Method for detecting phase fractions of a multiphase flow

Abstract

The application provides a method for detecting phase content rate of multiphase flow. The method comprises: sampling the multiphase flow to be detected to obtain a multiphase flow sample, and performing three-phase separation on oil, gas and water in the multiphase flow sample; performing nuclear magnetic resonance on pure water and water and oil in the multiphase flow sample respectively to obtain corresponding first amplitude values of free decay signals, and determining hydrogen-containing indexes corresponding to the water and the oil by using the first amplitude values; applying a diffusion editing pulse sequence to the water and the oil to obtain diffusion coefficients corresponding to the water and the oil; performing pulse emission on the multiphase flow to be detected by using a variable echo interval pulse sequence to obtain echo signals, and determining the phase content rate of the multiphase flow to be detected according to the echo signals, the hydrogen-containing indexes and the diffusion coefficients. The application makes up for the deficiency that it is difficult to distinguish oil and water, realizes quantitative determination of different fluid component contents, does not need to collect relaxation information of the measured fluid, has fast measurement speed, and can realize online measurement of multiphase flow phase content rate with full range, high efficiency, environmental protection, safety and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of petroleum industry, in particular to a detection method of phase content of multiphase flow. BACKGROUND

[0002] In the industrial links of oil exploitation, gathering and transportation, fracturing and oil testing, there are a large number of complex multiphase fluids that need to be detected. These complex fluids are mainly composed of three different components, i.e. crude oil, formation water and natural gas. In addition, due to the needs of industrial production, the multiphase flow often maintains a continuous flow state, which needs to be detected online. This brings great difficulty to the quantitative detection of phase content, which means that the traditional method relying on relaxation spectrum and diffusion spectrum for phase content measurement is no longer applicable.

[0003] The existing detection method periodically (once a day or even longer) samples the multiphase flow to be detected, and then separates the layers based on the density difference of each component by natural sedimentation or centrifugation, and then measures. The disadvantages of this method are obvious: (1) the fluid flow state needs to be blocked for sampling (hinders production); (2) the sample after detection is discarded, causing pollution; (3) the sampling process needs time to detect in the laboratory, causing the detection data to lag and low efficiency; (4) the change of sample temperature and pressure during the sampling process may cause the change of its physical parameters, and the measurement result cannot reflect the real data of the fluid in the pipeline.

[0004] The application of nuclear magnetic resonance technology in the quantitative detection of complex fluids is very mature, and it is outstanding among other technologies due to its advantages of accuracy, greenness and safety. However, the current nuclear magnetic resonance detection technology of complex fluids also relies on sampling measurement, that is, it cannot be used for online measurement of flowing fluid. SUMMARY

[0005] The main purpose of the embodiment of the present application is to provide a detection method of phase content of multiphase flow, which can realize online measurement of phase content of multiphase flow and overcome the difficulty in distinguishing components when using relaxation time parameter.

[0006] In order to achieve the above purpose, the embodiment of the present application provides a detection method of phase content of multiphase flow, which comprises:

[0007] Sampling the multiphase flow to be detected to obtain a multiphase flow sample, and performing three-phase separation on oil, gas and water in the multiphase flow sample;

[0008] Performing nuclear magnetic resonance on pure water and water and oil in the multiphase flow sample respectively to obtain the first amplitude value of the corresponding free decay signal, and determining the hydrogen index corresponding to water and oil in the multiphase flow sample by using the first amplitude value;

[0009] applying a diffusion editing pulse sequence to the water and the oil in the multi-phase flow sample to obtain a diffusion coefficient corresponding to the water and the oil in the multi-phase flow sample;

[0010] applying a variable echo spacing pulse sequence to the multi-phase flow under test to obtain echo signals, and determining phase fractions corresponding to the oil, the gas and the water in the multi-phase flow under test according to the echo signals, the hydrogen index and the diffusion coefficient.

[0011] Optionally, in an embodiment of the present application, the method further comprises: using the phase fractions corresponding to the oil, the gas and the water in three single-phase fluids to carry out oil exploitation, gathering and transportation, fracturing and oil testing.

[0012] Optionally, in an embodiment of the present application, the three-phase separation of the oil, the gas and the water in the multi-phase flow sample comprises: using a static method or a centrifugal technique to carry out three-phase separation on the multi-phase flow sample to obtain the oil, the gas and the water in three single-phase fluids.

[0013] Optionally, in an embodiment of the present application, the measurement of the free induction decay signal first amplitude corresponding to the pure water and the water and the oil in the multi-phase flow sample comprises: placing the pure water and the water and the oil in the multi-phase flow sample into a test container; wherein the inner diameter and the outer diameter of the test container are the same as the fluid pipe inner diameter and the fluid pipe outer diameter of the multi-phase flow nuclear magnetic resonance flowmeter, and the length of the test container is greater than the antenna length of the multi-phase flow nuclear magnetic resonance flowmeter; and placing the test container in a detection area of the multi-phase flow nuclear magnetic resonance flowmeter to measure the free induction decay signal first amplitude corresponding to the pure water and the water and the oil in the multi-phase flow sample.

[0014] Optionally, in an embodiment of the present application, the determination of the hydrogen index corresponding to the water and the oil in the multi-phase flow sample using the first amplitude comprises: determining the hydrogen index of the water in the multi-phase flow sample according to the ratio of the first amplitude of the free induction decay signal of the water in the multi-phase flow sample to the first amplitude of the free induction decay signal of the pure water; and determining the hydrogen index of the oil in the multi-phase flow sample according to the ratio of the first amplitude of the free induction decay signal of the oil in the multi-phase flow sample to the first amplitude of the free induction decay signal of the pure water.

[0015] Optionally, in an embodiment of the present application, the application of the variable echo spacing pulse sequence to the multi-phase flow under test to obtain echo signals comprises: connecting the multi-phase flow under test with a multi-phase flow nuclear magnetic resonance flowmeter so that the multi-phase flow under test continuously flows under a probe of the multi-phase flow nuclear magnetic resonance flowmeter, and applying a variable echo spacing pulse sequence to the multi-phase flow under test to carry out twice pulse emission with different half echo spacings to obtain echo signals including first echo signals and second echo signals.

[0016] Optionally, in an embodiment of the present application, the using the variable echo interval pulse sequence to perform twice pulse emission with different half echo intervals for the multi-phase flow to be measured comprises: performing pulse emission for the multi-phase flow to be measured using a 90-degree pulse and an 180-degree pulse with a first half echo interval, to obtain a first echo signal and a first scan value; performing pulse emission for the multi-phase flow to be measured using a 90-degree pulse and an 180-degree pulse with a second half echo interval, to obtain a second echo signal.

[0017] Optionally, in an embodiment of the present application, the determining the phase content rates of oil, gas and water in the multi-phase flow to be measured according to the echo signals, the hydrogen index and the diffusion coefficient comprises: determining the phase content rates of oil, gas and water in the multi-phase flow to be measured according to the first echo signal, the second echo signal, the first half echo interval, the second half echo interval, the hydrogen index and the diffusion coefficient.

[0018] The present application makes up for the deficiency that it is difficult to distinguish oil and water using the relaxation time difference, realizes the quantification of the content of different fluid components based on the difference of the diffusion coefficients of the fluid components, does not need to collect the relaxation information of the measured fluid, has a fast measurement speed, and can realize the online measurement of the phase content rate of the multi-phase flow with full range, high efficiency, environmental protection and safety. BRIEF DESCRIPTION OF DRAWINGS

[0019] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the drawings needed in the following embodiment description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without any creative effort.

[0020] Figure 1 A flow chart of a multi-phase flow phase content rate detection method in an embodiment of the present application;

[0021] Figure 2 A flow chart of determining the first amplitude value of the free attenuation signal in an embodiment of the present application;

[0022] Figure 3 A flow chart of a variable echo interval pulse sequence scanning in an embodiment of the present application;

[0023] Figure 4 A flow chart of a multi-phase flow phase content rate detection in a specific embodiment of the present application;

[0024] Figure 5A And Figure 5B A schematic diagram of a variable echo interval pulse sequence in a specific embodiment of the present application. DETAILED DESCRIPTION

[0025] The embodiment of the present application provides a kind of detection method of multiphase flow phase content rate, and the present application is applicable to all laboratory and engineering application fields involved in (three-phase and within) multiphase flow phase content rate online measurement.

[0026] The technical solutions in the embodiments of the present application will be described clearly and completely in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor belong to the scope of protection of the present application.

[0027] At present, the existing detection method of multiphase flow phase content rate involves online detection of phase content rate of oil-gas-water three-phase flow, mainly detects phase content rate according to the relaxation time difference of each component of three-phase flow. This technical solution cannot distinguish oil-gas-water three-phase, especially the relaxation time difference between oil and water, but the reality is that the relaxation time of light oil is close to water, and the relaxation time of fracturing fluid is close to medium and heavy oil, so this technical solution has limitations.

[0028] As Figure 1 The flow chart of the detection method of multiphase flow phase content rate in the embodiment of the present application is shown, and the method shown in the figure includes:

[0029] Step S1, sampling the multiphase flow to be measured to obtain a multiphase flow sample, and three-phase separation of oil, gas and water in the multiphase flow sample.

[0030] Among them, the multiphase flow to be measured is sampled, and then oil, gas and water are separated by standing or centrifugation. The gas in the multiphase flow sample is natural gas.

[0031] Step S2, nuclear magnetic resonance is performed on pure water and water and oil in the multiphase flow sample respectively to obtain the first amplitude value of the corresponding free decay signal, and the hydrogen content index corresponding to water and oil in the multiphase flow sample is determined by using the first amplitude value.

[0032] Among them, nuclear magnetic resonance is performed on pure water and water and oil in the multiphase flow sample by using a multiphase flow nuclear magnetic resonance flowmeter, and the first amplitude value of the free decay (FID) signal is measured. Further, the ratio of the FID first amplitude value of the oil and water sample to the FID first amplitude value of the pure water reagent is the hydrogen content index of the oil and water.

[0033] Step S3, diffusion editing pulse sequence is applied to water and oil in the multiphase flow sample to obtain the diffusion coefficient corresponding to water and oil in the multiphase flow sample.

[0034] The diffusion editing pulse sequence is applied to the oil and water samples in the multiphase flow sample, and the diffusion coefficients of the oil and water are measured.

[0035] In step S4, the pulse sequence with variable echo spacing is used to pulse the multiphase flow to be measured to obtain echo signals, and the phase fractions of the oil, gas and water in the multiphase flow to be measured are determined according to the echo signals, the hydrogen index and the diffusion coefficient.

[0036] In step S4, the pulse sequence with variable echo spacing is used to pulse the multiphase flow to be measured to obtain echo signals, and the phase fractions of the oil, gas and water in the multiphase flow to be measured are determined according to the echo signals, the hydrogen index and the diffusion coefficient.

[0037] As an embodiment of the present application, the method further comprises: using the phase fractions of the oil, gas and water to carry out oil extraction, gathering and transportation, fracturing and oil testing. For example, in oil extraction, the oil content in the liquid phase can be used to understand the reservoir dynamic state and guide the optimization of the extraction strategy; in the gathering and transportation stage, the water content can be used to guide the water mixing operation; in the fracturing and oil testing stage, the gas content, water content and oil content are dynamically changing, and real-time monitoring is very important for accurately grasping the fracturing effect and evaluating the production capacity.

[0038] As an embodiment of the present application, the three-phase separation of the oil, gas and water in the multiphase flow sample comprises: using the static method or the centrifugal technology to separate the oil, gas and water in the multiphase flow sample into three single-phase fluids.

[0039] As an embodiment of the present application, as shown in Figure 2 As an embodiment of the present application, as shown in

[0040] In step S21, the pure water and the water and oil in the multiphase flow sample are respectively put into test containers; the inner diameter and the outer diameter of the test containers are the same as the inner diameter and the outer diameter of the fluid pipe of the multiphase flow nuclear magnetic resonance flowmeter, and the length of the test containers is greater than the length of the antenna of the multiphase flow nuclear magnetic resonance flowmeter.

[0041] In step S21, the pure water and the water and oil in the multiphase flow sample are respectively put into test containers; the inner diameter and the outer diameter of the test containers are the same as the inner diameter and the outer diameter of the fluid pipe of the multiphase flow nuclear magnetic resonance flowmeter, and the length of the test containers is greater than the length of the antenna of the multiphase flow nuclear magnetic resonance flowmeter.

[0042] Step S22, placing the test container in the detection area of the multiphase flow NMR flowmeter, and measuring the first amplitude value of the free induction signal corresponding to water and oil in the pure water and the multiphase flow sample.

[0043] The three test containers are respectively placed in the detection area of the multiphase flow NMR flowmeter, and the first amplitude value of the free induction (FID) signal is measured. The FID signal is a continuous decay signal, and the maximum amplitude value at the beginning of the decay is the first amplitude value. The ratio of the FID first amplitude value of oil and water to the FID first amplitude value of pure water is the hydrogen index of oil and water. The hydrogen index of natural gas is proportional to the pressure in the pipe, which can be obtained by looking up the table. A pressure gauge can be installed on the NMR pipeline to read the pressure in the pipe in real time.

[0044] In this embodiment, the hydrogen index of water and oil in the multiphase flow sample is determined by using the first amplitude value, which includes:

[0045] According to the ratio of the first amplitude value of the free induction signal of water in the multiphase flow sample to the first amplitude value of the free induction signal of the pure water, the hydrogen index of water in the multiphase flow sample is determined.

[0046] According to the ratio of the first amplitude value of the free induction signal of oil in the multiphase flow sample to the first amplitude value of the free induction signal of the pure water, the hydrogen index of oil in the multiphase flow sample is determined.

[0047] As an embodiment of the present application, the pulsed emission of the measured multiphase flow by using the variable echo interval pulse sequence includes:

[0048] The measured multiphase flow is connected to the fluid pipe of the multiphase flow NMR flowmeter, so that the measured multiphase flow continuously flows under the probe of the multiphase flow NMR flowmeter. The pulsed emission of the measured multiphase flow by using the variable echo interval pulse sequence includes twice pulsed emission with different half echo intervals, and the obtained echo signal includes the first echo signal and the second echo signal.

[0049] In this embodiment, as shown in Figure 3 The pulsed emission of the measured multiphase flow by using the variable echo interval pulse sequence includes:

[0050] Step S31, pulsed emission of the measured multiphase flow by using a 90-degree pulse and an 180-degree pulse separated by a first half echo interval, to obtain the first amplitude value and the first echo signal;

[0051] Step S32, pulsed emission of the measured multiphase flow by using a 90-degree pulse and an 180-degree pulse separated by a second half echo interval, to obtain the second echo signal.

[0052] Wherein, the pulse sequence used in the first scan is composed of a 90° pulse and a 180° pulse. The 90° pulse excites to generate a FID signal, the first amplitude of the FID signal is scanned, the 180° pulse is emitted after the first half echo interval, and then the first echo signal is collected after the first half echo interval. Then, the second scan is performed. The pulse sequence of the second scan is also composed of a 90° pulse and a 180° pulse, the difference is that the second half echo interval is used to collect the second echo signal.

[0053] In the embodiment, determining the phase content rates of oil, gas and water in the measured multiphase flow according to the echo signal, hydrogen index and diffusion coefficient comprises:

[0054] Determining the phase content rates of oil, gas and water in the measured multiphase flow according to the first echo signal, the second echo signal, the first half echo interval, the second half echo interval, the hydrogen index and the diffusion coefficient.

[0055] Specifically, the phase content rates S 油 , S 水 and S 气 are derived by formula (1) to (4).

[0056]

[0057]

[0058] M(0) = S 水 M 0,水 HI 水 + S 油 M 0,水 HI 油 + S 气 M 0,水 HI 气 (3)

[0059] S 水 + S 油 + S 气 = 1 (4)

[0060] Wherein, T 2,水 , T 2,油 are the transverse relaxation times of water and oil respectively, γ is the gyromagnetic ratio, which is a fixed value, M 0,油 , M 0,水 are the first amplitudes of the free induction (FID) signals corresponding to oil and water respectively, τ1 is the first half echo interval, τ2 is the second half echo interval, HI 油 , HI 水 and HI 气 are the hydrogen indexes of oil, water and natural gas respectively, M(0) is the scanning first amplitude, D 油 , D水 respectively are the diffusion coefficients of oil and water, G is the magnetic field gradient of the multiphase flow nuclear magnetic resonance flowmeter, M(2τ1) is the echo amplitude collected in the first scan, M(2τ2) is the echo amplitude collected in the second scan, S 油 , S 水 , S 气 respectively are the phase fractions of oil, gas and water in the multiphase flow to be measured. The unknowns in the above formulas (1) to (4) include S 油 , S 水 , S 气 , and the others are known parameters.

[0061] The present application is to use the nuclear magnetic resonance technology to measure the phase fractions of oil, gas and water in a multiphase flow online, and the principle is to realize quantitative differentiation based on the difference in the diffusion coefficients of different components of the multiphase flow. The technology replaces the existing sampling measurement method, and at the same time, makes up for the deficiency that individual components cannot be distinguished when using the relaxation time parameter to distinguish the components, and realizes an online phase fraction detection method for complex fluids with full range, high efficiency, environmental protection and safety.

[0062] In a specific embodiment of the present application, as shown in Figure 4 is a flow chart of the multiphase flow nuclear magnetic resonance online phase fraction measurement of the present application, which includes two parts of a pre-scale method and an official measurement method. The pre-scale method needs to be sampled to detect the basic parameters of the multiphase flow; the official measurement method only needs two times of fast scanning with variable echo intervals to quickly obtain the phase fractions of the multiphase flow, and the process can be repeated. The method makes up for the deficiency that oil and water cannot be distinguished in individual application scenarios by using the difference in the relaxation time, and realizes quantitative evaluation of the content of different fluid components based on the difference in the diffusion coefficients of the components of the fluid. The main carrier of the implementation of the present application is a multiphase flow nuclear magnetic resonance flowmeter, but is not limited to the device. On the hardware, there is a uniform gradient magnetic field (magnetic field gradient G) region in the static magnetic field generated by the nuclear magnetic resonance probe, and the detection antenna is placed in the uniform gradient magnetic field region. In actual implementation, the method includes two parts of a pre-scale method and an official measurement method, and the process is as shown in Figure 4 .

[0063] (I) Pre-scale method

[0064] First, the multiphase flow is sampled, and then the oil, gas and water three phases are separated by standing or centrifugation. Three test containers are prepared, the inner and outer diameters of the test containers are the same as the inner and outer diameters of the fluid pipe of the multiphase flow nuclear magnetic resonance flowmeter, and the length is greater than the length of the antenna of the multiphase flow nuclear magnetic resonance flowmeter. Two single-phase fluids (oil and water) are respectively filled into two test containers, and pure water reagent is filled into another test container. The three test containers are respectively filled into the detection region of the multiphase flow nuclear magnetic resonance flowmeter, and the first amplitude of the free induction decay (FID) signal is measured to obtain M 0,油 , M 0,水The ratio of the initial FID value of oil and water samples to the initial FID value of pure water is the hydrogen content index (HI) of oil and water. 油 HI 水 Then, diffusion encoding pulse sequences were applied to the oil and water samples, and the diffusion coefficients D of the oil and water were measured. 油 D 水 .

[0065] (II) Formal Measurement Method

[0066] During formal measurement, the multiphase flow nuclear magnetic resonance flowmeter is connected to the manifold of the fluid to be measured, allowing the fluid to pass through the probe in continuous flow. Figure 5A and Figure 5B The pulse sequence shown is used to pulse the multiphase flow inside the pipe. Two scans with different half-echo intervals are performed. The pulse sequence used in the first scan consists of a 90° pulse and a 180° pulse. After the 90° pulse excitation, an FID signal is generated. The FID signal scan has an initial amplitude of M(0), and after a half-echo interval τ1, a 180° pulse is emitted. Then, after τ1, the echo signal M(2τ1) is acquired. Then, a second scan is performed. The pulse sequence for the second scan also consists of a 90° pulse and a 180° pulse, but this time with a half-echo interval τ2, and the echo signal M(2τ2) is acquired. Finally, the phase content S is derived using the following formula. 油 S 水 S 气 .

[0067]

[0068]

[0069] M(0)=S 水 M 0,水 HI 水 +S 油 M 0,水 HI 油 +S 气 M 0,水 HI 气

[0070] S 水 +S 油 +S 气 =1

[0071] Where G is the magnetic field gradient, M(2τ1) and M(2τ2) are the echo amplitudes acquired in the two scans, M(0) is the FID signal amplitude acquired in the first scan, and S 油 S 水 S 气S, S, S, and S are unknowns in the above formula 油 , S 水 , S 气 , and the others are known parameters.

[0072] The present application makes up for the deficiency that it is difficult to distinguish oil and water by using relaxation time difference, realizes quantitative measurement of different fluid component content based on the difference of diffusion coefficient of each component of the fluid, does not need to collect relaxation information of the measured fluid, has fast measurement speed, and can realize online measurement of full-range, efficient, environment-friendly, and safe multiphase flow phase content.

[0073] Those skilled in the art will understand that embodiments of the present application can be provided as methods, systems, or computer program products. Therefore, the present application can take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present application can take the form of a computer program product implemented on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROMs, optical storage, etc.) containing computer-usable program code.

[0074] The present application is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present application. It should be understood that each flow and / or block in the flowcharts and / or block diagrams, and combinations of flows and / or blocks in the flowcharts and / or block diagrams can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing apparatus to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing apparatus produce a device that implements the functions specified in the flowcharts and / or block diagrams. Figure 1 one or more flows and / or blocks Figure 1 means for performing the functions specified in the flowchart

[0075] These computer program instructions can also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to work in a specific manner, so that the instructions stored in the computer-readable memory produce a manufactured product including instruction means, which implements the functions specified in the flowcharts and / or block diagrams. Figure 1 one or more flows and / or blocks Figure 1 means for performing the functions specified in the flowchart

[0076] These computer program instructions can also be loaded onto a computer or other programmable data processing apparatus, so that a series of operation steps are performed on the computer or other programmable data processing apparatus to produce a computer-implemented process, so that the instructions executed on the computer or other programmable data processing apparatus provide a process for implementing the functions specified in the flowcharts and / or block diagrams. Figure 1one or more processes and / or blocks Figure 1 the steps of the functions specified in the one or more blocks.

[0077] The principles and implementation manners of the present application are described in the specific embodiments. The above description of the embodiments is only used to help understand the method and core idea of the present application. Meanwhile, for those skilled in the art, according to the idea of the present application, the specific implementation manners and application scope will be changed. In summary, the content of the specification should not be understood as a limitation of the present application.

Claims

1. A method for detecting the phase content of a multiphase flow, characterized in that, The method includes: The multiphase flow to be tested is sampled to obtain a multiphase flow sample, and the oil, gas and water in the multiphase flow sample are separated into three phases. Nuclear magnetic resonance was performed on pure water and water and oil in the multiphase flow sample to obtain the first amplitude value of the corresponding free decay signal, and the hydrogen content index of water and oil in the multiphase flow sample was determined by the first amplitude value. A diffusion editing pulse sequence is applied to water and oil in the multiphase flow sample to obtain the diffusion coefficients of water and oil in the multiphase flow sample. A pulsed emission of pulses with varying echo intervals is used to obtain echo signals for the multiphase flow under test. Based on the echo signals, hydrogen content index, and diffusion coefficient, the phase content of oil, gas, and water in the multiphase flow under test is determined. The method of using a variable echo interval pulse sequence to pulse-transmit the multiphase flow under test and obtain the echo signal includes: The multiphase flow to be measured is connected to the fluid tube of the multiphase flow nuclear magnetic resonance flowmeter so that the multiphase flow to be measured flows continuously under the probe of the multiphase flow nuclear magnetic resonance flowmeter. Using a variable echo interval pulse sequence, the multiphase flow to be measured is emitted with two pulses with different half-echo intervals. The obtained echo signals include the first echo signal and the second echo signal. The method of using a variable echo interval pulse sequence to perform two pulse transmissions with different half-echo intervals for the multiphase flow under test includes: The multiphase flow under test is pulsed by using a 90-degree pulse and a 180-degree pulse separated by the first half-echo interval to obtain the first scan amplitude value and the first echo signal. The multiphase flow under test is pulsed by a 90-degree pulse and a 180-degree pulse separated by the second half-echo interval to obtain the second echo signal; The step of determining the phase content of oil, gas, and water in the multiphase flow under test based on the echo signal, hydrogen content index, and diffusion coefficient includes: Based on the first echo signal, the second echo signal, the first half-echo interval, the second half-echo interval, the hydrogen content index, and the diffusion coefficient, the phase content of oil, gas, and water in the multiphase flow to be tested is determined. The determination of the phase content of oil, gas, and water in the multiphase flow under test based on the first echo signal, the second echo signal, the first half-echo interval, the second half-echo interval, the hydrogen content index, and the diffusion coefficient includes: The phase fractions of oil, gas, and water in the multiphase flow to be measured are determined by simultaneously solving the following four formulas: M(0)=S 水 M 0,水 HI 水 +S 油 M 0,水 HI 油 +S 气 M 0,水 HI 气 ; S 水 +S 油 +S 气 =1; Among them, T 2,水 T 2,油 These are the transverse relaxation times of water and oil, respectively; γ is the gyromagnetic ratio, a fixed value; and M... 0,油 M 0,水 τ1 and τ2 represent the initial amplitude values ​​of the free attenuation signals corresponding to oil and water, respectively. HI is the first half-echo interval, τ1 is the first half-echo interval, and τ2 is the second half-echo interval. 油 HI 水 and HI 气 These represent the hydrogen content indices of oil, water, and natural gas, respectively; M(0) is the first scan value; and D... 油 D 水 S0 represents the diffusion coefficients of oil and water, respectively; G is the magnetic field gradient of the multiphase flow nuclear magnetic resonance flowmeter; M(2τ1) is the echo amplitude acquired in the first scan; M(2τ2) is the echo amplitude acquired in the second scan; and S0 represents the diffusion coefficients of oil and water, respectively. 油 S 水 S 气 These represent the phase content of the three phases (oil, gas, and water) in the multiphase flow to be tested.

2. The method according to claim 1, characterized in that, The method also includes: using the phase content corresponding to the three single-phase fluids of oil, gas and water for oil extraction, gathering and transportation, fracturing and oil testing.

3. The method according to claim 1, characterized in that, The three-phase separation of oil, gas and water in the multiphase flow sample includes: using a static method or centrifugation technology to separate the multiphase flow sample into three single-phase fluids: oil, gas and water.

4. The method according to claim 1, characterized in that, The initial amplitude values ​​of the corresponding free decay signals obtained by performing nuclear magnetic resonance on pure water and water and oil in the multiphase flow sample include: Pure water and water and oil from the multiphase flow sample are placed into test containers respectively; wherein the inner and outer diameters of the test containers are the same as the inner and outer diameters of the fluid tube of the multiphase flow nuclear magnetic resonance flowmeter, and the length of the test containers is greater than the antenna length of the multiphase flow nuclear magnetic resonance flowmeter. The test container is placed in the detection area of ​​the multiphase flow nuclear magnetic resonance flowmeter, and the first amplitude of the free decay signal corresponding to the pure water and the water and oil in the multiphase flow sample is measured.

5. The method according to claim 4, characterized in that, The step of determining the hydrogen content index of water and oil in the multiphase flow sample using the initial amplitude value includes: The hydrogen content index of water in the multiphase flow sample is determined based on the ratio of the first amplitude of the free decay signal of water in the multiphase flow sample to the first amplitude of the free decay signal of pure water. The hydrogen content index of the oil in the multiphase flow sample is determined based on the ratio of the first amplitude of the free decay signal of the oil in the multiphase flow sample to the first amplitude of the free decay signal of the pure water.

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