RU2531036C1 - Method to measure flow rate of multi-phase fluid - Google Patents

Abstract

FIELD: measurement equipment.

SUBSTANCE: method to measure flow rate of a multi-phase fluid, which consists in measurement of acoustic noise created by liquid movement as it flows via the available cross section, the speed of fluid passage is determined by frequency of acoustic noise caused by unevenness of liquid motion, previously they measure flow temperature and pressure in the pipe, density of each phase, and then, based on proposed dependences they calculate volume or mass fractions of each phase. At the same time, using laboratory results, they make equations of dependence of sound speed in each phase on pressure and temperature, and the equation of sound speed for water is complemented with the dependence on water salinity, at the same time the produced equations are recorded into a computing unit, they measure pressure and temperature in the pipeline, water salinity, they measure and record amplitudes and frequencies of oscillations in the pipe, along which the multi-phase liquid is flowing, the measured range of frequencies is divided into parts that correspond to each phase, in each of the parts after application of quick Fourier transforms they identify maximum values of amplitudes and appropriate frequencies, and calculate the volume flow rate of each phase of liquid in accordance with the appropriate formula.

EFFECT: reduced error of measurement in each phase.

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Description

A method for measuring the flow rate of a multiphase fluid relates to the oil and gas producing field and, in particular, can be used to measure the flow rate of multiphase flows of production gas, gas condensate and oil wells.

The well-known "ACOUSTIC GAS-LIQUID FLOW METER" (Patent number: US 5415048, patent class (s): G01F1B 47/10, G01F 1/74), in which the differential pressure in the pipe is measured, the acoustic frequencies and amplitudes generated by the moving pipe the liquid, they convert and analyze the electrical signals of the sensors, perform a fast Fourier transform for visual control of the flow, write the received data to the base for subsequent connection of the characteristic frequencies with the mass of one of the phases of the multiphase pumped liquid. The objective of the invention is to simplify the process of controlling the flow of multiphase fluid flowing through the pipeline. The disadvantage of the analogue is the measurement of differential pressure to determine the flow rate. In accordance with GOST 8.563.1-97 "Measurement of the flow rate and the amount of liquids and gases by the method of variable differential pressure" such a measurement is justified only for the flow rate and the number of fluids in one phase. The next drawback is the need for preliminary accumulation of data in the database for subsequent analysis and calculation of the mass of each phase.

Also known is a method for measuring the flow rate of a multiphase liquid (US 7401530 B2 from Jul. 22 2008 "SONAR BASED MULTIPHASE FLOWMETER"), in which the sound velocity in individual phases of a multiphase fluid moving in a pipe is measured, the wave propagation velocity along the pipe is measured, the volume fraction of one of phases, measure the average velocity of the multiphase fluid in the pipe, pre-measure the density of each phase, and then based on the proposed dependencies calculate the volume or mass fraction of each phase. In this case, the speed of sound is used only as a label for the appearance of a phase in the pipe, assuming that the change in speed from the concentration of phases is known in advance.

As a prototype, the method and device for measuring multiphase flow (US 7526966 B2 dated May 05, 2009), in which a certain number of sensors of physical quantities (pressure, temperature, sound velocity) are installed on the vertical section of the pipeline and based on the information received, according to the proposed the authors of the dependencies, calculate the percentage composition and mass flow rate of multiphase liquids.

The disadvantages of this method when measuring the flow rate of a multiphase water-gas-oil emulsion in relation to oil and gas wells are given below.

The authors calculate the resonant frequency of gas bubbles without taking into account the composition of the gas mixture itself. Note that under real conditions the composition of light hydrocarbons and gases in a well’s production varies within a very wide range and the proposed dependencies will give very large errors, in addition, for light hydrocarbon fractions, it is possible to be in both liquid and gaseous states.

The measurement of the phase density of water-gas-oil emulsions by a source of ionizing radiation is, firstly, dangerous, and secondly, gives large errors due to the influence of salinity of produced water.

Mass flow measurement with a Coriolis flowmeter is applicable only to pure liquids or gases, without mechanical impurities and for full-flow flows.

The authors proposed the dependence of the speed of sound on the gas factor in a narrow pressure range without taking into account the temperature, which can also give an uncertain error. The dependence of the speed of sound on the percentage of water without taking into account the effects of pressure, temperature and salinity is proposed.

It is known that ultrasonic flow velocity meters have disadvantages:

- the need for significant lengths of linear sections before and after the converter;

- the effect on the readings of air bubbles in the stream;

- the need to control deposits in the pipeline at its working site;

- the complexity and high cost of devices, which, all other things being equal, is 3-4 times higher than the cost of tachometric and electromagnetic flow meters;

- restrictions on the minimum flow rate.

The use of ultrasonic sensors also requires high-quality installation work and regular maintenance.

In addition, the total cost of equipment for the implementation of the device will be quite high, reaching several million rubles, especially in the version with a Coriolis flowmeter and a source of ionizing radiation.

To eliminate these disadvantages, the invention is proposed.

Effect: reducing the measurement error of each phase.

The technical result is achieved due to the fact that the proposed method for measuring the flow rate of a multiphase liquid provides the following differences:

1. using laboratory results, make equations of the dependence of the speed of sound of each phase on pressure and temperature, and the equation of speed of sound for water is supplemented by a dependence on the salinity of the water, the resulting equations are written in the calculation block;

2. measure the pressure and temperature in the pipeline, measure the salinity of the water, determine the speed of sound and the density of each phase, determine the speed of sound in each phase of the liquid in the operating temperature range, measure and record the vibration amplitudes of the pipeline through which the multiphase fluid flows, and the corresponding frequency. Select a frequency range with maximum amplitudes. The measured frequency range is divided into three parts, the lower frequencies correspond to the gas phase, the middle ones to the oil phase and the high to water phase, in each of which, after applying the fast Fourier transforms [1, 2, 3], the maximum amplitudes are extracted, and the volumetric flow rate of each phase is calculated liquids according to:

$$Q=\frac{\pi \cdot R^{\mathrm{four}}\cdot {\mathrm{<figure-callout\; id="3"\; label="F"\; filenames="00000005.png"\; state="\{\{state\}\}">F</figure-callout>}}^3\cdot A\cdot K}{\mathrm{four}\cdot {\mathrm{<figure-callout\; id="2"\; label="C"\; filenames="00000005.png,00000006.png"\; state="\{\{state\}\}">C</figure-callout>}}^2},(\mathrm{one})$$

where Q is the volumetric flow rate of an individual phase of a multiphase liquid, m ³ / s;

R is the radius of the pipe, m;

F - maximum vibration frequency in the range allocated for an individual phase, 1 / s;

A is the maximum amplitude of oscillations at a frequency of F, m;

K is the dimensionless coefficient of proportionality, taking into account the features of the multiphase fluid flowing through the pipeline when calibrating the vibroacoustic sensor on the pipeline;

C is the speed of sound in the measured phase of a multiphase liquid, calculated from empirical dependences on pressure and temperature, and for water, additionally on salinity.

Example

Let us determine the error in measuring the flow rate when salinity changes in the range from 2 to 50 ppm. Note that the salinity of 35 ppm corresponds to the average salinity of the oceans. The change in salinity in this range is accurately recorded by the applied instrument complex.

1. The radius of the pipe, m:

R = 0.0254;

2. Initial frequency, Hz:

F = 1000;

3. The amplitude of the oscillations is conventionally assumed to be the same for all components, m:

A = 0.00001;

4. The speed of sound in water:

4.1. The speed of sound in water is constant and equal to 1500 m / s;

4.2. The speed of sound changes depending on the salinity of the water, temperature and pressure in the pipe. We use the website page http://www.akin.ru/spravka/s i svel.htm to calculate the speed of sound in water depending on its salinity according to the Wilson formula.

We calculate the change in the speed of sound in water with a change in salinity from 2 to 50 ppm (g / dm ³ ).

M = 2 ppm C1 = 1485.1 (m / s); M = 50 ppm C5 = 1539 (m / s).

The remaining values correspond to 0.1 MPa and 20 ° C.

The calculation results are shown in Fig. 1.

Substituting the calculated values of sound velocity (from 1485.1 m / s to 1539 m / s) into equation (1), we obtain a graph of the effect of formation water salinity on the measurement of water flow (see Fig. 2).

The maximum difference in readings is 6.99% at a frequency of 5000 Hz.

The technical result is obtained in the following way.

A piezoelectric microphone was connected to a computer with DASYLab - 11 software (see User Manual Data Acquisition, Controlling, and Monitoring "Data Acquisition System Laboratory"), which in turn was attached to the pipeline. In the program, the signal is amplified, divided by filters into three parts, the frequency of measuring the signal according to the Nyquist is set, each part passes through its own spectrum analyzer, the selected signals are checked for maximum amplitude and fed to a block of mathematical transformations, where sound speed and proportionality coefficient are also entered. At the output, we get either numerical values in Excel tables or graphic materials in the form of a digital screen or a two-dimensional graph.

Experimental study: instrument readings were recorded (flow rate, pressure, pump speed), as well as the frequency and amplitude of the pipeline oscillations, using a ring pouring stand specially made of a 2-inch pipe (Fig. 3), consisting of pump 1, pipeline 2, a flow meter 3, gauge 4 (other devices not shown). The results were processed in the DASYLab-11 and MathCAD-14 programs.

As multiphase liquid, tap water, vegetable oil, air, and edible salt (NaCl) were used.

Salt was added to the liquid at a rate of 2 g / liter and 50 g / liter, which corresponds to 2 and 50 ppm.

Used emulsions of 25%, 50% and 75% of a mixture of oil with water. The air volume was regulated by changing the volume of liquid in the pouring stand. A piezoelectric microphone was rigidly mounted on the pipe. The measurements were carried out at fixed temperatures +20, +50, + 80 ° C and fixed values of the pump speed - 100, 350, 700 rpm.

During the experiments, it was found that measuring salinity, calculating the speed of sound in salt water using the Wilson formula or the like, and entering the data into a formula for calculating the flow rate of a multiphase gas-oil-liquid fluid, in particular the aqueous phase, reduces the measurement error from 5% to 2% (see Fig. .four).

List of sources used

1. Kristalinsky R.E., Kristalinsky V.R. Fourier and Laplace transforms in computer mathematics systems: Textbook for universities. - M .: Hot line - Telecom, 2006 .-- 216 p.

2. Panferov A.I., Loparev A.V., Ponomarev V.K. The use of MathCAD in engineering calculations: Textbook / SPbGUAP. St. Petersburg, 2004 .-- 88 p.

3.http: //www.akin.ru/spravka/s i svel.htm

4. User Manual Data Acquisition, Controlling, and Monitoring "Data Acquisition System Laboratory".

5. http://www.eti.su/articles/izmeritelnaya-tehnika/izmeritelnaya-tehnika_529.html

Claims (1)

A method of measuring the flow rate of a multiphase liquid, which consists in measuring the acoustic noise generated by the movement of the liquid when it flows through a known section, the speed of passage of the liquid is determined by the frequency of acoustic noise caused by uneven movement of the liquid, the flow temperature and pressure in the pipe, the density of each phase are pre-measured, and then, based on the proposed dependencies, the volume or mass fractions of each phase are calculated, characterized in that, using laboratory results, the composition equations for the dependence of the speed of sound of each phase on pressure and temperature are developed, and the equation for the speed of sound for water is supplemented by a dependence on the salinity of the water, while the equations obtained are written into the calculation block, the pressure and temperature in the pipeline are measured, the salinity of the water is measured, and the amplitudes and frequencies are measured and recorded oscillations of the pipe through which the multiphase fluid flows, the measured frequency range is divided into parts corresponding to each phase, in each of the parts after applying fast Fourier transforms, m ksimalnye amplitudes and corresponding frequencies and calculating the volumetric flow rate of each liquid phase by the formula:

where Q is the volumetric flow rate of an individual phase of a multiphase liquid, m ³ / s;
R is the radius of the pipe, m;
F - maximum vibration frequency in the range allocated for an individual phase, 1 / s;
And - the maximum amplitude of the oscillations at a frequency F, m;
K is the dimensionless coefficient of proportionality, taking into account the features of the multiphase fluid flowing through the pipeline when calibrating the vibroacoustic sensor on the pipeline;
C is the speed of sound in the measured phase of a multiphase liquid, calculated from empirical dependences on pressure and temperature, and for water, additionally on salinity.

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