Fiber bragg grating pressure sensor for monitoring total pressure in reservoir and manufacturing method of fiber bragg grating pressure sensor

Abstract

The invention discloses a fiber bragg grating pressure sensor for monitoring total pressure in a reservoir and a manufacturing method of the fiber bragg grating pressure sensor. The two cap bodies are provided with grooves, and openings of the grooves of the two cap bodies are oppositely arranged. The elastic body is of a columnar structure. The two ends of the elastic body extend into the grooves of the two cap bodies respectively and are spaced from the bottom walls of the grooves of the two cap bodies by preset distances respectively. The number of the sealing rings is two. And the two sealing rings are respectively arranged between the inner peripheral walls of the grooves of the two cap bodies and the outer peripheral wall of the elastic body in a sealing manner. The support is supported between the two cap bodies and connected with the two cap bodies. The fiber bragg grating is packaged in the center of the elastic body. According to the sensor, when the reservoir deforms, the elastomer is extruded to stretch, the fiber grating in the elastomer also stretches, the refractive index of the fiber grating changes, the change is read through a demodulator, conversion is carried out in combination with the mechanical property of an elastomer material, pressure data in a soil body is obtained, and the total pressure in the reservoir is monitored.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of geotechnical mechanics testing, in particular to a fiber grating pressure sensor for monitoring total pressure in a reservoir and a manufacturing method thereof. BACKGROUND

[0002] Natural gas hydrate is a high-efficiency clean energy with abundant resources, and is one of the strategic commanding points for future global energy development. To realize the commercial exploitation of natural gas hydrate, the problems of safety and green environmental protection must be solved, and reliable physical and mechanical parameter measurement technology in the laboratory and on site is needed.

[0003] At present, the measurement technology for parameters such as reservoir density, temperature, pressure, gas composition and hydrate saturation in the laboratory and on site is relatively mature. However, unlike conventional oil and gas reservoirs, the soil body becomes soft after the decomposition of natural gas hydrate reservoirs, and it is very difficult to measure the internal deformation and total pressure of the soil layer under the environment of significant changes in pressure, temperature and deformation.

[0004] Multi-source, multi-resolution, multi-type, multi-platform and multi-scale measurement sensor technology, computer technology and information technology begin to be integrated and applied to mountain landslide monitoring, and landslide early warning enters the stage of real-time tracking dynamic prediction, numerical prediction and comprehensive prediction using big data.

[0005] Fiber grating sensing technology is a new sensing technology that has emerged with the development of fiber grating manufacturing technology and fiber grating communication technology. It has good stability, high measurement accuracy, and is convenient to use wavelength division multiplexing technology to connect multiple fiber gratings to form a distributed sensing network, so fiber grating sensing technology has broad application prospects.

[0006] However, these existing monitoring technologies and equipment cannot be directly applied to the measurement of total pressure of deep-sea natural gas hydrate reservoir soil, so the new technology and new equipment based on fiber grating sensing technology to form the total pressure of natural gas hydrate reservoir is a potentially effective method. SUMMARY

[0007] The present application provides a fiber grating pressure sensor for monitoring total pressure in a reservoir and a manufacturing method thereof, which can monitor the total pressure in the reservoir.

[0008] The embodiment of the present application provides a fiber grating pressure sensor for monitoring total pressure in a reservoir, comprising a cap body, an elastic body, a sealing ring, a support and a fiber grating. The cap body comprises two. The two cap bodies are provided with grooves, and the groove openings of the two cap bodies are oppositely arranged. The elastic body is in a columnar structure. The two ends of the elastic body respectively extend into the grooves of the two cap bodies and are spaced apart from the groove bottom walls of the two cap bodies by a preset distance. The sealing ring comprises two. The two sealing rings are respectively arranged between the inner circumferential walls of the grooves of the two cap bodies and the outer circumferential wall of the elastic body. The support is supported between the two cap bodies and connected with the two cap bodies. The fiber grating is encapsulated at the center of the elastic body, so that when the reservoir is deformed, the elastic body is extruded to be elongated, the fiber grating in the elastic body is also elongated, and the refractive index of the fiber grating changes, so as to obtain total pressure data in the reservoir.

[0009] In some embodiments, the inner circumferential wall of the two cap bodies is provided with an annular groove for mounting the sealing ring.

[0010] In some embodiments, the two cap bodies each comprise a cylindrical cap made of stainless steel, the outer diameter of the cylindrical cap is 1 cm, the wall thickness is 0.5 cm, the outer height is 1 cm, and the inner height is 0.5 cm to 0.7 cm.

[0011] In some embodiments, the elastic body comprises a cylinder made of modified acrylate, the diameter of the cylinder is 0.5 cm, and the height is 1 cm.

[0012] In some embodiments, the temperature range of the fiber grating pressure sensor is -30-100 DEG C, and the pressure range is 0-30 MPa.

[0013] The embodiment of the present application also provides a manufacturing method of the fiber grating pressure sensor, comprising the following steps: manufacturing two cap bodies and manufacturing a support. A mold with a cylindrical groove is manufactured, and then a fiber grating with a calibrated protection layer outside the fiber grating is suspended and placed at the cylindrical axis position of the mold. A and B glue of modified acrylate are taken respectively and mixed in a container to obtain mixed glue. Then the fiber grating suspended and placed at the cylindrical axis position of the mold is poured into the mold by using the mixed glue, and the two ends of the fiber grating are sealed. Subsequently, the entire mold and the fiber grating poured into the mold are placed in a constant temperature box, kept at a preset temperature for a preset time, then the temperature of the constant temperature box is lowered, and after the glue solidifies, an elastic body encapsulating the fiber grating is obtained. A sealing ring is selected, the sealing ring is sleeved on the elastic body, and the two cap bodies are combined, then the support is connected and fixed with the two cap bodies, and the fiber grating pressure sensor is obtained.

[0014] In some embodiments, the preset temperature is lower than the highest temperature value of the mixed A and B glue of modified acrylate.

[0015] In some embodiments, after the encapsulation of the fiber grating into the elastic body, the fiber grating is connected to a demodulator, and the elastic body is subjected to a quantitative load for calibration. If the calibration result shows that the fiber grating is intact and linearly deformed, the encapsulation of the fiber grating is successful.

[0016] In some embodiments, after the fiber grating pressure sensor is obtained, the measurement effect of the fiber grating pressure sensor is tested under preset experimental conditions to determine whether the fiber grating pressure sensor is intact and the range size.

[0017] In some embodiments, after the fiber grating is placed in the position of the cylindrical axis of the mold, the fiber grating is lightly pressed by the object to keep the position and stretching state of the fiber grating.

[0018] According to the fiber grating pressure sensor for monitoring the total pressure in the reservoir provided by the embodiments of the present application, the fiber grating pressure sensor comprises a cap body, an elastic body, a sealing ring, a support and a fiber grating. The cap body comprises two. The two cap bodies are provided with grooves, and the groove openings of the two cap bodies are oppositely arranged. The elastic body is in a columnar structure. The two ends of the elastic body extend into the grooves of the two cap bodies, respectively, and are spaced apart from the bottom walls of the grooves of the two cap bodies by a preset distance. The sealing ring comprises two. The two sealing rings are sealingly arranged between the inner circumferential walls of the grooves of the two cap bodies and the outer circumferential wall of the elastic body. The support is supported between the two cap bodies and connected to the two cap bodies. The fiber grating is encapsulated at the center of the elastic body, so that when the reservoir is deformed, the elastic body is extruded to be elongated, the fiber grating inside the elastic body is also elongated, and the refractive index of the fiber grating changes to obtain the total pressure data in the reservoir. The fiber grating pressure sensor of the present application uniformly wraps the fiber grating with the elastic body, so that when the external structure is deformed by more than the limit deformation of the fiber grating, the deformation effect first acts on the elastic body, the elastic body is extruded to be relatively uniformly elongated on both sides, thereby uniformly elongating the fiber grating inside the elastic body on both sides, so that the refractive index of the fiber grating changes correspondingly, and then the change is read by a demodulator to convert the pressure data in the soil body, and the total pressure in the reservoir is monitored. BRIEF DESCRIPTION OF DRAWINGS

[0019] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creating laborious work.

[0020] Figure 1 It is a structural schematic diagram of the fiber grating pressure sensor in the embodiments of the present application. DETAILED DESCRIPTION

[0021] In order to make the purpose, technical solutions and advantages of the present application clearer, the present application is further described in detail below in combination with the drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application and do not limit the present application.

[0022] At present, the main monitoring method of the internal pressure of the soil layer is electric sensing measurement, such as piezoelectric sensor, etc. Another monitoring method is optical fiber grating measurement, which realizes the measurement of pressure through grating strain. The commonly used electric measurement sensor is easily affected by electromagnetic interference and chemical corrosion and is difficult to maintain long-term stable work in complex environments such as low temperature, high pressure, high salinity, etc. The optical fiber grating sensor has high sensitivity, is not easy to be corroded and has wide measurement range, but there is still a lack of simple structure and small volume sensor to monitor the internal pressure data of the soil body while reducing the influence on the soil body. For this reason, referring to Figure 1 The embodiment of the present application provides an optical fiber grating pressure sensor for monitoring the total pressure in the reservoir, which comprises a cap body 1, an elastic body 2, a sealing ring 3, a support 4 and an optical fiber grating 5.

[0023] The number of the cap body 1 is two. Both of the two cap bodies 1 have grooves. The grooves can be cylindrical grooves. The groove openings of the two cap bodies 1 are oppositely arranged, such as being arranged in correspondence with each other.

[0024] The inner circumferential wall of the two cap bodies 1 can each have an annular groove for mounting the sealing ring 3.

[0025] Both of the two cap bodies 1 are rigid caps. Both of the two cap bodies 1 can be cylindrical caps made of stainless steel. The outer diameter of the cylindrical cap can be 1 cm, the wall thickness can be 0.5 cm, the outer height can be 1 cm, and the inner height can be 0.5 cm to 0.7 cm.

[0026] The elastic body 2 is a columnar structure, such as a cylindrical structure. Both ends of the elastic body 2 extend into the grooves of the two cap bodies 1 and are spaced apart from the groove bottom walls of the two cap bodies 1 by a predetermined distance to leave a certain cavity.

[0027] The elastic body 2 can be a cylinder cast by modified acrylic ester or a cylinder cast by rubber and epoxy resin, which is completed according to the actual measurement requirements. The diameter of the cylinder can be 0.5 cm, and the height can be 1 cm. The elastic body 2 shows elasticity when subjected to pressure within the range.

[0028] The number of the sealing ring 3 is two. The two sealing rings 3 are sealingly arranged between the inner circumferential walls of the grooves of the two cap bodies 1 and the outer circumferential wall of the elastic body 2.

[0029] Both sealing rings 3 can be Glyd rings, which are rubber rings used to achieve liquid sealing.

[0030] The bracket 4 is positioned between the two cap bodies 1 and connects them, ensuring that the two cap bodies 1 maintain their relative positions during installation. The bracket 4 is fixed to the two cap bodies 1 by welding.

[0031] Optionally, the number of supports 4 is at least three, with each support 4 arranged around the center line of the groove of the cap body 1. Alternatively, the support 4 is a cylindrical structure to limit the maximum tensile displacement of the two cap bodies 1.

[0032] The fiber grating 5 is encapsulated at the center of the elastic body 2, so that the strain of the fiber grating 5 is increased through the sensitization of the elastic body 2. Specifically, when the reservoir deforms, the elastic body 2 is subjected to... Figure 1 The elastic body 2 elongates due to compression in the indicated pressure direction, and the fiber grating 5 inside also elongates, causing a change in the refractive index of the fiber grating 5 to obtain total pressure data within the reservoir. Specifically, the fiber grating 5 is a Bragg fiber grating 5.

[0033] The fiber optic pressure sensor has a temperature range of -30 to 100°C and a pressure range of 0 to 30 MPa, which can meet the needs of laboratories and can also be deployed in seabed strata for a long time.

[0034] An embodiment of this application also provides a method for manufacturing the above-mentioned fiber Bragg grating pressure sensor, comprising the following steps:

[0035] (1) Make two hat bodies 1 and make a support 4.

[0036] (2) A mold with a cylindrical groove is made. Then, the calibrated fiber Bragg grating 5, along with its external protective layer, is suspended and placed on the cylindrical axis of the mold. Modified acrylic A and B adhesives are taken separately and mixed in a small container to obtain a mixed adhesive. The fiber Bragg grating 5, suspended on the cylindrical axis of the mold, is then quickly poured into the mold using the mixed adhesive, and both ends of the fiber Bragg grating 5 are sealed. The entire mold, along with the fiber Bragg grating 5 poured into it, is then placed in a constant temperature chamber. The chamber is maintained at a preset temperature for a preset time, and then the temperature is gradually reduced until the adhesive solidifies, resulting in an elastomer 2 encapsulating the fiber Bragg grating 5.

[0037] In the above steps, when making the mold with the cylindrical groove, the mold can be made of a slightly hard material such as plastic or wood. The cylindrical groove is carved into the mold, and the size can be determined according to the actual needs.

[0038] After suspending the fiber grating 5 in the cylindrical axis position of the mold, gently press the fiber grating 5 with a small block to maintain its position and tension.

[0039] When taking the A glue and the B glue of the modified acrylic ester respectively, take the same volume of sufficient A glue and B glue.

[0040] The preset temperature is slightly lower than the highest temperature value measured after the A glue and the B glue of the modified acrylic ester are mixed to make the heating of the whole mold as uniform as possible.

[0041] After obtaining the elastic body 2 encapsulating the fiber grating 5, the fiber grating 5 is connected to a demodulator, and the elastic body 2 is calibrated by applying a quantitative load. If the calibration result shows that the fiber grating 5 is intact and linearly deformed, the fiber grating 5 is successfully encapsulated.

[0042] (3) Selecting a suitable sealing ring 3, the sealing ring 3 is sleeved on the elastic body 2, and is combined with the two cap bodies 1. Then, the connection and fixation of the bracket 4 and the two cap bodies 1 are completed, and a complete fiber grating pressure sensor is obtained.

[0043] In the above steps, when selecting a suitable sealing ring 3, the actual sensor size is selected.

[0044] After obtaining the fiber grating pressure sensor, the measurement effect of the fiber grating pressure sensor is tested under specific experimental conditions to determine whether the fiber grating pressure sensor is intact and the range size.

[0045] The fiber grating pressure sensor after completion of the production has good air tightness and appropriate strength, and can be directly placed in the experimental environment. Using the fiber grating pressure sensor, only the fiber grating pressure sensor needs to be directly buried in the target position during the sample preparation process of the experiment, and the orientation of the fiber grating pressure sensor is adjusted. If there are higher requirements for the position and posture of the fiber grating pressure sensor, a fine wire and a stand can be used to control the posture of the fiber grating pressure sensor. Then, the sample preparation is completed, and the experiment is completed. During the experiment, the demodulator can be connected to complete the whole process of data recording.

[0046] The main principle of the fiber sensing technology based on the Bragg fiber grating for measurement is that the strain, temperature and other external influences will cause the change of the Bragg grating refractive index, and then the reflection wavelength within the grating bandwidth will change. The change is read by the fiber grating demodulator, and then the spectrum change is converted into the actual measurement value. Since the fiber grating itself is easy to break due to brittleness, the strain of the external soil layer directly acting on the grating will cause the grating to break due to the small maximum deformation amplitude that the grating itself can accept. The mechanical effect not directly acting on the grating is not easy to change the grating structure, so the grating subjected to non-direct action needs to be sensitized to make the grating more sensitive to non-direct mechanical effect.

[0047] The optical fiber grating pressure sensor for measuring the total pressure inside the structure of the application is uniformly wrapped by the elastomer 2, so that when the external structure is deformed more than the limit deformation of the optical fiber grating 5, the deformation effect first acts on the elastomer 2, and the elastomer 2 is extruded and elongated on both sides relatively uniformly, thereby also elongating the optical fiber grating 5 inside the elastomer 2 on both sides uniformly, so that the refractive index of the optical fiber grating 5 changes correspondingly, and then the change is read by the demodulator and converted by combining the mechanical properties of the elastomer 2 to obtain the pressure data inside the soil body.

[0048] The same or similar reference numerals in the drawings of the embodiments correspond to the same or similar components; in the description of the present application, it should be understood that if the terms "upper", "lower", "left", "right" and the like indicate the orientation or positional relationship shown in the drawings, they are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, therefore the terms describing the positional relationship in the drawings are only used for exemplary illustration, and cannot be understood as a limitation of the present patent, for those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0049] The above only describes the preferred embodiments of the present application, and does not limit the present application, any modifications, equivalent replacements and improvements made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A fiber Bragg grating pressure sensor for monitoring total pressure in a reservoir, characterized by, The application relates to a fiber grating pressure sensor, which comprises the following parts: two caps, an elastic body, two sealing rings and a support. The two caps are provided with grooves, and the groove openings of the two caps are oppositely arranged; the elastic body is in a columnar structure, and the two ends of the elastic body are respectively inserted into the grooves of the two caps and are spaced apart from the groove bottom walls of the two caps by a preset distance; the two sealing rings are respectively arranged between the inner circumferential walls of the grooves of the two caps and the outer circumferential wall of the elastic body; the support is arranged between the two caps and is connected with the two caps; and a fiber grating is arranged at the center of the elastic body, so that when the reservoir is deformed, the elastic body is extruded to be elongated, the fiber grating in the elastic body is also elongated, and the refractive index of the fiber grating is changed to obtain total pressure data in the reservoir.

2. The fiber grating pressure sensor according to claim 1, wherein the inner circumferential walls of the two caps are provided with annular grooves for mounting the sealing rings.

3. The fiber grating pressure sensor according to claim 1, wherein the two caps are both cylindrical caps made of stainless steel, and the outer diameter of the cylindrical cap is 1cm, the wall thickness is 0.5cm, the outer height is 1cm, and the inner height is 0.5cm-0.7cm.

4. The fiber grating pressure sensor according to claim 1, wherein the elastic body is a cylinder made of modified acrylate, and the diameter of the cylinder is 0.5cm and the height is 1cm.

5. The fiber grating pressure sensor according to claim 1, wherein the temperature range of the fiber grating pressure sensor is -30-100 DEG C, and the pressure range is 0-30MPa. The application further discloses a manufacturing method of the fiber grating pressure sensor, which comprises the following steps: manufacturing two caps and a support; manufacturing a mold with a cylindrical groove, and then suspending a fiber grating with a protective layer outside the fiber grating in the cylindrical axis position of the mold after the fiber grating is calibrated; mixing A glue and B glue of modified acrylate in a container to obtain mixed glue, and then pouring the mixed glue into the mold to pour the fiber grating suspended in the cylindrical axis position of the mold into the mold and seal the two ends of the fiber grating; then placing the entire mold with the fiber grating poured into the mold into a thermostat, keeping the preset temperature for a preset time, then reducing the temperature of the thermostat, and obtaining the elastic body encapsulating the fiber grating after the glue solidifies. selecting a sealing ring, sleeving the sealing ring on the elastic body, combining the sealing ring with the two caps, then fixing the support and the two caps, and obtaining the fiber grating pressure sensor.

7. The manufacturing method according to claim 6, wherein the preset temperature is lower than the highest temperature value of the mixed A glue and B glue of the modified acrylate.

8. The manufacturing method according to claim 6, wherein ​ 6. A method of manufacturing the fiber grating pressure sensor according to any one of claims 1 to 5, characterized by, ​ ​ ​ ​ ​ ​ ​ ​ After the encapsulation of the fiber grating into the elastic body, the fiber grating is connected to a demodulator, and the elastic body is calibrated under a quantitative load. If the calibration result shows that the fiber grating is intact and linearly deformed, the encapsulation of the fiber grating is successful.

9. The manufacturing method of claim 6, wherein, After the fiber grating pressure sensor is obtained, the measurement effect of the fiber grating pressure sensor is tested under preset experimental conditions to determine whether the fiber grating pressure sensor is intact and the range size.

10. The manufacturing method of claim 6, wherein, After the fiber grating is placed in the position of the cylindrical axis of the mold, the fiber grating is lightly pressed by a block to keep the position and the stretched state of the fiber grating.

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