A reservoir rock mass temperature-strain detection system and method

Abstract

The present application discloses a reservoir rock temperature-strain detection system and method, which relate to the field of rock engineering geomechanics testing and measurement. The reservoir rock temperature-strain detection system includes: a light source, a strain measurement module, a temperature measurement module, a sensing optical fiber and a processing module; the light source is connected to the strain measurement module and the temperature measurement module respectively; the strain measurement module and the temperature measurement module are both connected to the processing module; the strain measurement module and the temperature measurement module are both connected to the sensing optical fiber; the sensing optical fiber is arranged in the reservoir rock; and an ultra-weak grating array is engraved on the sensing optical fiber. The present application can realize the coordinated detection of reservoir rock temperature and strain under true triaxial high-temperature loading conditions.

Description

Technical Field

[0001] This application relates to the field of rock mass engineering geological mechanics testing and measurement, and particularly to a reservoir rock mass temperature-strain detection system and method under true triaxial high-temperature loading conditions. Background Technique

[0002] When supercritical carbon dioxide is injected into deep geological bodies, under the coupling action of multiphase fields, complex physical, chemical, and mechanical responses will occur. During the process of supercritical carbon dioxide enhanced deep oil and gas exploitation and carbon dioxide enhanced deep geothermal exploitation, supercritical carbon dioxide has acid corrosion when dissolved in reservoir fluids, and has short-term and long-term effects on the porosity, permeability, and mechanical properties of rock masses. When supercritical carbon dioxide with a relatively low temperature contacts a deep geological body with a relatively high temperature, the supercritical carbon dioxide produces a temperature shock effect on the reservoir rock mass, resulting in changes in parameters such as the geometric morphology of the primary cracks and the effective stress of the rock pore structure and fracture fissures, which may cause significant changes in the physical and mechanical properties, seepage path, and reservoir stability of the rock mass.

[0003] In order to quantitatively characterize the multiphase field coupling response of supercritical carbon dioxide injection disturbing reservoir rock masses, a large number of numerical simulations have been carried out, and most of the initial parameters of the numerical simulations are derived from indoor test measurements. The fiber optic sensing technology has many advantages such as light weight, small size, soft texture, bendability, low transmission loss, high temperature and high pressure resistance, corrosion resistance, and electromagnetic interference resistance, and has been widely used in scientific research and engineering fields. In terms of temperature and strain measurement, fiber optic monitoring has been successfully applied to laboratory rock mass supercritical carbon dioxide displacement tests and rock mass false triaxial tests, but there is no academic report on the collaborative detection of temperature and strain during the deformation and failure process of reservoir rock masses under true triaxial high-temperature loading conditions. Summary of the Invention

[0004] The purpose of this application is to provide a reservoir rock mass temperature-strain detection system and method, which can realize the collaborative detection of the temperature and strain of reservoir rock masses under true triaxial high-temperature loading conditions.

[0005] To achieve the above purpose, this application provides the following solutions:

[0006] In the first aspect, this application provides a reservoir rock mass temperature-strain detection system, and the reservoir rock mass temperature-strain detection system is applied to the temperature-strain detection of reservoir rock masses under true triaxial high-temperature loading conditions; the reservoir rock mass temperature-strain detection system includes: a light source, a strain measurement module, a temperature measurement module, a sensing optical fiber, and a processing module;

[0007] The light source is respectively connected to the strain measurement module and the temperature measurement module; both the strain measurement module and the temperature measurement module are connected to the processing module; both the strain measurement module and the temperature measurement module are connected to the sensing optical fiber; the sensing optical fiber is arranged in the reservoir rock mass; an ultra-weak grating array is engraved on the sensing optical fiber; the ultra-weak grating array includes a plurality of ultra-weak gratings;

[0008] The strain measurement module includes a first optical coupler, a main interference unit and an auxiliary interference unit; the light source is respectively connected to the main interference unit and the auxiliary interference unit after passing through the first optical coupler; both the main interference unit and the auxiliary interference unit are connected to the processing module;

[0009] The main interference unit uses a Mach-Zehnder interference structure to obtain the strain signal of the sensing optical fiber; the auxiliary interference unit uses a Michelson interference structure to sample the strain signal of the sensing optical fiber at a frequency point to obtain a strain reference signal;

[0010] The temperature measurement module uses a coherent detection structure to measure the temperature signal and temperature reference signal of the sensing optical fiber through the backward Rayleigh scattering signal;

[0011] The processing module is used to obtain the strain data and temperature data of the reservoir rock mass based on the strain signal of the sensing optical fiber, the strain reference signal, the temperature signal of the sensing optical fiber, and the temperature reference signal.

[0012] Optionally, the reservoir rock mass temperature-strain detection system further includes a first optical switch and a second optical switch;

[0013] The light source is respectively connected to the first optical coupler and the temperature measurement module through the first optical switch;

[0014] Both the strain measurement module and the temperature measurement module are connected to the sensing optical fiber through the second optical switch.

[0015] Optionally, the Mach-Zehnder interference structure adopted by the main interference unit includes: a second optical coupler, a polarization controller, a first optical circulator, a third optical coupler and a first photodetector;

[0016] One end of the second optical coupler is connected to the first optical coupler; the other end of the second optical coupler is respectively connected to one end of the polarization controller and the first end of the first optical circulator; the other end of the polarization controller is connected to one end of the third optical coupler; the other end of the third optical coupler is connected to one end of the first photodetector; the other end of the first photodetector is connected to the processing module; the third end of the first optical circulator is connected to one end of the third optical coupler; the second end of the first optical circulator is connected to the second optical switch.

[0017] Optionally, the Michelson interference structure adopted by the auxiliary interference unit includes: a second optical circulator, a fourth optical coupler, a first reference optical fiber, a first Faraday rotator, and a second photodetector;

[0018] The first end of the second optical circulator is connected to the first optical coupler; the second end of the second optical circulator is connected to one end of the fourth optical coupler; the other end of the fourth optical coupler is divided into two branches, and the optical signal of one branch is incident on the first Faraday rotator through the first reference optical fiber, and the optical signal of the other branch is incident on the first Faraday rotator; the third end of the second optical circulator is connected to the first end of the second photodetector; the second end of the second photodetector is connected to one end of the fourth optical coupler; the third end of the second photodetector is connected to the processing module.

[0019] Optionally, the coherent detection structure adopted by the temperature measurement module includes: an optical isolator, a fifth optical coupler, a second reference optical fiber, a third photodetector, and a second Faraday rotator;

[0020] One end of the optical isolator is connected to the first optical switch; the other end of the optical isolator is connected to one end of the fifth optical coupler; the other end of the fifth optical coupler is respectively connected to the second optical switch and the second reference optical fiber; the optical signal is incident on the second Faraday rotator after passing through the second reference optical fiber; one end of the fifth optical coupler is also connected to one end of the third photodetector; the other end of the third photodetector is connected to the processing module; the temperature reference signal is obtained based on the second reference optical fiber.

[0021] Optionally, the central wavelength of the ultra-weak gratings in the ultra-weak grating array is 1525 nm to 1565 nm; the reflectivity of the sensing optical fiber is less than 0.1%; the outer diameter of the sensing optical fiber is less than or equal to 250 μm.

[0022] Optionally, the coating material of the sensing optical fiber is one or more of gold, aluminum, and polyimide.

[0023] Optionally, the processing module includes a data acquisition card and a host computer;

[0024] The data acquisition card is respectively connected to the main interference unit, the auxiliary interference unit, the temperature measurement module and the host computer.

[0025] Optionally, the light source is a tunable laser.

[0026] In a second aspect, the present application provides a method for detecting temperature and strain of a reservoir rock mass. The method for detecting temperature and strain of a reservoir rock mass is implemented by using the above-provided system for detecting temperature and strain of a reservoir rock mass; the method for detecting temperature and strain of a reservoir rock mass includes:

[0027] Obtain the strain signal and the strain reference signal of the reservoir rock mass to be detected;

[0028] Use the discrete Fourier transform to transform the strain signal and the strain reference signal from the frequency domain to the spatial domain to obtain spatial domain complex values;

[0029] Determine the phase angle of the spatial domain complex value, and generate a phase spectrum based on the phase angle;

[0030] Divide the phase spectrum along the sensing optical fiber to obtain a segmentation result, and obtain the differential phase of each segment of the sensing optical fiber based on the segmentation result;

[0031] Based on the differential phase, use the position and wavelength change of each ultra-weak grating in the ultra-weak grating array to correct the phase of the phase spectrum;

[0032] Perform unwrapping and smoothing processing on the corrected phase spectrum, and obtain the strain data of the reservoir rock mass to be detected by differentiation;

[0033] Perform a fast Fourier transform on the temperature reference signal to obtain the position of each ultra-weak grating after strain occurs;

[0034] Use a sliding window to select the position of the ultra-weak grating, perform an inverse fast Fourier transform on the segmentation result within the sliding window, and separate the beat signal and spectrum at the position of the selected ultra-weak grating from the temperature signal;

[0035] Based on the beat signal and spectrum, perform wavelength peak tracking on each ultra-weak grating in the measurement through the wavelength peak tracking algorithm, and obtain the wavelength peak tracking result;

[0036] Based on the coupling relationship between the position of the ultra-weak grating and the temperature and strain in the sensing optical fiber, obtain the temperature data of the reservoir rock mass to be detected based on the wavelength peak tracking result.

[0037] According to the specific embodiments provided by the present application, the following technical effects are disclosed in the present application:

[0038] The present application provides a reservoir rock temperature-strain detection system and method. The sensing optical fiber is sensitized by an ultra-weak grating array, the strain information is calculated by phase demodulation, and the temperature measurement is realized by wavelength demodulation. During the long-term operation of the reservoir rock temperature-strain detection system, the temperature change induces the thermal expansion and contraction of the sensing optical fiber, thereby changing the position of the ultra-weak grating, and thus a strain error will be introduced accordingly to realize the strain measurement. By using the principle that the deviation in the optical path is related to the wavelength shift of the ultra-weak grating, the temperature or strain distribution along the sensing optical fiber can be obtained at a relatively high spatial resolution and a relatively long measurement length, and thus the collaborative detection of the temperature and strain of the reservoir rock can be realized under the condition of true triaxial high-temperature loading. Description of the Drawings

[0039] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required to be used in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0040] Figure 1 It is a schematic structural diagram of a reservoir rock temperature-strain detection system provided by an embodiment of the present application;

[0041] Figure 2 It is a schematic structural diagram of a sensing optical fiber provided by an embodiment of the present application;

[0042] Figure 3 It is a data processing flow chart of a reservoir rock temperature-strain detection system provided by an embodiment of the present application;

[0043] Figure 4 It is a schematic flow chart of a reservoir rock temperature-strain detection method provided by an embodiment of the present application;

[0044] Figure 5 It is a schematic structural diagram of a computer device provided by an embodiment of the present application.

[0045] Description of the Reference Numerals:

[0046] 1 - Light source, 2 - First optical switch, 3 - Strain measurement module, 31 - First optical coupler, 32 - Auxiliary interference unit, 321 - Second optical circulator, 322 - Fourth optical coupler, 323 - First reference optical fiber, 324 - First Faraday rotator mirror, 325 Second photodetector, 33 - Main interference unit, 331 - Second optical coupler, 332 - Polarization controller, 333 - First optical circulator, 334 - Third optical coupler, 335 - First photodetector, 4 - Temperature measurement module, 41 - Optical isolator, 42 - Fifth optical coupler, 43 - Second reference optical fiber, 44 - Second Faraday rotator mirror, 45 - Third photodetector, 5 - Second optical switch, 6 - Processing module, 61 - Data acquisition card, 62 - Host computer, 7 - Sensing optical fiber, 71 - Core, 72 - Cladding, 73 - Gold-plated coating, 74 - Ultra-weak grating. Detailed implementation manner

[0047] Next, the technical solutions in the embodiments of the present application will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present application.

[0048] To make the above objects, features, and advantages of the present application more obvious and understandable, the present application will be further described in detail below in conjunction with the accompanying drawings and specific implementation manners.

[0049] This embodiment provides a reservoir rock temperature-strain detection system for detecting the temperature-strain of reservoir rock under true triaxial high-temperature loading conditions, as Figure 1 shown. The reservoir rock temperature-strain detection system includes: a light source 1, a strain measurement module 3, a temperature measurement module 4, a sensing optical fiber 7, and a processing module 6.

[0050] The light source 1 is respectively connected to the strain measurement module 3 and the temperature measurement module 4. Both the strain measurement module 3 and the temperature measurement module 4 are connected to the processing module 6. Both the strain measurement module 3 and the temperature measurement module 4 are connected to the sensing optical fiber 7. The sensing optical fiber 7 is arranged in the reservoir rock. An ultra-weak grating array is engraved on the sensing optical fiber 7. The ultra-weak grating array includes a plurality of ultra-weak gratings 74. Among them, the ultra-weak grating 74 is the abbreviation of the ultra-weak fiber grating proposed by the research group of Wang Anbo at Virginia Polytechnic University in 2011. The weak grating is formed by regularly engraving fiber gratings in the fiber core, and the reflectivity of a single grating is less than 1%, or even lower. In this application, the ultra-weak grating array is used for distributed optical fibers, which can effectively improve the optical signal-to-noise ratio (20 dB), and finally achieve the accurate measurement of temperature and strain signals. In addition, the gold-plated optical fiber can theoretically achieve a temperature resistance of 500 °C, meeting the basic requirements of the project environment.

[0051] The strain measurement module 3 includes a first optical coupler 31, a main interference unit 33, and an auxiliary interference unit 32. The light source 1 is connected to the main interference unit 33 and the auxiliary interference unit 32 respectively after passing through the first optical coupler 31. Both the main interference unit 33 and the auxiliary interference unit 32 are connected to the processing module 6.

[0052] The main interference unit 33 uses a Mach-Zehnder interference structure to obtain the strain signal of the sensing optical fiber 7, so as to complete the measurement of the signal of the sensing optical fiber 7. The auxiliary interference unit 32 uses a Michelson interference structure to sample the strain signal of the sensing optical fiber 7 at a frequency point to obtain a strain reference signal.

[0053] The temperature measurement module 4 adopts a coherent detection structure to measure the temperature signal and temperature reference signal of the sensing optical fiber 7 through the backward Rayleigh scattering signal, so as to realize temperature measurement.

[0054] The processing module 6 is used to obtain the strain data and temperature data of the reservoir rock mass based on the strain signal of the sensing optical fiber 7, the strain reference signal, the temperature signal of the sensing optical fiber 7, and the temperature reference signal.

[0055] Based on the above description, the reservoir rock mass temperature-strain detection system provided by this application is based on the optical frequency domain reflectometry (OFDR) technology of the Mach-Zehnder interference structure, detects the change of the Bragg wavelength of the ultra-weak fiber grating 74 (uwFBG) array, and uses the phase-sensitive optical frequency domain reflectometry (Φ-OFDR) of Rayleigh scattering. Through uwFBG sensitization, high spatial resolution and high-precision measurement of the temperature field and strain field are realized.

[0056] In another exemplary embodiment of this application, in order to realize independent measurement and joint settlement of two optical paths and ensure the stability and decoupling of temperature and strain measurement, an optical switch can be used to switch different measurement modules. Based on this, as Figure 1 shown, in this embodiment, the reservoir rock mass temperature-strain detection system further includes a first optical switch 2 and a second optical switch 5.

[0057] The light source 1 is connected to the first optical coupler 31 and the temperature measurement module 4 respectively through the first optical switch 2.

[0058] Both the strain measurement module 3 and the temperature measurement module 4 are connected to the sensing optical fiber 7 through the second optical switch 5.

[0059] In another exemplary embodiment of the present application, in order to complete the measurement of the signal of the sensing optical fiber 7 and mitigate the polarization fading on the measurement arm, in this embodiment, as Figure 1 shown, the Mach-Zehnder interference structure adopted by the main interference unit 33 includes: a second optical coupler 331, a polarization controller 332, a first optical circulator 333, a third optical coupler 334, and a first photodetector 335. Among them, the introduction of the polarization controller 332 can mitigate the polarization fading on the measurement arm.

[0060] One end of the second optical coupler 331 is connected to the first optical coupler 31. The other end of the second optical coupler 331 is respectively connected to one end of the polarization controller 332 and the first end of the first optical circulator 333. The other end of the polarization controller 332 is connected to one end of the third optical coupler 334. The other end of the third optical coupler 334 is connected to one end of the first photodetector 335. The other end of the first photodetector 335 is connected to the processing module 6. The third end of the first optical circulator 333 is connected to one end of the third optical coupler 334. The second end of the first optical circulator 333 is connected to the second optical switch 5.

[0061] In another exemplary embodiment of the present application, in order to accurately sample the main interference signal (i.e., the signal measured by the main interference unit 33) at a frequency point, in this embodiment, as Figure 1 shown, the Michelson interference structure adopted by the auxiliary interference unit 32 includes: a second optical circulator 321, a fourth optical coupler 322, a first reference optical fiber 323, a first Faraday rotator 324, and a second photodetector 325.

[0062] The first end of the second optical circulator 321 is connected to the first optical coupler 31. The second end of the second optical circulator 321 is connected to one end of the fourth optical coupler 322. The other end of the fourth optical coupler 322 is divided into two branches. The optical signal of one branch is incident on the first Faraday rotator 324 through the first reference optical fiber 323, and the optical signal of the other branch is incident on the first Faraday rotator 324. The third end of the second optical circulator 321 is connected to the first end of the second photodetector 325. The second end of the second photodetector 325 is connected to one end of the fourth optical coupler 322. The third end of the second photodetector 325 is connected to the processing module 6.

[0063] Based on the structure of the auxiliary interference unit 32 given above, the auxiliary interference unit 32 can complete the matching with the main interference unit 33 through the first reference optical fiber 323, the Faraday rotator, etc., so as to achieve the sampling of the main interference signal at a frequency point.

[0064] In another exemplary embodiment of the present application, in order to achieve more accurate temperature measurement, as Figure 1As shown, the coherent detection structure adopted by the temperature measurement module 4 includes: an optical isolator 41, a fifth optical coupler 42, a second reference optical fiber 43, a third photodetector 45, and a second Faraday rotator mirror 44.

[0065] One end of the optical isolator 41 is connected to the first optical switch 2. The other end of the optical isolator 41 is connected to one end of the fifth optical coupler 42. The other end of the fifth optical coupler 42 is respectively connected to the second optical switch 5 and the second reference optical fiber 43. The optical signal is incident on the second Faraday rotator mirror 44 after passing through the second reference optical fiber 43. One end of the fifth optical coupler 42 is also connected to one end of the third photodetector 45. The other end of the third photodetector 45 is connected to the processing module 6. The temperature reference signal is obtained based on the second reference optical fiber 43.

[0066] In another exemplary embodiment of the present application, a high-temperature-resistant optical fiber is used as the sensing optical fiber 7, and the outer diameter of the optical fiber is set to be less than or equal to 250 μm to ensure long-term stable operation in an environment of 500 °C. As Figure 2 shown, the sensing optical fiber 7 includes a core 71, a cladding 72, and a gold-plated coating 73. Among them, the material of the gold-plated coating 73 is one or more of gold, aluminum, and polyimide.

[0067] The ultra-weak grating array is engraved between the cladding 72 and the gold-plated coating 73. The central wavelength of the ultra-weak grating 74 in the ultra-weak grating array can be set to 1525 nm to 1565 nm, the grating pitch is set to 10 mm, the grating length is set to 9 mm, and the reflectivity is less than 0.1% to ensure the deployment of dense gratings on an extremely short optical fiber length to achieve array sensing. However, the values of the sensing optical fiber 7 and the ultra-weak grating array are not limited to the above description, and specific values can be set according to the measurement environment during actual application. Figure 2 In, D represents the grating pitch, and C represents the grating length.

[0068] In another exemplary embodiment of the present application, under the condition of true triaxial high-temperature loading, the sensing optical fiber 7 can be arranged in a snake shape on the surface of the reservoir rock mass. One end of the optical fiber is introduced from the pressure block, distributed between the pressure block and the reservoir rock mass, and the other end is led out from the pressure block and finally connected to the processing module 6. A snake-shaped groove is provided on the surface of the pressure block, and the position of the snake-shaped groove is replicated on the surface of the reservoir rock mass for placing the sensing optical fiber 7 to avoid damage to the sensing optical fiber 7 due to stress concentration caused by rigid loading, affecting its detection and monitoring performance. The inner side of the end of the sensing optical fiber 7 channel in the pressure block close to the reservoir rock mass is set to a round chamfer to ensure that the sensing optical fiber 7 is not damaged when passing through the end of the optical fiber channel of the pressure block.

[0069] Based on the above description, during actual application, the following points need to be noted when deploying the optical fiber:

[0070] (1)The surface of the pressing block applying the load is grooved to avoid the optical fiber being directly subjected to lateral pressure.

[0071] (2)The bending of the optical fiber will affect signal transmission, especially for the weak signals of backscattering, and stricter requirements are imposed. Therefore, there are requirements for the minimum bending radius during the laying of the optical fiber. This application can select a bend-resistant and low-loss optical fiber according to the actual situation to reduce the laying difficulty.

[0072] (3)Design and install a penetrator connecting the internal and external optical fibers to meet the requirements of high temperature and high pressure resistance.

[0073] In another exemplary embodiment of the present application, the processing module 6 includes a data acquisition card 61 and a host computer 62.

[0074] The data acquisition card 61 is respectively connected to the main interference unit 33, the auxiliary interference unit 32, the temperature measurement module 4, and the host computer 62.

[0075] For example, a 500M four-channel high-speed data acquisition card is used to collect the signals measured by the main interference unit 33, the auxiliary interference unit 32, and the temperature measurement module 4. The software implanted in the host computer 62 is written in LabView, and through timing control and embedded algorithms, system control, data processing, display, etc. are completed.

[0076] In another exemplary embodiment of the present application, the light source 1 can be a tunable laser (Tunable Laser, TLS).

[0077] In another exemplary embodiment of the present application, the working principle of strain field detection and monitoring of the reservoir rock temperature-strain detection system provided by the present application is as follows:

[0078] The scanning laser signal (i.e., the optical signal emitted by the light source 1) is injected into the auxiliary interference unit 32 and the main interference unit 33 according to a certain ratio through the first optical coupler 31. The auxiliary interference unit 32 can be a Michelson interference structure, such as Figure 1 shown, which includes a second optical circulator 321, a fourth optical coupler 322, a single-mode optical fiber (i.e., the connecting optical fiber between the fourth optical coupler 322 and the first Faraday rotator mirror), a first reference optical fiber 323 (i.e., delay optical fiber), a first Faraday rotator mirror, and a second photodetector 325. An external clock is used to trigger data acquisition, so as to sample the signal collected by the main interference unit 33 at uniform optical frequency points. The main interference unit 33 is a Mach-Zehnder interference structure, which includes a second optical coupler 331, a polarization controller 332, a first circulator, a first photodetector 335, and a third optical coupler 334. Among them, a polarization controller 332 is introduced into the reference arm of the main interference unit 33 to mitigate the polarization fading on the measurement arm.

[0079] In another exemplary embodiment of the present application, the working principle of temperature field detection and monitoring of the reservoir rock temperature-strain detection system provided by the present application is as follows:

[0080] The light source 1 performs wavelength scanning in the full band with a certain line width and rate. The scanned laser signal is incident into the reference branch (i.e., the path formed by the second reference optical fiber 43 and the second Faraday rotator 44) and the measurement branch (i.e., the path formed by the fifth optical coupler 42 and the sensing optical fiber 7) of the temperature measurement module 4 according to a certain ratio through isolation and the fifth optical coupler 42 to monitor the temperature change of the reservoir rock mass. The reference branch and the measurement branch form a beat signal in the fifth coupler, which is photoelectrically converted by the third photodetector 45, and the optical signal information at each uwFBG position is obtained by using a high-speed data acquisition card.

[0081] Performing a fast Fourier transform (FFT) on the reference branch can obtain the position information of each uwFBG in the frequency domain. A sliding window is preferably selected for a specific uwFBG and an inverse fast Fourier transform (IFFT) is performed to separate the beat signal and its specific spectrum at the selected uwFBG frequency (i.e., position) from the interference signal. By tracking the change of the peak wavelength of each uwFBG, distributed temperature detection and monitoring are realized.

[0082] In another exemplary embodiment of the present application, the data processing flow of the reservoir rock temperature-strain detection system provided by the present application is as follows:

[0083] The data acquisition card 61 acquires the frequency domain signal data of the main interference unit 33 and the auxiliary interference unit 32, and the upper computer 62 performs data processing. The data processing mainly includes temperature measurement and strain measurement as shown in Figure 3 In the specific implementation process, through demodulation, the reference signal of the auxiliary interference unit 32 and the measurement signal of the main interference unit 33 in the frequency domain are respectively obtained. The signals (i.e., the reference signal and the measurement signal) in the optical frequency domain are transformed into the spatial domain through discrete Fourier transform, and the phase spectrum is obtained by calculating the phase angle of the complex value in the spatial domain. The phase spectrum of the signal is divided into multiple segments along the optical fiber (i.e., phase segmentation). The differential phase of each segment is calculated through the reference and measurement phase spectra of the same segment. The differential phase of each segment is phase-corrected to obtain the complete phase, and then the complete phase is phase-unwrapped to obtain the change in optical fiber length. Further, the complete phase after phase-unwrapping is smoothed to obtain the optical fiber strain.

[0084] Based on the above description, the process of strain measurement includes:

[0085] Step 1: Obtain the spatial phase spectrum. Transform the signal in the obtained frequency domain into the spatial domain through the Discrete Fourier Transform (DFT), and obtain the phase spectrum by calculating the phase angle of the complex value in the spatial domain.

[0086] Step 2: Segment in space and perform phase correction. Divide the phase spectrum obtained in Step 1 along the optical fiber into multiple small segments, and calculate the differential phase of each segment through the reference and measured phase spectra of the same segment.

[0087] Step 3: Phase correction. Utilize the positions and wavelength changes of each ultra-weak grating in the ultra-weak grating array to achieve phase correction.

[0088] Step 4: Phase unwrapping and smoothing processing. Unwrap and smooth the differential phase of each segment and the total differential phase corrected in Step 3, and obtain the strain data through differentiation. In this step, it can also be to unwrap and smooth the obtained complete phase and obtain the strain data through differentiation.

[0089] The process of temperature measurement includes:

[0090] Step 1: Determine the accurate positions of the ultra-weak gratings. By performing a Fast Fourier Transform (FFT) on the signal of the reference branch, the specific positions of each ultra-weak grating 74 (after strain occurs) in the frequency domain can be obtained.

[0091] Step 2: Determine the specific spectrum of the ultra-weak grating. Combine the segmentation results in strain measurement, preferably select a sliding window and perform an Inverse Fast Fourier Transform (IFFT) to separate the beat signal and its specific spectrum at the frequency of the selected ultra-weak grating from the interference signal.

[0092] Step 3: Peak tracking and temperature calculation. Through the wavelength peak tracking algorithm, perform wavelength peak tracking on each ultra-weak grating in the measurement, and obtain the temperature information of the environment where the optical fiber is located through the coupling relationship between the positions of the ultra-weak gratings and the temperature and strain in the optical fiber.

[0093] The system provided by this application is based on an OFDR with a Mach-Zehnder interferometer structure, detects the Bragg wavelength changes of the uwFBG array, and uses the Φ-OFDR of Rayleigh scattering. Through uwFBG sensitization, high spatial resolution and high-precision measurement of the temperature field and strain field are achieved.

[0094] Further, in order to overcome the problem of collaborative detection of temperature field and strain field, the present application provides a key technology combining in-situ temperature calibration and position deviation compensation algorithm to achieve millimeter-level spatial resolution of strain and temperature of ultra-weak grating arrays. The sensing optical fiber is sensitized by the ultra-weak grating array, and the strain information is calculated by phase demodulation, and the temperature measurement is realized by wavelength demodulation. During the long-term operation of the system, the thermal expansion and contraction of the sensing optical fiber induced by temperature changes will change the position of the ultra-weak grating, thereby introducing strain errors. Select a single ultra-weak grating at the head / tail end of the ultra-weak grating array as the temperature calibration grating to determine the initial position deviation and / or cumulative position deviation. Use the correlation peak as the characteristic peak. Since the deviation in the optical path can be related to the wavelength shift, the quadratic term and dispersion are ignored during the scanning process covering the entire ultra-weak grating array, and the cumulative position deviation in the optical path is described by the continuous integration method. Using the cumulative deviation, the initial measurement spectrum of the ultra-weak grating is modified in turn to re-match its reference and restore the cross-correlation. According to the recurrence relation, the temperature or strain distribution along the optical fiber can be obtained at a higher spatial resolution and a longer measurement length.

[0095] Based on the same inventive concept, the embodiment of the present application also provides a reservoir rock temperature-strain detection method implemented based on the above-provided reservoir rock temperature-strain detection system. The implementation solutions provided by this method to solve problems are similar to the implementation solutions described in the above system. Therefore, the specific limitations in one or more embodiments of the reservoir rock temperature-strain detection method provided below can refer to the limitations on the reservoir rock temperature-strain detection system in the above text, and will not be repeated here.

[0096] In an exemplary embodiment, as Figure 4 shown, a reservoir rock temperature-strain detection method is provided, including:

[0097] Step 200: Obtain the strain signal and strain reference signal of the reservoir rock to be detected.

[0098] Step 201: Use the discrete Fourier transform to transform the strain signal and strain reference signal from the frequency domain to the spatial domain to obtain the complex value in the spatial domain.

[0099] Step 202: Determine the phase angle of the complex value in the spatial domain and generate a phase spectrum based on the phase angle.

[0100] Step 203: Divide the phase spectrum along the sensing optical fiber to obtain a segmentation result, and obtain the differential phase of each segment of the sensing optical fiber based on the segmentation result.

[0101] Step 204: Based on the differential phase, use the position and wavelength change of each ultra-weak grating in the ultra-weak grating array to correct the phase of the phase spectrum.

[0102] Step 205: Unwrap and smooth the corrected phase spectrum, and obtain the strain data of the reservoir rock mass to be detected by differentiation.

[0103] Step 206: Perform a fast Fourier transform on the temperature reference signal to obtain the position of each ultra-weak grating after strain occurs.

[0104] Step 207: Use a sliding window to select the positions of the ultra-weak gratings, perform an inverse fast Fourier transform on the segmented results within the sliding window, and separate the beat signal and spectrum at the positions of the selected ultra-weak gratings from the temperature signal.

[0105] Step 208: Based on the beat signal and spectrum, perform wavelength peak tracking on each ultra-weak grating in the measurement through a wavelength peak tracking algorithm, and obtain the wavelength peak tracking results.

[0106] Step 209: Based on the coupling relationship between the positions of the ultra-weak gratings and temperature and strain in the sensing optical fiber, obtain the temperature data of the reservoir rock mass to be detected based on the wavelength peak tracking results.

[0107] In addition, based on the above description, the optical fiber of the present application uses a reflective measurement method and is measured in a way that the head and tail are led out at both ends. If an abnormality occurs at a certain position of the optical fiber, for example, the optical fiber breaks into two sections, at this time, either end can be enabled for measurement, thereby ensuring the integrity of the optical fiber sensing information.

[0108] In an exemplary embodiment, a computer device is provided. The computer device can be a server or a terminal, and its internal structure diagram can be as Figure 5 shown. The computer device includes a processor, a memory, an input / output interface (Input / Output, abbreviated as I / O), and a communication interface. Among them, the processor, the memory, and the input / output interface are connected through a system bus, and the communication interface is connected to the system bus through the input / output interface. Among them, the processor of the computer device is used to provide computing and control capabilities. The memory of the computer device includes a non-volatile storage medium and an internal memory. The non-volatile storage medium stores an operating system, a computer program, and a database. The internal memory provides an environment for the operation of the operating system and the computer program in the non-volatile storage medium. The database of the computer device is used to store reservoir rock mass temperature-strain detection data. The input / output interface of the computer device is used to exchange information between the processor and external devices. The communication interface of the computer device is used to communicate with an external terminal through a network connection. When the computer program is executed by the processor, it implements a method for detecting the temperature and strain of a reservoir rock mass.

[0109] Those skilled in the art can understand, Figure 5The structure shown is only a block diagram of some of the structures related to the solution of this application, and does not constitute a limitation on the computer device to which the solution of this application is applied. The specific computer device may include more or fewer components than those shown in the figure, or combine certain components, or have a different component arrangement. In an exemplary embodiment, a computer device is provided, including a memory and a processor. A computer program is stored in the memory, and when the processor executes the computer program, the steps in the above method embodiments are implemented.

[0110] In an exemplary embodiment, a computer-readable storage medium is provided, storing a computer program, and when the computer program is executed by a processor, the steps in the above method embodiments are implemented.

[0111] In an exemplary embodiment, a computer program product is provided, including a computer program, and when the computer program is executed by a processor, the steps in the above method embodiments are implemented.

[0112] It should be noted that the user information (including but not limited to user device information, user personal information, etc.) and data (including but not limited to data for analysis, stored data, displayed data, etc.) involved in this application are all information and data authorized by the user or fully authorized by all parties, and the collection, use, and processing of relevant data need to comply with relevant regulations.

[0113] Those of ordinary skill in the art can understand that all or part of the processes in the methods of the above embodiments can be completed by instructing relevant hardware through a computer program. The computer program can be stored in a non-volatile computer-readable storage medium. When the computer program is executed, it can include the processes of the embodiments of the above methods. Among them, any reference to a memory, database, or other medium used in the embodiments provided in the present application can include at least one of non-volatile and volatile memories. Non-volatile memories can include read-only memory (ROM), magnetic tapes, floppy disks, flash memories, optical memories, high-density embedded non-volatile memories, resistive random access memories (ReRAM), magnetoresistive random access memories (MRAM), ferroelectric random access memories (FRAM), phase change memories (PCM), graphene memories, etc. Volatile memories can include random access memory (RAM) or external cache memories, etc. By way of illustration and not limitation, RAM can be in various forms, such as static random access memory (SRAM) or dynamic random access memory (DRAM), etc.

[0114] The databases involved in the embodiments provided in the present application can include at least one of relational databases and non-relational databases. Non-relational databases can include distributed databases based on blockchain, etc., without limitation. The processors involved in the embodiments provided in the present application can be general-purpose processors, central processors, graphics processors, digital signal processors, programmable logics, data processing logics based on quantum computing, etc., without limitation.

[0115] The technical features of the above embodiments can be combined arbitrarily. For the sake of concise description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope described in this specification.

[0116] Specific examples are used in this article to elaborate on the principles and implementation manners of the present application. The description of the above embodiments is only used to help understand the method and its core idea of the present application; at the same time, for those of ordinary skill in the art, according to the idea of the present application, there will be changes in the specific implementation manners and application scopes. In summary, the content of this specification should not be construed as a limitation to the present application.

Claims

1. A reservoir rock temperature-strain detection system, characterized in that: The reservoir rock mass temperature-strain detection system is applied to the temperature-strain detection of the reservoir rock mass under true triaxial high temperature loading conditions; The reservoir rock temperature-strain detection system comprises: a light source, a strain measurement module, a temperature measurement module, a sensing optical fiber, a processing module, a first optical switch and a second optical switch; The light source is connected to the strain measurement module and the temperature measurement module respectively; the strain measurement module and the temperature measurement module are both connected to the processing module; the strain measurement module and the temperature measurement module are both connected to the sensing optical fiber; the sensing optical fiber is arranged in the reservoir rock mass; an ultra-weak grating array is engraved on the sensing optical fiber; the ultra-weak grating array includes a plurality of ultra-weak gratings; a single ultra-weak grating at the head / tail end of the ultra-weak grating array is selected as a temperature calibration grating to determine the initial position deviation and / or the accumulated position deviation; The strain measurement module includes a first optical coupler, a main interference unit and an auxiliary interference unit; the light source is connected to the main interference unit and the auxiliary interference unit respectively after passing through the first optical coupler; the main interference unit and the auxiliary interference unit are both connected to the processing module; The main interference unit adopts a Mach-Zehnder interference structure to obtain the strain signal of the sensing optical fiber; the auxiliary interference unit adopts a Michelson interference structure to sample the strain signal of the sensing optical fiber at a frequency point to obtain a strain reference signal; The temperature measurement module adopts a coherent detection structure to measure the temperature signal and the temperature reference signal of the sensing optical fiber through the backscattered Rayleigh signal; The processing module is used to obtain strain data and temperature data of the reservoir rock mass based on the strain signal of the sensing optical fiber, the strain reference signal, the temperature signal of the sensing optical fiber, and the temperature reference signal; The light source is connected to the first optical coupler and the temperature measurement module respectively via the first optical switch; The strain measurement module and the temperature measurement module are both connected to the sensing optical fiber through the second optical switch; The Mach-Zehnder interference structure adopted by the main interference unit includes: a second optical coupler, a polarization controller, a first optical circulator, a third optical coupler and a first photodetector; One end of the second optical coupler is connected to the first optical coupler; the other end of the second optical coupler is respectively connected to one end of the polarization controller and the first end of the first optical circulator; the other end of the polarization controller is connected to one end of the third optical coupler; the other end of the third optical coupler is connected to one end of the first photodetector; the other end of the first photodetector is connected to the processing module; the third end of the first optical circulator is connected to one end of the third optical coupler; and the second end of the first optical circulator is connected to the second optical switch.

2. The reservoir rock temperature-strain detection system according to claim 1, characterized in that: The Michelson interference structure adopted by the auxiliary interference unit includes: a second optical circulator, a fourth optical coupler, a first reference optical fiber, a first Faraday rotation mirror and a second photodetector; The first end of the second optical circulator is connected to the first optical coupler; the second end of the second optical circulator is connected to one end of the fourth optical coupler; the other end of the fourth optical coupler is divided into two branches, wherein the optical signal of one branch is injected into the first Faraday rotator through the first reference optical fiber, and the optical signal of the other branch is injected into the first Faraday rotator; the third end of the second optical circulator is connected to the first end of the second photodetector; the second end of the second photodetector is connected to one end of the fourth optical coupler; and the third end of the second photodetector is connected to the processing module.

3. The reservoir rock temperature-strain detection system according to claim 1, characterized in that: The coherent detection structure adopted by the temperature measurement module includes: an optical isolator, a fifth optical coupler, a second reference optical fiber, a third photodetector and a second Faraday rotation mirror; One end of the optical isolator is connected to the first optical switch; the other end of the optical isolator is connected to one end of the fifth optical coupler; the other end of the fifth optical coupler is respectively connected to the second optical switch and the second reference optical fiber; the optical signal is emitted into the second Faraday rotation mirror after passing through the second reference optical fiber; one end of the fifth optical coupler is also connected to one end of the third photodetector; the other end of the third photodetector is connected to the processing module; the temperature reference signal is obtained based on the second reference optical fiber.

4. The reservoir rock temperature-strain detection system according to claim 1, characterized in that: The central wavelength of the ultra-weak grating in the ultra-weak grating array is 1525nm~1565nm; the reflectivity of the sensing optical fiber is less than 0.1%; and the outer diameter of the sensing optical fiber is less than or equal to 250μm.

5. The reservoir rock temperature-strain detection system according to claim 1, characterized in that: The coating material of the sensing optical fiber is one or more of gold, aluminum and polyimide.

6. The reservoir rock temperature-strain detection system according to claim 1, characterized in that: The processing module includes a data acquisition card and a host computer; The data acquisition card is connected to the main interference unit, the auxiliary interference unit, the temperature measurement module and the host computer respectively.

7. The reservoir rock temperature-strain detection system according to claim 1, characterized in that: The light source is a tunable laser.

8. A reservoir rock temperature-strain detection method, characterized in that: The reservoir rock mass temperature-strain detection method is implemented by using the reservoir rock mass temperature-strain detection system according to any one of claims 1 to 7; The reservoir rock mass temperature-strain detection method comprises: Obtaining strain signals and strain reference signals of the reservoir rock mass to be detected; The strain signal and the strain reference signal are transformed from the frequency domain to the spatial domain by using discrete Fourier transform to obtain a spatial domain complex value; determining a phase angle of the spatial domain complex value and generating a phase spectrum based on the phase angle; Segmenting the phase spectrum along the sensing optical fiber to obtain segmented results, and obtaining the differential phase of each segment of the sensing optical fiber based on the segmented results; Based on the differential phase, the phase spectrum is phase corrected by utilizing the position and wavelength variation of each ultra-weak grating in the ultra-weak grating array; The corrected phase spectrum is expanded and smoothed, and the strain data of the reservoir rock mass to be detected is obtained by differentiation; Performing a fast Fourier transform on the temperature reference signal to obtain the position of each ultra-weak grating after strain occurs; The position of the ultra-weak grating is selected by using a sliding window, and the segmentation results in the sliding window are subjected to inverse fast Fourier transform to separate the beat signal and spectrum at the position of the selected ultra-weak grating from the temperature signal; Based on the beat signal and spectrum, the wavelength peak tracking algorithm is used to track the wavelength peak of each ultra-weak grating in the measurement, and the wavelength peak tracking result; Through the coupling relationship between the ultra-weak grating position and the temperature and strain in the sensing optical fiber, the temperature data of the reservoir rock to be detected is obtained based on the wavelength peak tracking result.

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