Measuring system and measuring method of fluorescence type optical fiber high-temperature pressure gauge

Abstract

The invention discloses a measuring system and a measuring method of a fluorescence type optical fiber high-temperature pressure gauge. The measuring system comprises an optical fiber high-temperature pressure gauge, a demodulation host and a transmission optical cable, wherein the optical fiber high-temperature pressure gauge is used for collecting underground pressure and temperature; the demodulation host is used for outputting pulse pump light to the optical fiber high-temperature pressure gauge and receiving feedback signals; the demodulation host divides the signal into two identical paths, one path is transmitted to an underground optical fiber high-temperature pressure gauge, the other path is transmitted to the interference demodulation module and the temperature demodulation module, and a pressure value is obtained by simulating the change of the arm length difference between the interference optical cavity and the interference optical cavity of the optical fiber high-temperature pressure gauge; and a temperature value is obtained by comparing the fluorescence lifetime curve of the temperature demodulation module with the received fluorescence lifetime curve of the optical fiber high-temperature pressure gauge. According to the invention, temperature measurement and pressure measurement are simultaneously carried out in an underground high-temperature environment by using a fluorescence effect, and the stress surface of the optical fiber high-temperature pressure gauge under high pressure is directly used as a reflecting surface, so that the risk that an optical fiber grating is easy to fall off or break in the prior art is overcome.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of optical fiber sensors, and particularly relates to a measurement system and a measurement method based on an optical fiber high-temperature pressure gauge. BACKGROUND

[0002] In the exploration and development process of oil and coal bed gas, such as drilling, well completion and production, the downhole pressure needs to be detected, especially in the production process. In the current oil well pressure detection market, the downhole pressure is generally measured by using an electrically measured high-temperature pressure gauge. However, the traditional electrically measured high-temperature pressure gauge is prone to cause static electricity in the measurement system, and even ionization effect under the action of a strong electric field, which causes electric spark and has a safety hazard. In addition, the traditional electrically measured high-temperature pressure gauge is easily affected by environmental noise and electromagnetic interference in the signal amplification process, and the measured data result is insufficient in measurement accuracy and unstable in data transmission.

[0003] The optical fiber high-temperature pressure gauge is different from the traditional electrically measured high-temperature pressure gauge, and can work in a high-temperature and high-pressure environment for a long time. The optical fiber high-temperature pressure gauge generally uses the modulation principle of light. When the external pressure acts on the optical fiber, the phase, intensity and frequency of the modulated light transmitted in the optical fiber change. By using the basic interference principle and the light signal detection and conversion system, the relationship between the changes of the phase, intensity and frequency and the external pressure can be measured. Since the optical fiber itself is resistant to high temperature, it is feasible to make a high-temperature pressure gauge.

[0004] Many products of the optical fiber high-temperature pressure gauge currently adopt the optical fiber grating structure. The high-temperature pressure gauge with the optical fiber grating structure is simple in structure, easy to prepare successfully, and simple in demodulation signal. However, it still has the following disadvantages: 1) the cost of the demodulation equipment is relatively high; 2) in the high-temperature and high-pressure detection environment, the optical fiber is subjected to tension for a long time, and the optical fiber is prone to aging and fatigue, and the optical fiber is easily broken after a long working time. In the whole downhole optical fiber high-temperature pressure measurement system, the optical fiber high-temperature pressure gauge becomes a key research, and therefore a low-cost and efficient solution is urgently needed for measurement in the harsh environment of high temperature and high pressure. SUMMARY

[0005] In the following, a brief summary of embodiments of the present application is given in order to provide a basic understanding of some aspects of the present application. It should be understood that the following summary is not a comprehensive summary of the present application. It is not intended to determine the key or important parts of the present application, nor to limit the scope of the present application. Its purpose is only to give some concepts in a simplified form as a prelude to the more detailed description discussed later.

[0006] In order to solve the technical problems proposed in the background section, the purpose of the present application is to provide a fluorescence type optical fiber high temperature pressure gauge which can measure both high temperature and high pressure, a measurement system comprising the fluorescence type high temperature pressure gauge and a testing method to solve the above technical problems.

[0007] According to one aspect of the present application, a measurement system of a fluorescence type optical fiber high temperature pressure gauge is provided, comprising an optical fiber high temperature pressure gauge for collecting downhole pressure and temperature, a demodulation host for outputting pulsed pump light to the optical fiber high temperature pressure gauge and receiving a feedback signal, and a transmission optical cable for connecting the optical fiber high temperature pressure gauge and the demodulation host; wherein the optical fiber high temperature pressure gauge comprises a temperature measurement part and a pressure measurement part, the demodulation host comprises a pump laser generating device for outputting pulsed pump light to the optical fiber high temperature pressure gauge, an interference demodulation module for simulating an interference optical cavity, and a temperature demodulation module for obtaining a fluorescence lifetime curve, the simulated interference optical cavity of the interference demodulation module has the same configuration as the interference optical cavity of the pressure measurement part of the optical fiber high temperature pressure gauge (which can have the same parameters or be proportionally configured parameters), and the temperature demodulation module has the same gain medium as the temperature measurement part of the optical fiber high temperature pressure gauge; the pump laser generating device of the demodulation host divides the signal into two identical paths, one of which is transmitted to the optical fiber high temperature pressure gauge downhole, and the other of which is transmitted to the interference demodulation module and the temperature demodulation module, the downhole pressure value is demodulated by simulating the arm length difference of the interference optical cavity and the interference optical cavity of the optical fiber high temperature pressure gauge, and the downhole temperature value is obtained by comparing the fluorescence lifetime curve of the temperature demodulation module with the received fluorescence lifetime curve of the optical fiber high temperature pressure gauge.

[0008] As a further scheme, the optical fiber high temperature pressure gauge comprises a fiber collimator and a pump optical gain medium for temperature measurement, and an optical interference high pressure detection module for pressure measurement, one end of the fiber collimator is connected with the pump optical gain medium and the optical interference high pressure detection module in sequence, and the other end of the fiber collimator is connected with the transmission optical cable and the demodulation host in sequence; the optical interference arm length difference of the optical interference high pressure detection module has a linear relationship with the external pressure, when the external pressure acts on the optical interference high pressure detection module, the optical interference arm length difference changes, and the external pressure value is demodulated by comparison through the simulated interference optical cavity of the demodulation host; the pump optical gain medium generates a spontaneous radiation fluorescence effect after the pulsed pump light input through the transmission optical cable, and the temperature value is calculated by comparing the received fluorescence lifetime curve with the preset fluorescence lifetime curve through the temperature demodulation module of the demodulation host; the input light source of the optical interference high pressure detection module is a fluorescence broadband light source generated after the pulsed pump light passes through the pump optical gain medium.

[0009] The optical fiber high temperature pressure gauge is a fluorescent optical fiber high temperature pressure gauge capable of measuring high temperature and high pressure. The current optical fiber high temperature pressure gauge can only collect downhole pressure, and if temperature needs to be measured, another set of temperature measurement system is required. The application can realize synchronous temperature collection through the specially designed optical fiber high temperature pressure gauge and the cooperating demodulation host, thereby greatly reducing the cost of the temperature and pressure measurement demodulation system.

[0010] The optical interference high pressure detection module for pressure measurement is located at the end face or side face of the optical fiber high temperature pressure gauge. The end face or side face of the optical fiber high temperature pressure gauge is affected by external pressure, so that the signal arm length of the optical interference detection part changes. The optical interference of the optical interference high pressure detection module can be F-P interference, Michelson interference, or Mach-Zehnder interference. The arm length difference of the optical interference is designed to be small, that is, the signal arm and the reference arm of the optical interference are approximately equal. In the design of the high temperature pressure gauge detection part, the light source input into the optical interference high pressure detection module is a fluorescent broadband light source generated by the gain medium after pulsed pumping. Here, the fluorescent spectrum generated by the spontaneous emission is a broadband laser. When the optical path difference of the optical interference high pressure detection module is equal to the optical path difference of the analog interference cavity in the wavelength demodulation module in the demodulation host, the light intensity value will change greatly, and the arm length difference of the optical interference high pressure detection module and the external pressure are linearly related. When the external pressure acts on the optical interference high pressure detection module, the arm length difference of the optical interference changes, and the comparison is made through the analog interference optical cavity in the interference demodulation module, so that the external pressure value can be demodulated.

[0011] The above transmission optical cable, optical fiber collimator, and pump optical gain medium mainly function to measure the temperature of the environment and output the fluorescent broadband light source of the optical interference high pressure detection module. The main principle of measuring the temperature is that when the pulsed pumping light input through the optical fiber transmission part passes through the pump optical gain medium, the fluorescent effect of spontaneous emission is generated, and the fluorescent lifetime is related to the temperature of the environment. When the environmental temperature is relatively high, the fluorescent lifetime is very short, and when the environmental temperature is relatively low, the fluorescent lifetime is relatively long. The temperature demodulation module also has the same gain medium material and generates fluorescence. The fluorescent lifetime curve in the demodulation module and the fluorescent lifetime curve of the downhole optical fiber high temperature pressure gauge are compared, and finally the downhole temperature is calculated.

[0012] As a specific example, the optical fiber high temperature pressure gauge includes a shell, a high temperature optical fiber, a high temperature optical fiber collimator, an optical fiber collimator seal, a first optical gain medium, and a F-P interference cavity. The shell seals the high temperature optical fiber collimator, the first optical gain medium, and the F-P interference cavity through the optical fiber collimator seal, and the end face of the optical fiber high temperature pressure gauge is the stress face of the F-P interference cavity. The shell is preferably a metal shell.

[0013] As a specific example, the demodulation host comprises a broadband filter, a first coupler, a second coupler, a third coupler, a pulse pump generator, a fluorescence time-domain signal acquisition module, and a fluorescence wavelength demodulation module. The fluorescence time-domain signal acquisition module comprises a second optical fiber collimator, a second optical gain medium, a first photoelectric conversion module, a second photoelectric conversion module, and a signal acquisition processing module. The fluorescence wavelength demodulation module comprises a third optical fiber collimator, an analog optical interference cavity, a PZT piezoelectric ceramic, a third photoelectric conversion module, and a dual-channel signal acquisition module. The broadband filter, the first coupler, and the pulse pump generator are sequentially connected. The first coupler and the second coupler are connected to each other. The second optical gain medium, the second optical fiber collimator, the second coupler, and the first photoelectric conversion module are sequentially connected. The broadband filter, the third coupler, and the second photoelectric conversion module are sequentially connected. The first photoelectric conversion module and the second photoelectric conversion module are connected to the signal acquisition processing module. The third coupler is further connected to the third optical fiber collimator and the third photoelectric conversion module, respectively. The third optical fiber collimator is connected to the analog optical interference cavity and the PZT piezoelectric ceramic. The third photoelectric conversion module is connected to the dual-channel signal acquisition module. Pump light of the pulse pump generator is split into one path through the first coupler to the fiber high-temperature pressure gauge and another path through the first coupler and the second coupler to the second optical fiber collimator and the second optical gain medium to generate fluorescence. The generated fluorescence is converted into an electrical signal through the first photoelectric conversion module. The two paths of fluorescence are calculated by analogy, and the lifetime of the returned fluorescence of the fiber high-temperature pressure gauge is finally obtained. Pump light of the pulse pump generator is split into one path through the first coupler to the Fabry-Perot interference cavity of the fiber high-temperature pressure gauge to form broadband light of fluorescence interference fringes. The broadband light is returned through the fiber transmission cable, enters the fluorescence wavelength demodulation module through the broadband filter, and is returned to the interference light through the third optical fiber collimator and the analog optical interference cavity. The length of the interference cavity after the Fabry-Perot interference cavity is subjected to pressure is measured through the PZT piezoelectric ceramic, so that the external pressure is obtained.

[0014] The second optical gain medium has the same size and material as the first optical gain medium.

[0015] According to another aspect of the present application, a measurement method of a fluorescence type fiber high-temperature pressure gauge is provided, which comprises: The installation step is to fix the fluorescence type fiber high-temperature pressure gauge to the downhole end of the transmission optical cable. Then, the other end of the transmission optical cable is connected to the fluorescence type fiber high-temperature pressure gauge demodulation host. The specific process is as follows: the fiber high-temperature pressure gauge is fixed to the bottom end of the transmission optical cable (or logging optical cable) of the logging. After installation, the stress surface of the fiber high-temperature pressure gauge is in contact with the outside world, or an oil bladder is used for oil sealing. The optical fiber at the input end of the fiber high-temperature pressure gauge is connected to the transmission optical cable. At the same time, the connection between the fiber high-temperature pressure gauge and the end of the transmission optical cable downhole and the shell of the fiber high-temperature pressure gauge are sealed in a metal pipe. The transmission optical cable at the wellhead is connected to the demodulation host. The pressure measurement step is that the demodulation host outputs pulse pump light through a transmission optical cable into an optical fiber, and finally into a pump optical gain medium, so as to generate fluorescence; the fluorescence is output to an optical interference high-pressure detection module, and then returned to the demodulation host at the wellhead through the transmission optical cable; the downhole pressure value is obtained by the change of the arm length difference between the analog interference cavity and the interference cavity of the optical fiber high-temperature pressure gauge. The temperature measurement step is that the demodulation host divides the optical signal into two parts, one part measures the fluorescence lifetime of the returned optical signal, and the other part measures the interference fringes of the returned optical signal; when the optical fiber high-temperature pressure gauge is affected by the ambient temperature, the returned fluorescence lifetime will change, the higher the temperature, the shorter the fluorescence lifetime, and the lower the temperature, the longer the fluorescence lifetime; when the pulse output pump light is input to the gain medium, the optical power of the pulse pump light is enough to saturate the output of the fluorescence of the gain medium; when the gain medium is not pumped, the fluorescence will continue to output and then rapidly decay, and the decay time is related to the ambient temperature; the gain medium in the demodulation host and the gain medium of the optical fiber high-temperature pressure gauge are measured by using the pulse signal as a trigger signal after multiple accumulations, and the temperature value of the optical fiber high-temperature pressure gauge can be obtained by comparison and calculation.

[0016] Here, the fluorescence spectrum generated by spontaneous radiation is a broadband laser, and when the optical path difference of the optical interference high-pressure detection module is equal to the optical path difference of the analog interference cavity in the wavelength demodulation module in the demodulation host, the optical intensity value will change greatly, and the interference arm length difference of the optical interference high-pressure detection module is linearly related to the external pressure.

[0017] During measurement, the pulse pump laser generating device in the demodulation host outputs through the optical fiber coupler, the returned signal is also input to the fluorescence time domain signal acquisition module through the optical fiber coupler, and data processing is performed in the fluorescence wavelength demodulation module. The fluorescence time domain signal acquisition module finally outputs the environmental temperature of the optical fiber high-temperature pressure gauge; and the fluorescence wavelength demodulation module outputs the pressure information of the environment of the optical fiber high-temperature pressure gauge. The present application adopts the above technical scheme, measures the returned fluorescence lifetime through the fluorescence time domain module in the demodulation host, and after data processing, the temperature information of the downhole detection point can be obtained; detects the returned fluorescence interference spectrum through the fluorescence wavelength demodulation module in the demodulation host, and after data processing, the pressure information of the downhole detection point can be obtained. Compared with the prior art, the present application has the following advantages: (1) The fluorescence effect is used to measure the temperature of the downhole high-temperature environment. The demodulation host outputs pump light to the gain medium in the downhole, and the fluorescence generated by the gain medium returns to the demodulation host, so as to measure the lifetime of the fluorescence.

[0018] (2) The fluorescence effect is used to measure the downhole pressure. The fluorescence is input to the light interference high pressure detection module as a broadband light source, and the returned interference light signal reflects the interference arm length difference of the light interference detection part through the interference fringes on the spectrum, and the interference arm length difference is related to the external pressure.

[0019] (3) After the light transmission of the single-mode optical fiber, the real-time temperature and pressure of the downhole can be monitored at a remote location. At the same time, the temperature and pressure are measured remotely, and the fluorescence optical fiber high temperature and pressure gauge does not need to be provided with a power supply.

[0020] (4) The stress surface under high pressure directly serves as a reflection surface. Unlike the optical fiber grating, the optical fiber of the optical fiber grating is in contact with the stress surface, thereby there is a certain risk, that is, the optical fiber grating and the stress surface fall off, or the optical fiber grating is broken under the condition of long-term tension. The light interference high pressure detection module of the fluorescence optical fiber high temperature and pressure gauge reflects the light directly on the stress surface, so there is no risk like the optical fiber grating.

[0021] (5) By adjusting the interference arm length difference of the light interference cavity in the demodulation module, the interference arm length difference is within the range of the arm length difference variation of the light interference high pressure detection module of the optical fiber high temperature and pressure gauge, so that the light output intensity value returned by the fluorescence is within the measurable range.

[0022] (6) The temperature change information measured by the fluorescence optical fiber high temperature and pressure gauge is embodied by the change of the fluorescence lifetime, and the pressure change information is embodied by the change of the fluorescence interference spectrum. The fluorescence lifetime change and the fluorescence interference spectrum can be signal accumulated through multiple pulses, so that the signal-to-noise ratio is large. The laser carrying temperature information and pressure information can be returned to the remote signal processing equipment through the transmission optical fiber for data calculation. BRIEF DESCRIPTION OF DRAWINGS

[0023] The present application can be better understood by reference to the following description taken in connection with the accompanying drawings, in which like reference numerals refer to like elements or parts in the several figures. The drawings, together with the following detailed description, include in the specification and form a part thereof, and serve to further illustrate preferred embodiments of the present application and to explain the principles and advantages of the present application. In the drawings: Figure 1 It is a schematic diagram of the measurement system based on the optical fiber high temperature and pressure gauge of the present application; Figure 2 It is a schematic diagram of the overall structure of the measurement system based on the optical fiber high temperature and pressure gauge in the embodiment of the present application; Figure 3 It is a schematic diagram of the triangular wave signal of the PZT piezoelectric ceramic changing the optical cavity length by spectrum demodulation in the embodiment of the present application; Figure 4A schematic diagram of a fluorescence characteristic curve in an embodiment of the present application; In the figure: 1, high-temperature optical fiber; 2, optical fiber collimator seal; 3, housing (housing of the optical fiber high-temperature pressure gauge); 4, high-temperature optical fiber collimator; 5, first optical gain medium; 6, Fabry-Perot interference cavity (for stress detection); 100, optical fiber high-temperature pressure gauge; 8, transmission optical cable (logging high-temperature optical cable); 9, broadband filter; 10, first coupler, 101, second coupler, 102, third coupler, 11, pulse pump generator; 12, second optical fiber collimator; 13, optical gain medium (same size and material as 5); 14, first photoelectric conversion module; 15, second photoelectric conversion module; 16, signal acquisition and processing module; 210, fluorescence time-domain signal acquisition module; 18, third optical fiber collimator; 19, analog optical interference cavity; 20, PZT piezoelectric ceramic; 21, third photoelectric conversion module; 22, dual-channel signal acquisition module; 220, fluorescence wavelength demodulation module; 200, demodulation host. DETAILED DESCRIPTION

[0024] Embodiments of the present application will be described below with reference to the accompanying drawings. The elements and features described in one drawing or one embodiment of the present application can be combined with the elements and features shown in one or more other drawings or embodiments. It should be noted that, for the purpose of clarity, the representations and descriptions of components and processes unrelated to the present application and known to those of ordinary skill in the art are omitted from the drawings and the description.

[0025] In the description of the present application, it should be understood that the terms "first", "second", "third" are used only for the purpose of description, and cannot be understood as indicating or implying relative importance. In addition, unless otherwise explicitly specified and limited, the terms "mounting", "connection", "connection" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or integrally connected; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium, or it can be the communication inside two elements. For those of ordinary skill in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0026] The present application provides a fluorescence type optical fiber high-temperature pressure gauge measurement system and a measurement method, as shown in Figure 1The measurement system comprises a fiber-optic high-temperature pressure gauge, a demodulation host, and a transmission optical cable for connecting the fiber-optic high-temperature pressure gauge and the demodulation host; wherein the fiber-optic high-temperature pressure gauge comprises a temperature measurement part and a pressure measurement part, the demodulation host comprises a pump laser generating device for outputting pulsed pump light to the fiber-optic high-temperature pressure gauge, an interference demodulation module for simulating an interference optical cavity, and a temperature demodulation module for obtaining a fluorescence lifetime curve, the interference demodulation module has the same configuration as the interference optical cavity of the pressure measurement part of the fiber-optic high-temperature pressure gauge, and the temperature demodulation module has the same gain medium as the temperature measurement part of the fiber-optic high-temperature pressure gauge; the pump laser generating device of the demodulation host divides the signal into two equal parts, one part is transmitted to the fiber-optic high-temperature pressure gauge underground, and the other part is transmitted to the interference demodulation module and the temperature demodulation module, the demodulation of the downhole pressure value is realized by the change of the arm length difference between the simulated interference optical cavity and the interference optical cavity of the fiber-optic high-temperature pressure gauge, and the downhole temperature value is obtained by comparing the fluorescence lifetime curve of the temperature demodulation module with the fluorescence lifetime curve received by the fiber-optic high-temperature pressure gauge.

[0027] The fiber-optic high-temperature pressure gauge comprises a fiber collimator and a pump optical gain medium for temperature measurement, and an optical interference high-pressure detection module for pressure measurement, one end of the fiber collimator is connected with the pump optical gain medium and the optical interference high-pressure detection module in sequence, and the other end of the fiber collimator is connected with the transmission optical cable and the demodulation host in sequence; the optical interference arm length difference of the optical interference high-pressure detection module has a linear relationship with the external pressure, when the external pressure acts on the optical interference high-pressure detection module, the optical interference arm length difference changes, and the external pressure value is demodulated by comparison through the simulated interference optical cavity of the demodulation host; the pump optical gain medium generates a fluorescence effect of spontaneous radiation after pulsed pump light input through the transmission optical cable, and the temperature demodulation module of the demodulation host calculates the temperature value by comparing the received fluorescence lifetime curve with the preset fluorescence lifetime curve; the input light source of the optical interference high-pressure detection module is a fluorescence broadband light source generated after pulsed pump light passes through the pump optical gain medium.

[0028] Embodiment 1 As a specific implementation scheme, as Figure 2As shown in the middle part structure, the embodiment provides a measurement system based on fiber high temperature pressure gauge, which comprises 1, high temperature fiber; 2, fiber collimator seal; 3, shell (shell of fiber high temperature pressure gauge); 4, high temperature fiber collimator; 5, first optical gain medium; 6, (stress detection) Fabry-Perot interference cavity; 8, transmission cable (logging high temperature optical cable); 9, wideband filter; 10, first coupler, 101, second coupler, 102, third coupler, 11, pulse pump generator; 12, second fiber collimator; 13, optical gain medium (same size and material as 5); 14, first photoelectric conversion module; 15, second photoelectric conversion module; 16, signal acquisition and processing module; 18, third fiber collimator; 19, analog optical interference cavity; 20, PZT piezoelectric ceramic; 21, third photoelectric conversion module; 22, double-channel signal acquisition module; 200, demodulation host.

[0029] The fiber high temperature pressure gauge 100 mainly comprises high temperature fiber 1, fiber collimator seal 2, shell 3, high temperature fiber collimator 4, optical gain medium 5 and Fabry-Perot interference cavity 6. The shell 3 and the fiber collimator seal 2 seal the high temperature fiber collimator 4, the optical gain medium 5 and the Fabry-Perot interference cavity 6. The end face of the fiber high temperature pressure gauge 100 is the stress surface of the Fabry-Perot interference cavity 6.

[0030] The demodulation host 200 mainly comprises a pump laser generating device, a fluorescence time domain signal acquisition module 210 and a fluorescence wavelength demodulation module 220. The pump laser generating device comprises a wideband filter 9, a first coupler 10 and a pulse pump generator 11. The fluorescence time domain signal acquisition module 210 comprises a second fiber collimator 12, a second optical gain medium 13 (same size and material as the first optical gain medium 5), two photoelectric conversion modules (a first photoelectric conversion module 14 and a second photoelectric conversion module 15) and a signal acquisition and processing module 16. The fluorescence wavelength demodulation module 220 mainly comprises a third fiber collimator 18, an analog optical interference cavity 19, a PZT piezoelectric ceramic 20, a third photoelectric conversion module 21 and a double-channel signal acquisition module 22. The connection relationship is shown in the figure. The filter, the first coupler and the pulse pump generator are connected in sequence, the first coupler and the second coupler are connected with each other, the second optical gain medium, the second fiber collimator, the second coupler and the first photoelectric conversion module are connected in sequence, the wideband filter, the third coupler and the second photoelectric conversion module are connected in sequence, the first photoelectric conversion module and the second photoelectric conversion module are connected with the signal acquisition and processing module, the third coupler is further connected with the third fiber collimator and the third photoelectric conversion module respectively, the third fiber collimator is connected with the analog optical interference cavity and the PZT piezoelectric ceramic, and the third photoelectric conversion module is connected with the double-channel signal acquisition module. The interference demodulation module and the temperature demodulation module are realized by the fluorescence time domain signal acquisition module 210 and the fluorescence wavelength demodulation module 220.

[0031] The pump laser generating device outputs pulsed pump light to the high-temperature optical fiber. When the pulsed pump light is input to the pump gain medium, the gain medium generates fluorescence, which returns to the fluorescence time domain signal acquisition module. By measuring the fluorescence lifetime, the ambient temperature can be calculated. Meanwhile, the fluorescence is a broadband laser. When the broadband laser is input to the optical interference detection high-pressure part, the returned fluorescence is input to the fluorescence wavelength demodulation module. The arm length difference of the demodulated optical interference signal is obtained, thereby obtaining the change of the external pressure.

[0032] The optical fiber high-temperature pressure gauge 100 is connected with one end of the transmission optical cable 8 together and placed into the well. At the wellhead, the other end of the transmission optical cable 8 is connected with the output of the broadband filter 9 of the demodulation host 200 together.

[0033] The pulsed pump light generator 11 of the demodulation host 200 emits pulsed pump laser. The pump laser passes through the broadband first coupler 10 of the demodulation host 200, the broadband filter 9, the transmission optical cable 8, the high-temperature optical fiber 1 in the optical fiber high-temperature pressure gauge 100, the high-temperature optical fiber collimator 4 and the optical gain medium 5 in turn.

[0034] After the pulsed pump laser passes through the optical gain medium 5, the fluorescence effect occurs.

[0035] After the pulsed pump laser passes through the optical gain medium 5, part of the fluorescence directly returns to the broadband filter 9 through the transmission optical cable 8, is converted into an electrical signal through the first photoelectric conversion module 5 of the fluorescence time domain signal acquisition module 210 again through the broadband coupler. Meanwhile, the pulsed pump light also splits through the second coupler 101 to the collimator 12, the gain medium 13, and also generates fluorescence. This part of the fluorescence is converted into an electrical signal through the first photoelectric conversion module 4 of the fluorescence time domain signal acquisition module 210. The two fluorescence time domain signals are calculated by simulation, and the lifetime of the fluorescence returned by the optical fiber high-temperature pressure gauge 100 is finally obtained, and then the temperature value of the environment around the optical fiber high-temperature pressure gauge 100 can be calculated.

[0036] After the pulsed pump laser passes through the optical gain medium 5, another part of the fluorescence directly passes through the Fabry-Perot interference cavity 6. The broadband light forms fluorescence interference fringes in the Fabry-Perot interference cavity 6. This part of the light returns to the transmission optical cable 8, then passes through the broadband filter 9, and then enters the fluorescence wavelength demodulation module 220 through the third coupler 102. The returned interference light passes through the third optical fiber collimator 18 and the analog optical interference cavity 19. When the PZT piezoelectric ceramic 20 is driven, the PZT piezoelectric ceramic 20 causes the cavity length of the analog optical interference cavity 19 to change. When the length of the cavity length is the same as the cavity length of the stress detection interference cavity, the intensity value of the light changes greatly, thereby measuring the length of the interference cavity of the Fabry-Perot interference cavity 6 after the Fabry-Perot interference cavity 6 is subjected to pressure through the cavity length of the PZT piezoelectric ceramic. The optical interference cavity length value has a linear relationship with the external pressure.

[0037] The pressure at the downhole measurement point is set to P and the temperature to T. When there is no stress, the length of the Fabry-Perot interferometer cavity used for stress detection is L.

[0038] The stress surface diaphragm of the Fabry-Perot interferometer cavity used for stress detection has a radius of R1, a thickness of t, an elastic modulus of E1, a Poisson's ratio of u1, and a hard core radius of r1 at the center of the diaphragm.

[0039] When the pressure at the measurement point reaches a stable state, i.e., when the pressure is P, the displacement of the hard core of the stress diaphragm is:

[0040] like Figure 3 As shown, the PZT piezoelectric ceramic changes the optical cavity length by using the triangular wave signal from the spectral demodulation module of the demodulator. Therefore, the relationship between the optical cavity length and time is:

[0041] When the pressure measured by the fiber optic high-temperature pressure gauge is 0, and the time is t1,

[0042] When the length of the simulated optical interference cavity is t1, the length of the simulated optical interference cavity is the same as that of the interference cavity of the fiber optic high-temperature pressure gauge, and the measured light intensity value is an extreme value.

[0043] When the pressure measured by the fiber optic high-temperature pressure gauge is P, and the time is t2...

[0044] When the simulated optical interference cavity length is t2, it is the same as the interference cavity length of the fiber optic high-temperature pressure gauge after being subjected to pressure, and the measured light intensity value is an extreme value. Therefore, the variable of the cavity length is...

[0045] Within a certain temperature range, the fluorescence lifetime of optical gain media exhibits a certain temperature correlation under the action of pump light, and fluorescence lifetime thermometry is based on this temperature correlation principle.

[0046] When pump light illuminates an optical gain medium, its internal electrons gain energy to transition from the ground state to an excited state. The return energy from the excited state to the ground state is emitted as radiation, causing the optical gain medium to fluoresce. The duration of fluorescence emission after the pump light is removed depends on the lifetime of the excited state; this lifetime is called the fluorescence lifetime. The length of the fluorescence lifetime is determined by temperature. Fluorescence lifetime-based temperature sensors are temperature sensors based on this characteristic.

[0047] The optical gain medium under the action of pump light, will emit a certain linear spectrum, namely fluorescence and its afterglow. Through the semiconductor theory, the decay of afterglow until the disappearance is actually the process of light quenching, the increase of temperature makes the intensity of lattice vibration enhanced, and the intensity of lattice vibration enhanced makes the number of molecules involved in the absorption increased, eventually leading to the process of fluorescence quenching shortened, so the temperature of optical gain medium determines the speed of light quenching, that is, the size of decay time constant. Figure 4 The fluorescence characteristic curve is shown in FIG. 2.

[0048] The function relationship between the intensity of fluorescence afterglow and time is

[0049] In the formula, A is a constant coefficient; t is the afterglow decay time; I0 is the peak intensity of fluorescence when the excitation is stopped, which is a function of temperature T; τ is the fluorescence afterglow decay time constant, that is, the fluorescence afterglow lifetime, which is also a function of temperature T, and is irrelevant to light intensity.

[0050] The fluorescence curve obtained under normal temperature conditions in the fluorescence time domain module after the pump light excites the gain medium of the fiber high temperature pressure gauge is

[0051] The fluorescence curve obtained under high temperature conditions in the fluorescence time domain module after the pump light excites the gain medium of the fiber high temperature pressure gauge is

[0052] When the amplification coefficient of the photoelectric conversion module is changed, the fluorescence curve obtained under normal temperature conditions is

[0053] Then the following can be calculated:

[0054] Since the temperature of the demodulation host is known, the value of I0 is known. The fluorescence curve under normal temperature conditions is The fluorescence curve under high temperature conditions is After the fluorescence curve under normal temperature conditions is divided by the fluorescence curve under high temperature conditions, the following is obtained: Generally, the higher the temperature of the surrounding environment, the smaller the value of T; by measuring the fluorescence lifetime of the optical gain medium and the temperature value T, when the value of T is measured, the temperature value T can be obtained.

[0055]

[0056] ​​​The following provides one embodiment of the application with specific data: the full scale of the fluorescent fiber high temperature pressure gauge is 100 MPa, the stress film of the stress detection Fabry-Perot interference cavity is a sapphire crystal, the thickness t of the sapphire crystal is 0.13 mm, the radius R is 1.5 mm, the radius r of the hard core in the center is 0 mm, the elastic modulus E of the sapphire crystal is 380 GPa, and the Poisson's ratio u is 0.23; the pump laser is 980 nm, and the optical gain medium is Er, Yb doped laser glass, which generates a broadband fluorescent light source under the action of the pump laser.

[0057] When the fluorescent fiber high temperature pressure gauge is at a downhole pressure of 50 MPa and a temperature of 150°C, the cavity length change of the pressure detection Fabry-Perot cavity of the fluorescent fiber high temperature pressure gauge is :

[0058] Then the deformation of the central stress film reduces the cavity length of the stress detection Fabry-Perot optical interference cavity. In the case of no external pressure, the cavity length L is 500 um.

[0059] When the fiber high temperature pressure gauge is not subjected to external force, the cavity length of the simulated optical interference cavity is driven by a triangular wave signal, the cavity length slope of the PZT piezoelectric ceramic is , and the cavity length intercept is .

[0060]

[0061] Then the time at which the light intensity value extremum can be measured is .

[0062] When the cavity length is affected by stress, the cavity length becomes 446.2 um. The time at which the light intensity value extremum can be measured is

[0063]

[0064] Then when , the light intensity value extremum is measured.

[0065] When the maximum pressure value Pmax of the fluorescent fiber high temperature pressure gauge is 100 MPa, the maximum change of the stress detection Fabry-Perot optical interference cavity length is

[0066] When the cavity length is affected by stress, the cavity length becomes 392.4 um. The time at which the light intensity value extremum can be measured is

[0067]

[0068] Then when , the light intensity value extremum is measured.

[0069] Thus we can see that the PZT piezoelectric ceramic can measure the time of light intensity value extremum after being driven by the triangular wave signal That is, the pressure of the fiber high temperature pressure gauge is obtained.

[0070]

[0071] The fluorescence type fiber high temperature pressure gauge adopts Er, Yb doped laser glass. When the temperature is-20℃ to 200℃, the fluorescence lifetime of the Er, Yb doped laser glass changes from 11ms to 6.8ms linearly. The fluorescence time domain signal processing module of the demodulation host adopts an accumulation type data acquisition card. The pulse frequency of the pulse pumping laser generator is 50Hz, the pulse width is 5ms, the acquisition rate of the acquisition card is 2M / s, and the resolution is 12 bits.

[0072] Since the acquisition rate of the acquisition card is 2M / s, when the pulse signal of the pumping laser is output to the acquisition card, the data acquisition card directly acquires the fluorescence signal. When the temperature is-20℃ to 200℃, the change amount of the fluorescence lifetime is 4.2ms, and the temperature recognition accuracy is 4.2ms / 220℃=19us / ℃. The interval time of the data acquisition points of the acquisition card is 0.5us, so the recognizable accuracy of the acquisition card is 0.026℃ / us. Therefore, the temperature measurement accuracy of the fluorescence type fiber high temperature pressure gauge is 0.026℃ / us.

[0073] Embodiment 2 This embodiment is based on the measurement system of embodiment 1, and proposes a downhole pressure and temperature measurement method based on the above-mentioned fluorescence type fiber high temperature pressure gauge, which includes a mounting step and a measurement step.

[0074] The mounting step includes: fixing the fiber high temperature pressure gauge at the bottom end of the transmission cable (or logging cable) of the logging, after installation, the stress surface of the fiber high temperature pressure gauge is in contact with the outside, or an oil bladder is used for oil sealing; one end of the fluorescence type fiber high temperature pressure gauge is connected to one end of the logging cable, and is sealed and fixed in a metal piece. The wellhead end of the logging cable is connected to the demodulation host. At the same time, the connection between the fiber high temperature pressure gauge and the end of the transmission cable in the downhole and the shell of the fiber high temperature pressure gauge are sealed in a metal pipe; The measurement step includes a temperature measurement step and a pressure measurement step.

[0075] The pulse-pumped laser generating device in the host computer is output through the fiber coupler, and the returned signal is also input to the fluorescence time domain signal acquisition module through the fiber coupler and is processed in the fluorescence wavelength demodulation module. The temperature measurement step finally outputs the environmental temperature of the fiber high-temperature pressure gauge through the fluorescence time domain signal acquisition module; the pressure measurement step outputs the pressure information of the environment of the fiber high-temperature pressure gauge through the fluorescence wavelength demodulation module.

[0076] Specifically, in the pressure measurement step, the demodulation host outputs the pulse-pumped light through the transmission cable into the optical fiber and finally into the pumped optical gain medium, so as to generate fluorescence; after the fluorescence is output to the optical interference high-pressure detection module, it is returned to the demodulation host at the wellhead through the transmission cable; the wellbore pressure value is obtained by the change of the arm length difference between the analog interference optical cavity and the interference optical cavity of the fiber high-temperature pressure gauge; In the temperature measurement step, the demodulation host divides the optical signal into two parts, one part measures the fluorescence lifetime of the returned light signal, and the other part measures the interference fringes of the returned light signal; when the fiber high-temperature pressure gauge is affected by the environmental temperature, the returned fluorescence lifetime will change, the higher the temperature, the shorter the fluorescence lifetime, and the lower the temperature, the longer the fluorescence lifetime; when the pulse output pumped light is input to the gain medium, the optical power of the pulse pumped light is enough to saturate the output of the gain medium; when the gain medium is not pumped by the light, the fluorescence will continue to output and then rapidly decay, and the decay time is related to the temperature of the environment; by using a pulse signal as a trigger signal, the gain medium in the demodulation host and the gain medium of the fiber high-temperature pressure gauge are measured after multiple accumulations of the fluorescence lifetime, and the temperature value of the fiber high-temperature pressure gauge can be obtained by comparison and calculation.

[0077] The measurement system based on the fiber high-temperature pressure gauge realized by the above scheme mainly includes a downhole temperature measurement part and a downhole pressure measurement part. The temperature measurement part is mainly realized by an optical gain medium located between a high-temperature optical collimator and a Fabry-Perot interference cavity; the pressure measurement part is mainly measured by the optical wavelength interference generated by the fluorescence generated by the optical gain medium in the Fabry-Perot interference cavity. The temperature measurement part and the downhole pressure measurement part are both sealed in a metal shell. The whole measurement system can realize simultaneous measurement of temperature and pressure.

[0078] The downhole temperature detection is directly measured by the fluorescence lifetime of the optical gain medium. The downhole pressure detection is directly measured by the cavity length change of the Fabry-Perot interference cavity caused by the external pressure. The temperature detection and the pressure detection are both measured by fluorescence, which are realized by the optical gain medium, without the need for two sets of devices, and have the advantages of simple structure and ingenious structure.

[0079] In the specific implementation, the fiber high-temperature pressure gauge is connected with one end of the logging optical cable and is sealed and fixed in the metal part. The wellhead end of the logging optical cable is connected with the fluorescence type fiber high-temperature pressure gauge demodulation host. The pulse pumping laser generating device in the demodulation host is output through the fiber coupler, the returned signal is also input to the fluorescence time domain signal acquisition module through the fiber coupler, and data processing is performed in the fluorescence wavelength demodulation module. The fluorescence time domain signal acquisition module finally outputs the environmental temperature of the fiber high-temperature pressure gauge; and the fluorescence wavelength demodulation module outputs the pressure information of the environment of the fiber high-temperature pressure gauge. When the fluorescence type fiber high-temperature pressure gauge is installed, the fluorescence type fiber high-temperature pressure gauge is first fixed to the downhole end of the logging optical cable; then the other end of the logging optical cable is connected with the fluorescence type fiber high-temperature pressure gauge demodulation host; the returned fluorescence lifetime is measured through the fluorescence time domain module in the demodulation host, and after data processing, the temperature information of the downhole detection point can be obtained; the returned fluorescence interference spectrum is detected through the fluorescence wavelength demodulation module in the demodulation host, and after data processing, the pressure information of the downhole detection point can be obtained.

[0080] In addition, the double-channel signal acquisition module can be realized through a collection card, and the temperature measurement accuracy of the downhole detection point can be improved by improving the collection rate of the collection card; the pressure value of the downhole detection point is calculated through the total amount of the optical interference fringe phase.

[0081] The measurement system and the measurement method realized through the above scheme can realize temperature measurement and pressure measurement under high-temperature conditions in the well, and the reliability and stability of the temperature measurement and pressure measurement in the well are greatly improved because the optical part is not in contact with the external stress.

[0082] It should be emphasized that the term "comprises / comprising" as used herein is intended to indicate the presence of the features, elements, steps or components, but not the exclusion of one or more other features, elements, steps or components.

[0083] Although the present application has been disclosed by the description of the specific embodiments of the present application above, it should be understood that all the embodiments and examples described above are exemplary but not limiting. Those skilled in the art can design various modifications, improvements or equivalents of the present application within the spirit and scope of the appended claims. These modifications, improvements or equivalents should also be considered to be included in the protection scope of the present application.

Claims

1. A measurement system for a fluorescent fiber optic high-temperature pressure gauge, characterized in that: It includes a fiber optic high-temperature pressure gauge for collecting downhole pressure and temperature, a demodulation host for outputting pulsed pump light to the fiber optic high-temperature pressure gauge and receiving feedback signals, and a transmission optical cable for connecting the fiber optic high-temperature pressure gauge and the demodulation host. The fiber optic high-temperature pressure gauge includes a temperature measurement section and a pressure measurement section; The demodulation host includes a pump laser generator for outputting pulsed pump light to the fiber optic high-temperature pressure gauge, an interference demodulation module for simulating an interference cavity, and a temperature demodulation module for obtaining fluorescence lifetime curves. The simulated interference cavity of the interference demodulation module has the same configuration as the interference cavity of the pressure measurement section of the fiber optic high-temperature pressure gauge, and the temperature demodulation module has the same gain medium as the temperature measurement section of the fiber optic high-temperature pressure gauge. The pump laser generator of the demodulation host splits the signal into two identical paths. One path is transmitted to the downhole fiber optic high-temperature pressure gauge, and the other path is transmitted to the interferometric demodulation module and the temperature demodulation module. The downhole pressure value is obtained by simulating the change in the arm length difference between the interferometric cavity and the interferometric cavity of the fiber optic high-temperature pressure gauge. The downhole temperature value is obtained by comparing the fluorescence lifetime curve of the temperature demodulation module with the fluorescence lifetime curve of the received fiber optic high-temperature pressure gauge.

2. The measurement system of the fluorescent fiber optic high-temperature pressure gauge according to claim 1, characterized in that: The fiber optic high-temperature pressure gauge includes a fiber optic collimator and a pump optical gain medium for temperature measurement, and an optical interference high-pressure detection module for pressure measurement. One end of the fiber optic collimator is connected sequentially to the pump optical gain medium and the optical interference high-pressure detection module, and the other end of the fiber optic collimator is connected sequentially to the transmission optical cable and the demodulation host. The optical interference arm length difference of the optical interference high-pressure detection module is linearly related to the external pressure. When the external pressure acts on the optical interference high-pressure detection module, the optical interference arm length difference changes. By comparing the change with the simulated interference cavity of the demodulation host, the external pressure value is demodulated. After the pulsed pump light input through the transmission optical cable, the pump optical gain medium generates a spontaneous emission fluorescence effect. The temperature demodulation module of the demodulation host calculates the temperature value by comparing the received fluorescence lifetime curve with a preset fluorescence lifetime curve.

3. The measurement system of the fluorescent fiber optic high-temperature pressure gauge according to claim 2, characterized in that: The input light source of the optical interference high-voltage detection module is a fluorescent broadband light source generated after the pulse pump light passes through the pump optical gain medium.

4. The measurement system of the fluorescent fiber optic high-temperature pressure gauge according to claim 2, characterized in that: The optical interference high-pressure detection module is located on the end face or side of the fiber optic high-temperature pressure gauge.

5. The measurement system of the fluorescent fiber optic high-temperature pressure gauge according to claim 2, characterized in that: The optical interference of the optical interference high-voltage detection module is Fabry-Perot interference, Michelson interference, or Mach-Zehnder interference.

6. The measurement system of the fluorescent fiber optic high-temperature pressure gauge according to claim 1, characterized in that: The fiber optic high-temperature pressure gauge includes a housing, a high-temperature optical fiber, a high-temperature optical fiber collimator, an optical fiber collimator seal, a first optical gain medium, and a Fabry-Perot interferometer cavity. The housing seals the high-temperature optical fiber collimator, the first optical gain medium, and the Fabry-Perot interferometer cavity through the optical fiber collimator seal. The end face of the fiber optic high-temperature pressure gauge is the stress surface of the Fabry-Perot interferometer cavity used for stress detection.

7. The measurement system of the fluorescent fiber optic high-temperature pressure gauge according to claim 6, characterized in that: The demodulation host includes a broadband filter, a first coupler, a second coupler, a third coupler, a pulse pump generator, a fluorescence time-domain signal acquisition module, and a fluorescence wavelength demodulation module. The fluorescence time-domain signal acquisition module includes a second fiber collimator, a second optical gain medium, a first photoelectric conversion module, a second photoelectric conversion module, and a signal acquisition and processing module. The fluorescence wavelength demodulation module includes a third fiber collimator, an analog optical interference cavity, a PZT piezoelectric ceramic, a third photoelectric conversion module, and a dual-channel signal acquisition module. The broadband filter, the first coupler, and the pulse pump generator are connected in sequence; the first coupler and the second coupler are interconnected; the second optical gain medium, the second fiber collimator, the second coupler, and the first photoelectric conversion module are connected in sequence; the broadband filter, the third coupler, and the second photoelectric conversion module are connected in sequence; and both the first and second photoelectric conversion modules are connected to... The signal acquisition and processing module is connected, and the third coupler is also connected to the third fiber collimator and the third photoelectric conversion module respectively. The third fiber collimator is connected to the analog optical interference cavity and PZT piezoelectric ceramic, and the third photoelectric conversion module is connected to the dual-channel signal acquisition module. One path of the pump light from the pulse pump generator is split by the first coupler to the fiber optic high-temperature pressure gauge, and the other path is split by the first coupler and the second coupler to the second fiber collimator and the second optical gain medium to generate fluorescence. The generated fluorescence is converted into an electrical signal by the first photoelectric conversion module. The lifetime of the fluorescence returned by the fiber optic high-temperature pressure gauge is finally obtained through simulation calculation. One path of the pump light from the pulse pump generator is split by the first coupler to the Fabry-Perot interference cavity of the fiber optic high-temperature pressure gauge to form a broadband light with fluorescence interference fringes. The broadband light returns to the transmission cable through the optical fiber and enters the fluorescence wavelength demodulation module after passing through the broadband filter. The returning interference light passes through a third fiber collimator and a simulated optical interference cavity. The length of the interference cavity after being subjected to pressure is then measured by the cavity length of the PZT piezoelectric ceramic, thus obtaining the external pressure.

8. The measurement system of the fluorescent fiber optic high-temperature pressure gauge according to claim 7, characterized in that: The second optical gain medium has the same size and material as the first optical gain medium.

9. A measurement method for a fluorescent fiber optic high-temperature pressure gauge, applied to the measurement system of the fluorescent fiber optic high-temperature pressure gauge according to any one of claims 1-8, characterized in that: include: Installation steps: First, fix the fluorescent fiber optic high-temperature pressure gauge to the lower end of the transmission optical cable; then connect the other end of the transmission optical cable to the demodulation host of the fluorescent fiber optic high-temperature pressure gauge. Pressure measurement steps: The demodulation host outputs pulse pump light, which is input into the optical fiber through the transmission optical cable and finally into the pump optical gain medium, thereby generating fluorescence; after the fluorescence is output to the optical interference high-pressure detection module, it is returned to the demodulation host at the wellhead through the transmission optical cable; the downhole pressure value is obtained by simulating the change in the arm length difference between the interference optical cavity and the interference optical cavity of the fiber optic high-temperature pressure gauge. Temperature measurement steps: The demodulation host divides the optical signal into two parts. One part measures the fluorescence lifetime of the returned optical signal, and the other part measures the interference fringes of the returned optical signal. When the fiber optic high-temperature pressure gauge is affected by the ambient temperature, the returned fluorescence lifetime will change. The higher the temperature, the shorter the fluorescence lifetime, and the lower the temperature, the longer the fluorescence lifetime. When the pulsed pump light is input to the gain medium, the optical power of the pulsed pump light is sufficient for the fluorescence saturation output of the gain medium. When there is no pump light in the gain medium, the fluorescence will continue to be output and then decay rapidly. The decay time is related to the ambient temperature. By using a pulse signal as a trigger signal, the fluorescence lifetime of the gain medium in the demodulation host and the gain medium of the fiber optic high-temperature pressure gauge are accumulated multiple times and then measured. The temperature value of the fiber optic high-temperature pressure gauge can be obtained by comparison and calculation.

10. The measurement method of the fluorescent fiber optic high-temperature pressure gauge according to claim 9, characterized in that: The connection between the fiber optic high-temperature pressure gauge and the underground transmission optical cable, as well as the outer casing of the fiber optic high-temperature pressure gauge, are all sealed inside a metal tube.

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