CN104197999A - Optical fiber multiphase flowmeter - Google Patents

Abstract

The invention discloses an optical fiber multiphase flowmeter, relates to a petroleum logging instrument and aims to solve the problem that a conventional differential pressure density instrument is low in accuracy of measuring the total flow cross-section and each phase fluid holdup of a multi-phase fluid. The optical fiber multiphase flowmeter comprises a diaphragm, a stress rod and an optical fiber grating, and is characterized in that when the fluid flows through the diaphragm, the diaphragm is deformed due to the impact force of the fluid to enable the stress rod to be compressed, the optical fiber grating pasted on the stress rod is deformed synergistically and subjected to wavelength shift, wavelength shift information carried by the reflected light of the optical fiber grating reaches an optical fiber grating interrogator, finally the wavelength shift amount of the optical fiber grating is measured to obtain by the optical fiber grating interrogator, and the total flow of the multiphase fluid is further obtained. According to the invention, an optical fiber and an optical fiber brillouin interrogator are adopted, so that the two-phase components of the fluid are measured; according to the relation of brillouin frequency shift and holdup, the holdup of the multiphase fluid is finally obtained; the optical fiber multiphase flowmeter is further applicable to sever environment and environment in which people and equipment are not accessible conveniently for monitoring.

Description

Optical fiber multi-phase flowmeter

Technical field

The present invention relates to a kind of oil well logging instrument, be specifically related to a kind of total flow section of heterogeneous fluid in Oil/gas Well and optical fiber multi-phase flowmeter of each phase fluid holdup of obtaining.

Background technology

In order to carry out oil reservoir monitoring and field management, the link of most critical is to stablize the total flow section of believable heterogeneous fluid and the holdup of each phase fluid in acquisition Oil/gas Well.Yet, most of oil well delamination exploitations, every layer of water cut difference, and also flow velocity is larger sometimes, has brought huge difficulty to the production status that utilizes conventional production logging device measuring and analyze oil well.The frictional resistance of fluid in oil pipe and make the pressure reduction density instrument cannot Measurement accuracy to the injection in pit shaft from oil reservoir, electronic probe cannot detect the little oil gas bubble in fluid especially.

For above problem, a lot of measurement mechanisms and method have been there is at present, comprise: be entitled as " a kind of have for measuring the equipment of multi-band sensor assembly of the parameter of fluid mobile in pipeline stream ", be entitled as " by the apparatus and method of the ducted fluid parameter of sound pressure measurement ", the article that is entitled as " downhole optic fiber multi-phase flowmeter ", introduced a kind of volume flow rate that relevant function method is measured fluid-mixing of applying, and then derive volumetric flow rate, and the metering system that adopts transient pressure is measured the velocity of sound of fluid-mixing, and then calculate the volume fraction of each phase fluid, and the article of a piece " the oil well multiphase flow rates metering method research based on Fibre Optical Sensor " of Northwestern Polytechnical University, the principle that the mean refractive index that introduction utilizes heterogeneous fluid changes with the difference of each phase ratio is measured each single-phase proportion, and this kind of method need to be measured light reflectivity and transmissivity.

Structure in above-mentioned several article, all exists noise to disturb, thereby cause measuring accuracy low, and oil causes greatly accurately measuring the problem of each phase fluid holdup to the absorption loss of light.

Summary of the invention

The present invention measures the total flow section of heterogeneous fluid and the low problem of measuring accuracy of each phase fluid holdup in order to solve existing pressure reduction density instrument, has proposed optical fiber multi-phase flowmeter.

Optical fiber multi-phase flowmeter, it comprises grating demodulation instrument and optical fiber Brillouin (FBG) demodulator, it also comprises diaphragm, stress bar, fiber grating, housing and optical fiber;

Housing is that xsect is the staving of rectangle, and this staving opening down arranges a dividing plate in the middle of described housing and make housing be divided into epicoele and cavity of resorption, has a perforate on the sidewall of described epicoele, and a bucket end for housing has No. two perforates;

The open side of housing is coated with diaphragm,

Stress bar is positioned at cavity of resorption, and its two ends contact with diaphragm with dividing plate respectively, and described stress bar is perpendicular to diaphragm; Fiber grating is attached to the outside surface of stress bar;

One end of optical fiber is positioned at the outside of housing, and the other end of optical fiber is connected with No. two perforates and with the signal input part of optical fiber Brillouin (FBG) demodulator through a perforate;

The wave length shift signal output part of fiber grating is connected with the wave length shift signal input part of grating demodulation instrument.

Optical fiber multi-phase flowmeter of the present invention, adopt diaphragm, stress bar and fiber grating, when having fluid to flow through diaphragm, thereby diaphragm is subject to the impulsive force generation distortion of fluid drives stress bar to produce compression, the fiber grating being pasted on stress bar produces cooperative transformation, fiber grating produces wave length shift, the reflected light of fiber grating carries wave length shift information and arrives fiber Bragg grating (FBG) demodulator, finally by fiber Bragg grating (FBG) demodulator, measure the wavelength shift that obtains fiber grating, and then obtain the total flow of heterogeneous fluid.Whole process is carried out flowmeter is inner, disturb, and diaphragm and stress bar all adopts pressure-sensing device without any noise, has reached the Measurement accuracy of the multiphase flow rates of convection cell, compares existing pressure reduction density instrument, and measuring accuracy has improved more than 10%.

The present invention, also by optical fiber and optical fiber Brillouin (FBG) demodulator, records two phase components of fluid, according to the relation between Brillouin shift and holdup, finally obtains the holdup of heterogeneous fluid.The present invention has utilized the Brillouin scattering of light, and real-time is good, reflection efficiency is high, gain intensity is large, be conducive to acquisition of signal, and signal to noise ratio (S/N ratio) is high, makes measurement more accurate, belongs to noncontact and surveys.The present invention is also applicable to the monitoring of the environment that rugged surroundings and personnel, equipment inconvenience directly arrives.

Accompanying drawing explanation

Fig. 1 is the structural representation of the optical fiber multi-phase flowmeter described in the application; Square frame 8 in figure is oil pipe, the flow direction that arrow 9 is fluid.

Embodiment

Embodiment one, with reference to Fig. 1, illustrate present embodiment, the optical fiber multi-phase flowmeter described in present embodiment, it comprises grating demodulation instrument 6 and optical fiber Brillouin (FBG) demodulator 7, it also comprises diaphragm 1, stress bar 2, fiber grating 3, housing 4 and optical fiber 5;

The staving that housing 4 is rectangle for xsect, this staving opening down, arranges a dividing plate 4-1 in the middle of described housing 4 and makes housing be divided into epicoele 4-2 and cavity of resorption 4-3, has perforate 4-4 on the sidewall of described epicoele 4-2 No. one, and a bucket end for housing 4, has perforate 4-5 No. two;

The open side of housing 4 is coated with diaphragm 1,

Stress bar 2 is positioned at cavity of resorption 4-3, and its two ends contact with diaphragm 1 with dividing plate 4-1 respectively, and described stress bar 2 is perpendicular to diaphragm 1; Fiber grating 3 is attached to the outside surface of stress bar 2;

One end of optical fiber 5 is positioned at the outside of housing 4, the other end of optical fiber 5 through perforate 4-4 with No. two perforate 4-5 and be connected with the signal input part of optical fiber Brillouin (FBG) demodulator 7;

The wave length shift signal output part of fiber grating 3 is connected with the wave length shift signal input part of grating demodulation instrument 6.

In the optical fiber multiphase flow rates timing described in use present embodiment, optical fiber multi-phase flowmeter is placed in the oil pipe 8 of Oil/gas Well, while having fluid perpendicular to diaphragm 1 motion of flowmeter in oil pipe 8, the Zona transformans dynamic stress bar 2 that diaphragm 1 is subject to the impulsive force generation of fluid has produced compression, the fiber grating 3 being pasted on stress bar 2 produces cooperative transformation, the Bragg wavelength of fiber grating 3 produces drift, diaphragm is subject to the effect of thrust, the size of power is directly proportional to the area of the kinetic energy of fluid and diaphragm, when the Reynolds number of pipeline is greater than the boundary Reynolds number of flowmeter, the power that flow and diaphragm are subject to has definite numerical value corresponding relation, and the power that diaphragm is subject to is also relevant with optic fiber grating wavelength drift value, so record fiber grating Bragg wavelength drift value by fiber Bragg grating (FBG) demodulator, and then the total flow of acquisition heterogeneous fluid.Its principle of work is after embodiment six.

Optical fiber Brillouin (FBG) demodulator 7 sends a branch of pulsed light, this pulsed light is sent to fluid through optical fiber 5, this pulsed light produces Brillouin scattering and forms scattered light after injecting fluid, the frequency displacement of back-scattering light is relevant to the velocity of sound of fluid, by the measurement of Brillouin shift being calculated to the velocity of sound of fluid-mixing, and the velocity of sound of fluid and the velocity of sound of each monophasic fluid and density have correlativity, and this correlativity is prevalent in two-phase gas/liquid and liquid/liquid fluid-mixing system, also be applicable to heterogeneous fluid-mixing system, so the difference by the velocity of sound that records is distinguished two phase components in heterogeneous fluid, finally by the relation between Brillouin shift and holdup, obtain each phase fluid holdup.By measuring Brillouin shift, obtain in actual applications the holdup of heterogeneous fluid.

The present invention is simple in structure, by fiber grating, stress bar and fluid isolation, has also played the effect of protection sensing element.

Diaphragm is as the sensing element of the acting force of fluid, and by force transmission to stress bar and fiber grating, avoided the problems such as sensing material oxidation corrosion and structural fatigue, improved the sensitivity of measuring heterogeneous fluid total flow.

Embodiment two, present embodiment are that in present embodiment, housing 4 is alloy steel housing to the further illustrating of the optical fiber multi-phase flowmeter described in embodiment one.

Embodiment three, present embodiment are that in present embodiment, diaphragm 1 is fluororubber diaphragm to the further illustrating of the optical fiber multi-phase flowmeter described in embodiment one.

In present embodiment, diaphragm employing stiff stability, the fluororubber that elastic range is large, yield stress is large, its strong adaptability, is quick on the draw, and the adaptability to changes of acquisition is accurate, has further guaranteed the precision of the total flow of Oil/gas Well.

Embodiment four, present embodiment are that in present embodiment, stress bar 2 is chromium nickel stainless steel stress bar to the further illustrating of the optical fiber multi-phase flowmeter described in embodiment one.

Embodiment five, present embodiment are to the further illustrating of the optical fiber multi-phase flowmeter described in embodiment one, and in present embodiment, between a perforate 4-4 of optical fiber 5 and housing and No. two perforate 4-5, are tightly connected.

Embodiment six, present embodiment are that in present embodiment, the span of the centre wavelength of fiber grating 3 is 1525nm～1605nm to the further illustrating of the optical fiber multi-phase flowmeter described in embodiment one.

Obtain the principle of the total flow of heterogeneous fluid:

Basic thought is that the Bragg wavelength shift by measuring optical fiber grating obtains heterogeneous fluid total flow, and wherein force bearing formulae when diaphragm and fluid contact is: $F=\frac{\mathrm{k\ρ}{\stackrel{\‾}{\mathrm{\ν}}}^2{A}_1}{2}$ (formula 1)

Wherein F is the suffered power of diaphragm, and k is resistance coefficient, and ρ is fluid density, for the mean flow rate between diaphragm and circulation face, A ₁the long-pending A of fluoran stream surface for diaphragm ₁=π d ²/ 4, d is target footpath.

When stress bar is subject to the acting force of diaphragm and compresses, the normal stress being subject on stress bar xsect is:

σ=N/A ₂(formula 2)

Wherein σ is the normal stress on stress bar xsect, and N is that the axle power on xsect is the F in above formula, and A2 is bar cross-sectional area.

In Hooke's law, the pass of normal stress and line strain is:

σ=E ε (formula 3)

Wherein σ is normal stress, the elastic modulus that E is material, and ε is line strain.

Wave length shift formula when fiber grating is subject to axial stress is:

△ λ _b=(1-P _e) ε _xλ _b(formula 4)

Δ λ wherein _bfor wavelength shift, P _efor valid round light constant, ε _xfor longitudinal extension strain is ε, λ _bbragg wavelength for fiber grating.

The pass of flow and mean flow rate is:

$Q=S\·\stackrel{\‾}{\mathrm{\ν}}$ (formula 5)

Wherein, S is the interior cross-sectional area S=π r of pipe of oil pipe 1 ², r is the internal diameter of oil pipe 1, Q is flow, for mean flow rate.

Arrange formula 1 and can obtain flow Q and grating wavelength drift value Δ λ to formula 5 _brelation:

$Q={[\frac{2{\mathrm{\π}}^{2}r{A}_{2}E}{\mathrm{k\ρ}{A}_1{\mathrm{\λ}}_B(1-P_e)}\·\mathrm{\Δ}{\mathrm{\λ}}_B]}^{1/2}$

Wherein, Q is flow, and r is the internal diameter of oil pipe 1, A ₂for bar cross-sectional area, the elastic modulus that E is material, Δ λ _bwavelength shift when fiber grating is subject to axial stress, k is resistance coefficient, ρ is fluid density, A ₁long-pending (the A of fluoran stream surface for target ₁=π d ²/ 4, d is target footpath), λ _bfor the Bragg wavelength of fiber grating, P _efor valid round light constant.

Therefore the Bragg wavelength shift by fiber grating in measure equation 5 just can obtain heterogeneous fluid total flow.

Obtain the principle of each phase fluid holdup:

Basic thought is by measuring Brillouin frequency shifts, to obtain the velocity of sound of fluid, and formula is:

$V=\±\frac{\mathrm{\λ\Δ}{\mathrm{\ν}}_B}{2n\sin \frac{\mathrm{\θ}}{2}}$ (formula 6)

Wherein, V is the velocity of sound in medium, △ ν _bfor Brillouin frequency shifts, λ is lambda1-wavelength, and n is medium refraction index, and θ is scattering angle, and n, V are subject to the impact of medium temperature and density.

Because the velocity of sound of heterogeneous fluid and the velocity of sound of each monophasic fluid and density have correlativity.This correlativity is prevalent in two-phase gas/liquid and liquid/liquid fluid-mixing system, and is applicable to heterogeneous fluid-mixing system.Therefore can distinguish two phase components in fluid-mixing by velocity of sound difference, thereby obtain the holdup of heterogeneous fluid, by measuring Brillouin shift, just can obtain the holdup of heterogeneous fluid.

Oil, gas, the density of water three-phase fluid-mixing and the pass of each phase density and holdup are:

ρ _mix=ρ _oilφ _oil+ ρ _wφ _w+ ρ _gasφ _gas(formula 7)

Wherein ρ represents density, and φ represents holdup, and mix represents oil, gas, water three-phase fluid-mixing, and oil represents oil, and w represents water, and gas represents gas.

The velocity of sound of oil, gas, water three-phase fluid-mixing with the pass of each phase velocity of sound, density and holdup is

$\frac{1}{{\mathrm{\ρ}}_{\mathrm{mix}}{V}_{\mathrm{mix}}^2}=\frac{{\mathrm{\φ}}_{\mathrm{oil}}}{{\mathrm{\ρ}}_{\mathrm{oil}}{V}_{\mathrm{oil}}^2}+\frac{{\mathrm{\φ}}_w}{{\mathrm{\ρ}}_w{V}_w^2}+\frac{{\mathrm{\φ}}_{\mathrm{gas}}}{{\mathrm{\ρ}}_{\mathrm{gas}}{V}_{\mathrm{gas}}^2}$ (formula 8)

Wherein V represents the velocity of sound.By formula 2, formula 3, know, for two-phase fluid-mixing, have

$V_{\mathrm{mix}}=\sqrt{\frac{1+\frac{{\mathrm{\ρ}}_1}{{\mathrm{\ρ}}_2}\frac{{\mathrm{\φ}}_2}{{\mathrm{\φ}}_1}}{\frac{1}{{V_1}^2}+\frac{{\mathrm{\ρ}}_1}{{\mathrm{\ρ}}_2}\frac{{\mathrm{\φ}}_2}{{\mathrm{\φ}}_1}\frac{1}{{V_2}^2}}},{\mathrm{\φ}}_1+{\mathrm{\φ}}_2=1$ (formula 9)

By formula 9, can obtain each phase holdup.

By formula 6 be updated to each phase holdup that can obtain respectively three-phase fluid-mixing and two-phase fluid-mixing in formula 8, formula 9.

Explanation of nouns: flow, refers to the volume that passes through the fluid of a certain xsect in the unit interval.

Total flow section: the profile of flowrate of each productive section.

Holdup: the area that contains monophasic fluid on a certain xsect accounts for the percentage of this area of section.

Claims (6)

1. optical fiber multi-phase flowmeter, it comprises grating demodulation instrument (6) and optical fiber Brillouin (FBG) demodulator (7), it is characterized in that, it also comprises diaphragm (1), stress bar (2), fiber grating (3), housing (4) and optical fiber (5);

The staving that housing (4) is rectangle for xsect, this staving opening down, in the middle of described housing (4), a dividing plate (4-1) being set makes housing be divided into epicoele (4-2) and cavity of resorption (4-3), on the sidewall of described epicoele (4-2), have a perforate (4-4), the bucket end of housing (4), has No. two perforates (4-5);

The open side of housing (4) is coated with diaphragm (1),

Stress bar (2) is positioned at cavity of resorption (4-3), and its two ends contact with diaphragm (1) with dividing plate (4-1) respectively, and described stress bar (2) is perpendicular to diaphragm (1); Fiber grating (3) is attached to the outside surface of stress bar (2);

One end of optical fiber (5) is positioned at the outside of housing (4), and the other end of optical fiber (5) is connected with No. two perforates (4-5) and with the signal input part of optical fiber Brillouin (FBG) demodulator (7) through a perforate (4-4);

The wave length shift signal output part of fiber grating (3) is connected with the wave length shift signal input part of grating demodulation instrument (6).

2. optical fiber multi-phase flowmeter according to claim 1, is characterized in that, housing (4) is alloy steel housing.

3. optical fiber multi-phase flowmeter according to claim 1, is characterized in that, diaphragm (1) is fluororubber diaphragm.

4. optical fiber multi-phase flowmeter according to claim 1, is characterized in that, stress bar (2) is chromium nickel stainless steel stress bar.

5. optical fiber multi-phase flowmeter according to claim 1, is characterized in that, between a perforate (4-4) of optical fiber (5) and housing and No. two perforates (4-5), is tightly connected.

6. optical fiber multi-phase flowmeter according to claim 1, is characterized in that, the span of the centre wavelength of fiber grating (3) is 1525nm～1605nm.