Reservoir rock mass temperature-strain detection system and method

Abstract

The invention discloses a reservoir rock mass temperature-strain detection system and method, and relates to the field of rock mass engineering geomechanics test and measurement. The reservoir rock mass temperature-strain detection system comprises a light source, a strain measurement module, a temperature measurement module, a sensing optical fiber and a processing module, the light source is connected with the strain measurement module and the temperature measurement module. The strain measurement module and the temperature measurement module are connected with the processing module. The strain measurement module and the temperature measurement module are connected with the sensing optical fiber; the sensing optical fiber is arranged in a reservoir rock mass; and an ultra-weak grating array is carved on the sensing optical fiber. According to the invention, collaborative detection of the temperature and strain of the reservoir rock mass can be realized under the true triaxial high-temperature loading condition.

Description

Technical Field

[0001] The present application relates to the field of rock mass engineering geomechanics testing and measurement, and in particular to a reservoir rock mass temperature-strain detection system and method under true triaxial high-temperature loading conditions. Background Art

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

[0003] In order to quantitatively characterize the multiphase field coupling response of reservoir rock mass disturbed by supercritical carbon dioxide injection, a large number of numerical simulation explorations have been carried out, and the initial parameters of the numerical simulation are mostly derived from indoor test tests. 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 anti-electromagnetic interference, 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 supercritical carbon dioxide displacement tests and rock pseudo-triaxial tests, but there has been no academic report on the coordinated detection of temperature and strain in the deformation and destruction process of reservoir rock mass under true triaxial high temperature loading conditions. Summary of the invention

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

[0005] To achieve the above objectives, this application provides the following solutions: In a first aspect, the present application provides a reservoir rock temperature-strain detection system, which is applied to the temperature-strain detection of reservoir rock 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 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 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; 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.

[0006] Optionally, the reservoir rock mass temperature-strain detection system further includes a first optical switch and a second optical switch; 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.

[0007] 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; 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.

[0008] 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 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.

[0009] 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 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.

[0010] Optionally, 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.

[0011] Optionally, the coating material of the sensing optical fiber is one or more of gold, aluminum and polyimide.

[0012] Optionally, 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.

[0013] Optionally, the light source is a tunable laser.

[0014] In a second aspect, the present application provides a reservoir rock temperature-strain detection method, which is implemented by using the reservoir rock temperature-strain detection system provided above; the reservoir rock 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.

[0015] According to the specific embodiments provided in this application, this application discloses the following technical effects: The present application provides a reservoir rock temperature-strain detection system and method, wherein the sensing optical fiber is sensitized by an ultra-weak grating array, strain information is calculated by phase demodulation, and temperature measurement is achieved by wavelength demodulation. During the long-term operation of the reservoir rock temperature-strain detection system, temperature changes induce thermal expansion and contraction of the sensing optical fiber, thereby changing the position of the ultra-weak grating, thereby introducing strain errors and achieving strain measurement. By utilizing the principle that the deviation in the optical path is related to the wavelength offset of the ultra-weak grating, the temperature or strain distribution along the sensing optical fiber can be obtained at a higher spatial resolution and a longer measurement length, thereby achieving coordinated detection of reservoir rock temperature and strain under true triaxial high-temperature loading conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0017] Figure 1 A schematic diagram of the structure of a reservoir rock temperature-strain detection system provided in one embodiment of the present application; Figure 2 This is a schematic diagram of the structure of a sensing optical fiber provided in one embodiment of the present application; Figure 3 A data processing flow chart of a reservoir rock temperature-strain detection system provided in one embodiment of the present application; Figure 4 A schematic diagram of a flow chart of a reservoir rock mass temperature-strain detection method provided in an embodiment of the present application; Figure 5 A schematic diagram of the structure of a computer device provided in one embodiment of the present application.

[0018] Description of reference numerals: 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, 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, 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 coating, 74-ultra-weak grating. DETAILED DESCRIPTION

[0019] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0020] In order to make the above-mentioned objects, features and advantages of the present application more obvious and easy to understand, the present application is further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0021] This embodiment provides a reservoir rock mass temperature-strain detection system for detecting the temperature-strain of a reservoir rock mass under true triaxial high-temperature loading conditions, such as Figure 1As 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.

[0022] The light source 1 is connected to the strain measurement module 3 and the temperature measurement module 4 respectively. The strain measurement module 3 and the temperature measurement module 4 are both connected to the processing module 6. The strain measurement module 3 and the temperature measurement module 4 are both connected to the sensing optical fiber 7. The sensing optical fiber 7 is set in the reservoir rock mass. 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 Wang Anbo's research group at Virginia Tech in 2011. The weak grating is a method of regularly engraving a fiber grating on the optical fiber core, and the reflectivity of a single grating is less than 1%, or even lower. This application uses an ultra-weak grating array for distributed optical fiber, which can effectively improve the optical signal-to-noise ratio (20dB) and ultimately achieve accurate measurement of temperature strain signals. In addition, gold-plated optical fiber can theoretically achieve a temperature resistance of 500°C, meeting the basic requirements of the project environment.

[0023] 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. The main interference unit 33 and the auxiliary interference unit 32 are both connected to the processing module 6.

[0024] The main interference unit 33 uses a Mach-Zehnder interference structure to obtain the strain signal of the sensing optical fiber 7 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.

[0025] The temperature measurement module 4 adopts a coherent detection structure and measures the temperature signal and the temperature reference signal of the sensing optical fiber 7 through the backscattered Rayleigh signal, so as to achieve temperature measurement.

[0026] The processing module 6 is used to obtain strain data and temperature data of the reservoir rock mass based on the strain signal and strain reference signal of the sensing optical fiber 7 and the temperature signal and temperature reference signal of the sensing optical fiber 7 .

[0027] Based on the above description, the reservoir rock temperature-strain detection system provided in the present application detects the Bragg wavelength change of the ultra-weak grating 74 (ultra-weak Fiber Grating, uwFBG) array based on the optical frequency domain reflectometry (Optical Frequency Domain Reflectometry, OFDR) technology of the Mach-Zehnder interference structure, and utilizes the phase-sensitive optical frequency domain reflectometry (Phase-Sensitive Optical Frequency Domain Reflectometry, Φ-OFDR) of Rayleigh scattering. Through uwFBG sensitization, high spatial resolution and high-precision temperature field and strain field measurement are achieved.

[0028] In another exemplary embodiment of the present application, in order to achieve 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 between different measurement modules. Figure 1 As shown, in this embodiment, the reservoir rock temperature-strain detection system also includes a first optical switch 2 and a second optical switch 5.

[0029] The light source 1 is connected to the first optical coupler 31 and the temperature measurement module 4 respectively via the first optical switch 2 .

[0030] The strain measurement module 3 and the temperature measurement module 4 are both connected to the sensing optical fiber 7 via the second optical switch 5 .

[0031] In another exemplary embodiment of the present application, in order to complete the measurement of the signal of the sensing optical fiber 7 and alleviate the polarization fading on the measuring arm, in this embodiment, Figure 1 As 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. The introduction of the polarization controller 332 can alleviate the polarization fading on the measurement arm.

[0032] 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 connected to one end of the polarization controller 332 and the first end of the first optical circulator 333 respectively. 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.

[0033] 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 As 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 rotation mirror 324 and a second photodetector 325 .

[0034] 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, wherein the optical signal of one branch is injected into the first Faraday rotator 324 via the first reference optical fiber 323, and the optical signal of the other branch is injected into 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.

[0035] Based on the structure of the auxiliary interference unit 32 given above, the auxiliary interference unit 32 can be matched with the main interference unit 33 through the first reference optical fiber 323, the Ferrari rotating mirror, etc., so as to achieve sampling of the main interference signal at the frequency point.

[0036] In another exemplary embodiment of the present application, in order to achieve more accurate temperature measurement, as Figure 1 As 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 rotation mirror 44 .

[0037] 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 connected to the second optical switch 5 and the second reference optical fiber 43 respectively. The optical signal is injected into the second Faraday rotation 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.

[0038] 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. Figure 2 As shown, the sensing optical fiber 7 includes a core 71, a cladding 72 and a gold-plated coating 73. The material of the gold-plated coating 73 is one or more of gold, aluminum and polyimide.

[0039] 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 1525nm~1565nm, the grating pitch is set to 10mm, the grating length is set to 9mm, and the reflectivity is less than 0.1%, so as to ensure that dense gratings are deployed on a very 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. In actual application, specific values ​​can be set according to the measurement environment. Figure 2 In the figure, D represents the gate pitch and C represents the gate length.

[0040] In another exemplary embodiment of the present application, under true triaxial high temperature loading conditions, the sensing optical fiber 7 can be arranged in a serpentine shape on the surface of the reservoir rock mass, wherein one end of the optical fiber is introduced from the pressing block and distributed between the pressing block and the reservoir rock mass, and the other end is led out from the pressing block and finally connected to the processing module 6. A serpentine groove is set on the surface of the pressing block, and the position of the serpentine groove is replicated on the surface of the reservoir rock mass for placing the sensing optical fiber 7 to prevent the sensing optical fiber 7 from being damaged by the stress concentration of rigid loading, thereby affecting its detection and monitoring performance. The inner side of the end of the channel of the sensing optical fiber 7 in the pressing block close to the reservoir rock mass is set as a rounded chamfer to ensure that the sensing optical fiber 7 is not damaged when passing through the end of the optical fiber channel of the pressing block.

[0041] Based on the above description, in actual application, the following points should be noted when deploying optical fibers: (1) The surface of the load-applying block is grooved to prevent the optical fiber from being directly subjected to lateral pressure.

[0042] (2) The bending of optical fiber will affect signal transmission, especially for weak backscattered signals, which require more stringent transmission. Therefore, there is a minimum bending radius requirement when laying optical fiber. This application can select bending-resistant and low-loss optical fiber according to actual conditions to reduce the difficulty of laying.

[0043] (3) Design and install through-holes that connect internal and external optical fibers to meet the requirements of high temperature and high pressure resistance.

[0044] In another exemplary embodiment of the present application, the processing module 6 includes a data acquisition card 61 and a host computer 62 .

[0045] The data acquisition card 61 is connected to the main interference unit 33 , the auxiliary interference unit 32 , the temperature measurement module 4 and the host computer 62 respectively.

[0046] 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 embedded in the host computer 62 is written in LabView, and completes system control, data processing and display through timing control and embedded algorithms.

[0047] In another exemplary embodiment of the present application, the light source 1 may be a tunable laser (TLS).

[0048] In another exemplary embodiment of the present application, the strain field detection and monitoring working principle of the reservoir rock temperature-strain detection system provided by the present application is: The scanning laser signal (i.e., the light 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 As shown, it includes a second optical circulator 321, a fourth optical coupler 322, a single-mode optical fiber (i.e., a connecting optical fiber between the fourth optical coupler 322 and the first Ferrari rotating mirror), a first reference optical fiber 323 (i.e., a delay optical fiber), a first Ferrari rotating mirror, and a second photodetector 325. An external clock is used to trigger data acquisition, so that the signal collected by the main interference unit 33 is sampled at a uniform optical frequency point. 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, the reference arm of the main interference unit 33 introduces a polarization controller 332 to alleviate the polarization fading on the measurement arm.

[0049] In another exemplary embodiment of the present application, the temperature field detection and monitoring working principle of the reservoir rock temperature-strain detection system provided by the present application is: The light source 1 sets a certain line width and rate to perform full-band wavelength scanning, and the scanning laser signal is incident on the reference branch (i.e., the path formed by the second reference optical fiber 43 and the second Faraday rotation mirror 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 in a certain proportion through isolation and the fifth optical coupler 42, which is used to monitor the temperature change of the reservoir rock mass. The reference branch and the measurement branch form a beat frequency signal in the fifth coupler, which is converted into photoelectricity by the third photodetector 45, and the optical signal information of each uwFBG position is obtained by a high-speed data acquisition card.

[0050] By performing Fast Fourier Transform (FFT) on the reference branch, the position information of each uwFBG in the frequency domain can be obtained. For a specific uwFBG, a sliding window is optimized 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. Distributed temperature detection and monitoring can be achieved by tracking the changes in the peak wavelength of each uwFBG.

[0051] 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: The data acquisition card 61 obtains the frequency domain signal data of the main interference unit 33 and the auxiliary interference unit 32, and the host computer 62 performs data processing. The data processing mainly includes the following steps: Figure 3 The temperature measurement and strain measurement shown. In the specific implementation process, by 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 obtained respectively, and the signals in the optical frequency domain (i.e., the reference signal and the measurement signal) are transformed into the spatial domain by 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 is performed), and the differential phase of each segment is calculated by the reference and measured phase spectra of the same segment, and 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, and the complete phase after phase unwrapping is further smoothed to obtain the optical fiber strain.

[0052] Based on the above description, the strain measurement process includes: Step 1: Obtain the spatial phase spectrum. The obtained signal in the frequency domain is transformed into the spatial domain through Discrete Fourier Transform (DFT), and the phase spectrum is obtained by calculating the phase angle of the complex value in the spatial domain.

[0053] Step 2: Segmentation in space and phase correction. The phase spectrum obtained in step 1 is divided into multiple small segments along the optical fiber, and the differential phase of each segment is calculated using the reference and measured phase spectra of the same segment.

[0054] Step 3: Phase correction: Phase correction is achieved by changing the position and wavelength of each ultra-weak grating in the ultra-weak grating array.

[0055] Step 4: Phase unwrapping and smoothing. Unwrap and smooth each differential phase and the total differential phase corrected in step 3, and obtain strain data by differentiation. In this step, the obtained complete phase can also be unwrapped and smoothed, and strain data can be obtained by differentiation.

[0056] The temperature measurement process includes: Step 1: Determine the exact position of the ultra-weak grating. By performing a fast Fourier transform (FFT) on the signal of the reference branch, the specific position of each ultra-weak grating 74 (after strain) in the frequency domain can be obtained.

[0057] Step 2: Determine the specific spectrum of the ultra-weak grating. Combined with the segmented results in the strain measurement, the sliding window is optimized and the inverse fast Fourier transform (IFFT) is performed to separate the beat signal and its specific spectrum at the selected ultra-weak grating frequency from the interference signal.

[0058] Step 3: Peak tracking and temperature calculation. The wavelength peak tracking algorithm is used to track the wavelength peak of each ultra-weak grating in the measurement, and the temperature information of the environment in which the optical fiber is located is obtained through the coupling relationship between the ultra-weak grating position and the temperature and strain in the optical fiber.

[0059] The system provided in this application is based on OFDR with a Mach-Zehnder interferometer structure to detect the Bragg wavelength change of the uwFBG array, and uses Φ-OFDR of Rayleigh scattering to achieve high spatial resolution and high-precision measurement of temperature and strain fields through uwFBG sensitization.

[0060] Further, in order to overcome the problem of coordinated detection of temperature field and strain field, the present application provides a key technology based on the combination of temperature in-situ calibration and position deviation compensation algorithm to achieve millimeter-level spatial resolution of strain and temperature of ultra-weak grating array. The sensing fiber is sensitized by ultra-weak grating array, strain information is calculated by phase demodulation, and temperature measurement is achieved by wavelength demodulation. During the long-term operation of the system, temperature changes induce thermal expansion and contraction of the sensing fiber, which will change the position of the ultra-weak grating, thereby introducing strain errors. 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 cumulative position deviation. The correlation peak is used as the characteristic peak, and the deviation in the optical path can be related to the wavelength offset. The quadratic term and dispersion are ignored in 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 sequence to re-match its reference and restore the cross-correlation. According to the recursive relationship, the temperature or strain distribution along the optical fiber can be obtained at a higher spatial resolution and a longer measurement length.

[0061] 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 reservoir rock temperature-strain detection system provided above. The implementation solution provided by the method to solve the problem is similar to the implementation solution recorded in the above system, so the specific limitations in one or more reservoir rock temperature-strain detection method embodiments provided below can refer to the limitations of the reservoir rock temperature-strain detection system above, and will not be repeated here.

[0062] In an exemplary embodiment, Figure 4 As shown, a reservoir rock temperature-strain detection method is provided, comprising: Step 200: Acquire the strain signal and strain reference signal of the reservoir rock mass to be detected.

[0063] Step 201: transform the strain signal and the strain reference signal from the frequency domain to the space domain using discrete Fourier transform to obtain a complex value in the space domain.

[0064] Step 202: Determine the phase angle of the spatial domain complex value, and generate a phase spectrum based on the phase angle.

[0065] Step 203: segment the phase spectrum along the sensing optical fiber to obtain segmented results, and obtain the differential phase of each segment of the sensing optical fiber based on the segmented results.

[0066] Step 204: Based on the differential phase, the phase spectrum is phase corrected using the position of each ultra-weak grating in the ultra-weak grating array and the wavelength change.

[0067] Step 205: unfolding and smoothing the corrected phase spectrum, and obtaining strain data of the reservoir rock mass to be detected by differentiation.

[0068] Step 206: Perform fast Fourier transform on the temperature reference signal to obtain the position of each ultra-weak grating after strain occurs.

[0069] Step 207: Use a sliding window to select the position of the ultra-weak grating, perform inverse fast Fourier transform on the segmented results within the sliding window, and separate the beat signal and spectrum at the position of the selected ultra-weak grating from the temperature signal.

[0070] Step 208: Based on the beat signal and the spectrum, a 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 is obtained.

[0071] Step 209: The temperature data of the reservoir rock mass to be detected is obtained based on 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.

[0072] In addition, based on the above description, the optical fiber of the present application uses a reflective measurement method and adopts a head and tail double-end lead-out method for measurement. If an abnormality occurs at a certain position of the optical fiber, for example, the optical fiber is broken into two sections, at this time, either end can be enabled for measurement, thereby ensuring the integrity of the optical fiber sensing information.

[0073] In an exemplary embodiment, a computer device is provided. The computer device may be a server or a terminal. The internal structure diagram thereof may be as follows: Figure 5 As shown. The computer device includes a processor, a memory, an input / output interface (Input / Output, referred to as I / O) and a communication interface. 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. 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 temperature-strain detection data. The input / output interface of the computer device is used to exchange information between the processor and an external device. 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, a reservoir rock temperature-strain detection method is implemented.

[0074] Those skilled in the art will understand that Figure 5 The structure shown in the figure is only a block diagram of a part of the structure related to the solution of the present application, and does not constitute a limitation on the computer device to which the solution of the present 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 arrangement of components. In an exemplary embodiment, a computer device is provided, including a memory and a processor, wherein a computer program is stored in the memory, and the processor implements the steps in the above-mentioned method embodiments when executing the computer program.

[0075] 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.

[0076] 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.

[0077] 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 used 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 must comply with relevant regulations.

[0078] Those skilled in the art can understand that all or part of the processes in the above-mentioned embodiment methods can be completed by instructing the relevant hardware through a computer program, and 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-mentioned methods. Among them, any reference to the memory, database or other medium used in the embodiments provided in this application can include at least one of non-volatile and volatile memory. Non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory, optical memory, high-density embedded non-volatile memory, resistive random access memory (ReRAM), magnetoresistive random access memory (MRAM), ferroelectric random access memory (FRAM), phase change memory (PCM), graphene memory, etc. Volatile memory can include random access memory (RAM) or external cache memory, etc. By way of illustration and not limitation, RAM may be in various forms, such as Static Random Access Memory (SRAM) or Dynamic Random Access Memory (DRAM).

[0079] The database involved in each embodiment provided in this application may include at least one of a relational database and a non-relational database. The non-relational database may include a distributed database based on blockchain, etc., but is not limited thereto. The processor involved in each embodiment provided in this application may be a general-purpose processor, a central processing unit, a graphics processor, a digital signal processor, a programmable logic device, a data processing logic device based on quantum computing, etc., but is not limited thereto.

[0080] The technical features of the above embodiments may be arbitrarily combined. To make the description concise, 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, they should be considered to be within the scope of this specification.

[0081] This article uses specific examples to illustrate the principles and implementation methods of this application. The description of the above embodiments is only used to help understand the method and core ideas of this application. At the same time, for those skilled in the art, according to the ideas of this application, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting this 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 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 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; 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.

2. The reservoir rock temperature-strain detection system according to claim 1, characterized in that: The reservoir rock mass temperature-strain detection system further includes a first optical switch and a second optical switch; 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.

3. The reservoir rock temperature-strain detection system according to claim 2, characterized in that: 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.

4. 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.

5. The reservoir rock temperature-strain detection system according to claim 2, 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.

6. 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.

7. 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.

8. 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.

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

10. A reservoir rock mass 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 9; 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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