CN104389581B - Underground fluid induction device and fluid flow velocity measuring system using same - Google Patents

Abstract

The invention provides a downhole fluid sensing device and a fluid velocity measurement system using the device. The downhole fluid sensing device includes: a pressure guiding tube; a partition; a first piston, a first spring, and a diaphragm arranged on the left side of the partition. The first grating; the second piston, the second spring, and the second grating symmetrically arranged on the right side of the partition; a Venturi tube. The invention uses the grating to sense the pressure exerted on the pipe wall when the fluid flows in the Venturi pipe, and obtains the fluid flow velocity in the pipe according to the characteristic that the pressure applied to the pipe wall is different according to the fluid flow rate. The invention can realize accurate fluid measurement in the limited space and severe environment conditions of several kilometers underground oil and gas wells.

Description

Downhole fluid sensing device and fluid velocity measurement system using the device

technical field

The present invention relates to fluid flow rate monitoring technology, in particular to fluid flow rate measurement technology in the field of petroleum industry, in particular to a downhole fluid sensing device and a fluid flow rate measurement system using the device.

Background technique

The flow rate/flow rate of fluid is an important parameter in daily life, industrial production process, energy measurement and environmental protection monitoring. Currently commonly used flow rate/flow sensors include volumetric flowmeters, vortex flowmeters, turbine flowmeters, electromagnetic flowmeters, ultrasonic flowmeters, and acoustic Doppler flowmeters. These flow rate/flow sensors have their own characteristics and scope of application, and have been widely used in daily life and industrial production, but these flow rate/flow sensors also have certain limitations, such as volumetric flowmeters are bulky , It is not suitable for high temperature and low temperature occasions. Although the electromagnetic flow meter and the acoustic Doppler flow meter have high measurement accuracy, they are easily disturbed by electromagnetic waves and the cost is high.

Velocity/flow sensor plays an important role in promoting the development of industry and agriculture, so it has been highly valued since it came out. Nowadays, with the rapid development of modern industry and agriculture, some special fields, such as the upstream exploration and development of the petroleum industry, have extremely stringent requirements for fluid velocity meters, because oil and gas wells several kilometers underground not only have limited space but also very harsh environmental conditions, due to Currently commonly used flow velocity/flow sensors are large in size and are susceptible to electromagnetic interference limitations, so the current commonly used flow velocity/flow sensors cannot be applied.

Therefore, how to develop a new fluid velocity measurement device, which can adapt to the upstream exploration and development field of the petroleum industry, and realize accurate fluid velocity measurement under the limited space and high temperature and high pressure environmental conditions of several kilometers of oil and gas wells underground is an art field. urgent technical issues to be resolved.

Contents of the invention

The technical problem to be solved by the present invention is to provide a downhole fluid sensing device and a fluid flow rate measurement system using the device. The grating is used to sense the pressure exerted on the pipe wall when the fluid in the pipe flows. Furthermore, the flow rate of the fluid in the pipe is obtained according to the pressure difference, which solves the problems of the flow rate meter in the prior art that is easily disturbed, has a large volume, and has low measurement accuracy.

In one embodiment of the present invention, a downhole fluid sensing device is provided, wherein the downhole fluid sensing device includes: a venturi tube for guiding downhole fluid, the venturi tube has an inlet section and a throat section , the diameter of the inlet section is larger than the diameter of the throat section; the pressure guide tube is connected to the Venturi tube; the partition is arranged at the center of the pressure guide tube; the first spring is arranged on the partition On the left side, one end is connected to the partition, and the other end is connected to a first piston. The pressure of the fluid in the inlet section acts on the first spring through the first piston; the second spring is symmetrically arranged on the On the right side of the partition, one end is connected to the partition, and the other end is connected to a second piston, the pressure of the fluid in the throat section acts on the second spring through the second piston; the first grating, One end is connected to the partition, and the other end is connected to the first piston. The first grating is always in a stretched state under the joint action of the first spring force and the fluid pressure of the inlet section. A grating receives an incident light and reflects a first reflected light; and a second grating, one end is connected with the partition, and the other end is connected with the second piston, and the second grating is connected to the second spring Under the joint action of the elastic force and the fluid pressure of the throat section, it is always in a stretched state, and the second grating receives the incident light and reflects a second reflected light.

In another embodiment of the present invention, a fluid flow rate measurement system is provided, wherein the fluid flow rate measurement system includes the downhole fluid sensing device in the above embodiment, and the fluid flow rate measurement system also includes a laser light source, a grating demodulator and processing device, the laser light source is connected with the downhole fluid sensing device, and the laser light source is used to emit the incident light; the grating demodulator is connected with the downhole fluid sensing device, and the grating demodulator is used for After demodulating the first reflected light to obtain a first reflected spectrum, and demodulating the second reflected light to obtain a second reflected spectrum; the processing device is connected to the grating demodulator, and the processing device uses and determining the fluid flow velocity at the inlet section of the Venturi tube based on the first reflectance spectrum and the second reflectance spectrum.

The invention provides a downhole fluid sensing device and a fluid flow rate measurement system using the device. The Venturi tube and the grating are organically combined, and the grating is used to sense the pressure exerted on the tube wall when the fluid in the Venturi tube flows. The fluid flow rate is different, the pressure exerted on the pipe wall is different, the pressure exerted by the fluid on the pipe wall is finally applied to the grating, the grating is subjected to different forces, and the length of the peak wavelength of the reflection spectrum of the laser passing through the grating is also different. The pressure difference is obtained from the length of the peak wavelength of the reflection spectrum, and then the fluid velocity in the pipe is obtained by using the Bernoulli equation according to the pressure difference. The downhole fluid sensing device has the advantages of simple structure, convenient installation, low cost, anti-electromagnetic interference, working Reliable, high measurement accuracy, small footprint, and can work in harsh environments such as high temperature, high pressure, noise, and strong corrosion for a long time.

Description of drawings

Fig. 1 is a schematic structural diagram of the downhole fluid sensing device of the present invention.

Fig. 2 is a schematic diagram of a preferred structure of the downhole fluid sensing device of the present invention.

Fig. 3 is a schematic structural diagram of a Venturi tube of the downhole fluid sensing device of the present invention.

Fig. 4 is a schematic diagram of the internal structure of the pressure guiding tube of the downhole fluid sensing device of the present invention.

Fig. 5 is a schematic structural diagram of a fluid flow rate measuring system of the present invention.

Fig. 6 is a schematic structural diagram of a processing device of the fluid flow rate measurement system of the present invention.

Symbol Description:

1 first raster

2 second raster

3 first spring

4 Second spring

5 first piston

6 Second piston

7 partitions

8 First snap ring

9 Second snap ring

10 Upstream pressure guide port

11 Downstream pressure port

12 venturi

13 pressure guiding tube

14 Entry section

15 throat section

100 downhole fluid sensing device

200 laser light source

300 grating demodulator

400 processing units

401 Spectrum receiving unit

402 Spectral peak wavelength determination unit

403 wavelength difference determination unit

404 Differential Pressure Determination Unit

405 Fluid Flow Rate Determination Unit

406 display unit

detailed description

In order to make the purpose, technical solutions and advantages of the embodiments of the present invention more clear, the embodiments of the present invention will be further described in detail below in conjunction with the accompanying drawings. Here, the exemplary embodiments and descriptions of the present invention are used to explain the present invention, but not to limit the present invention.

Fig. 1 is a schematic structural view of a downhole fluid sensing device 100 of the present invention, as shown in Fig. 4. The first piston 5, the second piston 6, the first grating 1, the second grating 2, the venturi tube 12 is used to guide downhole fluid, and the venturi tube 12 has an inlet section 14 and a throat section 15 , the diameter of the inlet section 14 is greater than the diameter of the throat section 15; the pressure guide tube 13 is connected to the venturi tube 12; the partition plate 7 is arranged at the center of the pressure guide tube 13; the first spring 3 is arranged on On the left side of the partition 7, one end of the first spring 3 is connected to the partition 7, the other end of the first spring 3 is connected to the first piston 5, and the pressure of the fluid in the inlet section 14 passes through the first The piston 5 acts on the first spring 3; the second spring 4 is symmetrically arranged on the right side of the partition 7, one end of the second spring 4 is connected to the partition 7, and the other end of the second spring 4 is connected to the second The piston 6 is connected, and the pressure of the fluid in the throat section 15 acts on the second spring 4 through the second piston 6; one end of the first grating 1 is connected with the partition 7, and the other end of the first grating 1 One end is connected to the first piston 5, and the first grating 1 is always in a stretched state under the joint action of the elastic force of the first spring 3 and the fluid pressure of the inlet section 14, and the first grating 1 receives the incident light, and reflect the first reflected light; one end of the second grating 2 is connected to the partition 7, and the other end of the second grating 2 is connected to the second piston 6, and the second grating 2 is connected to the second piston 6. The elastic force of the second spring 4 and the fluid pressure of the throat section 15 are always in a stretched state. The second grating 2 receives the incident light and reflects the second reflected light. The fluid is shown by the arrow in FIG. 1 The direction flows through the Venturi tube 12.

As shown in Figure 1, the grating is subjected to different stresses (spring force minus fluid pressure), and the reflected incident light is also different. The diameter of the entrance section 14 is larger than the diameter of the throat section 15. Inner tube 12, or when the fluid is in a static state, according to the Bernoulli equation, the pressure that the fluid acts on the first piston 5 in the inlet section 14 is equal to the pressure that the fluid acts on the second piston 6 in the throat section 15, and the incident light passes through The grating reflects reflected light. When a fluid flows through the Venturi tube 12 in the direction shown by the arrow in Figure 1, since the diameter of the inlet section 14 is greater than the diameter of the throat section 15, the flow velocity of the fluid at the inlet section 14 is small and the pressure is high, and the fluid In the throat section 15, the flow velocity is high and the pressure is low, at this time, the reflected light passing through the grating will change.

Usually, the Venturi tube 12 and the pressure guiding tube 13 are located at the site to be tested, for example, the Venturi tube 12 and the pressure guiding tube 13 are located in an oil and gas well several kilometers underground. Since the present invention uses laser to measure fluid flow velocity, the laser has the characteristics of anti-electromagnetic interference, reliable operation, and high measurement accuracy, and can realize accurate fluid flow velocity measurement under high-temperature and high-pressure environmental conditions in oil and gas wells thousands of meters underground.

FIG. 2 is a schematic diagram of a preferred structure of the downhole fluid sensing device 100 of the present invention. As shown in FIG. 2 , the downhole fluid sensing device 100 further includes: a first snap ring 8 and a second snap ring 9 . Wherein, the first snap ring 8 is fixedly arranged on the inner wall of the pressure guide tube 13 on the left side of the first piston 5, the first snap ring 8 is used to limit the movement of the first piston 5 to the left, and prevent the first grating 1 from Too large and damaged; the second snap ring 9 is fixedly arranged on the inner wall of the pressure guide tube 13 on the right side of the second piston 6, and the second snap ring 9 is used to limit the movement of the second piston 6 to the right and prevent the second grating 2 Damaged due to excessive force, and the first snap ring 8 and the second snap ring 9 are symmetrical with respect to the separator 7 .

As shown in Figure 2, the arrangement of the first snap ring 8 and the second snap ring 9 can well protect the first grating 1 and the second grating 2, when there is no fluid flowing through the Venturi tube 12, no fluid flows to the first grating. The piston 5 and the second piston 6 apply pressure, and the elastic force of the spring is fully applied to the grating. At this time, the first snap ring 8 can prevent the leftward displacement of the first piston 5 from exceeding the maximum bearing range of the first grating 1. The second snap ring 9 can prevent the rightward displacement of the second piston 6 from exceeding the maximum bearing range of the second grating 2, and prevent the grating from being damaged due to excessive force.

As shown in Figures 1 and 2, the pressure guiding tube 13 is arranged along the Venturi tube 12, and the pressure guiding tube 13 is a tubular element, which can effectively control the lateral size of the downhole fluid sensing device 100, so the present invention can be used in limited environmental space Measurement of fluid velocity in medium, such as real-time monitoring of downhole fluid velocity in oil and gas wells. In addition, each component (spring, grating, piston, etc.) in the pressure guiding tube 13 is a common physical component, so the downhole fluid sensing device 100 also has the advantages of simple structure, convenient installation, and reliable operation, which further improves measurement accuracy.

Fig. 3 is a schematic diagram of the internal structure of the pressure guiding tube of the downhole fluid sensing device 100 of the present invention. The pressure inside is always in equilibrium.

As shown in Figure 3, since the partition plate 7 has a through hole (not marked in the figure), it can ensure that the left cavity between the partition plate 7 and the first piston 5, and the gap between the partition plate 7 and the second piston 6 The air pressure in the right cavity between them is always equal, and the equal air pressure in the left cavity and the right cavity can prevent the air pressure from affecting the measurement result, and further improve the measurement accuracy.

In one embodiment of the present invention, as shown in FIG. 2 and FIG. 3 , the material and shape of the first piston 5 and the second piston 6 are exactly the same. The first piston 5 and the second piston 6 can be displaced within the range defined by the first snap ring 8 and the second snap ring 9 but strictly prevent fluid communication.

As shown in Figure 2 and Figure 3, the material and shape of the first piston 5 and the second piston 6 are exactly the same, ensuring that the pressure on the first piston 5 and the second piston 6 is only related to the fluid flow rate and is not affected by the first piston 5. Influenced by the material and shape of the second piston 6, the measurement accuracy is further improved.

In one embodiment of the present invention, as shown in FIG. 2 and FIG. 3 , the shape and various parameters of the first grating 1 and the second grating 2 are completely the same.

As shown in Figure 2 and Figure 3, the shapes and parameters of the first grating 1 and the second grating 2 are exactly the same, ensuring that the reflected light formed after the incident light is reflected by the first grating 1 and the second grating 2 is only the same as the first grating The first grating 1 is related to the stress on the second grating 2 (spring force minus fluid pressure), which further improves measurement accuracy.

In one embodiment of the present invention, as shown in FIG. 2 and FIG. 3 , the shape and various parameters of the first spring 3 and the second spring 4 are exactly the same.

As shown in Figure 2 and Figure 3, the shapes and parameters of the first spring 3 and the second spring 4 are exactly the same, ensuring that the deformation of the first spring 3 and the second spring 4 is only affected by the first piston 5 and the second spring 4. The two pistons are related to 6 pressures, which further improves the measurement accuracy. In addition, the detection range of the present invention can be changed by changing the elastic modulus of the first spring 3 and the second spring 4, further expanding the applicability of the present invention and providing users with more extensive choices.

Fig. 4 is a structural schematic diagram of the Venturi tube 12 of the downhole fluid sensing device 100 of the present invention. As shown in Fig. 4, the Venturi tube 12 has an inlet section 14 and a throat section 15, and the diameter of the inlet section 14 is larger than the The diameter of the passage section 15, the inlet section 14 is provided with an upstream pressure guiding interface 10, the throat section 15 is provided with a downstream pressure guiding interface 11, the upstream pressure guiding interface 10 is connected with the left end of the pressure guiding pipe 13, The downstream pressure guide interface 11 is connected to the right end of the pressure guide pipe 13 , and the fluid in the venturi tube 12 flows along the direction from the inlet section 14 to the throat section 15 .

As shown in FIG. 2 , the left end of the pressure guiding tube 13 is screwed to the upstream pressure guiding interface 10 , and the right end of the pressure guiding tube is screwed to the downstream pressure guiding interface 11 . In other embodiments of the present invention, the left end of the pressure guiding tube 13 is welded to the upstream pressure guiding interface 10, and the right end of the pressure guiding tube is welded to the downstream pressure guiding interface 11, as long as the pressure guiding tube 13 is firmly sealed with the Venturi tube 12. Yes, the present invention is not limited thereto.

As shown in FIG. 2 , the pressure guiding tube 13 and the Venturi tube 12 are threadedly connected, which is easy to disassemble. If only the pressure guiding tube 13 or the Venturi tube 12 is damaged, it is not necessary to discard them all, which saves energy, protects the environment, and reduces maintenance costs. In addition, if there is no need to sense the flow rate of the fluid, only the pressure guiding tube 13 can be removed, and then the upstream pressure guiding interface 10 and the downstream pressure guiding interface 11 on the Venturi tube 12 can be sealed with a plug with a suitable thread. Immediately remove the Venturi tube 12 at the same time for easy use.

Fig. 5 is a schematic structural diagram of a fluid flow rate measuring system of the present invention. As shown in FIG. 5 , the fluid flow rate measurement system includes the downhole fluid sensing device 100 in the above embodiment, and the fluid flow rate measurement system also includes a laser light source 200 , a grating demodulator 300 , and a processing device 400 . The laser light source 200 is connected to the downhole fluid velocity sensing device 100, and the laser light source 200 is used to emit incident light; the grating demodulator 300 is connected to the downhole fluid sensing device 100, and the grating demodulator 300 is used to resolve Adjust the first reflected light to obtain a first reflected spectrum, and demodulate the second reflected light to obtain a second reflected spectrum; the processing device 400 is connected to the grating demodulator 300, and the processing device 400 is used for The first reflectance spectrum and the second reflectance spectrum obtain the fluid velocity at the inlet section 14 of the Venturi tube 12. Since the diameter of the inlet section 14 of the Venturi tube 12 is equal to the diameter of the fluid transmission pipeline, the Venturi obtained by the processing device 400 The fluid velocity at the inlet section 14 of the inner tube 12 is the fluid velocity in the fluid transmission pipeline (fluid velocity in the tube).

Since the laser light emitted by the laser light source 200 has good directionality and singleness, and is not affected by electromagnetic interference, the measurement accuracy of the present invention is further improved; the grating demodulator 300 has better stability than other non-optical demodulators, and is resistant to electromagnetic interference , to further improve the fluid measurement accuracy.

As shown in Figure 5, specifically, the incident light emitted by the laser light source 200 is transmitted to the first grating 1 and the second grating 2 through an optical fiber; the incident light is reflected by the first grating 1 to form the first reflected light, and the incident light The second reflected light is formed after being reflected by the second grating 2; the first reflected light and the second reflected light are transmitted to the grating demodulator 300 through an optical fiber; the grating demodulator 300 demodulates the first reflected light Obtain the first reflection spectrum, and the grating demodulator demodulates the second reflection light to obtain a second reflection spectrum, the change of the peak wavelength of the first reflection spectrum is proportional to the change of the stress on the first grating 1, and the peak value of the second reflection spectrum The change of the wavelength is proportional to the change of the stress on the second grating 2 .

FIG. 6 is a schematic structural diagram of a processing device 400 of the fluid velocity measurement system of the present invention. As shown in Figure 6, the processing device 400 includes a spectrum receiving unit 401, a spectrum peak wavelength determination unit 402, a wavelength difference determination unit 403, a pressure difference determination unit 404, a fluid flow rate determination unit 405 and a display unit 406. The spectrum receiving unit 401 is used to receive the first reflection spectrum and the second reflection spectrum; the spectrum peak wavelength determination unit 402 is connected to the spectrum reception unit 401, and the spectrum peak wavelength determination unit 402 is used to determine the first reflection spectrum The first reflection spectrum peak wavelength of the spectrum and the second reflection spectrum peak wavelength of the second reflection spectrum; the wavelength difference determination unit 403 is connected to the spectrum peak wavelength determination unit 402, and the wavelength difference determination unit 403 is used to determine the first reflection spectrum A difference between the peak wavelength of the reflection spectrum and the second peak wavelength of the reflection spectrum; the pressure difference determination unit 404 is connected to the wavelength difference determination unit 403, and the pressure difference determination unit 404 is used to determine the first The pressure difference between the grating 1 and the second grating 2; the fluid flow rate determination unit 405 is connected to the pressure difference determination unit 404, and the fluid flow rate determination unit 405 is used to determine the fluid in the Venturi tube 12 according to the pressure difference The flow rate of the fluid; the display unit 406 is connected with the fluid flow rate determination unit 405, and the display unit 406 is used for displaying the fluid flow rate. Since the wavelength of the reflection spectrum peak corresponds to the stress on the grating when the wavelength of the emitted light, the specification of the grating, and the elastic coefficient of the spring are determined, the pressure difference determination unit 404 is based on the peak wavelength of the first reflection spectrum and the second reflection spectrum The difference between the spectral peak wavelengths is used to obtain the pressure difference (also referred to as stress difference) experienced by the first grating and the second grating.

The pressure difference determination unit 404 directly obtains the pressure difference according to the difference between the peak wavelength of the first reflection spectrum and the peak wavelength of the second reflection spectrum, which is simple to calculate and easy to implement, reducing the implementation cost of the present invention; the fluid flow rate determination unit 405 according to The pressure difference directly obtains the fluid flow rate, which is simple to calculate and easy to implement, further reducing the implementation cost of the present invention; the display unit 406 can simultaneously display the fluid flow rate (the fluid flow rate in the inlet section 14), which is convenient for testers to observe and record, and makes the measurement results more intuitive.

As shown in FIG. 6 , the fluid flow rate determining unit 405 determines the flow rate of the fluid in the pipe (ie, the fluid flow rate at the inlet section 14 of the Venturi tube 12 ) by using the Bernoulli equation according to the pressure difference obtained by the pressure difference determining unit 404 . The following formula reveals the equivalence of fluid flow in inlet section 14 to fluid flow in throat section 15:

A ₁ V ₁ =A ₂ V ₂ (Formula 1)

Among them, A ₁ V ₁ is the fluid flow rate of the inlet section, A ₂ V ₂ is the fluid flow rate of the throat section; V ₁ is the fluid velocity of the inlet section, V ₂ is the fluid velocity of the throat section, A ₁ is the cross-sectional area of the inlet section, A ₂ is the cross-sectional area of the throat section.

The following formula gives the cross-sectional area of the inlet section 14:

(Formula 2)

Among them, A ₁ is the cross-sectional area of the inlet section, and d ₁ is the diameter of the inlet section.

The following formula gives the throat section 15 cross-sectional area:

(Formula 3)

Among them, A ₂ is the cross-sectional area of the throat section, and d ₂ is the diameter of the throat section.

The following formula is the Bernoulli equation:

(Formula 4)

Among them, V ₁ is the fluid velocity in the inlet section, V ₂ is the fluid velocity in the throat section; P ₁ is the fluid pressure in the inlet section, P ₂ is the fluid pressure in the throat section; ρ is the fluid density; h ₁ is the vertical height of the fluid in the inlet section , h ₂ is the vertical height of the fluid in the throat section, h ₁ =h ₂ in the present invention; g is the acceleration due to gravity.

It can be determined by formula 1:

(Formula 5)

Among them, A ₁ V ₁ is the fluid flow rate of the inlet section, A ₂ V ₂ is the fluid flow rate of the throat section; V ₁ is the fluid velocity of the inlet section, V ₂ is the fluid velocity of the throat section, A ₁ is the cross-sectional area of the inlet section, A ₂ is the cross-sectional area of the throat section.

V ₂ can be determined from formula 2, formula 3 and formula 5:

(Formula 6)

Among them, d ₁ is the diameter of the inlet section, d ₂ is the diameter of the throat section, V ₁ is the fluid velocity of the inlet section, and V ₂ is the fluid velocity of the throat section.

V ₁ can be determined from Formula 4 and Formula 6:

(Formula 7)

Wherein, P is the pressure difference, P=P ₁ -P ₂ , ρ is the fluid density, d ₁ is the diameter of the inlet section, and d ₂ is the diameter of the throat section.

According to Formula 7, it can be seen that when the diameter of the Venturi tube 12 is known, the fluid flow rate in the Venturi tube 12 (ie, the fluid flow rate in the inlet section 14) is only related to the pressure difference P, and the fluid flow rate determination unit 405 is based on the pressure difference P The fluid flow rate in the tube (ie, the fluid flow rate V ₁ in the inlet section 14 of the Venturi tube 12 ) can be easily obtained.

As shown in Figure 5, when the fluid in the venturi tube 12 is at rest, or when no fluid passes through the venturi tube 12, the pressure applied by the fluid to the first piston 5 is equal to the pressure applied by the fluid to the second piston 6, that is, the first The pressure on the piston 5 and the second piston 6 is the same. At this time, the tension on the first grating 1 is the elastic force of the first spring 3 minus the pressure applied by the fluid to the first piston 5, and the tension on the second grating 2 is the first The elastic force of the second spring 4 subtracts the pressure applied by the fluid to the second piston 6. Since the first spring 3 is the same as the second spring 4, and the first piston 5 is the same as the second piston 6, the pulling force on the first grating 1 is equal to that of the second piston 6. The tension of the second grating 2. Since the first grating 1 and the second grating 2 are the same, the peak wavelength of the first reflection spectrum formed after the incident light is reflected by the first grating 1 and the second grating 2 is the same as the peak wavelength of the second reflection spectrum, which indicates that the flow rate of the fluid is 0.

When the fluid flows through the Venturi tube 12 in the direction shown by the arrow in Figure 5, throttling occurs because the inner diameter of the inlet section 14 is greater than the inner diameter of the throat section 15; The fluid pressure at the inlet section 14 is greater than the pressure at the throat section 15. At this time, the tension (stress) received by the first grating 1 is the elastic force of the first spring 3 minus the pressure applied by the fluid to the first piston 5, and the tension (stress) received by the second grating 2 is the elastic force of the second spring 4 minus the pressure applied by the fluid to the first piston 5. In addition to the pressure applied by the fluid to the second piston 6, since the first spring 3 is the same as the second spring 4, and the first piston 5 is the same as the second piston 6, the pulling force on the first grating 1 is smaller than that on the second grating 2 . Since the first grating 1 and the second grating 2 are the same, the peak wavelength of the first reflection spectrum and the peak wavelength of the second reflection spectrum formed after the incident light is reflected by the first grating 1 and the second grating 2 are no longer equal, and the pressure difference determination unit 404 The pressure difference between the inlet section 14 and the throat section 15 can be obtained according to the difference between the peak wavelengths of the two reflection spectra.

The fluid flow velocity determining unit 405 obtains the flow velocity of the fluid in the tube by using the Bernoulli equation according to the pressure difference obtained by the pressure difference determining unit 404 . It can be seen from formula 7 that when the cross-sectional area of the inlet section 14 and the throat section 15 is determined, the fluid velocity in the inlet section 14 or the throat section 15 is proportional to the square root of the pressure difference P, for example, it can be known that when the inlet When the diameter of the section 14 is twice the diameter of the throat section 15, the fluid flow velocity in the throat section 15 is 4 times that of the fluid flow velocity in the inlet section 14. Assuming that the crude oil density is 1000kg/m ³ , the fluid flow velocity in the tube of an embodiment ( Inlet section 14 fluid flow rate) as shown in Table 1 below:

Table 1

It can be seen from Table 1 that the pressure difference determination unit 404 can conveniently determine the fluid flow rate according to the pressure difference, and the display unit 406 can simultaneously display the fluid flow rate (fluid flow rate in the inlet section 14), which is convenient for testers to observe and record, and the measurement results are more intuitive.

Here, since the first piston 5 is the same as the second piston 6, the first spring 3 is the same as the second spring 4, and the first grating 1 is the same as the second grating 2, the measurement results can be analyzed without considering environmental factors such as air pressure and temperature. The resulting influence makes the measurement data more accurate.

Compared with the prior art, the downhole fluid sensing device and fluid velocity measurement system provided by the present invention have the following beneficial effects:

1. Since the sensing element grating is placed along the pressure guiding tube 13, the inner diameter of the pressure guiding tube 13 can be made very small, so the lateral dimension of the downhole fluid sensing device 100 can be effectively controlled, so the present invention can be applied in limited environmental spaces Measurement of fluid velocity, such as real-time monitoring of downhole fluid velocity in oil and gas wells.

2. The present invention adopts the differential method to obtain the pressure difference before and after the throttling of the Venturi tube 12, and the pressure detection elements on the left and right sides of the partition plate 7 are completely the same, so there is no need to consider environmental factors such as temperature in the process of using the measurement results. , which effectively simplifies the processing of measurement data.

3. After using the present invention to measure the fluid flow rate, there is no need to deal with some residual fluid that may exist in the section between the piston and the pressure guiding interface, because the fluid in this section only plays the role of transmitting pressure, which is very important in many cases. The maintenance process of the fluid flow rate measurement system is greatly simplified.

The above are only illustrative specific implementations of the present invention. Under the premise of not departing from the concept and principle of the present invention, any equivalent changes and modifications made by those skilled in the art shall fall within the protection scope of the present invention. .

Claims (9)

1. A downhole fluid sensing device, characterized in that the downhole fluid sensing device comprises: a venturi for guiding downhole fluid, the venturi having an inlet section and a throat section, the inlet section having a diameter greater than the diameter of the throat section; A pressure guide tube connected to the Venturi tube; A baffle, arranged in the center of the pressure guiding tube, wherein a through hole is opened on the baffle; A first spring is arranged on the left side of the partition, one end is connected to the partition, and the other end is connected to a first piston. The pressure of the fluid in the inlet section acts on the first piston through the first piston. a spring; A second spring is arranged symmetrically on the right side of the partition, one end is connected to the partition, and the other end is connected to a second piston. The pressure of the fluid in the throat section acts on the partition through the second piston. the second spring; A first grating, one end is connected to the partition, and the other end is connected to the first piston, the first grating is always stretched under the joint action of the first spring force and the fluid pressure of the inlet section state, the first grating receives an incident light and reflects a first reflected light; and A second grating, one end is connected with the partition, and the other end is connected with the second piston, and the second grating is always in tension under the joint action of the second spring force and the fluid pressure of the throat section. In an extended state, the second grating receives the incident light and reflects a second reflected light. 2. The downhole fluid sensing device according to claim 1, wherein the downhole fluid sensing device further comprises: a first snap ring, arranged on the inner wall of the pressure guide tube on the left side of the first piston; and A second snap ring is symmetrically arranged on the inner wall of the pressure guiding tube on the right side of the second piston. 3. The downhole fluid sensing device according to claim 1, wherein the first piston is the same as the second piston; the first grating is the same as the second grating; the first spring is the same as the second grating The second springs are identical. 4. The downhole fluid sensing device according to claim 1, wherein an upstream pressure guiding interface is provided on the inlet section, a downstream pressure guiding interface is provided on the throat section, and the left end of the pressure guiding tube It is connected with the upstream pressure guiding interface, and the right end of the pressure guiding tube is connected with the downstream pressure guiding interface. 5. The downhole fluid sensing device according to claim 4, wherein the left end of the pressure guiding tube is threadedly connected to the upstream pressure guiding interface, and the right end of the pressure guiding tube is threaded to the downstream pressure guiding interface. connect. 6. A fluid velocity measurement system, characterized in that the fluid velocity measurement system comprises the downhole fluid sensing device as claimed in any one of claims 1-5, the fluid velocity measurement system also comprises a laser light source, a grating demodulator instrument, a processing device, wherein the downhole fluid sensing device includes a partition arranged at the center of the pressure guiding tube, and a through hole is opened on the partition; The laser light source, connected to the downhole fluid sensing device, is used to emit the incident light; The grating demodulator, connected to the downhole fluid sensing device, is used to demodulate the first reflected light to obtain a first reflected spectrum, and demodulate the second reflected light to obtain a second reflected spectrum; and The processing device, connected with the grating demodulator, is used to determine the fluid velocity at the inlet section of the Venturi tube according to the first reflection spectrum and the second reflection spectrum. 7. The fluid velocity measurement system according to claim 6, wherein the processing device comprises: a spectrum receiving unit, configured to receive the first reflection spectrum and the second reflection spectrum; A spectral peak wavelength determining unit, connected to the spectral receiving unit, for determining the first reflected spectral peak wavelength and the second reflected spectral peak wavelength; A wavelength difference determining unit, connected to the spectral peak wavelength determining unit, for determining the difference between the first reflected spectral peak wavelength and the second reflected spectral peak wavelength; A pressure difference determination unit, connected to the wavelength difference determination unit, configured to determine the pressure difference between the first grating and the second grating according to the difference in spectral peak wavelength; and A fluid flow rate determination unit, connected to the pressure difference determination unit, for determining the fluid flow rate at the inlet section of the Venturi tube according to the pressure difference. 8. The fluid velocity measurement system according to claim 7, wherein the fluid velocity determining unit utilizes the following formula to determine the fluid velocity at the inlet section of the Venturi tube: ${\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>\sqrt{\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; P</span>}}{\mathrm{<span\; class="notranslate">\; \&rho;</span>}<span\; class="notranslate">\; \&lsqb;</span>{<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}{{\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; \&rsqb;</span>}}<span\; class="notranslate">\; ,</span>$ Among them, V ₁ is the fluid flow velocity in the inlet section, P is the pressure difference, ρ is the fluid density, d ₁ is the diameter of the inlet section, and d ₂ is the diameter of the throat section. 9. The fluid flow rate measurement system according to claim 7, wherein the processing device further comprises a display unit connected with the fluid flow rate determination unit for displaying the fluid flow rate.