RU2503929C1 - Method of simultaneous detection of flow rates of liquid and gas phases of flow of gas liquid mixture - Google Patents

Abstract

FIELD: measurement equipment.

SUBSTANCE: method of simultaneous detection of flow rates of liquid and gas phases of a flow of a gas liquid mixture, including probing of the ascending flow of the non-separated gas liquid mixture with a continuous ultrasonic signal, reception of a signal reflected from irregularities, complex detection, which separates a cophased component with a probing signal and a quadrature component, performance of spectral analysis with detection of a sign of dominant frequency, detection of frequency of the signal and share of time, when the dominant frequency becomes negative. At the same time the capacity of the received signal is determined, the capacity is compared with the threshold value, and they exclude those signal sections, where the capacity is less than the threshold, from the determination of signal frequency and time share, when the dominant frequency becomes negative. During calibration they determine dependencies of the frequency and time share, when the dominant frequency becomes negative, on flow rates of liquid and gaseous phases. According to dependences of frequency and share of time received during calibration, when the dominant frequency becomes negative, they determine flow rates of liquid and gaseous phases.

EFFECT: simplified method for detection of flow rate of liquid and gas phases of a flow rate of a gas liquid mixture with simultaneous increase of measurement accuracy and expansion of a range of measured values.

Description

The invention relates to a control and measuring technique and can be used to determine the multiphase flow rate without preliminary separation, for example, to measure the flow rate of oil wells.

A known method for determining the flow rate of components of a two-phase flow (RU, patent No. 2339915C1, G01F 1/74, 11/27/2008), comprising a measuring section of the pipeline with two electro-acoustic transducers installed on its outer surface diametrically located and offset along the axis of the pipeline; and an electronic unit for exciting ultrasonic waves in the pipeline. For radiation and reception, overhead transducers made in the form of multi-element phased arrays are used, which are sets of piezoelectric elements. Electro-acoustic transducers and temperature and pressure sensors of the medium in the measuring section are connected through differential amplifiers to the microprocessor of the electronic unit.

Using a moving spectral analysis of the sequences of samples of the signal, the current Doppler frequency shift (DSC) determines the ratio of the durations of the sections of the implementation of the DSC with different signs.

Using the implementation of the Doppler frequency shift from two different strobe signals received by the first electro-acoustic transducer, to determine the velocity of the gas cavities by the correlation method, the shift of the maximum of the correlation function of the temporal realizations of the MPS obtained from the strobes shifted relative to each other by time is determined.

Then, using the ratio of the durations of the sections of the differential frequency spectrum with different signs and the shift of the maximum of the correlation function, the gas and liquid flows are determined by solving the system of equations.

The disadvantages of this system for measuring the components of a two-phase flow are the design complexity, as well as the fact that the ultrasonic signal practically does not propagate through the gas-liquid mixture over a long distance.

Closest to the proposed method is a method for simultaneously determining the flow rate of liquid and gas (RU, application for the invention No. 2009116975, G01F 1/00, 05/04/2009, published 10.11.2010) including sensing the upward flow of an unseparated mixture of liquid and gas continuous using an ultrasonic signal, receiving a signal reflected from inhomogeneities, complex detection is used to extract the difference frequency, which isolates the common-mode signal with the probing signal and the quadrature components, the difference frequency of the received and radiation signal, spectral analysis is performed to determine the sign of the prevailing frequency, counting the fraction of time when the prevailing frequency takes a negative value, during calibration, the dependences of the frequency and the fraction of time when the prevailing frequency takes a negative value on the flow rates of the liquid and gaseous phases are determined, and calibration time of dependencies, frequency and fraction of time when the prevailing frequency takes a negative value determines the flow rate of the liquid and gas phases.

The disadvantage of this method, adopted as a prototype, is that when the projectile mode of flow of the gas-liquid mixture, the probe periodically enters the gas bubble. There is no Doppler frequency. However, there are noises due to the noise of the electronics and small movements of the liquid films on the surface of the probe. After spectral analysis of the noise signal, time intervals appear when the sign of the prevailing frequency changes and these changes do not reflect the movement of the liquid.

This phenomenon leads to an increase in the error in determining the gas content and, as a consequence, of costs.

The objective of the invention is to simplify the method of determining the flow rate of the liquid and gas phases of the flow of a gas-liquid mixture while increasing the accuracy of measurement and expanding the range of measured values.

This is achieved by the fact that in the proposed method for simultaneously determining the flow rates of the liquid and gas phases of the gas-liquid mixture flow, including sensing the upward flow of the unseparated gas-liquid mixture by a continuous ultrasonic signal, receiving a signal reflected from the inhomogeneities, complex detection, isolating in-phase with the probing signal and quadrature components, conducting spectral analysis with the determination of the sign of the prevailing frequency, the determination of the signal frequency and the fraction of time when the prevailing the giving frequency takes a negative value, the power of the received signal is determined, the power is compared with a threshold value and excluded from the determination of the signal frequency and the fraction of time when the predominant frequency takes a negative value, those signal sections where the power is less than the threshold determine the dependence of the frequency and fraction during calibration the time when the prevailing frequency takes a negative value, from the flow rates of the liquid and gaseous phases, and from the dependences of the frequency and fraction of time obtained during calibration nor when the predominant frequency takes a negative value, determine the cost of the liquid and gas phases.

Consider an example of an upward fluid flow. Ultrasound is reflected from the inhomogeneities of the flow, arrives at the detector, which selects the difference frequency.

In the presence of a small amount of gas in the liquid stream, the so-called "bubble" flow regime is realized, in which the gas is contained in small bubbles floating up in the liquid. In this case, the signal will contain both a component obtained by reflection from inhomogeneities in the liquid, and from the surface of gas bubbles. In addition, the bubbles have different sizes and, accordingly, float at different speeds. The flow of fluid around the bubbles leads to an increase in the degree of turbulence of the flow.

As a result of all these effects, at some points in time, the local part of the liquid moves in the opposite direction, flowing around gas bubbles.

With a further increase in the amount of gas, a so-called “shell” flow regime is formed, in which individual gas bubbles merge into shells. In this case, gas shells are concentrated towards the center of the measuring hydrochannel, and the liquid along the walls. A significant fraction of the time the fluid moves in the opposite direction, flowing around the gas shell. The larger the amount of gas, the more pronounced this effect will be (see Polyanin L.N. Drobkov V.P. Applied hydromechanics of ascending gas-liquid flows. M. Energoatomizdat, 2004, Fig. 1.3, p. 9).

The proposed method is as follows.

A gas-liquid stream is passed through a measuring hydrochannel in a vertical upward direction. In this case, with a small fraction of gas, a bubbly flow mode is formed, and with a large fraction - slug flow.

Local sounding of the gas-liquid flow by ultrasound is carried out and the signal reflected from the inhomogeneities is received. To implement the proposed method, it is necessary to distinguish the direction of movement up to the probe or down from the probe.

For this purpose, complex detection is used, which isolates in-phase with a probing signal and quadrature components.

One of these components is considered as a real component, the other as imaginary components of a single complex signal. After the complex Fourier transform, we obtain the signal spectrum.

If the reflector moves up to the probe, then the frequency of the signal before complex detection will be higher than the frequency of the probing ultrasound. Accordingly, after complex detection and Fourier transform in the spectrum, the frequency will have a positive value.

In the case of moving down - on the contrary, negative.

Thus, the sign of the prevailing frequency in the spectrum indicates the direction of motion of the inhomogeneities, which makes it possible to distinguish the direction of movement up towards the sensor or down from it.

Fractions of time when the prevailing frequency takes a negative value (fractions of negative frequencies) carries information about the amount of gas.

In projectile mode, the probe periodically enters the gas bubble. Doppler frequency is absent. However, there are noises due to the noise of the electronics and small movements of the liquid films on the surface of the probe. Intervals appear in the noise signal when the sign of the prevailing frequency randomly changes and these changes do not reflect the movement of the liquid.

At the same time, while the probe is in the gas bubble, the signal power drops sharply. This power drop allows you to determine the time intervals when the sign data is false and exclude them from consideration.

Information about the frequency of the signal while the probe is in the gas bubble is also unreliable.

Power rejection eliminates inaccurate data.

During calibration, the dependences of the frequency and the fraction of time are determined when the predominant frequency takes a negative value (fractions of negative frequencies) on the flow rates of the liquid and gaseous phases.

According to the dependences obtained during calibration, the frequencies and fractions of negative frequencies determine the flow rates of the liquid and gaseous phases. A necessary condition for the possibility of determining the flow rates of liquid and gas is that the dependence of the proportion of negative frequencies on the flow rates of liquid and gas was different from the dependence of the frequency.

At the applicant enterprise, a multiphase flow meter was manufactured in which the proposed methods for simultaneously determining the flow rate of the liquid and gas phases of the gas-liquid mixture flow were realized and positive results were obtained.

Claims (1)

A method for simultaneously determining the flow rates of the liquid and gas phases of a gas-liquid mixture stream, including sensing the upward flow of an unseparated gas-liquid mixture by a continuous ultrasonic signal, receiving a signal reflected from inhomogeneities, complex detection, which isolates in-phase with the probing signal and quadrature components, performing spectral analysis with determining the sign of the prevailing frequency, determination of the signal frequency and the fraction of time when the prevailing frequency takes a negative a value characterized in that the power of the received signal is determined, the power is compared with a threshold value and excluded from the determination of the signal frequency and the fraction of time when the predominant frequency takes a negative value, those signal portions where the power is less than the threshold determine the dependence of the frequency and fraction during calibration the time when the prevailing frequency takes a negative value, on the flow rates of the liquid and gaseous phases, and according to the dependences of the frequency and fraction of time obtained during calibration when the prevailing frequency yuschaya frequency takes a negative value, determine the cost of the liquid and gas phases.