CN115900789A - Underground fiber bragg grating temperature and pressure sensor and linear array temperature and pressure sensing system - Google Patents
Underground fiber bragg grating temperature and pressure sensor and linear array temperature and pressure sensing system Download PDFInfo
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- CN115900789A CN115900789A CN202211714299.8A CN202211714299A CN115900789A CN 115900789 A CN115900789 A CN 115900789A CN 202211714299 A CN202211714299 A CN 202211714299A CN 115900789 A CN115900789 A CN 115900789A
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Abstract
The invention discloses a temperature and pressure sensor for an underground fiber grating, which comprises a sensing cavity, a pressure sensing film, and a pressure sensing fiber grating and a temperature sensing fiber grating which are connected in series; the sensing cavity is provided with a rigid cavity body, and the rigid cavity body is provided with a temperature sensing fixing plate extending outwards; the rigid cavity of the sensing cavity is hermetically matched with the pressure sensing diaphragm to form a cavity communicated with the target fluid; the pressure sensing diaphragm is influenced by the pressure of fluid in the cavity and the temperature of the fluid to generate strain; the temperature sensing fixing plate is influenced by the temperature of the fluid to generate strain; the temperature sensing fiber grating is arranged on the central surface of the temperature sensing pressure film, and the temperature sensing fiber grating is arranged on the surface of the temperature sensing fixing plate. The invention ensures that the pressure measurement is hardly influenced by temperature, reduces high-temperature drift and improves the pressure measurement precision under the underground high-temperature environment. The invention realizes underground distributed point measurement by forming a linear array temperature and pressure sensing system by mutually connecting multiple sensors in series and isolating and sealing.
Description
Technical Field
The invention belongs to the field of optical fiber sensing, and particularly relates to an underground fiber bragg grating temperature and pressure sensor and a linear array temperature and pressure sensing system.
Background
The real-time online monitoring of multiple parameters such as pressure, temperature and the like is carried out on the oil well, the actual condition in the oil well can be known at any time under the condition of no production stop, and the online monitoring system has important significance for optimizing oil production and improving oil gas recovery rate and yield. The traditional electronic sensor and the logging mode thereof have great limitations, even can not work normally in severe environments such as underground high temperature and high pressure, and the measurement precision is not high.
The fiber grating is a diffraction grating formed by axial periodic modulation of refractive index, is a passive filter device, has the advantages of small volume, low welding loss, full compatibility with optical fibers, capability of being embedded in intelligent materials, high sensitivity, electromagnetic interference resistance, easiness in realization of remote transmission and distributed measurement, easiness in working in severe environment and the like, and is widely applied to the field of sensing.
In recent years, the existing fiber grating sensor is also applied to downhole monitoring, but the existing sensor has a large size, cannot be applied to a small-size casing, and has a low measurement range or low sensitivity, and cannot realize a large measurement range under high sensitivity, for example, the downhole fiber grating sensor provided by chinese patent CN115452021A adopts two independent fiber gratings to measure hydraulic pressure and ambient temperature respectively. However, the fiber grating sensor has high sensitivity of the pressure grating in a high-temperature and high-pressure environment, is sensitive to temperature influence, is easy to drift, and cannot accurately monitor pressure and temperature. Particularly, under the condition that the temperature change in the underground is severe, for example, in deep wells of oil fields, the temperature rises sharply during the operation of the drill bit, the temperature of the drill bit stops decreasing sharply, and along with the working rule of the drill bit, the fiber grating sensor is repeatedly in the change of sharp rise and sharp fall of the environmental temperature, and is influenced by thermal shock, so that the test result is inaccurate.
Disclosure of Invention
Aiming at the defects or the improvement requirements of the prior art, the invention provides an underground fiber bragg grating temperature and pressure sensor and a linear array temperature and pressure sensing system, which aim to adopt a sensing cavity capable of simultaneously sensing pressure and temperature and avoid crosstalk caused by simultaneous pressure and temperature changes.
In order to achieve the above object, according to one aspect of the present invention, there is provided a downhole fiber grating temperature and pressure sensor, comprising a sensing cavity, a pressure sensing diaphragm, and a pressure sensing fiber grating and a temperature sensing fiber grating connected in series;
the sensing cavity is provided with a rigid cavity body, and the rigid cavity body is provided with a temperature sensing fixing plate extending outwards; the rigid cavity of the sensing cavity is hermetically matched with the pressure sensing film to form a cavity communicated with target fluid;
the pressure sensing diaphragm is influenced by the pressure of fluid in the cavity and the temperature of the fluid to generate strain;
the temperature sensing fixing plate is influenced by the temperature of the fluid to generate strain;
the pressure sensing fiber grating is arranged on the central surface of the pressure sensing film, and the temperature sensing fiber grating is arranged on the surface of the temperature sensing fixing plate.
Preferably, the direction of the pressure sensing diaphragm of the downhole fiber bragg grating temperature and pressure sensor stressed by fluid pressure is orthogonal to the direction of the strain generated by the fluid of the temperature sensing fixing plate under the influence of fluid temperature.
Preferably, the direction of the pressure-sensing fiber grating and the direction of the temperature-sensing fiber grating of the downhole fiber grating temperature and pressure sensor are the same.
Preferably, the distance between the pressure-sensing fiber grating and the temperature-sensing fiber grating of the downhole fiber grating temperature and pressure sensor is greater than the distance between the center of the pressure-sensing diaphragm and the temperature-sensing fixing plate at the position where the temperature-sensing fiber grating is arranged.
Preferably, the rigid cavity of the sensing cavity of the downhole fiber bragg grating temperature and pressure sensor is a good thermal conductor, and the thermal conductivity of the downhole fiber bragg grating temperature and pressure sensor is preferably greater than 10W/(m DEG C).
Preferably, in the downhole fiber bragg grating temperature and pressure sensor, the thermal expansion coefficient of the rigid cavity of the sensing cavity is equivalent to that of the optical fiber adopted by the temperature sensing fiber bragg grating, and the variation of the thermal expansion coefficient per degree centigrade is preferably less than 0.01x10 -6 The elastic modulus is preferably more than 195GPa.
Preferably, the rigid cavity of the downhole fiber grating temperature and pressure sensor is made of a corrosion-resistant material, and the corrosion-resistant depth of the sensor cavity is less than 0.005 mm/year.
Preferably, the downhole fiber grating temperature and pressure sensor further comprises a base; the base is provided with an L-shaped fluid channel, one end of the L-shaped fluid channel is communicated with the cavity, and the other end of the L-shaped fluid channel is opened on the side surface of the sensor.
Preferably, the downhole fiber grating temperature and pressure sensor comprises a straight-bar-shaped shell, the base is radially embedded in the shell, the base is provided with a through hole, the pressure sensing fiber grating and the temperature sensing fiber grating which are connected in series penetrate through the through hole, and two ends of the base respectively penetrate out of the leading-out holes at the corresponding ends of the shell.
According to another aspect of the invention, a downhole linear array temperature and pressure sensing system is provided, which comprises a plurality of downhole fiber bragg grating temperature and pressure sensors which are connected in series.
In general, compared with the prior art, the above technical solution contemplated by the present invention can achieve the following beneficial effects:
1. according to the invention, by designing the structure of the sensing cavity, the sensitivity of the pressure grating is effectively increased, the temperature measurement is carried out through the temperature sensing fiber grating pasted on the temperature sensing fixing plate, the inaccurate temperature measurement caused by vibration of the optical fiber and inconsistency of the measurement target and the measurement target of the pressure sensing fiber grating is avoided, the accurate temperature compensation is carried out, and the sensitivity of the pressure sensing fiber grating to the external temperature change is reduced, so that the pressure measurement is hardly influenced by the temperature, the high temperature drift is reduced, and the pressure measurement precision under the underground high-temperature environment is improved.
2. The invention realizes underground distributed point measurement by mutually connecting the multiple sensors in series and isolating and sealing.
Drawings
FIG. 1 is a schematic diagram of a sensing cavity structure of a downhole fiber grating temperature and pressure sensor provided by the invention;
FIG. 2 is a schematic structural diagram of a downhole fiber grating temperature and pressure sensor provided by the invention;
FIG. 3 is a diagram of a finite element simulation result of a pressure sensing diaphragm of a sensing cavity of a downhole FBG temperature and pressure sensor provided by an embodiment of the invention;
fig. 4 is a structural diagram of a downhole linear array temperature and pressure sensing system provided by the invention.
The same reference numbers will be used throughout the drawings to refer to the same elements or structures, wherein: 1 is the base, 2 is the sensing chamber, 201 is the pressure sensing diaphragm, 202 is the temperature sensing fixed plate, 3 is the pressure sensing fiber grating, 4 is the temperature sensing fiber grating, 5 is optic fibre, 6 is the one end of shell, 7 is the other end of shell, 8 is the seal structure outside, 9 is the seal structure inboard, 10 is the steel pipe, 11 is the recess at base both ends, 12 is the recess of base opening part.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
The invention provides an underground fiber grating temperature and pressure sensor which comprises a sensing cavity, a pressure sensing film, a pressure sensing fiber grating, a temperature sensing fiber grating, a base and a shell, wherein the pressure sensing fiber grating and the temperature sensing fiber grating are connected in series;
the sensing cavity is provided with a rigid cavity body, and the rigid cavity body is provided with a temperature sensing fixing plate extending outwards; the rigid cavity of the sensing cavity is hermetically matched with the pressure sensing diaphragm to form a cavity communicated with the target fluid; the rigid cavity of the sensing cavity is a good thermal conductor, the thermal conductivity coefficient of the rigid cavity is preferably greater than 10W/(m DEG C), the good thermal conductivity can be transmitted to the temperature of the fluid, the temperature of the temperature sensing fixing plate can be used for representing the temperature of the fluid, effective temperature compensation is carried out, the thermal stress of the temperature sensing fixing plate is stably and accurately associated with the temperature of the fluid by matching with the temperature sensing fixing plate which extends outwards, and the accuracy of measurement is ensured. In a preferable scheme, the thermal expansion coefficient of the rigid cavity of the sensing cavity is equivalent to that of the optical fiber adopted by the temperature sensing optical fiber grating, namely the two values are in the same order of magnitude and have a difference of less than 5 times; meanwhile, the thermal expansion coefficient of the material changes less along with the rise of the temperature, and the change amount per degree centigrade is less than 0.01x10 -6 The modulus of elasticity is preferably greater than 195GPa. The too small elastic modulus can lead the pressure sensing diaphragm to be insensitive to the external pressure, and meanwhile, the loss exists in force transmission, so that the strain sensed by the pressure sensing fiber grating is too small, and the sensitivity and the precision of the sensor are limited. The rigid cavity of the sensing cavity is made of anti-fatigue materials, the fatigue service life of the sensing cavity is longer than 10 years theoretically, and the corrosion resistance depth is less than 0.005 mm/year.
The pressure sensing diaphragm is influenced by the pressure of fluid in the cavity and the temperature of the fluid to generate strain; a cavity in fluid communication with the target, a pressure sensing cavity, the pressure load causing a positive strain on the pressure sensing diaphragm,
the temperature sensing fixing plate is influenced by the temperature of the fluid to generate strain;
the direction of the pressure sensing diaphragm under the influence of fluid pressure is orthogonal to the direction of strain generated by the influence of fluid temperature on the temperature sensing fixing plate fluid, so that the strain sensed by the temperature sensing fiber grating is completely caused by the temperature change of the temperature sensing fixing plate and is not influenced by the fluid pressure.
The pressure-sensitive fiber grating and the temperature-sensitive fiber grating are in the same direction. The fiber gratings connected in series are generally processed by the same optical fiber, the thermal expansion and the thermo-optic coefficient of the fiber gratings are consistent, when the thermal expansion and the thermo-optic coefficient of the two fiber gratings are the same and the gluing mode is the same, the wavelength interval change caused by the environmental temperature can be small and ignored, and the temperature compensation is effectively carried out.
The pressure sensing fiber grating is arranged on the central surface of the pressure sensing film, and the temperature sensing fiber grating is arranged on the surface of the temperature sensing fixing plate. For the fiber grating of current unsettled setting, fix the fiber grating on temperature sensing fixed plate surface, experience the temperature sensing fixed plate because the thermal stress expansion that the temperature influence brought, it is stable and accurate, can not acutely lead to the temperature drift phenomenon because of temperature variation, avoided the sound wave vibrations to influence the measuring error that fiber grating leads to simultaneously, guaranteed that the actual meeting an emergency of temperature sensing fiber grating receives other factor influences and can neglect, effectively improved the SNR.
The pressure sensing fiber grating is tightly attached to the surface of the pressure sensing diaphragm and used for sensing the forward strain of the diaphragm, and the temperature sensing fiber grating is tightly attached to the surface of the temperature sensing fixing plate and used for sensing the surrounding temperature signals. Therefore, the pressure measuring sensitivity and precision under the underground high-temperature and high-pressure environment are improved through the pressure cavity and the temperature sensing fixing plate.
The distance between the pressure sensing fiber grating and the temperature sensing fiber grating is greater than the distance between the center of the pressure sensing film and the temperature sensing fixing plate, so that the temperature sensing fiber grating is prevented from being stretched due to the deflection change of the pressure sensing fiber grating.
The base is provided with an L-shaped fluid channel, one end of the L-shaped fluid channel is communicated with the cavity, and the other end of the L-shaped fluid channel is opened on the side surface of the sensor. The shell is a straight strip type, the base is radially embedded in the shell, the base is provided with a through hole, the pressure-sensitive fiber grating and the temperature-sensitive fiber grating which are connected in series penetrate through the through hole, and two ends of the base penetrate out of the leading-out holes at the corresponding ends of the shell respectively.
The invention provides an underground linear array temperature and pressure sensing system which comprises a plurality of underground fiber bragg grating temperature and pressure sensors connected in series. The fiber bragg grating temperature and pressure sensor in series connection is connected with a fiber temperature/pressure demodulating system, pressure sensing fiber bragg gratings or temperature sensing fiber bragg gratings at different positions are represented through different wavelengths in the underground, and the fiber temperature/pressure demodulating system reads pressure or temperature data measured by the fiber bragg gratings through reflection spectrums.
The following are examples:
as shown in fig. 1 and fig. 2, the downhole fiber grating temperature and pressure sensor provided in this embodiment includes a sensing cavity 2, a pressure sensing diaphragm 201, and a pressure sensing fiber grating 3 and a temperature sensing fiber grating 4 connected in series, a base 1, and shells 6 and 7;
one end of the sensing cavity 2 is a cylindrical tube, which penetrates through the base 1 and is fixed with the base 1, one surface of a cavity which is formed inside the sensing cavity and is communicated with the target fluid is a sensing membrane 201, and the sensing membrane 201 is used for converting the pressure in the cavity into the strain of the membrane. Preferably, the sensing cavity may be made of nickel alloy 718. The sensing cavity 2 is provided with a rigid cavity body, and the rigid cavity body is provided with a temperature sensing fixing plate 202 extending outwards;
the surface of the pressure sensing diaphragm 201 is provided with a pressure sensing fiber grating 3 for sensing pressure; the temperature sensing fiber grating 4 is disposed at the center of the surface of the temperature sensing fixing plate 202 for sensing temperature and has a temperature compensation function.
The pressure-sensitive fiber grating 3 and the temperature-sensitive fiber grating 4 are formed by femtosecond laser transmission coating and writing, and the outer coating material of the optical fiber 5 is polyimide.
The pressure sensing fiber grating 3 is connected with the temperature sensing fiber grating 4 in series and is led out through a through hole on the base 1. Wherein, in order to prevent the deflection change of the pressure sensing fiber grating 3 from stretching the temperature sensing fiber grating 4, the distance between the pressure sensing fiber grating 3 and the temperature sensing fiber grating 4 is larger than the center distance between the pressure sensing film 201 and the temperature sensing fixing plate 202.
The wavelength induced by the change of temperature and stress can be known from the mechanics knowledge B Can be expressed as
Simplified to
Δλ B ＝(K T ΔT+K ε ε)λ B
Wherein ε is the stress, P ij Is the light pressure coefficient, v is the poisson's ratio, alpha is the thermal expansion coefficient, and delta T is the temperature change; k T Is the temperature sensitivity coefficient, K ε Is the pressure sensitivity coefficient.
According to the force analysis of the pressure-sensitive fiber grating and the temperature-sensitive fiber grating,
therefore, the temperature compensation scheme can be obtained,
Δλ B1 －Δλ B2 ＝(K ε ε)λ B +(K T1 λ B1 －K T2 λ B2 )ΔT
when the thermal expansion and the thermo-optic coefficient of the two fiber gratings are the same and the gluing mode is the same, K is provided T1 ＝K T2 ＝K T
K T1 ΔTλ B1 －K T2 ΔTλ B2 ≈0
Therefore, the wavelength interval change caused by the ambient temperature is small and can be ignored.
The strain distribution of the sensing cavity under the pressure of 60MPa is calculated by using a finite element method, and is shown in figure 3. As can be seen from the figure, the maximum strain of the sensing cavity under the pressure of 60MPa is 3.558x10-3, namely the micro-strain is 3558 mu epsilon. The wavelength change corresponding to grating 1 mu epsilon is about 1.2pm, and the sensitivity of the sensor is 49.4pm/Mpa.
The invention can change the range or the pressure sensitivity by selecting membranes with different thicknesses, realize the flexible adjustment of the pressure sensitivity and the range, and determine the range and the sensitivity by finite element simulation, as shown in figure 3; the invention carries out temperature compensation by coating and pasting the grating on the fixing plate, greatly reduces the temperature sensitivity of the pressure-sensitive fiber grating and improves the pressure measurement precision of the underground high-temperature and high-pressure environment.
In conclusion, the pressure cavity is arranged, so that the measuring range and the sensitivity of pressure measurement are effectively improved, temperature compensation is performed in a mode that the temperature sensing fixing plate is coated and adhered with the pressure sensing fiber bragg grating, and the temperature sensitivity of the pressure sensing fiber bragg grating is greatly reduced, so that the temperature is not influenced as much as possible during high-temperature and high-pressure measurement, and the accuracy of underground measurement is improved; the invention realizes underground distribution point type measurement through the protection device and the multi-stage sealing structures 8 and 9.
The base 1 has an L-shaped fluid channel, one end of which communicates with the cavity and the other end of which opens at the side of the sensor. The shell 6, 7 are the cylinder type, the base radially embedded in the shell to it is sealed to place fluorine-containing O type circle through base both ends recess 11, the base has the through-hole, and pressure sensing fiber grating and the temperature sensing fiber grating that have the series connection pass the through-hole, its both ends are worn out from the hole of drawing forth of the corresponding end of shell respectively, and are sealed.
The optical fiber 5 is protected by a high-temperature-resistant polytetrafluoroethylene capillary tube, and when the optical fiber passes through the leading-out holes of the base 1 and the protective shells 6 and 7, high-temperature-resistant glue is coated at the hole openings for sealing, so that external liquid is prevented from entering a sensitive element area of the sensor.
The downhole linear array temperature and pressure sensing system provided by the embodiment comprises a plurality of downhole fiber bragg grating temperature and pressure sensors which are connected in series. The fiber bragg grating temperature and pressure sensor in series connection is connected with a fiber temperature/pressure demodulating system, pressure sensing fiber bragg gratings or temperature sensing fiber bragg gratings at different positions are represented through different wavelengths in the underground, and the fiber temperature/pressure demodulating system reads pressure or temperature data measured by the fiber bragg gratings through reflection spectrums.
The series connection of the sensors and the mutual isolation and sealing of the multistage sealing structures 8 and 9 are carried out by the fusion of the optical fibers led out from the two ends, so that the distributed point type measurement is realized. The steel pipe 10 is adopted to protect the optical fiber between the sensors, and the steel pipe 10 can be made of nickel alloy 718 or 316 stainless steel. Specifically, two adjacent underground fiber bragg grating temperature and pressure sensors are in sealed connection through a steel pipe 10, or are in sealed connection with an optical fiber fusion protection device and then are in sealed connection with an optical cable special for an oil well, so that point type series connection measurement of the sensors is achieved.
The sensor is connected with an external object to be measured in a groove direct-insert flange mode, a double-layer high-temperature-resistant sealing ring is placed in a groove 12 in the opening of the base, and preferably, the sealing ring can be a fluororubber ring or a nickel-coated metal sealing ring.
As shown in fig. 4, the downhole fiber grating temperature and pressure sensor of the present embodiment is fixed outside an oil pipe, a casing is disposed outside the oil pipe, a plurality of downhole fiber grating temperature and pressure sensors are hermetically connected by an optical cable splicing device, an uppermost sensor is connected with an optical fiber temperature/pressure demodulation system by an optical cable, wherein an optical cable fixing clamp is disposed between the oil pipe and the optical cable for protecting and fixing the optical cable. In practical use, a small hole is formed in the wall of the oil pipe and is communicated with the underground fiber bragg grating temperature and pressure sensor, liquid/gas in a layer to be measured enters the pressure cavity through the small hole, the sensor senses temperature and pressure changes of the oil layer to be measured, and then measured data are transmitted to the optical fiber temperature/pressure demodulation system through the optical cable.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (10)
1. The underground fiber bragg grating temperature and pressure sensor is characterized by comprising a sensing cavity, a pressure sensing film, and a pressure sensing fiber bragg grating and a temperature sensing fiber bragg grating which are connected in series;
the sensing cavity is provided with a rigid cavity body, and the rigid cavity body is provided with a temperature sensing fixing plate extending outwards; the rigid cavity of the sensing cavity is hermetically matched with the pressure sensing film to form a cavity communicated with target fluid;
the pressure sensing diaphragm is influenced by the pressure of the fluid in the cavity and the temperature of the fluid to generate strain;
the temperature sensing fixing plate is influenced by the temperature of the fluid to generate strain;
the pressure sensing fiber grating is arranged on the central surface of the pressure sensing film, and the temperature sensing fiber grating is arranged on the surface of the temperature sensing fixing plate.
2. The downhole fiber grating temperature and pressure sensor of claim 1, wherein the direction of the pressure sensing diaphragm under the influence of fluid pressure is orthogonal to the direction of the strain of the fluid of the temperature sensing fixing plate under the influence of fluid temperature.
3. The downhole fiber grating temperature and pressure sensor of claim 1, wherein the pressure sensitive fiber grating and the temperature sensitive fiber grating are oriented in the same direction.
4. The downhole fiber grating temperature and pressure sensor of claim 1, wherein the distance between the pressure sensing fiber grating and the temperature sensing fiber grating is greater than the distance between the center of the pressure sensing diaphragm and the position of the temperature sensing fixing plate where the temperature sensing fiber grating is arranged.
5. The downhole fiber grating temperature and pressure sensor of claim 1, wherein the rigid cavity of the sensing chamber is a good conductor of heat, preferably having a thermal conductivity greater than 10W/(m-c).
6. The downhole FBG temperature and pressure sensor of claim 1, wherein the rigid cavity of the sensing cavity has a CTE comparable to that of the fiber used in the temperature sensitive FBG, and preferably has a CTE less than 0.01x10 per degree Celsius -6 The modulus of elasticity is preferably greater than 195GPa.
7. The downhole fiber grating temperature and pressure sensor of claim 1, wherein the rigid cavity of the sensing cavity is made of a corrosion resistant material having a corrosion resistant depth of less than 0.005 mm/year.
8. The downhole fiber grating temperature and pressure sensor of claim 1, further comprising a base; the base is provided with an L-shaped fluid channel, one end of the L-shaped fluid channel is communicated with the cavity, and the other end of the L-shaped fluid channel is opened on the side surface of the sensor.
9. The downhole FBG temperature and pressure sensor of claim 8 including a straight strip-shaped housing, the base being radially embedded in the housing, the base having a through hole through which the series connection of the pressure sensitive FBG and the temperature sensitive FBG passes, the ends of the base passing through respective exit holes at respective ends of the housing.
10. A downhole linear array temperature and pressure sensing system comprising a plurality of downhole fiber grating temperature and pressure sensors of any one of claims 1 to 9 connected in series.
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| CN202211714299.8A CN115900789A (en) | 2022-12-29 | 2022-12-29 | Underground fiber bragg grating temperature and pressure sensor and linear array temperature and pressure sensing system |
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