Shale gas well pressure measuring device and method based on fiber bragg grating

Abstract

The invention discloses a shale gas well pressure measuring device and method based on a fiber bragg grating, and the device comprises a housing which is provided with a first end side and a second end side, a containing cavity is defined in the housing, and at least two stop plates are formed in the containing cavity; the at least two transmission rods are movably connected in the containing cavity, one end of one transmission rod is arranged on the first end side, and the other end of the transmission rod abuts against one of the stop plates; one end of the other transmission rod is arranged on the second end side, and the other end of the transmission rod abuts against the other stop plate. The fiber bragg grating is connected to the backstop plate and used for measuring the strain of the backstop part, and the fiber bragg grating is coupled with the demodulator through an optical fiber; the first piston is located on the first end side and connected with one of the transmission rods, and the second piston is located on the second end side and connected with the other transmission rod; one end of the connecting rod is connected with the first piston, and the other end of the connecting rod is connected with the second piston.

Description

Technical Field

[0001] The present invention relates to the field of gas extraction from shale gas reservoir formations, and particularly to a pressure measurement device and method for shale gas wells based on fiber Bragg gratings. Background Art

[0002] Most shale gas reservoir formations exhibit low permeability characteristics, with a permeability usually not exceeding 0.001 mD. To ensure mining safety and improve extraction efficiency, physical and chemical methods such as deep hole blasting, hydraulic fracturing, hydraulic punching, and hydrochloric acid chemical methods are generally used to transform unconventional gas reservoir formations to generate macroscopic fractures to enhance gas extraction. The above fracturing methods have problems in aspects such as water resource consumption, environmental pollution, and groundwater layer damage. At the same time, some gas reservoir formations are not suitable for hydraulic fracturing or acidification treatment. Therefore, the anhydrous fracturing method based on in-situ methane combustion explosion has gradually received extensive attention. A major difficulty in the in-situ methane combustion explosion technology in the wellbore is how to monitor and feedback the pressure in the shale gas well in real time. The electromagnetic environment of the shale reservoir is complex, and traditional piezoelectric, electromagnetic, and other gas pressure measurement devices are easily interfered, making the monitoring results unable to be timely feedback, thus affecting the normal extraction of shale gas. Summary of the Invention

[0003] In view of the problems and requirements mentioned above, the present solution proposes a pressure measurement device and method for shale gas wells based on fiber Bragg gratings. Due to the following technical features, the above technical objectives can be achieved, and many other technical effects can be brought.

[0004] An object of the present invention is to provide a pressure measurement device for shale gas wells based on fiber Bragg gratings, comprising:

[0005] A housing having a first end side and a second end side, defining an accommodation cavity therein, and at least two stop baffles are formed in the accommodation cavity;

[0006] At least two transmission rods, at least two of the transmission rods are movably connected in the accommodation cavity, one end of at least one transmission rod is disposed on the first end side, and the other end thereof abuts against one of the stop baffles; one end of at least another transmission rod is disposed on the second end side, and the other end thereof abuts against another one of the stop baffles;

[0007] Fiber Bragg gratings are connected to the stop baffles for measuring the strain of the stop baffles, and the fiber Bragg gratings are coupled to a demodulator through optical fibers;

[0008] A first piston and a second piston, wherein the first piston is located on the first end side and is connected to one of the transmission rods, and the second piston is located on the second end side and is connected to another one of the transmission rods;

[0009] A connecting rod, one end of which is connected to the first piston and the other end of which is connected to the second piston;

[0010] Wherein, when there is a pressure difference between the first piston and the second piston, the first piston or the second piston moves towards the stop baffle, and through the connecting rod, the second piston or the first piston moves away from the stop baffle. At the same time, the first piston or the second piston drives the transmission rod to abut against the stop baffle and causes it to deform.

[0011] In addition, the shale gas well pressure measurement device based on fiber Bragg grating according to the present invention may further have the following technical features:

[0012] In an example of the present invention, the accommodation cavity includes: a first chamber and a second chamber respectively formed on the first end side and the second end side, and at least one auxiliary chamber formed between the first chamber and the second chamber; wherein, two of the stop baffles are formed in at least one auxiliary chamber, the first piston and the second piston are respectively fitted in the first chamber and the second chamber, and at least one auxiliary chamber is respectively communicated with the first chamber and the second chamber through a first through hole and a second through hole;

[0013] At least one transmission rod passes through the first through hole and its two ends respectively extend into the first chamber and the auxiliary chamber; at least another transmission rod passes through the second through hole and its two ends respectively extend into the second chamber and the auxiliary chamber.

[0014] In an example of the present invention, there are at least two auxiliary chambers, at least four transmission rods, the two auxiliary chambers are symmetrically arranged on both sides of the connecting rod, and two transmission rods are correspondingly arranged in each auxiliary chamber.

[0015] In an example of the present invention, it further includes: a dust-proof filter screen,

[0016] which is arranged on the first chamber and configured to isolate the first chamber from the shale gas well.

[0017] In an example of the present invention, it further includes: an elastic member,

[0018] One end of the elastic member is connected to at least one transmission rod, and the other end of the elastic member is connected to the first through hole or the second through hole, and is configured to enable the transmission rod to have an elastic force to return to the initial position when driven by the first piston or the second piston.

[0019] In an example of the present invention, the elastic member is one of a compression spring, a tension spring, a spring plate and a rubber member.

[0020] In an example of the present invention, lubricating grooves are provided on the inner walls of both the first chamber and the second chamber.

[0021] In an example of the present invention, it further includes: a guiding pipe,

[0022] One end of the guiding pipe is hermetically connected to the second end side of the housing, and the other end of the guiding pipe extends to the ground and communicates with the external environment.

[0023] Another object of the present invention is to provide a measurement method for a shale gas well pressure measurement device based on fiber Bragg grating as described above, including the following steps:

[0024] First, the first piston and the second piston on both sides of the measurement device sense the internal gas pressure and the external gas pressure of the shale gas well. When there is a pressure difference between the external gas pressure and the internal gas pressure, this pressure difference drives the first piston or the second piston to move towards the stop baffle, and at the same time, the second piston or the first piston moves away from the stop baffle. The transmission rod acts on the stop baffle under the drive of the first piston or the second piston, forcing the stop baffle to deform. At the same time, the fiber Bragg grating located on the stop baffle deforms synchronously; then, the change amount of the central wavelength of the fiber Bragg grating corresponding to the strain of the stop baffle is detected and obtained by the fiber Bragg grating; finally, the pressure inside the shale gas well is calculated from the central wavelength of the fiber Bragg grating.

[0025] In an example of the present invention, the relationship expression between the change amount of the central wavelength of the fiber Bragg grating and the internal pressure of the shale gas well is:

[0026]

[0027] In the formula, Δλ B is the drift amount of the Bragg wavelength; ne ff is the effective refractive index of the optical fiber considering the influence factors of temperature and humidity; Λ is the grating period; p e is the effective photoelastic coefficient considering the influence factors of temperature and humidity; P is the gas pressure; E is the Young's modulus.

[0028] In an example of the present invention, the correction method for the effective refractive index ne of the optical fiber considering the influence factors of temperature and humidity is as follows: ff First, at different temperature-humidity combinations, measure at intervals of a first specific value of temperature and humidity, and measure the Bragg wavelength λ of the optical fiber

[0029] ; then change the temperature and humidity in sequence according to a second characteristic value, and measure λ B1 ; at the same time, record the temperature T and humidity H values corresponding to each measurement point; B2 ;

[0030] Then, according to the formula λB = 2ne ff Λ, in the case of a known grating period Λ, fit the measured λ values under different temperature - humidity conditions, where a multiple linear regression fitting method is adopted, assuming ne B = a + bT + cH, where a, b, and c are coefficients to be determined; ff

[0031] Finally, substitute the measured data into the above equation, and determine the values of coefficients a, b, and c through mathematical methods such as the least squares method, so as to obtain the relationship between the effective refractive index ne ff and temperature and humidity: ne ff (T, H) = a + bT + cH.

[0032] In an example of the present invention, the correction method for the effective photo - elastic coefficient p considering the influence factors of temperature and humidity is as follows: e

[0033] First, under different temperature - humidity conditions, apply different pressures P to the optical fiber, and measure the change amount Δλ of the fiber Bragg wavelength under each pressure application; B ;

[0034] Then, according to the formula known grating period Λ, Young's modulus E, and the above - mentioned effective refractive index ne ff (T, H), calculate the effective photo - elastic coefficient p under different temperature - humidity and pressure conditions e , and its expression is as follows:

[0035]

[0036] where T is the temperature; H is the humidity; P is the pressure.

[0037] In the following, the optimal embodiments of implementing the present invention will be described in more detail with reference to the accompanying drawings, so as to facilitate the understanding of the features and advantages of the present invention. Brief Description of the Drawings

[0038] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings of the embodiments of the present invention will be briefly introduced below. Among them, the accompanying drawings are only used to show some embodiments of the present invention, rather than limiting all embodiments of the present invention thereto.

[0039] Figure 1 It is a schematic structural diagram of a shale gas well pressure measurement device based on an optical fiber grating according to an embodiment of the present invention;

[0040] Figure 2 It is Figure 1 A - A sectional view; ​​

[0041] Figure 3 is Figure 1 the sectional view taken along line B-B;

[0042] Figure 4 is Figure 1 the top view.

[0043] List of reference numerals:

[0044] Measuring device 100;

[0045] Housing 110;

[0046] First end side 111;

[0047] Second end side 112;

[0048] First chamber 113;

[0049] Second chamber 114;

[0050] Auxiliary chamber 115;

[0051] First through hole 116;

[0052] Second through hole 117;

[0053] Stop baffle 118;

[0054] Through hole 119;

[0055] Transfer rod 120;

[0056] Fiber Bragg grating 130;

[0057] First piston 140;

[0058] Second piston 150;

[0059] Connecting rod 160;

[0060] Dust-proof filter screen 170;

[0061] Elastic member 180. Detailed implementation manners

[0062] In order to make the objectives, technical solutions and advantages of the technical solutions of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the drawings of the specific embodiments of the present invention. The same reference numerals in the drawings represent the same components. It should be noted that the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the described embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0063] Unless otherwise defined, technical or scientific terms used herein shall have the ordinary meanings as understood by those of ordinary skill in the art to which this invention pertains. The terms "first", "second" and similar terms used in the description and claims of this patent application for invention do not denote any order, quantity or importance, but are only used to distinguish different components. Similarly, terms such as "a" or "an" do not necessarily denote a quantity limitation. Terms such as "comprising" or "including" mean that the elements or items appearing before such terms cover the elements or items listed after such terms and their equivalents, without excluding other elements or items. Terms such as "connected" or "coupled" are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. Terms such as "upper", "lower", "left" and "right" are only used to indicate relative positional relationships, and when the absolute position of the object being described changes, the relative positional relationships may also change accordingly.

[0064] A shale gas well pressure measurement device 100 based on a fiber Bragg grating 130 according to a first aspect of the present invention, as Figures 1 to 4 shown, includes:

[0065] A housing 110 having a first end side 111 and a second end side 112, defining an accommodation cavity therein, and at least two stop plates 118 are formed in the accommodation cavity; wherein, the first end side 111 is located in the shale gas well, and the second end side 112 is in communication with the external environment;

[0066] At least two transfer rods 120, at least two of the transfer rods 120 are movably connected in the accommodation cavity, one end of at least one transfer rod 120 is disposed at the first end side 111, and the other end thereof abuts against one of the stop plates 118; wherein one end of at least another of the transfer rods 120 is disposed at the second end side 112, and the other end thereof abuts against another of the stop plates 118;

[0067] A fiber Bragg grating 130, connected to the stop plate 118 for measuring the strain of the stop plate 118, and the fiber Bragg grating 130 is coupled to a demodulator through an optical fiber; preferably, at least one optical fiber grating 130 is disposed on both sides of the stop plate 118, and the optical fiber grating 130 is disposed at the middle position of the stop plate 118.

[0068] A first piston 140 and a second piston 150, the first piston 140 is located at the first end side 111 and is connected to one of the transfer rods 120, and the second piston 150 is located at the second end side 112 and is connected to another of the transfer rods 120;

[0069] A connecting rod 160, one end of which is connected to the first piston 140 and the other end of which is connected to the second piston 150;

[0070] Wherein, when there is a pressure difference between the first piston 140 and the second piston 150, the first piston 140 or the second piston 150 moves towards the stop baffle 118, and through the connecting rod 160, the second piston 150 or the first piston 140 moves away from the stop baffle 118. At the same time, the first piston 140 or the second piston 150 drives the transmission rod 120 to abut against the stop baffle 118 and deforms it.

[0071] The working process of the measuring device 100 is as follows:

[0072] When the relative pressure in the shale gas well exceeds the standard air pressure, the first piston 140 moves towards its corresponding stop baffle 118. Driven by the first piston 140, the connecting rod 160 moves to drive the second piston 150 to move away from its corresponding stop baffle 118. At the same time, the first piston 140 drives the transmission rod 120 to abut against the stop baffle 118 and deforms it. The strain of the stop portion is measured by the fiber Bragg grating 130, converted into a change in the central wavelength of the fiber Bragg grating 130, and the signal of the central wavelength change is transmitted by the optical fiber to the demodulator for demodulation and then analyzed by a computer through calculation to obtain the pressure of the shale gas well;

[0073] When the relative pressure in the shale gas well is lower than the standard air pressure, the second piston 150 moves towards its corresponding stop baffle 118. Driven by the second piston 150, the connecting rod 160 moves to drive the first piston 140 to move away from its corresponding stop baffle 118. At the same time, the second piston 150 drives the transmission rod 120 to abut against the stop baffle 118 and deforms it. The strain of the stop portion is measured by the fiber Bragg grating 130, converted into a change in the central wavelength of the fiber Bragg grating 130, and the signal of the central wavelength change is transmitted by the optical fiber to the demodulator for demodulation and then analyzed by a computer through calculation to obtain the pressure of the shale gas well;

[0074] The measuring device 100 can be applied to the complex electromagnetic environment of shale reservoirs without being disturbed, and can monitor and feedback the pressure in the shale gas well in real time, so that the monitoring results can be timely feedback, greatly improving the efficiency of normal extraction of shale gas. Moreover, the measuring device has a simple structure, strong anti-electromagnetic interference ability, accurate measurement, and can greatly reduce the workload.

[0075] In an example of the present invention, the accommodation cavity includes: a first chamber 113 and a second chamber 114 respectively formed at the first end side 111 and the second end side 112, and at least one auxiliary chamber 115 formed between the first chamber 113 and the second chamber 114; wherein, two of the stop plates 118 are formed in at least one auxiliary chamber 115, the first piston 140 and the second piston 150 are respectively fitted in the first chamber 113 and the second chamber 114, and at least one auxiliary chamber 115 is respectively communicated with the first chamber 113 and the second chamber 114 through a first through hole 116 and a second through hole 117;

[0076] At least one transfer rod 120 passes through the first through hole 116 and its two ends respectively extend into the first chamber 113 and the auxiliary chamber 115, and one end of the transfer rod 120 located in the auxiliary chamber 115 abuts against one of the stop plates 118; at least one other transfer rod 120 passes through the second through hole 117 and its two ends respectively extend into the second chamber 114 and the auxiliary chamber 115, and one end of the transfer rod 120 located in the auxiliary chamber 115 abuts against the other stop plate 118;

[0077] For example, a through hole 119 is formed in the housing 110, the through hole 119 communicates the first chamber 113 and the second chamber 114, the connecting rod 160 is fitted in the through hole 119 and its two ends respectively extend into the first chamber 113 and the second chamber 114, one end of the connecting rod 160 is connected to the first piston 140, and the other end of the connecting rod 160 is connected to the second piston 150.

[0078] Specifically, when the relative pressure in the shale gas well exceeds the standard air pressure, the first piston 140 moves towards the corresponding stop baffle 118 in the first chamber 113. The connecting rod 160 is driven by the first piston 140 to move and drive the second piston 150 to move away from the corresponding stop baffle 118 in the second chamber 114. At the same time, the first piston 140 drives the transmission rod 120 to abut against the stop baffle 118 and deform it, and the strain of the stop portion is measured by the fiber Bragg grating 130. When the relative pressure in the shale gas well is lower than the standard air pressure, the second piston 150 moves towards the corresponding stop baffle 118 in the second chamber 114. The connecting rod 160 is driven by the second piston 150 to move and drive the first piston 140 to move away from the corresponding stop baffle 118 in the first chamber 113. At the same time, the second piston 150 drives the transmission rod 120 to abut against the stop baffle 118 and deform it, and the strain of the stop portion is measured by the fiber Bragg grating 130. By separately providing the first chamber 113, the second chamber 114 and at least one auxiliary chamber 115 on the housing 110, the first piston 140, the second piston 150 and the stop baffle 118 have independent movement spaces, and can play a role in protecting and limiting the first piston 140, the second piston 150 and the stop baffle 118. The provision of the first through hole 116 and the second through hole 117 facilitates the connection of the transmission rod 120.

[0079] In an example of the present invention, there are two at least one auxiliary chamber 115, and four at least two transmission rods 120. The two auxiliary chambers 115 are symmetrically arranged on both sides of the connecting rod 160, and two transmission rods 120 are correspondingly provided for each auxiliary chamber 115.

[0080] That is to say, two transmission rods 120 correspond to each auxiliary chamber 115. The two transmission rods 120 are respectively arranged along the extending direction of the housing 110, and the two auxiliary chambers 115 are arranged along the radial direction of the housing 110 (for example, symmetrically arranged). The auxiliary chamber 115 is provided at the middle position in the extending direction of the housing 110. Two transmission rods 120 are provided at the first end side 111 and are both connected to the first piston 140. Two transmission rods 120 are provided at the second end side 112 and are both connected to the second piston 150. By providing a plurality of transmission rods 120, the connection between the transmission rod 120 and the first piston 140 or the second piston 150 can be made more reliable and stable.

[0081] In an example of the present invention, it further includes: a dust-proof filter screen 170,

[0082] which is provided on the first chamber 113 and configured to isolate the first chamber 113 from the shale gas well.

[0083] That is to say, the first chamber 113 is located inside the shale gas well, while the second chamber 114 is located outside the shale gas well. By providing a dust-proof filter screen 170 at the first chamber 113, it can isolate the downhole particles inside the shale gas well, preventing the downhole particles from entering the measuring device 100 through the first chamber 113, thereby affecting the measurement accuracy of the measuring device 100.

[0084] The outer wall of the second chamber 114 is provided with spiral threads, which match the threaded pipe. The threaded pipe is combined in multiple sections and extends to the ground to provide fixation for the shale gas well pressure measuring device.

[0085] It can be understood that each chamber of the housing 110 is vacuum-treated. The outside of the second chamber 114 is connected to a threaded pipe, and the threaded pipe is at standard atmospheric pressure.

[0086] In an example of the present invention, it further includes: an elastic member 180.

[0087] One end of the elastic member 180 is connected to at least one transfer rod 120, and the other end of the elastic member 180 is connected to the first through hole 116 or the second through hole 117, configured such that the transfer rod 120 has an elastic force to return to its initial position when driven by the first piston 140 or the second piston 150.

[0088] That is to say, when the relative pressure inside the shale gas well exceeds the standard atmospheric pressure, the first piston 140 moves towards the corresponding stop baffle 118 in the first chamber 113. The connecting rod 160 is driven by the first piston 140 to move and drive the second piston 150 to move away from the corresponding stop baffle 118 in the second chamber 114. During this process, the transfer rod 120 corresponding to the first piston 140 acts on the elastic member 180 to generate an elastic force to return to its initial position; at the same time, the first piston 140 drives the transfer rod 120 to abut against the stop baffle 118 and causes it to deform, and the strain of the stop portion is measured by the fiber Bragg grating 130; after the pressure difference disappears, under the action of the elastic force of the elastic member 180, the transfer rod 120 drives the first piston 140 to return to its initial position.

[0089] When the relative pressure in the shale gas well is lower than the standard air pressure, the second piston 150 moves toward the corresponding stop plate 118 in the second chamber 114, and the connecting rod 160, driven by the second piston 150, drives the first piston 140 to move away from the corresponding stop plate 118 in the first chamber 113. During this process, the transmission rod 120 corresponding to the second piston 150 acts on the elastic member 180 to generate an elastic force to restore it to its initial position; at the same time, the second piston 150 drives the transmission rod 120 to abut against the stop plate 118 and deform it, and the strain of the stop portion is measured by the fiber grating 130; after the pressure difference disappears, the transmission rod 120 drives the second piston 150 to restore to its initial position under the elastic force of the elastic member 180.

[0090] By providing the elastic member 180 , the measuring device 100 can be restored to its initial position when there is no pressure difference between the shale gas well and the external environment, and can protect the measuring device 100 when there is a pressure difference between the shale gas well and the external environment.

[0091] In one example of the present invention, the elastic member 180 is one of a compression spring, a tension spring, a spring sheet, and a rubber member;

[0092] When the elastic member 180 is a tension spring, the tension spring is sleeved on the transmission rod 120, one end pin of the tension spring is fixedly connected to the transmission rod 120, and the other end pin of the tension spring is fixedly connected to the first through hole 116 or the second through hole 117. When the transmission rod 120 is driven by the first piston 140 or the second piston 150, the tension spring is stretched to move so that the tension spring generates an elastic force that can restore the transmission rod 120 to its initial position;

[0093] When the elastic member 180 is a compression spring, the compression spring is sleeved on the transmission rod 120, one end of the compression spring is abutted on the transmission rod 120 (for example, a limiting protrusion is set on the transmission rod 120), and the other end is abutted on the first through hole 116 or the second through hole 117 (for example, the first through hole 116 and the second through hole 117 are both stepped holes, and the compression spring is sleeved at a position where the stepped hole diameter is larger, and is abutted at the intersection of the stepped holes). When the transmission rod 120 is driven by the first piston 140 or the second piston 150, the compression spring will be compressed to move so that the compression spring generates an elastic force that can restore the transmission rod 120 to its initial position.

[0094] Of course, the present invention is not limited thereto, and the elastic member 180 may also be a spring sheet or a rubber member, etc., as long as the elastic force can restore the transmission rod 120 to the initial position.

[0095] In an example of the present invention, lubricating grooves are provided on the inner walls of the first chamber 113 and the second chamber 114;

[0096] By providing the lubricating grooves, lubricating oil can be stored, thereby lubricating the first piston 140 or the second piston 150, and then the service life of the measuring device 100 can be extended.

[0097] In an example of the present invention, it further includes: a guiding tube,

[0098] One end of the guiding tube is hermetically connected to the second end side 112 of the housing 110, and the other end of the guiding tube extends to the ground and communicates with the external environment.

[0099] For example, one end of the guiding tube is provided with internal threads, and the second end side 112 of the housing 110 is formed with external threads adapted to the internal threads. The disassembly and assembly between the guiding tube and the housing 110 can be facilitated through threaded connection.

[0100] According to a measuring method of the shale gas well pressure measuring device 100 based on the fiber Bragg grating 130 as described above according to the second aspect of the present invention, it includes the following steps:

[0101] First, the first piston 140 and the second piston 150 on both sides of the measuring device 100 sense the internal air pressure and the external air pressure of the shale gas well. When a pressure difference is generated between the external air pressure and the internal air pressure, the pressure difference drives the first piston 140 or the second piston 150 to move towards the stop baffle 118. At the same time, through the connecting rod 160, the second piston 150 or the first piston 140 moves away from the stop baffle 118. The transmission rod 120 acts on the stop baffle 118 under the drive of the first piston 140 or the second piston 150, forcing the stop baffle 118 to deform. At the same time, the fiber Bragg grating 130 located on the stop baffle 118 deforms synchronously; then the fiber Bragg grating 130 detects and obtains the change amount of the central wavelength of the fiber Bragg grating 130 corresponding to the strain of the stop baffle 118; finally, the pressure inside the shale gas well is calculated from the central wavelength of the fiber Bragg grating 130.

[0102] This measuring method can be applicable to the complex electromagnetic environment of the shale reservoir, is not interfered with, can monitor and feedback the pressure inside the shale gas well in real time, enables the monitoring results to be timely feedback, and greatly improves the efficiency of normal extraction of shale gas; moreover, this measuring method is simple, the measuring device used has strong anti-electromagnetic interference ability, accurate measurement, and can greatly reduce the workload.

[0103] In an example of the present invention, the relationship expression between the change amount of the central wavelength of the fiber Bragg grating 130 and the internal pressure of the shale gas well is:

[0104]

[0105] In the formula, Δλ B is the drift amount of the Bragg wavelength; ne ff is the effective refractive index of the optical fiber considering the influence factors of temperature and humidity; Λ is the grating period; p e is the effective photoelastic coefficient considering the influence factors of temperature and humidity; P is the gas pressure; E is the Young's modulus.

[0106] One end of the transfer rod 120 is connected to the first piston 140 or the second piston 150, and the other end of the transfer rod 120 acts on the stop baffle 118. The transfer rod 120 moves under the curve of the first piston 140 or the second piston 150 towards the stop baffle 118 and forces the stop baffle 118 to deform. The fiber grating 130 is connected to the stop baffle 118, and the fiber grating 130 deforms synchronously, detecting the strain of the stop baffle 118 and correspondingly outputting the change amount of the central wavelength of the fiber grating 130; finally, the pressure in the shale gas well is calculated from the central wavelength of the fiber grating 130.

[0107] Derive the relationship between strain, wavelength, and pressure:

[0108] According to the wavelength change and the sensitivity of the material, convert the wavelength change into strain ε, and the formula is as follows:

[0109] λ B = 2ne ff Λ

[0110] Where: λ B is the initial Bragg wavelength; ne ff is the effective refractive index of the optical fiber; Λ is the grating period;

[0111] Δλ B = λ B (1 - p e )ε

[0112] P = E×ε

[0113] Where: Δλ B is the drift amount of the Bragg wavelength; p e is the effective photoelastic coefficient; P is the gas pressure (Pa or N / m 2 ); E is the Young's modulus

[0114] By combining the above formulas, the relationship between gas pressure and wavelength can be obtained:

[0115]

[0116] In an example of the present invention, the correction method for the effective refractive index ne of the optical fiber considering the influence factors of temperature and humidity is as follows: ff is as follows:

[0117] First, at different temperature - humidity combinations, measurements are made at intervals of the temperature and humidity of the first specific value, and the Bragg wavelength λ of the optical fiber is measured. B1 ; Then, the temperature and humidity are sequentially changed according to the second eigenvalue, and λ is measured. B2 ; At the same time, the temperature T and humidity H values corresponding to each measurement point are recorded.

[0118] Then, according to the formula λ B = 2ne ff Λ, in the case where the grating period Λ is known, the λ values under different temperature - humidity conditions obtained by measurement are fitted. Among them, the multiple linear regression fitting method is adopted, and it is assumed that ne B = a + bT + cH, where a, b, and c are coefficients to be determined. ff

[0119] Finally, the measurement data are substituted into the above equation, and the values of the coefficients a, b, and c are determined by mathematical methods such as the least - squares method, so as to obtain the relationship between the effective refractive index ne ff varying with temperature and humidity: ne ff (T, H) = a + bT + cH.

[0120] The effective refractive index ne obtained by the above correction method ff is more in line with the actual measurement environment of shale gas wells.

[0121] The specific derivation process of the effective refractive index ne ff is as follows:

[0122] 1. Experimental design and data acquisition

[0123] Environmental chamber setting: A high - precision environmental chamber is used, which can accurately control the temperature in the range of - 20°C to 80°C and the humidity in the range of 20% to 90%. The temperature control accuracy is ±0.1°C, and the humidity control accuracy is ±2%.

[0124] Optical fiber preparation: Select the same optical fiber as in the actual measurement device, with a length of 1 - 2 meters, and good optical processing is carried out at both ends to ensure the optical transmission performance.

[0125] Measurement process: At different temperature - humidity combinations, measurements are made at intervals of 5°C and 10% humidity. For example, first set the temperature to - 20°C and the humidity to 20%, and measure the Bragg wavelength λ of the optical fiber. B1 ; Then, the temperature and humidity are sequentially changed. For example, the temperature becomes - 15°C and the humidity is 30%, and λ is measured. B2 etc. At the same time, the temperature T and humidity H values corresponding to each measurement point are recorded.

[0126] 2. Data analysis and model establishment

[0127] Fitting method: According to the formula λ B =2ne ff Λ, when the grating period Λ is known, the measured λ under different temperature-humidity conditions B The multivariate linear regression fitting method can be used, assuming that ne ff =a+bT+cH (where a, b, c are coefficients to be determined).

[0128] Determine the coefficients: Substitute the measured data into the above equation and determine the values ​​of coefficients a, b, and c by mathematical methods such as the least squares method to obtain the effective refractive index ne ff The relationship between temperature and humidity ff (T,H)=a+bT+cH).

[0129] In one example of the present invention, the effective elastic-optic coefficient p considering the influence of temperature and humidity is e The correction method is as follows:

[0130] First, different pressures P were applied to the optical fiber under different temperature-humidity conditions, and the change in the optical fiber Bragg wavelength Δλ was measured each time the pressure was applied. B ;

[0131] Then, according to the formula Given the grating period Λ, Young's modulus E and the effective refractive index ne mentioned above ff (T,H), calculate the effective elastic coefficient p under different temperature-humidity and pressure conditions e , which is expressed as follows:

[0132]

[0133] Where T is temperature, H is humidity, and P is pressure.

[0134] The effective elastic-optic coefficient p of the correction method mentioned above e It is more in line with the actual measurement environment of shale gas wells.

[0135] Effective elastic coefficient p e The specific derivation process is as follows:

[0136] 1. Experimental Setup and Operation

[0137] Pressure application system: Using a high-precision pressure application device, it can accurately apply a pressure of 0-100MPa, and the pressure control accuracy is ±0.1MPa.

[0138] Optical fiber measurement system: One end of the optical fiber is connected to a stable light source, and the other end is connected to a spectral analyzer, which is the same as the optical fiber for measuring the effective refractive index described above.

[0139] Measurement process: Under different temperature-humidity conditions (such as the environmental condition settings in the above-mentioned effective refractive index measurement), different pressures P are applied to the optical fiber. For example, under the conditions of a temperature of 20 °C and a humidity of 50%, pressures such as 10 MPa and 20 MPa are applied in sequence, and the change amount Δλ of the fiber Bragg wavelength is measured under each pressure application. B 。

[0140] 2. Data analysis and correction

[0141] Calculation method: According to the formula Given the grating period Λ, Young's modulus E (obtained through standard material tests), and the previously determined effective refractive index ne ff (T, H), the effective elasto-optic coefficient p under different temperature-humidity and pressure conditions can be calculated. e 。For example, at a certain temperature T1, humidity H1, and pressure P1,

[0142]

[0143] In the above, the exemplary embodiments of the shale gas well pressure measurement device 100 and the measurement method based on the fiber Bragg grating 130 proposed by the present invention have been described in detail with reference to the preferred embodiments. However, those skilled in the art can understand that, without departing from the concept of the present invention, various modifications and variations can be made to the above specific embodiments, and various combinations can be made to the various technical features and structures proposed by the present invention, without exceeding the protection scope of the present invention. The protection scope of the present invention is determined by the appended claims.

Claims

1. A pressure measurement device for shale gas wells based on fiber Bragg gratings, characterized in that, Comprising: A housing (110) having a first end side (111) and a second end side (112), defining an accommodation cavity therein, and at least two stop plates (118) are formed in the accommodation cavity; At least two transfer rods (120), at least two of the transfer rods (120) are movably connected in the accommodation cavity, wherein one end of at least one transfer rod (120) is disposed at the first end side (111), and the other end thereof abuts against one of the stop plates (118); wherein at least one other of the transfer rods (120) has one end disposed at the second end side (112), and the other end thereof abuts against another one of the stop plates (118); An optical fiber grating (130) connected to the stop plate (118) for measuring the strain of the stop plate (118), and the optical fiber grating (130) is coupled to a demodulator through an optical fiber; A first piston (140) and a second piston (150), wherein the first piston (140) is located at the first end side (111) and is connected to one of the transfer rods (120), and the second piston (150) is located at the second end side (112) and is connected to one of the other transfer rods (120); A connecting rod (160) having one end connected to the first piston (140) and the other end connected to the second piston (150); Wherein, when there is a pressure difference between the first piston (140) and the second piston (150), the first piston (140) or the second piston (150) moves towards the stop plate (118), and through the connecting rod (160), the second piston (150) or the first piston (140) moves away from the stop plate (118), and at the same time, the first piston (140) or the second piston (150) drives the transfer rod (120) to abut against the stop plate (118) and deform it.

2. The fiber optic grating-based shale gas well pressure measurement device according to claim 1, wherein The accommodation cavity includes: a first chamber (113) and a second chamber (114) respectively formed at the first end side (111) and the second end side (112), and at least one auxiliary chamber (115) formed between the first chamber (113) and the second chamber (114); wherein, two of the stop plates (118) are formed in at least one auxiliary chamber (115), the first piston (140) and the second piston (150) are respectively fitted in the first chamber (113) and the second chamber (114), and at least one of the auxiliary chambers (115) is respectively communicated with the first chamber (113) and the second chamber (114) through a first through hole (116) and a second through hole (117); At least one of the transfer rods (120) passes through the first through hole (116) and its two ends respectively extend into the first chamber (113) and the auxiliary chamber (115); at least one of the other transfer rods (120) passes through the second through hole (117) and its two ends respectively extend into the second chamber (114) and the auxiliary chamber (115).

3. The fiber Bragg grating-based shale gas well pressure measurement device according to claim 2, wherein at least one auxiliary chamber (115) includes two, at least two transmission rods (120) include four, the two auxiliary chambers (115) are symmetrically arranged on both sides of the connecting rod (160), and two transmission rods (120) are correspondingly arranged for each auxiliary chamber (115).

4. The fiber Bragg grating-based shale gas well pressure measurement device according to claim 2, wherein it further includes: a dust-proof filter screen (170), which is arranged on the first chamber (113) and configured to isolate the first chamber (113) from the shale gas well.

5. The fiber Bragg grating-based shale gas well pressure measurement device according to claim 2, wherein it further includes: an elastic member (180), one end of the elastic member (180) is connected to at least one transmission rod (120), and the other end of the elastic member (180) is connected to the first through hole (116) or the second through hole (117), and is configured to enable the transmission rod (120) to have an elastic force to return to the initial position when driven by the first piston (140) or the second piston (150).

6. The fiber Bragg grating-based shale gas well pressure measurement device according to claim 5, wherein the elastic member (180) is one of a compression spring, a tension spring, a spring sheet, and a rubber member.

7. A measurement method of the fiber Bragg grating-based shale gas well pressure measurement device according to any one of claims 1 to 6, characterized in that, It includes the following steps: First, the first piston (140) and the second piston (150) on both sides of the measurement device (100) sense the internal air pressure and the external air pressure of the shale gas well. When a pressure difference is generated between the external air pressure and the internal air pressure, the pressure difference drives the first piston (140) or the second piston (150) to move towards the stop baffle (118), and at the same time, the second piston (150) or the first piston (140) moves away from the stop baffle (118). The transmission rod (120) acts against the stop baffle (118) under the drive of the first piston (140) or the second piston (150), forcing the stop baffle (118) to deform. At the same time, the fiber Bragg grating (130) located on the stop baffle (118) deforms synchronously. Then, the change amount of the central wavelength of the fiber Bragg grating (130) corresponding to the strain of the stop baffle (118) is detected and obtained by the fiber Bragg grating (130). Finally, the pressure inside the shale gas well is calculated from the central wavelength of the fiber Bragg grating (130).

8. The measurement method of the fiber Bragg grating-based shale gas well pressure measurement device according to claim 7, wherein the relationship expression between the change amount of the central wavelength of the fiber Bragg grating (130) and the internal pressure of the shale gas well is: where Δλ B is the drift of the Bragg wavelength; ne ff is the effective refractive index of the optical fiber considering the influence factors of temperature and humidity; Λ is the grating period; p e is the effective elasto-optic coefficient considering the influence factors of temperature and humidity; P is the gas pressure; E is the Young's modulus.

9. The measurement method of the fiber Bragg grating-based shale gas well pressure measurement device according to claim 8, wherein Effective refractive index ne of an optical fiber considering temperature and humidity influencing factors ff The correction method is as follows: First, at different temperature-humidity combinations, measurements are made at intervals of temperature and humidity with a first specific value, and the Bragg wavelength λ of the optical fiber is measured. B1 ; Then, the temperature and humidity are sequentially changed according to a second characteristic value, and λ is measured. B2 ; At the same time, the temperature T and humidity H values corresponding to each measurement point are recorded. Then, according to the formula λ B =2ne ff Λ, when the grating period Λ is known, the measured λ under different temperature-humidity conditions B The value is fitted, where the multiple linear regression fitting method is used, assuming that ne ff =a+bT+cH, where a, b, c are coefficients to be determined; Finally, substitute the measured data into the above equation, and determine the values of coefficients a, b, and c by mathematical methods such as the least squares method, so as to obtain the effective refractive index ne ff Relationship formula varying with temperature and humidity: ne ff (T, H) = a + bT + cH.

10. The measurement method of the fiber Bragg grating-based shale gas well pressure measurement device according to claim 9, wherein Effective elasto-optic coefficient p considering temperature and humidity influencing factors e The correction method is as follows: First, under different temperature-humidity conditions, different pressures P are applied to the optical fiber, and the change amount Δλ of the optical fiber Bragg wavelength is measured for each pressure application. B ; Then, according to the formula given the grating period Λ, Young's modulus E, and the effective refractive index ne described above ff (T, H), the effective elasto-optic coefficient p under different temperature-humidity and pressure conditions is calculated e , and its expression is as follows: in the formula, T is the temperature; H is the humidity; P is the pressure.

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