A downhole temperature and vibration monitoring system and method for oil and gas wells

Abstract

The application belongs to the field of weak grating demodulation, and relates to a system and method for monitoring downhole temperature and vibration of an oil and gas well, comprising a laser emission module, a weak grating array, a CCD module, an interference coupling module and an acquisition module, wherein the laser emission module is used for emitting a pulsed light signal and inputting the pulsed light signal into the weak grating array; the weak grating array is used for generating emitted light; the CCD module is used for receiving a part of reflected light signals and transmitting the reflected light signals to the acquisition module; the interference coupling module is used for receiving another part of the reflected light signals, generating FBG-FP interference signals and transmitting the FBG-FP interference signals to the acquisition module; and the acquisition module is used for obtaining downhole temperature and / or stress characteristics through the reflected light signals and vibration characteristics through the FBG-FP interference signals. The system can simultaneously acquire reflected wave wavelength signals and FBG-FP interference signals, and simultaneously monitor physical quantities such as temperature, stress and vibration.

Description

TECHNICAL FIELD

[0001] The present application relates to a kind of for oil and gas well downhole temperature and vibration monitoring system and method, belong to weak grating demodulation field. BACKGROUND

[0002] Optical fiber sensing technology is a kind of with light wave as carrier, optical fiber as transmission medium, by the change of light wave characteristic parameter caused by outside temperature, stress, vibration etc. Physical quantity is detected, to realize the measurement of these physical quantities. The advantage of ordinary optical fiber grating is fast response, many measurement parameters, the shortcoming is that the scale of sensing network is small, it is difficult to apply long distance, large range sensing system. How to measure multiple physical parameters, long distance, distributed sensing, has been a challenge for optical fiber sensing technology.

[0003] According to research, the lower the reflectivity of fiber grating, the more fiber gratings are needed to multiplex, so as to realize large-scale FBG (Fiber Bragg Grating) sensing network. Weak fiber grating has very weak grating area reflection energy, only one ten thousandth to several ten thousandth of fiber grating, about 6 dB higher than Rayleigh reflection. According to the principle of time division multiplexing, the reflection light return time of each grating in the weak grating array is different, and this principle can be used for positioning each weak grating, and the temperature or stress at the corresponding position can be obtained by demodulation, but this method cannot monitor vibration and other physical quantities.

[0004] When monitoring vibration and other physical quantities, two adjacent FBGs are usually used as reflectors. At this time, FBG can be regarded as an intrinsic wavelength selection characteristic optical fiber end reflector. By selecting a weak grating with appropriate width, a FBG-based Fabry-Perot cavity (FP) can be formed. By demodulating the interference light reflected by FP, the vibration signal at the position can be obtained.

[0005] In the prior art, since the monitoring methods of static physical quantities such as temperature and stress and dynamic physical quantities such as stress are different, different systems need to be set up for monitoring. This is very difficult to achieve in small monitoring spaces such as oil and gas wells, and using different systems for monitoring also increases the monitoring cost and brings inconvenience to the monitoring personnel. SUMMARY

[0006] To solve the above problems, the present application provides a kind of for oil and gas well downhole temperature and vibration monitoring system and method, it can simultaneously collect reflected wave wavelength signal and FBG-FP interference signal, realize the simultaneous monitoring of temperature, stress and vibration and other physical quantities.

[0007] To achieve the above objectives, the present invention proposes the following technical solution: a downhole temperature and vibration monitoring system for oil and gas wells, comprising: a laser emitting module, a weak grating array, a CCD module, an interference coupling module, and a data acquisition module. The laser emitting module is used to emit pulsed light signals and input the pulsed light signals into the weak grating array. The weak grating array is used to reflect the pulsed light signals to generate reflected light signals. The CCD module is used to receive a portion of the reflected light signals and transmit them to the data acquisition module. The interference coupling module is used to receive another portion of the reflected light signals, generate FBG-FP interference signals, and transmit the FBG-FP interference signals to the data acquisition module. The data acquisition module is used to obtain downhole temperature and / or stress characteristics through the reflected light signals and vibration characteristics through the FBG-FP interference signals.

[0008] Furthermore, the laser emitting module includes a broadband light source, a bandpass filter, and a first semiconductor laser amplifier. The broadband light source is used to generate an optical signal; the bandpass filter is used to perform bandpass filtering on the optical signal to generate narrowband light; and the first semiconductor laser amplifier is used to amplify the narrowband light to generate a pulsed optical signal.

[0009] Furthermore, the first semiconductor laser amplifier includes a semiconductor laser and an erbium-doped fiber laser amplifier. The semiconductor laser modulates the light into pulses and performs a first-stage amplification, and then the erbium-doped fiber laser amplifier performs a second-stage amplification.

[0010] Furthermore, the pulsed light signal generated by the laser emission module illuminates the weak grating array through an optical circulator, and the reflected light from the weak grating array enters the second semiconductor laser amplifier through the optical circulator. The second semiconductor laser amplifier is used to amplify the reflected light from the weak grating array in a third stage.

[0011] Furthermore, the reflected light return time τ of the i-th weak grating array is... i The calculation formula is:

[0012] τ i =2n eff L i / c,

[0013] Among them, L i Approximately the distance from the i-th weak grating to the optical circulator, where c is the speed of light, n eff It is the effective refractive index.

[0014] Furthermore, the method for generating the FBG-FP interference signal is as follows: receiving another part of the reflected light signal, which is reflected into four beams after passing through the two arms of the interferometer. When the two arms of the interferometer are matched with the FP cavity length, the two beams that are in the middle in the timing sequence meet on the 3×3 coupler and generate an interference signal.

[0015] Furthermore, the acquisition module includes a detector, an acquisition card, and a host computer. The detector is used to acquire the three interference signals output by the 3×3 coupler. The acquisition card is used to acquire the signals from the detector. The host computer is used to acquire the FBG-FP interference signals and reflected light signals from the detector and the CCD module, and to demodulate the FBG-FP interference signals and the reflected light signals.

[0016] Furthermore, the calculation formula for the three interference signals is as follows:

[0017]

[0018] Where A is the DC quantity parameter, B is the AC quantity amplitude parameter, I1, I2 and I3 are the first, second and third interference signals respectively, and φ(t) is the phase of the optical signal with time.

[0019] Furthermore, the 3×3 coupler connects to several Faraday rotators, which are used to eliminate polarization fading.

[0020] This invention also discloses a method for monitoring downhole temperature and vibration in oil and gas wells, used in the downhole temperature and vibration monitoring system for oil and gas wells as described in any of the preceding claims, comprising the following steps: using a weak grating array as a sensing unit, filtering the reflected signals of the target grating based on the different time intervals of the reflected signals of each weak grating, thereby achieving the positioning of the target grating; irradiating the weak grating array with a pulsed laser to generate emitted light at the position of the target grating; dividing the reflected light into two parts, collecting the first part of the reflected light, and transmitting the collected signal to a host computer for wavelength demodulation to obtain downhole temperature and / or stress characteristics; introducing the other part of the reflected light into an interferometer, the reflected light signal being reflected into four beams after passing through the two arms of the interferometer, and when the two arms of the interferometer are matched with the FP cavity length, the two beams in the middle of the timing sequence meet at the 3×3 coupler and generate three sets of interference signals; collecting the three sets of interference signals through a data acquisition card, and performing phase demodulation on the three sets of interference signals to obtain downhole vibration characteristics.

[0021] The present invention, by adopting the above technical solution, has the following advantages: The weak grating hybrid demodulation method of the present invention, based on the principle of time-division multiplexing, filters the time interval of reflected light to obtain wavelength data. A weak grating of suitable bandwidth and length is selected to construct an FBG-FP sensor. By demodulating the interference signal of its FP cavity, its vibration signal can be obtained. This achieves two uses with a single demodulation device, enabling simultaneous monitoring of physical quantities such as temperature, stress, and vibration, while also improving acquisition efficiency. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of a downhole temperature and vibration monitoring system for oil and gas wells according to an embodiment of the present invention. Detailed Implementation

[0023] To enable those skilled in the art to better understand the technical solutions of the present invention, the present invention is described in detail through specific embodiments. However, it should be understood that the specific embodiments are provided only for a better understanding of the present invention and should not be construed as limiting the present invention. In the description of the present invention, it should be understood that the terminology used is for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0024] To address the problems in existing technologies where different methods are used to monitor static physical quantities such as temperature and stress compared to dynamic physical quantities such as stress, requiring the establishment of different systems for monitoring, which is difficult to implement in operations with limited monitoring space, such as oil and gas wells, and also increases monitoring costs and inconveniences monitoring personnel, this invention proposes a system and method for monitoring downhole temperature and vibration in oil and gas wells. The system includes: measuring the temperature and / or vibration of each weak grating array by demodulating the return time of reflected light from each weak grating array based on the principle of time-division multiplexing; constructing a field-field (FP) segment using two weak gratings, demodulating the interference waveform using an interferometer, and obtaining the vibration signal of that FP segment. This significantly improves the application range and acquisition efficiency of weak grating arrays. The following detailed description of the invention, with reference to the accompanying drawings and embodiments, illustrates the solution in detail.

[0025] Example 1

[0026] This embodiment discloses a downhole temperature and vibration monitoring system for oil and gas wells, such as... Figure 1 As shown, it includes: a laser emission module, a weak grating array, a CCD module, an interference coupling module, and a data acquisition module.

[0027] The laser emitting module is used to emit pulsed light signals and input the pulsed light signals into the weak grating array;

[0028] A weak grating array is used to generate emitted light;

[0029] The CCD module is used to receive a portion of the reflected light signal and transmit it to the acquisition module.

[0030] The interference coupling module is used to receive another part of the reflected light signal, generate FBG-FP interference signal, and transmit the FBG-FP interference signal to the acquisition module;

[0031] The acquisition module is used to obtain downhole temperature and / or stress characteristics by wavelength demodulation of reflected light signals, and to obtain vibration characteristics by demodulation of FBG-FP interferometric signals based on low coherence interference.

[0032] In this embodiment, a single monitoring system can simultaneously monitor static characteristics such as downhole temperature and stress, as well as dynamic characteristics such as vibration in oil and gas wells. The two monitoring and demodulation methods share multiple modules, and the system's measurement parameter ranges are complementary, reducing downhole monitoring costs, avoiding confusion for personnel, and improving data acquisition efficiency. It should be noted that in this embodiment, " / " represents "or," meaning "obtain downhole temperature and / or stress characteristics" should be understood as being able to obtain downhole temperature characteristics, downhole stress characteristics, or both downhole temperature and stress characteristics.

[0033] like Figure 1 As shown, the laser emission module includes a broadband light source ASE, a bandpass filter, and a first semiconductor laser amplifier.

[0034] Broadband light source ASE is used to generate optical signals;

[0035] A bandpass filter is used to filter optical signals to generate narrowband light.

[0036] The first semiconductor laser amplifier is used to amplify narrowband light to generate pulsed light signals. The first semiconductor laser amplifier includes a semiconductor laser (SOA) and an erbium-doped fiber laser amplifier (EDFA). The light is modulated into pulses by the SOA and undergoes a first-stage amplification. Then, it undergoes a second-stage amplification by the EDFA, becoming a typical pulsed light source.

[0037] Wavelength demodulation is based on time-division multiplexing technology, using weak fiber gratings as sensing units. Based on the different time intervals of the reflected signals from each weak grating, an optical switch is used to filter the reflected signals of the target grating, thereby achieving the location of the target grating. The return time τ of the reflected light from the i-th weak grating in the weak grating array is... i The calculation formula is:

[0038] τ i =2n eff L i / c,

[0039] Among them, Li Approximately the distance from the i-th weak grating to the optical circulator, where c is the speed of light, n eff It is the effective refractive index.

[0040] The typical pulsed light signal generated by the laser emission module illuminates a weak grating array through an optical circulator. The weak grating array reflects a series of pulsed light back. The reflected light from the weak grating array passes through the optical circulator and enters a 2×2 coupler for coupling. The coupled reflected light then enters a second semiconductor laser amplifier, which performs a third-stage amplification of the reflected light from the weak grating array. The amplified reflected light then enters a CCD module, which transmits the acquired signal to the host computer of the acquisition module for wavelength demodulation.

[0041] By detecting the interference signal between two adjacent broadband weak gratings using a matched interferometer, dynamic physical quantities such as vibrations can be measured. The two adjacent weak gratings are considered as mirrors, forming a fiber optic grating Fabry-Perot (FP) sensor as the sensing unit. Demodulation is based on low-coherence interference. In the weak grating array, the light reflected by adjacent FBGs is reflected back at different times, and their optical path difference is much greater than the coherence of the light source. Therefore, a Michelson interferometer is used to reduce the optical path difference of the reflected light from adjacent FBGs. When the difference between the two arms of the interferometer matches the spacing between the two adjacent gratings, the two beams of light in the middle of the time sequence meet in the coupler and produce interference. Specifically, the pulsed light signal enters the weak grating array through an optical circulator, the reflected light enters the interferometer to generate an interference signal, and another part of the reflected light signal is received. The reflected light signal is reflected into four beams after passing through the two arms of the interferometer. When the two arms of the interferometer match the FP cavity length, the two beams of light in the middle of the time sequence meet on the 3×3 coupler and generate an interference signal. The interference signal consists of three channels, which are acquired by detectors in the acquisition module. After conversion, the signals are acquired by the acquisition card, converted into voltage signals, and transmitted to the host computer in the acquisition module for processing.

[0042] In this embodiment, each detector corresponds to a set of interference signals, that is, there are 3 detectors.

[0043] The interference signal is demodulated using a 3×3 fiber optic coupler demodulation technique. The 3×3 coupler acts as a power divider and also ensures a 120° phase difference between each output signal. Three detectors detect the three output signals of the 3×3 coupler, respectively. The three interference signals are represented as follows:

[0044]

[0045] Where A is the DC quantity parameter, B is the AC quantity amplitude parameter, I1, I2 and I3 are the first, second and third interference signals respectively, and φ(t) is the phase of the optical signal with time.

[0046] The 3×3 coupler is also connected to several Faraday rotator mirrors, such as... Figure 1 As shown, in this embodiment, the preferred number of Faraday rotator mirrors is two, but this is not a limitation. The function of the Faraday rotator mirrors is to eliminate polarization fading.

[0047] To ensure a clear interference spectrum, the weak grating bandwidth selected for FBG-FP should be as wide as possible. A wider bandwidth provides better tolerance for spectral mismatch, avoiding the impact of spectral drift caused by perturbations on the visibility of interference fringes. However, excessively wide bandwidth can affect the coherence of reflected light; therefore, a suitable bandwidth should be selected while maintaining clear interference fringes. In this embodiment, a preferred weak grating length of 500 μm and a 3dB bandwidth of 1.6 nm are preferred, but these values ​​are merely preferred embodiments of this scheme and are not limiting.

[0048] In addition to ensuring that the coherence length of the light source is greater than the optical path difference between the reflected light from the two gratings, the vibration directions (polarization states) of the two reflected light beams must also be consistent. Due to manufacturing defects and external factors, ordinary single-mode optical fibers can cause birefringence during propagation, leading to random changes in the polarization state. The interference fringes are most ideal when the polarization states of the two beams are consistent; when the polarization states are perpendicular, the contrast of the interference fringes is 0, which is called polarization-induced signal fading.

[0049] The acquisition module includes a detector, an acquisition card, and a host computer. The detector is used to acquire the three interference signals output by the 3×3 coupler. The acquisition card is used to acquire the signals from the detector. The host computer is used to acquire the FBG-FP interference signals and reflected light signals from the detector and CCD module, and to demodulate the FBG-FP interference signals and reflected light signals.

[0050] In this embodiment, the host computer includes an FPGA delay module, which is used to control the timing of generating and acquiring optical signals. It generates two pulse signals, one of which drives the semiconductor laser SOA, and the other pulse signal triggers the acquisition card to acquire the signal.

[0051] In this embodiment, the common parts of the two demodulation methods are integrated to form a complete system that simultaneously performs wavelength demodulation and low-coherence interferometric demodulation. This system fully utilizes the sensing characteristics of weak grating arrays, using weak gratings as sensing units to realize a quasi-distributed sensing network for static parameter measurement. Simultaneously, it utilizes FBG-FP sensing units to realize an interferometric distributed sensing network for dynamic parameter measurement. The system in this embodiment has advantages such as low cost and simple structure, and has excellent prospects for engineering applications.

[0052] Example 2

[0053] Based on the same inventive concept, this embodiment discloses a method for monitoring downhole temperature and vibration in oil and gas wells, used in any of the above-mentioned downhole temperature and vibration monitoring systems for oil and gas wells, comprising the following steps:

[0054] S1 uses a weak grating array as a sensing unit. Based on the different time intervals of the reflection signals of each weak grating, it filters the reflection signals of the target grating, thereby achieving the positioning of the target grating.

[0055] S2 generates emitted light at the target grating position by irradiating the weak grating array with a pulsed laser;

[0056] S3 splits the reflected light into two parts, collects the first part of the reflected light, and transmits the collected signal to the host computer for wavelength demodulation to obtain downhole temperature and / or stress characteristics;

[0057] S4 introduces another reflected light into the interferometer. The reflected light signal is reflected into four beams after passing through the two arms of the interferometer. When the two arms of the interferometer are matched with the length of the FP cavity, the two beams that are in the middle in terms of timing meet on the 3×3 coupler and generate three sets of interference signals.

[0058] The S5 acquires three sets of interference signals through a data acquisition card and performs phase demodulation on the three sets of interference signals to obtain the downhole vibration characteristics.

[0059] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific embodiments of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the protection scope of the claims of the present invention. The above content is only a specific embodiment of this application, but the protection scope of this application is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be covered within the protection scope of this application. Therefore, the protection scope of this application should be determined by the protection scope of the claims.

Claims

1. A method for monitoring downhole temperature and vibration in oil and gas wells, characterized in that, This is used in a downhole temperature and vibration monitoring system for oil and gas wells. The downhole temperature and vibration monitoring system includes: a laser emission module, a weak grating array, a CCD module, an interferometric coupling module, and a data acquisition module. The laser emitting module is used to emit pulsed light signals and input the pulsed light signals into the weak grating array; The weak grating array is used to reflect pulsed light signals to generate reflected light signals; The CCD module is used to receive a portion of the reflected light signal and transmit it to the acquisition module; The interference coupling module is used to receive another part of the reflected light signal, generate an FBG-FP interference signal, and transmit the FBG-FP interference signal to the acquisition module; The acquisition module is used to obtain the downhole temperature through the reflected light signal and to obtain the vibration characteristics through the FBG-FP interference signal; The reflected light return time τ of the i-th weak grating array is... i The calculation formula is: τ i =2n eff L i / c, Among them, L i Approximately the distance from the i-th weak grating to the optical circulator, where c is the speed of light, n eff It is the effective refractive index; The method for generating the FBG-FP interference signal is as follows: receiving another part of the reflected light signal, which is reflected into four beams after passing through the two arms of the interferometer. When the two arms of the interferometer are matched with the FP cavity length, the two beams that are in the middle in the timing sequence meet on the 3×3 coupler and generate an interference signal. The method for monitoring downhole temperature and vibration in oil and gas wells includes the following steps: Using a weak grating array as the sensing unit, the reflected signal of the target grating is filtered according to the different time intervals of the reflected signals of each weak grating, thereby realizing the positioning of the target grating; The weak grating array is irradiated with a pulsed laser to generate emitted light at the target grating location; The reflected light is divided into two parts. The first part of the reflected light is collected, and the collected signal is transmitted to the host computer for wavelength demodulation to obtain the downhole temperature characteristics. Another reflected light is introduced into the interferometer. The reflected light signal is reflected into four beams after passing through the two arms of the interferometer. When the two arms of the interferometer are matched with the length of the FP cavity, the two beams that are in the middle in terms of timing meet on the 3×3 coupler and generate three sets of interference signals. The three sets of interference signals are acquired by a data acquisition card, and the phase demodulation of the three sets of interference signals is performed to obtain the downhole vibration characteristics.

2. The method for monitoring downhole temperature and vibration in oil and gas wells as described in claim 1, characterized in that, The laser emitting module includes a broadband light source, a bandpass filter, and a first semiconductor laser amplifier. The broadband light source is used to generate optical signals; The bandpass filter is used to perform bandpass filtering on the optical signal to generate narrowband light; The first semiconductor laser amplifier is used to amplify the narrowband light to generate a pulsed light signal.

3. The method for monitoring downhole temperature and vibration in oil and gas wells as described in claim 2, characterized in that, The first semiconductor laser amplifier includes a semiconductor laser and an erbium-doped fiber laser amplifier. The semiconductor laser modulates the light into pulses and amplifies it in the first stage, and then the erbium-doped fiber laser amplifier amplifies it in the second stage.

4. The method for monitoring downhole temperature and vibration in oil and gas wells as described in claim 3, characterized in that, The pulsed light signal generated by the laser emitting module illuminates the weak grating array through an optical circulator. The reflected light from the weak grating array enters the second semiconductor laser amplifier through the optical circulator. The second semiconductor laser amplifier is used to amplify the reflected light from the weak grating array in a third stage.

5. The method for monitoring downhole temperature and vibration in oil and gas wells as described in claim 1, characterized in that, The acquisition module includes a detector, an acquisition card, and a host computer. The detector is used to acquire the three interference signals output by the 3×3 coupler, and the acquisition card is used to acquire the signals from the detector.

6. The method for monitoring downhole temperature and vibration in oil and gas wells as described in claim 5, characterized in that, The calculation formula for the three interference signals is as follows: Where A is the DC quantity parameter and B is the AC quantity amplitude parameter. , and These are the first, second, and third interference signals, respectively. It is the phase of the optical signal over time.

7. The method for monitoring downhole temperature and vibration in oil and gas wells as described in claim 5, characterized in that, The 3×3 coupler connects to several Faraday rotating mirrors, which are used to eliminate polarization fading.

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