A lever type fiber grating flow sensor for a water injection well and a detection method

Abstract

A lever type fiber grating flow sensor for water injection wells and a detection method, the base is fixed with a flexible hinge lever structure through a flexible hinge; the dynamic arm of the flexible hinge lever structure is fixed with a resistance target through a force transmission rod; a tray is fixed at the end of the resistance arm of the flexible hinge lever structure; the upper end of the base is provided with a fiber grating setting groove, a fiber grating B is fixed between the tray and the outlet end of the fiber grating setting groove; a fiber grating A is fixed between the inlet and outlet of the fiber grating setting groove. The structure is smaller in size, easy to install in water injection wells, high in sensitivity, capable of realizing simultaneous detection of flow and temperature, retaining the characteristics of the conventional target type fiber grating flow sensor that is convenient to change the range, and solving the problem that the conventional target type fiber grating flow sensor and the differential pressure type fiber grating flow sensor are large in size and difficult to be used in small-diameter pipelines such as water injection wells.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of sensors, and particularly relates to a lever type fiber Bragg grating flow sensor for a water injection well and a detection method. BACKGROUND

[0002] In the later stage of oilfield exploitation, the problem of reduced formation pressure and reduced crude oil production is faced. The method of underground water injection is mainly used in China to maintain and improve the formation pressure and achieve stable production. The measurement of downhole layered flow of the water injection well is of great significance to oilfield development. The commonly used electromagnetic flow sensor and electronic flow sensor have the problems of being susceptible to electronic interference and being difficult to work stably in a high temperature and high pressure environment.

[0003] The fiber Bragg grating sensor has the characteristics of intrinsic safety, high sensitivity, anti-electromagnetic interference and easy realization of quasi-distributed sensing, and can effectively monitor various physical quantities by detecting the change of the center wavelength of the fiber Bragg grating. With the development of fiber Bragg grating sensing technology, researchers have proposed target type fiber Bragg grating flow sensors, differential pressure type fiber Bragg grating flow sensors, hot-wire type fiber Bragg grating flow sensors and other flow sensor structures.

[0004] Compared with the differential pressure type fiber Bragg grating flow sensor structure, the target type fiber Bragg grating flow sensor has the advantages of simple structure, large range, small pressure loss and strong anti-purity ability. For the flow measurement in the water injection well, compared with the hot-wire type fiber Bragg grating flow sensor, the hot-wire type fiber Bragg grating flow sensor needs to use an electric wire to heat the optical fiber, which not only makes the sensor installation more complex, but also has safety hazards in the flammable and explosive working environment such as oil exploitation, while the target type fiber Bragg grating flow sensor retains the intrinsic safety characteristics of the optical fiber sensor. In addition, the target type fiber Bragg grating flow sensor only needs to replace cantilever beams with different thicknesses to realize range conversion, which is very convenient.

[0005] However, the traditional target type fiber grating flow sensor structure has some shortcomings. On the one hand, the traditional target type fiber grating flow sensor needs to install a three-way pipe, a valve body and other devices to provide space for accommodating the cantilever beam when used in small caliber pipelines. However, the pipeline in the water injection well is extremely narrow, and it is difficult to install the three-way pipe, the valve body and other devices. On the other hand, it is difficult to process the equal strength cantilever beam matched with the pipe diameter of the water injection well, and the problem of fiber grating chirp cannot be solved. When the strain of the cantilever beam is not uniform, the fiber grating is prone to chirp. The traditional target type fiber grating flow sensor solves this problem by installing an equal strength cantilever beam with uniform strain distribution. However, due to the requirement of the equal strength cantilever beam for the length-width-thickness ratio, it is difficult to process the equal strength cantilever beam that can be used in the water injection well. Finally, under the condition that the area of the flow resistance target plate is constant, the sensitivity of the traditional target type fiber grating flow sensor depends on the strain change of the cantilever beam. The strain change of the cantilever beam is often small, so the center wavelength change of the fiber grating is small, and therefore the sensitivity of the traditional target type fiber grating flow sensor is low. SUMMARY

[0006] In order to overcome the shortcomings of the prior art, the purpose of the present application is to provide a lever type fiber grating flow sensor for a water injection well, which has a smaller structure size, is easy to install in the water injection well, has high sensitivity, can realize simultaneous detection of flow and temperature, retains the characteristic of the traditional target type fiber grating flow sensor that is easy to change the range, and solves the problem that the traditional target type fiber grating flow sensor and the differential pressure type fiber grating flow sensor are large in size and difficult to be used in small caliber pipelines such as water injection wells.

[0007] In order to achieve the above purpose, the technical scheme adopted by the present application is:

[0008] A lever type fiber grating flow sensor for a water injection well, comprising a base (2), characterized in that the base (2) fixes a flexible hinge lever structure (3) through a flexible hinge; a flow resistance target plate (4) is fixed on the power arm of the flexible hinge lever structure (3) through a force transmission rod (5); a tray (6) is fixed at the end of the resistance arm of the lever of the flexible hinge lever structure (3); an optical fiber grating placement groove (7) is arranged at the upper end of the base (2), an optical fiber grating B (9) is fixed between the tray (6) and the outlet end of the optical fiber grating placement groove (7), and an optical fiber grating A (8) is fixed between the inlet and outlet of the optical fiber grating placement groove (7).

[0009] The flow resistance target plate (4) and the lever of the flexible hinge lever structure (3) are perpendicular to the pipeline axis direction.

[0010] The height of the tray (6) is horizontally aligned with the groove on the base.

[0011] The optical fiber grating A (8) is a temperature compensation grating.

[0012] The fiber grating B (9) is a sensing grating.

[0013] The flexible hinge lever structure (3) is made of elastic material.

[0014] The fiber grating installation groove (7) is a semi-cylindrical groove.

[0015] A lever type fiber grating flow sensor detection method for a water injection well, characterized in that it comprises the following steps:

[0016] The flow resistance target plate of the sensor is fixed to the pipeline in the direction of the flow, if the fluid density is p, the target plate area is A1, the resistance coefficient is zeta, the fluid velocity is v, and the pressure is P, according to the Bernoulli equation, the flow resistance target plate is subjected to the pressure of the fluid:

[0017]

[0018] Suppose the lever is a rigid body, K M is the hinge rotation stiffness, K f is the fiber elastic coefficient, the hinge deformation caused by shear force is ignored, the lever dynamic arm length is l1, the resistance arm length is l2, and the lever resistance arm output displacement is x out According to the force analysis, there are:

[0019] Pl1=x out K f l2+K M θ (2);

[0020] Pe is the effective photoelastic coefficient, and epsilon is the axial strain, so the relationship between the grating wavelength change and the strain is:

[0021] Delta lambda = epsilon (1-P e ) lambda Β (3);

[0022] If the distance between the two sticking points of the grating is a, then:

[0023]

[0024] In the pipeline with an area A2, the flow rate Q and the flow rate v have the following relationship:

[0025] Q=A2v (5);

[0026] The relationship between the FBG center wavelength and the flow rate is obtained by combining equations (1)-(5):

[0027]

[0028] The beneficial effects of the present application are:

[0029] The present application can change the range and sensitivity of the flow sensor by changing the position of the hinge to amplify or reduce the impact force and changing the thickness of the hinge according to the measurement requirements. In addition, the range can be changed by replacing the optical fiber grating with different grid distances. The optical fiber grating A (8) and the optical fiber grating B (9) are packaged in the base recess, which not only avoids the corrosion and impact of the fluid on the optical fiber grating, but also measures the temperature and flow of the fluid at the same time. BRIEF DESCRIPTION OF DRAWINGS

[0030] Fig. 1 Figure 1 is a schematic diagram of the base and flexible hinge lever structure of the optical fiber grating lever type flow sensor.

[0031] Fig. 2 Figure 2 is a schematic diagram of the flow blocking target and force transmission rod structure of the optical fiber grating lever type flow sensor.

[0032] Fig. 3 Figure 3 is a sectional view of the optical fiber grating lever type flow sensor installed in the water injection well pipe.

[0033] Wherein, 1-pipe, 2-base, 3-flexible hinge lever structure, 4-flow blocking target, 5-force transmission rod (length 3mm), 6-tray, 7-optical fiber grating installation recess, 8-optical fiber grating 1, 9-optical fiber grating 2, 10-fan cap, 11-optical fiber lead hole, 12-base fixing hole. DETAILED DESCRIPTION

[0034] The present application will be further described below in conjunction with the drawings and examples, but the present application is not limited to the following embodiments.

[0035] Example 1:

[0036] As Figs. 1 to 3As shown: the embodiment provides a fiber grating lever flow sensor, the pipe 1 inner diameter of the embodiment is 23mm, the base 2 length is 35mm, the flexible hinge lever structure 3 lever length is 11mm, the hinge thickness is 1mm. The radius of the flow resistance target sheet 4 is 8mm, the length of the force transmission rod 5 is 3mm, the thickness of the tray 6 is 1mm, the fiber grating placement groove 7 is a semicylindrical groove with a diameter of 1mm. The center wavelength of the fiber grating A 8 is 1554.0938nm, the grating pitch is 10mm, the center wavelength of the fiber grating B 9 is 1537.9171nm, and the grating pitch is 10mm. The base is provided with a fan-shaped cap 10 and a base fixing hole 12, and the base is installed in the inner wall of the injection well pipe by using M4 bolts, so that the flow resistance target sheet and the lever are perpendicular to the pipe axis. Two-point sticking method is used to stick the fiber grating B 9 between the tray at the end of the resistance arm and the outlet end of the fiber grating placement groove with temperature-resistant glue 353ND, and the fiber grating A 8 is stuck between the inlet and outlet of the fiber grating placement groove with temperature-resistant glue 353ND. After the two fiber gratings are led out of the fiber leading-out hole 11 on the pipe, they are connected with the demodulator. The fiber leading-out hole can be sealed with a rubber cap. The pipeline as a whole is in a U shape, the pipe inlet is connected with the water storage tank through the water injection pump. The pipe outlet is also connected to the water storage tank, thus forming a loop.

[0037] After starting the water injection pump, the fluid impacts the flow resistance target sheet, and the impact force is amplified through the flexible hinge lever structure to stretch the fiber grating B 9, so that the center wavelength of the 8-fiber grating B changes. The fiber grating A and the fiber grating B are in the same temperature field, and the center wavelength change is only related to the fluid temperature and has nothing to do with the flow size, so it can be used for temperature compensation. In this way, the flow and temperature are measured at the same time.

[0038] Water is injected into the pipe through the plunger pump, and the plunger pump power is adjusted to increase the flow to 100m3 / d. The sensitivity of the embodiment is 14.7pm / (L / h), which is higher than that of the traditional target fiber grating flow sensor structure.

[0039] Embodiment 2

[0040] M4 bolts are used to install the base in the inner wall of the injection well pipe, so that the flow resistance target sheet and the lever are perpendicular to the pipe axis. Two-point sticking method is used to stick the fiber grating B 9 between the tray at the end of the resistance arm and the outlet end of the fiber grating placement groove with temperature-resistant glue 353ND, and the fiber grating A 8 is stuck between the inlet and outlet of the fiber grating placement groove with temperature-resistant glue 353ND. After the two fiber gratings are led out of the fiber leading-out hole 11 on the pipe, they are connected with the demodulator. The center wavelength of the fiber grating B 9 is 1538.5672, and the grating pitch is 5mm. The fiber leading-out hole can be sealed with a rubber cap. The pipeline as a whole is in a U shape, the pipe inlet is connected with the water storage tank through the water injection pump. The pipe outlet is also connected to the water storage tank, thus forming a loop.

[0041] The water is injected into the pipeline by the plunger pump, and the plunger pump power is adjusted to increase the flow to 100 m3 / d. Compared with Example 1, the sensitivity of this example is doubled.

[0042] Example 3

[0043] The base is installed in the inner wall of the water injection well pipeline by using the bolt of M4, and the flow resistance target is perpendicular to the pipeline axis. Two-point sticking method is used to stick the fiber Bragg grating B9 between the tray at the end of the resistance arm and the outlet end of the fiber Bragg grating installation groove with temperature-resistant glue 353ND, and the fiber Bragg grating A8 is stuck between the inlet and outlet of the fiber Bragg grating installation groove with temperature-resistant glue 353ND. After the two fiber Bragg gratings are drawn out from the fiber draw-out hole on the pipeline, they are connected with the demodulator. The fiber Bragg grating B9 is a grating with a grating pitch of 3 mm and a central wavelength of 1541.3671 nm, which is written by a femtosecond laser. The fiber draw-out hole can be sealed with a rubber cap. The pipeline is in a U shape, and the pipeline inlet is connected with the water storage tank through the water injection pump. The pipeline outlet is also connected to the water storage tank, thus forming a loop.

[0044] The water is injected into the pipeline by the plunger pump, and the plunger pump power is adjusted to increase the flow to 100 m3 / d. Compared with Example 1, the sensitivity of this example is doubled.

Claims

1. A lever type fiber grating flow sensor detection method for water injection wells, comprising a base (2) that fixes a flexible hinge lever structure (3) through a flexible hinge; a resistance target plate (4) is fixed on the power arm of the flexible hinge lever structure (3) through a force transmission rod (5); a tray (6) is fixed at the end of the resistance arm of the lever of the flexible hinge lever structure (3); the upper end of the base (2) is provided with a fiber grating installation groove (7), a fiber grating B (9) is fixed between the tray (6) and the outlet end of the fiber grating installation groove (7); a fiber grating A (8) is fixed between the inlet and outlet of the fiber grating installation groove (7), characterized in that, The sensor detection method comprises the following steps: The flow resistance target of the sensor is fixed to the pipeline in the flow direction, if the fluid density is p, the target area is A1, the flow resistance coefficient is zeta, the fluid velocity is v, and the pressure is P, according to the Bernoulli equation, the flow resistance target is subjected to the pressure of the fluid: Let the lever be a rigid body, K M is the hinge rotational stiffness, K f is the optical fiber elastic coefficient, ignoring the hinge deformation caused by shear force, the lever dynamic arm length l1, the resistance arm length l2, and the lever resistance arm output displacement x out According to the force analysis, there are: Pl1 = x out K f l2+K M θ (2); Pe is the effective photoelastic coefficient, and epsilon is the axial strain, so the relationship between the wavelength variation of the fiber grating and the strain is: Δλ = ε(1 - P e )λ Β (3) If the distance between the two sticking points of the fiber grating is a, then: In the pipeline with the area A2, the flow rate Q and the flow velocity v have the following relationship: Q=A2v (5); The relationship between the center wavelength of the fiber grating and the flow rate is obtained by combining equations (1)-(5):

2. The method according to claim 1, wherein, The flow resistance target (4) and the flexible hinge lever structure (3) are perpendicular to the pipeline axis direction.

3. The method of claim 1, wherein the method is characterized by: The height of the tray (6) is horizontally aligned with the fiber grating arrangement groove (7) on the base.

4. The method of claim 1, wherein the method is characterized by: The fiber grating A (8) is a temperature compensation grating.

5. The method of claim 1, wherein the method is used for detecting the flow rate of a water injection well. The fiber grating B (9) is a sensing grating.

6. The method of claim 1, wherein the method is used for a lever-type fiber-optic grating flow sensor for a water injection well. The flexible hinge lever structure (3) is made of an elastic material.

7. The method of claim 1, wherein the method is used for detecting the flow rate of a water injection well. The fiber grating arrangement groove (7) is a semicylindrical groove.

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