate of an oil-gas-water three-phase slug flow by using a pulse wave ultrasonic Doppler sensor. Background Art

[0002] Oil-gas-water three-phase flow is a common gas-liquid mixed flow form in the production process of oil extraction, transportation, and processing. Its flow process is highly random, nonlinear, non-uniform, and non-steady. Oil-gas-water three-phase slug flow is an intermittent flow pattern that often occurs under high flow rate conditions, with the alternating appearance of gas slugs and liquid slugs as typical flow characteristics. Under this flow pattern, the interaction between the gas phase and the liquid phase is very obvious, which can easily cause a strong impact on the pipeline and aggravate pipeline corrosion. In severe cases, it may even cause safety accidents and endanger the safety of the production process. Accurately measuring the flow process parameters of oil-gas-water three-phase slug flow is an important means to understand the flow behavior. Among the many flow process parameters, the length and alternation frequency of liquid and gas slugs, phase content, true flow rate, liquid film thickness, etc. can be used for detailed characterization of the flow state, which is of great significance for revealing and discovering new flow mechanisms and promoting the development of fluid mechanics. In addition, flow rate can be used for macroscopic characterization of flow state, which plays an important guiding role in production monitoring, safety assurance, and reservoir management.

[0003] At present, many researchers at home and abroad have developed a variety of sensing technologies for the measurement of slug flow, including electrical method, optical method, differential pressure method, ultrasonic method, etc. Among them, the electrical method uses the difference in electrical properties of different phases to realize the measurement of flow process parameters, such as conductivity sensor, capacitance sensor, wire mesh sensor, cross-sectional distributed sensor, etc. The electrical method has the advantages of fast dynamic response, low difficulty in test system design, safety and no radiation, and is mostly used for the measurement of detailed flow parameters of slug flow. However, the measurement range of the electrical method is easily limited. For example, the conductivity sensor requires that the continuous phase of the fluid must be a conductive phase, while the capacitance sensor requires that the continuous phase of the fluid must be a non-conductive phase or a weakly conductive phase. In addition, some electrical sensors have invasive characteristics and are prone to interfere with the flow field. The drastic fluctuations in the slug flow content and velocity also bring difficulties to invasive measurements. Laser has the characteristics of good directionality, good monochromaticity, high energy density, and good coherence. Therefore, optical methods often use the attenuation, scattering, interference, and diffraction of lasers to measure flow process parameters, such as particle image velocimetry (PIV) and laser Doppler velocimetry (LDV). However, the optical method requires light transmittance for fluids and pipe sections during measurement, and its measurement system is complex and expensive, which limits its industrial application. The differential pressure method uses the differential pressure generated before and after the fluid flows through the detection device to achieve flow measurement, and has the advantages of simple equipment, easy installation, and low price. However, Zhang et al. pointed out in an article titled "Flow measurement based on the combination of swirler and differential pressure under slug flow" published in Flow Measurement and Instrumentation, Vol. 88, No. 102263 in 2022 that the differential pressure method is effective and accurate for flow measurement of annular flow, stratified flow, and plug flow, but the huge pressure fluctuations in slug flow often lead to measurement failure. The ultrasonic method uses acoustic phenomena such as transmission, reflection, and scattering that occur when sound waves propagate in the fluid to measure flow process parameters. It has the advantages of simple sensor structure, easy installation and maintenance, no light transmittance requirements, and low cost, and shows great application potential in multiphase flow measurement.

[0004] Pulse wave ultrasonic Doppler technology is an important branch of ultrasonic method. This technology can not only measure the one-dimensional velocity profile through the range gate and the frequency information between the transmitted sound wave and the received sound wave, but also measure the gas-liquid interface position through amplitude attenuation and the transit time between the transmitted sound wave and the received sound wave. In recent years, pulse wave ultrasonic Doppler technology has been successfully applied in the study of flow characteristics of slug flow, but the research object is only for gas-water two-phase slug flow. Compared with the gas-water two-phase slug flow, the existence of two dispersed phases (bubbles and droplets) in the oil-gas-water three-phase slug flow aggravates the complexity of the phase distribution structure, velocity distribution and phase interaction. More parameters need to be measured to achieve accurate flow behavior characterization and flow measurement, which poses a challenge to the efficient acquisition and application of measurement information. The present invention proposes a method for measuring the total volume flow rate of oil-gas-water three-phase flow using pulse wave ultrasonic Doppler technology, which involves the comprehensive utilization of ultrasonic amplitude-frequency measurement information and the establishment of a measurement model. Summary of the invention

[0005] The purpose of the present invention is to provide an accurate, non-perturbing, low-cost method for measuring the total volume flow rate of a three-phase slug flow of oil, gas and water using a pulse wave ultrasonic Doppler sensor. The technical solution of the present invention is as follows:

[0006] A method for measuring the flow rate of an oil-gas-water three-phase slug flow based on pulse wave ultrasonic Doppler is provided. The method comprises the following steps: installing a pulse wave ultrasonic Doppler sensor obliquely at the bottom of a pipeline to ensure that the angle between the sound wave and the flow direction of the fluid is θ; based on the pulse echo intensity principle and the Doppler principle, using the pulse wave ultrasonic Doppler sensor to synchronously obtain echo intensity profile data reflecting the distribution characteristics of the phase interface and flow velocity profile data reflecting the distribution characteristics of the flow field; establishing a signal processing algorithm to realize the division of the slug flow unit structure according to the dynamic response of the test data to the flow process, and further extracting the relevant information of the proportion of different regions of the slug flow, the thickness and flow velocity of the liquid film in the gas-slug zone, the gas content in the gas-slug zone, and the flow velocity in the liquid-slug zone; finally, a physical model is used to fuse multiple information to realize the measurement of the total volume flow rate, which comprises the following steps:

[0007] (1) A pulse wave ultrasonic Doppler sensor is used to dynamically test the fully developed oil-gas-water three-phase slug flow, and the echo intensity profile data Amp(y, t) reflecting the distribution characteristics of the phase interface and the velocity profile data u(y, t) reflecting the distribution characteristics of the flow field are simultaneously obtained, where y∈(0, D) is the distance from the bottom of the pipeline, D is the pipeline diameter, t∈(0, T) is the time, and T is the sampling time. The sampling time T includes several complete slug flow unit structures; the pulse wave ultrasonic Doppler sensor is installed at an angle at the bottom of the pipeline to ensure that the angle between the sound wave and the fluid flow direction is θ; during the measurement, the piezoelectric ceramic chip is rotated at a repetition frequency f. PRF Intermittently transmit ultrasonic pulses into the fluid and receive echoes within the pulse interval;

[0008] (2) Using the echo intensity profile data Amp(y,t), the oil-gas-water three-phase slug flow unit structure is divided and the proportion of different areas is calculated, which is achieved by the following sub-steps:

[0009] (2.1) Input the echo intensity profile data Amp(y,t) and locate the position y where the echo peak appears in the echo intensity profile at each time t peak , and count the echo peak value y in the echo intensity profile within the sampling time T peak The probability distribution P(y) of appearing in the position interval [y,y+Δy];

[0010] (2.2) In the probability distribution P(y), find the maximum probability P max Corresponding pipeline radial position y max ;

[0011] (2.3)Use y max Divide the pipeline into two parts: when y ≥ y max When y < y max When , the position corresponding to y belongs to the lower part of the pipeline;

[0012] (2.4) At each time t, calculate the echo energy and Intensity(t) of the lower part of the pipeline:

[0013]

[0014] (2.5) Calculate the echo energy threshold Intensity th :

[0015]

[0016] Intensity_select(k)=Intensity(t),ifIntensity(t)>Intensity mean

[0017] K is the total number of Intensity_select(k);

[0018] (2.6) Using echo energy threshold Intensity th The echo energy and time series Intensity(t) of the lower part of the pipeline are determined to obtain the binary label time series Label(t):

[0019]

[0020] (2.7) Post-process the binary label time series Label(t) to remove the mislabeling caused by abnormal data points: In Label(t), if the time interval between two adjacent "1" labels is less than t s , then merge the two "1" labels to get Label r (t); After the merger is completed, Label r (t), if the duration of two “1” labels is less than t d , then reset the "1" label to the "0" label, and get Label f (t); In the final label time series Label f In (t), it is considered that the time when the label “1” appears corresponds to the time when the liquid elastic region appears, and the time when the label “0” appears corresponds to the time when the gas elastic region appears. s and t d The value of is empirically set according to the slug flow state;

[0021] (2.8) Let L u , L g and L l are the unit structure of the oil-gas-water three-phase slug flow, the length of the gas-slug zone and the liquid-slug zone, and the Label is counted within the sampling time T. f The number of label "0" and label "1" in (t) is calculated, and the proportion of liquid elastic area and gas elastic area in the oil-gas-water three-phase elastic flow unit structure is calculated. and

[0022] (3) Obtain the filtered liquid film thickness time series H r (t);

[0023] (4) Calculation of the average gas content α in the gas-elastic zone gg ;

[0024] (5) Calculate the average true flow velocity of the liquid film in the gas-elastic zone and the average true flow velocity of the liquid bomb in the liquid-elastic zone;

[0025] (6) Calculate the total volume flow rate Q of the oil, gas and water three-phase slug flow.

[0026] Furthermore, in step (2.1), the echo peak value y in the echo intensity profile within the sampling time T is peak The probability P(y) of appearing in the position interval [y,y+Δy] is:

[0027]

[0028] Where P(y) represents the peak value y of the echo in the echo intensity profile within the sampling time. peakThe probability of appearing in the position interval [y,y+Δy], Num(y≤y max ≤y+Δy) represents the peak value y of the echo in the echo intensity profile within the sampling time peak The number of occurrences in the position interval [y,y+Δy].

[0029] Furthermore, step (3) obtains the filtered liquid film thickness time series H r (t), which is implemented by the following sub-steps:

[0030] (3.1) Within the sampling time T, at each time t when the gas-elastic zone appears, the liquid film thickness value is set to the position where the maximum echo amplitude appears in the echo intensity profile data; at each time t when the liquid-elastic zone appears, the liquid film thickness value is set to the tube diameter D, that is:

[0031]

[0032] in, It represents the corresponding y value when any function f(y) with y as the variable takes the maximum value;

[0033] (3.2) The median filter algorithm is used to filter the liquid film thickness time series H(t) to obtain the filtered liquid film thickness time series H r (t):

[0034] H r (t) = MedFilter[H(t)]

[0035] Among them, MedFilter (*) represents the median filtering operation.

[0036] Furthermore, in step (4), the average gas content α of the gas-elastic zone is calculated gg The method is:

[0037]

[0038] Where R is the pipe radius, A is the pipe cross-sectional area, is the average liquid film thickness in the aeroelastic zone,

[0039] is the central angle corresponding to the chord length of the radial position of the pipe where the liquid film thickness is located,

[0040] And β<180°.

[0041] Furthermore, step (5) calculates the average true flow velocity of the liquid film in the gas-elastic zone and the average true flow velocity of the liquid bomb in the liquid-elastic zone, which is implemented by the following sub-steps:

[0042] (5.1) Calculate the average velocity fluctuation time series using the integral method

[0043]

[0044] (5.2) Calculate the average true velocity u of the liquid film in the gas-elastic zone f The average real velocity u of the liquid bomb in the liquid bomb area s :

[0045] t∈ gas-elastic zone

[0046] t∈Liquid-elastic region

[0047] Among them, M g and M l They are the flow velocity points occupied by the gas-elastic zone and the liquid-elastic zone respectively within the sampling time T.

[0048] Furthermore, in step (6), the method for solving the total volume flow rate Q of the oil-gas-water three-phase slug flow is as follows: Ignore the velocity slip between the oil and water in the liquid film and the velocity slip between the oil, gas and water in the liquid slug, and take the average gas content α of the gas-slug region as gg , the average true velocity u of the liquid film in the gas-elastic zone f , the average real velocity u of the liquid bomb in the liquid bomb area s , the proportion of different regions in the slug flow unit structure L l / L u , L g / L u Substitute the following equations to solve the total volume flow rate Q of the oil, gas and water three-phase slug flow:

[0049]

[0050] The essential features of the present invention are: using a single-mode pulse wave ultrasonic Doppler sensor to synchronously obtain echo intensity profile data reflecting the distribution characteristics of the phase interface and velocity profile data reflecting the distribution characteristics of the flow field; by making full and reasonable use of the test data, the division of the elastic flow unit structure is realized, and the proportion of different areas, the average liquid film thickness and average true flow velocity of the gas-elastic area, the gas content of the gas-elastic area, and the average true flow velocity of the liquid-elastic area are extracted; by fusing multiple information through a physical model, accurate measurement of the total volume flow rate is achieved. The beneficial effects and advantages of the present invention are as follows:

[0051] 1. This method uses a single-mode pulse wave ultrasonic Doppler sensor, which has the advantages of simple structure, low cost, and no interference with the flow process;

[0052] 2. This method can obtain the detailed parameters of the slug flow process by processing and comprehensively utilizing the echo intensity profile data and flow velocity profile data, and has important theoretical and engineering application value.

[0053] 3. This method can quickly and accurately measure the total volume flow rate by fusing multiple test information through a physical model. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] The following drawings describe selected embodiments of the present invention, which are exemplary and non-exhaustive or limiting, wherein:

[0055] Figure 1 The pulse wave ultrasonic Doppler sensor installation method and working timing diagram in the measurement method of the present invention;

[0056] Figure 2 Schematic diagram of the flow structure of the oil-gas-water three-phase slug flow in the measurement method of the present invention;

[0057] Figure 3 Flow chart of the structural division of the oil, gas and water three-phase slug flow unit in the measurement method of the present invention;

[0058] Figure 4 Schematic diagram of the median filtering algorithm in the measurement method of the present invention;

[0059] Figure 5 A flow chart for calculating the total volume flow rate of the oil, gas and water three-phase slug flow in the measurement method of the present invention;

[0060] Figure 6 It is the division result of the oil-gas-water three-phase slug flow unit structure in the measurement method of the present invention.

[0061] Figure 7 It is the measurement result of the total volume flow rate of the oil, gas and water three-phase slug flow in the measurement method of the present invention. DETAILED DESCRIPTION

[0062] The embodiments of the present invention are described in detail below with reference to the accompanying drawings and the appended tables.

[0063] Figure 1 The pulse wave ultrasonic Doppler sensor installation method and working sequence diagram in the measurement method of the present invention. The pulse wave ultrasonic Doppler sensor 0 used in the present invention patent needs to be installed at an angle at the bottom of the horizontal pipe 1 to ensure that the sound wave propagates against the fluid flow direction 2, and the angle between the sound wave center axis direction 3 and the fluid flow direction 2 is θ (45°≤θ≤60°). The center frequency of the pulse wave ultrasonic Doppler sensor is 1MHz, and the working sequence during measurement is: at a certain pulse repetition frequency f PRF Ultrasonic pulses 401 are intermittently emitted into the fluid, and ultrasonic echoes modulated by the fluid are received within the pulse interval 402. According to the pulse echo intensity principle, the amplitude information of the received sound wave is related to the distribution characteristics of the phase interface of the measured fluid; according to the Doppler principle, the frequency offset information between the received sound wave and the emitted sound wave is related to the flow velocity distribution characteristics of the measured fluid.

[0064] Figure 2 Schematic diagram of the flow structure of the oil-gas-water three-phase slug flow in the measurement method of the present invention. The oil-gas-water three-phase slug flow is a typical intermittent flow type, characterized by the alternating appearance of gas slugs and liquid slugs. A complete slug flow unit structure 5 consists of a length of L g The gas elastic zone 6 and the length L l The total length L of the elastic flow unit structure 5 is u Meet L u =L g +L l . In the gas-elastic zone 6, the liquid phase and the gas phase present an obvious stratified flow structure due to the density difference: the gas phase with lower density flows along the top of the pipe in the form of long bubbles, while the liquid phase with higher density flows along the bottom of the pipe in the form of a liquid film, and the oil phase in the liquid film is distributed in the water phase in the form of discrete droplets. In the liquid-elastic zone 7, under the influence of the vortex at the head of the liquid-elastic zone, both the gas phase and the oil phase are distributed in the water phase in the form of discrete phases. During the flow of the oil-gas-water three-phase slug flow, a "pick-up effect" occurs at the nose of the liquid-elastic zone 7, that is, the liquid bullet continuously picks up the liquid in the liquid film in the previous slug unit structure; at the same time, a "falling-off effect" occurs at the tail of the liquid-elastic zone 7, that is, the liquid in the liquid bullet continuously falls into the liquid film. When the flow is fully developed, the "pick-up rate" of the liquid at the head of the liquid bullet is almost equal to the "falling-off rate" of the liquid at the tail of the liquid bullet, and the length of the slug flow unit structure remains stable. In the oil-gas-water three-phase slug flow unit structure 5, the velocity slip between the oil phase, gas phase and water phase in the liquid slug zone 7 can be ignored, and the actual flow velocity is u s ; The actual flow rate of the gas phase in the liquid film zone 6 is u g , the velocity slip between the oil phase and the water phase in the liquid film can be ignored, and the actual flow rate is u f .

[0065] Figure 3 This is a flow chart for the division of the unit structure of the oil-gas-water three-phase elastic flow in the measurement method of the present invention. When ultrasonic waves propagate in the oil-gas-water three-phase flow, they will be reflected or scattered when they encounter the gas-liquid or oil-water interface. Since the difference in acoustic impedance of the gas-liquid interface is significantly greater than that of the oil-water interface, the echo intensity reflected by the gas-liquid interface is much greater than that of the oil-water interface. Therefore, in the oil-gas-water three-phase elastic flow, there are obvious differences in the distribution forms of the gas-liquid interface between the gas-elastic zone and the liquid-elastic zone. The division of the gas-elastic zone and the liquid-elastic zone can be achieved using echo intensity profile data, which specifically includes the following four key processes: 1) Input the time series Amp(y,t) of the echo intensity profile data; 2) Statistically calculate the probability distribution of the position where the maximum echo amplitude value appears in the echo intensity profile, and use the position y with the maximum probability to obtain the maximum echo value. maxDivide the pipeline into two parts, the upper and lower parts; 3) Calculate the time series of echo energy fluctuation Intensity(t) in the lower part of the pipeline, and use the energy threshold Intensity th (t) Obtain the binary label time series Label(t); 4) Post-process the labeled time series Label(t) to remove the mislabeling caused by abnormal data points. Finally, it is believed that the moment when the label "1" appears corresponds to the moment when the liquid elastic zone appears, and the moment when the label "0" appears corresponds to the moment when the gas elastic zone appears.

[0066] Figure 4 The figure is a schematic diagram of the median filter algorithm in the measurement method of the present invention. The median filter algorithm is a nonlinear smoothing filter signal processing method based on the sorting statistics theory, which can effectively suppress impulse noise. When performing median filtering on a one-dimensional time series, it is first necessary to determine a certain time t i The data x i The neighborhood (window) is the center; then all the data in the neighborhood are sorted in ascending order, and the median of the sorting is used as the new value of the neighborhood center, that is, replacing x i ; When the window moves along the time axis, the signal can be smoothed. Generally, the larger the window size, the smoother the median filter output will be, but it may also erase useful signal features. Therefore, the window size should be determined based on the actual signal and noise characteristics.

[0067] Figure 5 The figure is a flow chart for calculating the total volume flow rate of the three-phase slug flow of oil, gas and water in the measurement method of the present invention.

[0068] The method proposed in the present invention for obtaining the total volume flow rate of the oil, gas and water three-phase slug flow based on a pulse wave ultrasonic Doppler sensor comprises the following steps:

[0069] Step 1: Exploitation Figure 1 The pulse wave ultrasonic Doppler sensor shown in the figure performs dynamic testing on a fully developed oil-gas-water three-phase slug flow to obtain test data. The pulse wave ultrasonic sensor works in a self-transmitting and self-receiving mode, that is, during measurement, the piezoelectric ceramic chip transmits the pulse wave ultrasonic wave to the slug flow at a repetition frequency f. PRF Ultrasonic pulses are intermittently emitted into the fluid, and the echoes are received by the same piezoelectric ceramic chip during the pulse interval.

[0070] 1) When ultrasound propagates in the oil, gas and water three-phase elastic flow, it will emit reflection when it encounters the phase interface. According to the pulse echo intensity principle, the magnitude of the echo amplitude and the time of occurrence reflect the distribution of the phase interface in the pipeline. Therefore, by performing amplitude demodulation on the received echo, the echo intensity profile data Amp(y,t) can be obtained, where t∈(0,T) is the time, T is the sampling time, y∈(0,D) is the distance from the bottom of the pipeline, and D is the diameter of the pipeline. Each column in Amp(y,t) corresponds to an echo intensity profile at the radial position along the pipeline at time t.

[0071] 2) According to the Doppler effect, the relative movement of the discrete phase (bubbles or droplets) in the oil, gas and water three-phase slug flow relative to the pulse wave ultrasonic Doppler sensor causes a frequency offset between the transmitted sound wave and the received sound wave, and the offset is proportional to the relative motion speed. Therefore, the range gate is used to demodulate the frequency of the received wave and calculate the flow velocity, and the flow velocity profile data u(y,t) can be obtained, where t∈(0,T) is the time, T is the sampling time, y∈(0,D) is the distance from the bottom of the pipeline, and D is the diameter of the pipeline. Each column in u(y,t) corresponds to a flow velocity profile at the radial position along the pipeline at time t.

[0072] The sampling time T should be able to contain at least several complete Figure 2 The oil, gas and water three-phase slug flow unit structure is shown.

[0073] Step 2: Follow the steps below: Figure 3 The process shown uses echo intensity profile data to divide the oil, gas and water three-phase slug flow unit structure and calculate the proportion of different areas.

[0074] 1) Input the echo intensity profile data Amp(y,t) and locate the position y where the echo peak appears in the echo intensity profile at each time t peak , and statistically analyze its probability distribution within the sampling time T:

[0075]

[0076] Where P(y) represents the peak value y of the echo in the echo intensity profile within the sampling time. peak The probability of appearing in the position interval [y,y+Δy], Num(y≤y max ≤y+Δy) represents the peak value y of the echo in the echo intensity profile within the sampling time peak The number of occurrences in the position interval [y,y+Δy];

[0077] 2) In the probability distribution graph P(y), find the maximum probability P max Corresponding pipeline radial position y max :

[0078] ymax =y, when P = P max (2)

[0079] y max It reflects the radial position information of the pipeline where the lower interface of the long bubble in the gas-elastic zone in the oil-gas-water three-phase slug flow unit structure most often appears within the sampling time T.

[0080] 3)Use y max Divide the pipeline into two parts: for y ≥ y max , the position corresponding to y belongs to the upper part of the pipeline; for y<y max , at this time, the position corresponding to y belongs to the lower part of the pipeline;

[0081] 4) At each time t, the echo energy and Intensity(t) of the lower part of the pipeline are calculated using the following formula:

[0082]

[0083] 5) Calculate the echo energy threshold Intensity using the following formula: th :

[0084]

[0085] Intensity_select(k)=Intensity(t),ifIntensity(t)>Intensity mean (5)

[0086]

[0087] 6) Using echo energy threshold Intensity th The echo energy and time series Intensity(t) of the lower part of the pipeline are determined to obtain the binary label time series Label(t):

[0088]

[0089] 7) Post-process the binary label time series Label(t) to remove mislabeling caused by abnormal data points: In Label(t), if the time interval between two adjacent "1" labels is less than t s , then merge the two "1" labels to get Label r (t); Label after the merger r In (t), if the duration of two "1" labels is less than td, the "1" label is "reset" to the "0" label, and the Label is obtained. f(t). In the final label time series Label f In (t), it is considered that the moment when the label “1” appears corresponds to the moment when the liquid elastic region appears, and the moment when the label “0” appears corresponds to the moment when the gas elastic region appears.

[0090] 8) Count the labels within the sampling time T f The number of label "0" and label "1" in (t) is calculated, and the proportion of the liquid elastic area and the gas elastic area in the oil-gas-water three-phase elastic flow unit structure is calculated:

[0091]

[0092]

[0093] Among them, Number (*) is for Label f (t) is a counting operator for the value of Lu, Lg and Ll, respectively, are the lengths of the unit structure of the oil-gas-water three-phase slug flow, the gas slug zone and the liquid slug zone.

[0094] Figure 6 The unit structure division result of a typical oil-gas-water three-phase slug flow obtained in step 2 above (experimental conditions: water flow rate 3.99m 3 / h, oil flow rate 0.59m 3 / h, air flow rate 19.47m 3 / h). Among them, Figure 6 (a) is the echo intensity profile data Amp(y,t) displayed as a spectrum. It is found that: with the alternation of the gas-bomb area and the liquid-bomb area, the echo intensity profile shows a periodic change. Specifically, when the liquid bomb passes through, under the influence of the vortex at the head of the liquid bomb, discrete bubbles and oil droplets appear on the entire pipe cross-section. The bubbles will have a strong reflection effect on the ultrasound, resulting in strong echo points appearing at the radial position y of each pipe; and when the gas bomb passes through, the stratified flow of gas phase and liquid phase forms an open gas-liquid interface, which has a strong reflection effect on the ultrasound, and most of the discrete phases in the liquid film are oil droplets with only a small amount of bubbles, which causes the strong echo points to appear only near the radial position of the pipe where the gas-liquid interface is located. The dividing line y between the upper and lower parts of the pipe calculated using sub-steps 1)-3) of step 2 max Marked with a dotted line Figure 6 In (a), it is found that the location of the strong echo point in the echo intensity distribution of the lower part of the pipeline is significantly different when the liquid bomb passes through and when the gas bomb passes through. The echo energy and time series Intensity(t) of the lower part of the pipeline calculated by sub-step 4) of step 2 are as follows: Figure 6 As shown in (b), it is found that the echo energy and value when the liquid bullet passes through are greater than the echo energy and value when the gas bullet passes through. The binary label time series Label(t) obtained by step 2, sub-step 5) is as follows Figure 6 As shown in (c), it is found that: due to the large number of bubbles widely distributed in the pipe cross section in the liquid bomb, the high values ​​of the echo energy and the echo energy in the lower part of the pipe appear frequently, and most of the "1" labels appear in the liquid bomb area. However, some scattered "1" labels that are incorrectly calibrated can still be observed in the gas bomb area. The main reasons for their appearance include the following two aspects: on the one hand, due to the "shedding effect" at the tail of the liquid bomb, the high-speed liquid in the liquid bomb continuously falls into the low-speed liquid film, and the mixing of liquids with different flow rates causes more bubbles to be generated in the initial stage of the liquid film, resulting in strong echo data in the lower part of the pipe; on the other hand, due to the existence of the "wave" structure on the gas-liquid interface in the gas-bomb area, part of the gas-liquid interface height falls into the y max The following results in strong echo data in the lower part of the pipeline. In order to realize the division of different areas in the oil, gas and water three-phase elastic flow unit structure, it is necessary to further post-process the binary label time series Label(t). The result of post-processing Label(t) by "merging" and "resetting" in step 2 (7) is: r (t) and Label f (t) respectively as Figure 6 (d) and 6(e). The purpose of the “merge” operation is to merge the “1” labels that appear in the cluster. The criterion is: if the time interval between two adjacent “1” labels is less than t s , then the two "1" labels are "merged". Experimental tests have found that: s The value of is affected by the pulse repetition frequency and the slug flow state: the pulse repetition frequency determines t s The minimum value of t is that only one echo intensity profile data can be obtained under one pulse wave excitation. Therefore, the pulse repetition frequency is the sampling frequency of the echo intensity profile. s The minimum value of should be greater than 2 times the pulse repetition period (the inverse of the pulse repetition frequency); the influence of the slug flow state determines t s If the liquid bullet of the slug flow contains a large number of bubbles dispersed on the pipe cross section, high values ​​of the echo energy and the echo energy in the lower part of the pipe will appear frequently. At this time, t s The maximum value of should be less than 300 times the pulse repetition period. The purpose of the "reset" operation is to reset the scattered "1" labels. The criterion is: if the duration of two "1" labels is less than t d , then the "1" label is "reset" to the "0" label. Experimental tests have found that: t d The value range of is affected by the average duration of the liquid bullet in the bullet flow. The recommended value is t d The minimum value of should be greater than 1 / 5 of the average duration of the liquid bomb, t dThe maximum value of should be less than 1 / 2 of the average duration of the liquid bullet; however, the average duration of the liquid bullet in the slug flow is affected by the average flow velocity of the liquid bullet and the average length of the liquid bullet, so t d The value of should be set according to the actual slug flow state. In the embodiment of the present invention, t s Set to 0.028s, t d Set to 0.2s.

[0095] Step 3: Obtain the time series of liquid film thickness.

[0096] 1) Within the sampling time T, at each time t when the gas-elastic zone appears, the liquid film thickness value is set to the position where the maximum echo amplitude appears in the echo intensity profile data; at each time t in the liquid-elastic zone, the liquid film thickness value is set to the tube diameter D, that is:

[0097]

[0098] in, It represents the value of y corresponding to the maximum value of any function f(y) with y as the variable.

[0099] 2) Under the condition of single ultrasonic sensor measurement, the interface wave on the gas-liquid interface easily leads to echo leakage, resulting in some irregular pulse "noise" interference in the liquid film thickness time series H(t). In order to improve the calculation accuracy of liquid film thickness, the following method is used: Figure 4 The median filtering algorithm shown in the figure performs filtering on the liquid film thickness time series H(t) to obtain the filtered liquid film thickness time series H r (t):

[0100] H r (t)=MedFilter[H(t)] (11)

[0101] Among them, MedFilter(*) represents the filtering operation.

[0102] Step 4: Calculate the average gas content α in the gas-elastic zone using the following formula: gg :

[0103]

[0104] Where R is the pipe radius, A is the pipe cross-sectional area, is the average liquid film thickness in the aeroelastic zone, It is the central angle corresponding to the chord length at the radial position of the pipe where the liquid film thickness is located, and β is less than 180°.

[0105] Step 5: Calculate the average true flow velocity of the liquid film in the gas-elastic zone and the average true flow velocity of the liquid bomb in the liquid-elastic zone.

[0106] 1) Calculate the average velocity fluctuation time series using the integral method

[0107]

[0108] Due to the large acoustic impedance difference between gas and liquid, the sound wave is almost totally reflected at the large-scale gas-liquid interface. Therefore, in the gas-elastic region of the oil-gas-water three-phase slug flow, the "false velocity" outside the liquid film does not participate in the calculation of the average flow velocity.

[0109] 2) Calculate the average true velocity u of the liquid film in the gas-elastic zone using the following formula: f The average real velocity u of the liquid bomb in the liquid bomb area s :

[0110] t∈ gas-elastic zone (14)

[0111] t∈Liquid-elastic zone (15)

[0112] Among them, M g and M l They are the flow velocity points occupied by the gas-elastic zone and the liquid-elastic zone respectively within the sampling time T.

[0113] Step 6: For a fully developed oil-gas-water three-phase slug flow, the length of each region in the slug flow unit structure remains stable. Therefore, the gas phase, oil phase, and water phase satisfy the mass balance equation in a complete slug flow unit structure, and the gas phase and liquid phase also satisfy the mass balance equation in an independent liquid-slug zone. If the velocity slip between oil and water in the liquid film is ignored, and the velocity slip between oil, gas, and water in the liquid-slug is ignored, the total volume flow rate of the oil-gas-water three-phase slug flow can be solved by the following set of equations:

[0114]

[0115] Figure 7 The measurement result of the total volume flow rate of the oil-gas-water three-phase slug flow in the measurement method of the present invention. In the figure, the horizontal axis is the standard reference value of the total volume flow rate, and the vertical axis is the calculated value of the total volume flow rate using the method proposed by the present invention. It can be seen from the figure that there is a good consistency between the calculated value of the total volume flow rate of the method proposed by the present invention and the standard reference value, and the average relative error is 2.71%, which proves that the proposed method is effective and accurate.

Claims

1. A method for measuring the flow rate of oil, gas and water three-phase slug flow based on pulse wave ultrasonic Doppler, wherein the pulse wave ultrasonic Doppler sensor is obliquely installed at the bottom of the pipeline to ensure that the angle between the sound wave and the flow direction of the fluid is θ; based on the pulse echo intensity principle and the Doppler principle, the pulse wave ultrasonic Doppler sensor is used to synchronously obtain echo intensity profile data reflecting the distribution characteristics of the phase interface and flow velocity profile data reflecting the distribution characteristics of the flow field; according to the dynamic response of the test data to the flow process, a signal processing algorithm is established to realize the division of the slug flow unit structure, and further extract the proportion of different areas of the slug flow, the thickness and flow velocity of the liquid film in the gas-slug zone, the gas content in the gas-slug zone, and the flow velocity in the liquid-slug zone; finally, a variety of information is integrated through a physical model to realize the measurement of the total volume flow, which includes the following steps: (1) A pulse wave ultrasonic Doppler sensor is used to dynamically test the fully developed oil-gas-water three-phase slug flow, and the echo intensity profile data Amp(y, t) reflecting the distribution characteristics of the phase interface and the velocity profile data u(y, t) reflecting the distribution characteristics of the flow field are simultaneously obtained, where y∈(0, D) is the distance from the bottom of the pipeline, D is the pipeline diameter, t∈(0, T) is the time, T is the sampling time, and the sampling time T includes several complete slug flow unit structures; the pulse wave ultrasonic Doppler sensor is installed at an angle at the bottom of the pipeline to ensure that the angle between the sound wave and the fluid flow direction is θ; during the measurement, the piezoelectric ceramic chip is rotated at a repetition frequency f PRF Intermittently transmit ultrasonic pulses into the fluid and receive echoes within the pulse interval; (2) Using the echo intensity profile data Amp(y,t), the oil-gas-water three-phase slug flow unit structure is divided and the proportion of different areas is calculated, which is achieved by the following sub-steps: (2.1) Input the echo intensity profile data Amp(y,t) and locate the position y where the echo peak appears in the echo intensity profile at each time t peak , and count the echo peak value y in the echo intensity profile within the sampling time T peak The probability distribution P(y) of appearing in the position interval [y,y+Δy]; (2.2) In the probability distribution P(y), find the maximum probability P max Corresponding pipeline radial position y max ; (2.3)Use y max Divide the pipeline into two parts: when y ≥ y max When y < y max When , the position corresponding to y belongs to the lower part of the pipeline; (2.4) At each time t, calculate the echo energy and Intensity(t) of the lower part of the pipeline: (2.5) Calculate the echo energy threshold Intensity th : Intensity_select(k)=Intensity(t),ifIntensity(t)>Intensity mean K is the total number of Intensity_select(k); (2.6) Using echo energy threshold Intensity th The echo energy and time series Intensity(t) of the lower part of the pipeline are determined to obtain the binary label time series Label(t): (2.7) Post-process the binary label time series Label(t) to remove the mislabeling caused by abnormal data points: In Label(t), if the time interval between two adjacent "1" labels is less than t s , then the two "1" labels are "merged" to get Label r (t); Label after the merger r (t), if the duration of two "1" labels is less than t d , then reset the "1" label to the "0" label, and get Label f (t); In the final label time series Label f In (t), it is considered that the time when the label "1" appears corresponds to the time when the liquid elastic region appears, and the time when the label "0" appears corresponds to the time when the gas elastic region appears. s and t d The value of is empirically set according to the slug flow state; (2.8) Let L u , L g and L l are the unit structure of the oil-gas-water three-phase slug flow, the length of the gas-slug zone and the liquid-slug zone, and the Label is counted within the sampling time T. f The number of label "0" and label "1" in (t) is calculated, and the proportion of liquid elastic area and gas elastic area in the oil-gas-water three-phase elastic flow unit structure is calculated. and (3) Obtain the filtered liquid film thickness time series H r (t); (4) Calculation of the average gas content α in the gas-elastic zone gg ; (5) Calculate the average true flow velocity of the liquid film in the gas-elastic zone and the average true flow velocity of the liquid bomb in the liquid-elastic zone; (6) Calculate the total volume flow rate Q of the oil, gas and water three-phase slug flow.

2. The oil-gas-water three-phase slug flow measurement method according to claim 1 is characterized in that: In step (2.1), the peak value y of the echo intensity profile within the sampling time T is peak The probability P(y) of appearing in the position interval [y,y+Δy] is: Where P(y) represents the peak value y of the echo in the echo intensity profile within the sampling time. peak The probability of appearing in the position interval [y,y+Δy], Num(y≤y max ≤y+Δy) represents the peak value y of the echo in the echo intensity profile within the sampling time peak The number of occurrences in the position interval [y,y+Δy].

3. The oil-gas-water three-phase slug flow measurement method according to claim 1 is characterized in that: Step (3) Obtain the filtered liquid film thickness time series H r (t), which is implemented by the following sub-steps: (3.1) Within the sampling time T, at each time t when the gas-elastic zone appears, the liquid film thickness value is set to the position where the maximum echo amplitude appears in the echo intensity profile data; at each time t when the liquid-elastic zone appears, the liquid film thickness value is set to the tube diameter D, that is: in, It represents the corresponding y value when any function f(y) with y as the variable takes the maximum value; (3.2) The median filter algorithm is used to filter the liquid film thickness time series H(t) to obtain the filtered liquid film thickness time series H r (t): H r (t)=MedFilter[H(t)] Among them, MedFilter (*) represents the median filtering operation.

4. The oil-gas-water three-phase slug flow measurement method according to claim 1, characterized in that: In step (4), the average gas content α in the gas-elastic zone is calculated gg The method is: Where R is the pipe radius, A is the pipe cross-sectional area, is the average liquid film thickness in the aeroelastic zone, It is the central angle corresponding to the chord length at the radial position of the pipe where the liquid film thickness is located, and β is less than 180°.

5. The oil-gas-water three-phase slug flow measurement method according to claim 1, characterized in that: Step (5) calculates the average true flow velocity of the liquid film in the gas-elastic zone and the average true flow velocity of the liquid bomb in the liquid-elastic zone, which is achieved by the following sub-steps: (5.1) Calculate the average velocity fluctuation time series using the integral method (5.2) Calculate the average true velocity u of the liquid film in the gas-elastic zone f The average real velocity u of the liquid bomb in the liquid bomb area s : Among them, M g and M l They are the flow velocity points occupied by the gas-elastic zone and the liquid-elastic zone respectively within the sampling time T.

6. The oil-gas-water three-phase slug flow measurement method according to claim 1, characterized in that: In step (6), the method for solving the total volume flow rate Q of the oil-gas-water three-phase slug flow is as follows: Ignore the velocity slip between the oil and water in the liquid film and the velocity slip between the oil, gas and water in the liquid slug, and take the average gas content α of the gas slug region as gg , the average true velocity u of the liquid film in the gas-elastic zone f , the average real velocity u of the liquid bomb in the liquid bomb area s , the proportion of different regions in the slug flow unit structure L l / L u , L g / L u Substitute the following equations to solve the total volume flow rate Q of the oil, gas and water three-phase slug flow:

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