RU157556U1 - FIBER OPTICAL PRESSURE DISTRIBUTION SENSOR - Google Patents

Abstract

1. Fiber optic pressure distribution sensor containing a cylindrical core and at least one deformation-sensitive optical fiber that is wound around the core in a helical line and fixed to the core, characterized in that the core is a sealed tube sealed from the ends and filled a given fluid under a given pressure, and the sensor contains a fluid pressure sensor inside the core. 2. The sensor according to claim 1, characterized in that the core is made of metal. 3. The sensor according to claim 1, characterized in that it contains at least one additional, temperature-sensitive optical fiber. The sensor according to claim 1, characterized in that it contains at least one additional optical fiber which is longitudinally sensitive to deformation and which is mechanically connected to the core. The sensor according to claim 1, characterized in that it comprises a device for monitoring core pressure. The sensor according to claim 1, characterized in that acetone, benzene, methyl alcohol, ethane, ammonia or nitrogen are used as the core filling fluid. The sensor according to claim 1, characterized in that it contains an outer protective shell. The sensor according to claim 1, characterized in that the optical fiber wound around the core in a helix sensitive to deformation is located inside a protective metal tube mechanically connected to it. A sensor according to claim 1, characterized in that the fluid pressure sensor inside the core is a pressure gauge located at the end of the sensor and connected to the internal volume of the core.

Description

The invention relates to sensors, namely, to designs of fiber-optic sensors for hydrostatic pressure distribution based on recording the distribution of the fine structure of scattered optical radiation along the length of the optical fiber. The sensor can be used for monitoring and logging of hydrocarbon wells.

To measure the pressure distribution, a special fiber optic cable design is used that converts hydrostatic pressure to deformation of a sensitive optical fiber. To measure the strain distribution of the sensitive optical fiber, methods are used based on recording the distribution of the fine structure parameters of the scattered radiation, namely, Rayleigh scattering (PP), Raman scattering (Raman scattering, or Raman scattering) and Mandelstam-Brillouin scattering (RMB). The location at which the physical parameter is measured (pressure, deformation, temperature) is based on recalculating the delay time from sensing to recording the scattering signal to a distance that corresponds to the path of light radiation along the optical fiber from the analyzer to the scattering point and vice versa.

The PP effect is coherent light scattering without changing the wavelength of particles, inhomogeneities, or other objects that are smaller than the wavelength. When using the properties of scattering coherence, the optical fiber plays the role of a distributed interferometer, the reflected signal from which contains information about the temperature and strain at the scattering point. To accurately determine the deformation and, accordingly, the pressure, it is necessary to measure the temperature profile and subtract the temperature contribution to the signal, that is, temperature compensation. When protecting an optical fiber from external mechanical influences, the signal gives information exclusively about temperature.

The Raman effect is due to the interaction of radiation with thermal molecular vibrations in the medium. For measurement, the temperature dependence of the amplitude ratio of the anti-Stokes and Stokes components of the Raman signal is used. The Raman signal contains information only about the temperature at the scattering point. This effect can be used to measure the temperature distribution, including thermal compensation for measuring the strain distribution and, accordingly, the pressure distribution.

Mandelstam-Brillouin scattering in an optical fiber can be considered as light diffraction by a moving grating created by an acoustic wave. Thus, the reflected signal experiences a Doppler frequency shift, since the grating moves with the speed of sound. The speed of sound is directly related to the density of the material and depends both on its temperature and on internal mechanical stress (deformation). As a result, the magnitude of the Brillouin frequency shift carries information about the temperature and strain at the scattering point. To accurately determine the deformation and, accordingly, the pressure, it is necessary to measure the temperature profile and subtract the temperature contribution to the Brillouin frequency shift, i.e., thermal compensation. When protecting an optical fiber from external mechanical influences, the Brillouin shift depends solely on temperature.

There are commercially available polling devices (analyzers) based on PP (see, for example, URL: http://lunainc.com/growth-area/strain-and-temperatore-sensing/. Accessed 07/22/2015; URL: http : //www.neubrex.com/htm/products/pro-nbx7000.htm, accessed 07/22/2015), based on the RMB (see, for example, URL: http://www.ozoptics.com/ALLNEW_PDF/ DTS0115RU.pdf, accessed 07/22/2015; URL: http://www.neubrex.com/htm/products/pro-nbx-lineup.htm, accessed 07/22/2015; URL: http: // omnisens.ch/ditest/3511-ditest-aim.php, accessed 22/07/2015), and based on the Kyrgyz Republic (see, for example, URL: http://www.lios-support.com/LIOS_WELL_DONE_Oil_and_Gas_EN.pdf, reference date 07/22/2015; URL: http://silixa.com/technology/ultima-dts/, reference date 07/22/2015; URL: http://www.sensornet.co.uk/techn ology / distributed-temperature-sensing, accessed 07/22/2015), which are connected to fiber-optic sensors based on recording the distribution of the fine structure of the scattered optical radiation along the length of the optical fiber.

Known distributed fiber-optic pressure sensor (RF patent No. 135129, publication date 11/27/2013) for monitoring systems of geophysical wells based on recording parameters of the fine structure of the scattered radiation. The known sensor contains a core, in the form of a flexible tube, an optical fiber for measuring pressure, spirally wound around the core. The optical fiber is spirally wound around the core with a variable pitch, with sections with a minimum winding pitch used to measure the pressure distribution, and sections with a maximum winding pitch used to compensate for longitudinal deformations. A disadvantage of the known is the limited range of measured pressures, which is determined by the mechanical properties of the sensor, which are constant. Another disadvantage of the known sensor is the lack of protection of the sensor from increased external pressure, under the influence of which instability can develop and the core in the form of a tube will collapse (collapse).

The closest technical solution (prototype) is a touch fiber optic cable (URL: http://www.neubrex.com/pdf/SEAFOM_Houston_20080218_Neubrex_Paul.pdf http://www.neubrex.com/pdf/SEAFOM_Houston_20080218_Neubrex_Paul.07pdf. .2015 and URL: http://www.neubrex.com/htm/products/pro-fiber_6.htm. Access date 07/21/2015), designed to measure the distribution of hydrostatic pressure, which contains a central force element located near its two connected optical fibers, two freely laid temperature sensitive optical fibers and two optical fibers, a sensor GOVERNMENTAL compression to tensile strain. Then, on top of the power element and these fibers, a cylindrical layer of elastic material is applied, on which two optical fibers sensitive to tensile / compressive strain are wound in a helical line. In addition, the sensor is protected by an outer shell. The principle of operation of the sensor is as follows. Using the RMB analyzer, temperature and strain profiles are measured along the corresponding fibers. Under the action of external hydrostatic pressure, the layer of elastic material is compressed, which leads to a deformation of the longitudinal compression of the optical fibers wound on it. Taking into account the distribution of the longitudinal tensile / compression strain of the sensor and the temperature distribution along the sensor allows the pressure distribution along the sensor cable to be uniquely determined from the longitudinal compression strain of the optical fibers wound along the helical line.

A disadvantage of the known sensor cable is the small range of measured pressures (up to 20 atm) and the small range of permissible operating temperatures (from 5 C to 60 C), which makes it impossible to use it for monitoring or logging of most oil and gas wells.

The task was to develop a fiber-optic sensor for measuring pressure distribution with an increased range of measured pressures, which is resistant to increased pressure and is operable in an increased temperature range to make it possible to use it for monitoring and logging oil and gas wells.

The technical result is achieved due to the fact that the fiber-optic pressure distribution sensor contains a cylindrical core and at least one deformation-sensitive optical fiber that is wound around the core in a helical line and fixed to the core, the core being a sealed tube sealed with ends and filled with a given fluid under a given pressure, and the sensor contains fluid pressure inside the core.

The core may be made of metal. The sensor may comprise at least one additional temperature sensitive optical fiber. The sensor may contain at least one additional, located longitudinally sensitive to deformation of the optical fiber, which is mechanically connected to the core. The sensor may comprise a device for monitoring core pressure. Acetone, benzene, methyl alcohol, ethane, ammonia or nitrogen may be used as the core core fluid. Also, the sensor may comprise an outer protective sheath. Sensitive to deformation, an optical fiber wound around a core along a helix can be located inside a protective metal tube mechanically connected to it. The fluid pressure sensor inside the core may be a pressure gauge located at the end of the sensor and connected to the internal volume of the core.

The utility model is illustrated in the drawing:

in FIG. 1 shows a fiber optic pressure distribution sensor;

The inventive fiber-optic pressure distribution sensor contains a cylindrical core 1, on which a strain-sensitive optical fiber 2 is wound along a helix. Optical fiber 2 is mounted on the core 1. Core 1 is a sealed tube sealed from the ends and filled with a predetermined fluid under a predetermined pressure. Also, the sensor contains a fluid pressure sensor inside the core 3.

An additional temperature-sensitive optical fiber 4 is located longitudinally under the outer protective sheath 7. An additional, longitudinally sensitive to optical fiber 5, which is mechanically connected to the core, is located under the outer protective sheath 7. The fluid pressure sensor 3 inside the core 1, which can be a manometer, and the device 6 for monitoring pressure in the core 1 is connected to the inner sealed volume of the core 1.

The principle of operation of the fiber optic pressure distribution sensor is as follows. Under the influence of external hydrostatic pressure with the medium into which the sensor is placed, the sensor is compressed over its cross section, as a result of which the radius of the cylindrical core 1 decreases, and the optical fiber 2 that is sensitive to deformation and wound around the core 1 along a helix undergoes deformation longitudinal compression, the distribution of which is recorded by the methods described above based on recording the distribution of the parameters of the fine structure of the scattered radiation. Based on the data on the distribution of deformation of fiber 2, the distribution of external pressure along the sensor is calculated. Filling the core 1, which is a sealed tube, sealed at the ends, with a given fluid under a given pressure, can increase the resistance of the sensor to external pressure and increase the range of measured pressures. The range of measured pressures increases, including due to the fact that the optical fiber 2 and the core 1 due to internal pressure are in a pre-stressed state (tensile state). The fluid pressure sensor 3 inside the sensor core is used to monitor the state of core 1 and calibrate the measured pressure distribution.

To ensure resistance to high pressures in a wide temperature range, the core 1 can be made of metal.

An additional temperature-sensitive optical fiber 4 is used to measure the temperature distribution along the sensor using the methods described above based on recording the distribution of the fine structure parameters of the scattered radiation. The measured temperature distribution is used for thermal compensation in measuring the distribution of deformation and therefore pressure. Also, the measured temperature distribution can be used on its own, for example, when monitoring or logging oil or gas wells.

An additional optical fiber 5 located longitudinally sensitive to deformation is mechanically connected to the core and is used to measure the distribution of tensile / compression strain of the sensor using the methods described above based on recording the distribution of the fine structure parameters of the scattered radiation. The measured distribution of the tensile / compression strain of the sensor is used to compensate for its effect on the measurement results of the strain distribution of the optical fiber 2 and, therefore, the pressure.

The device 6 for monitoring the pressure in the core is used to change the fluid pressure inside the core (internal pressure), due to which the magnitude of the deformation of the core 1 and the optical fiber 2 is controlled, which, firstly, ensures the safe operation of the sensor, for example, by increasing the internal pressure at increasing the measured external pressure, and secondly, provides operational adjustment of the optimal conditions for measuring pressure, which is achieved in predetermined ranges of optical deformations fiber 2 and core 1, depending on both external and internal pressure.

As filling core, it is preferable to use fluids with low viscosity. So, when using a sensor located in a horizontal plane when measuring slow processes, it is preferable, due to greater safety and simplicity of pressure control, to use low-compressible liquid fluids, such as acetone, benzene, methyl alcohol.

When using a sensor whose different sections are located at different heights, it is necessary to take into account the force of gravity, which leads to the dependence of the internal pressure in the core 1 on the height, which can be calculated using known methods knowing the density of the fluid (which generally depends on temperature) and the geometry of the sensor. In this case, it is preferable to use a gaseous fluid with a low density, for example ethane, ammonia or nitrogen, the use of which does not cause a strong dependence of pressure on height, so that in some cases it can be neglected.

Note that the use of a fluid with a low viscosity makes it possible to measure faster processes, since at a lower viscosity the pressure inside the core stabilizes faster.

To protect the optical fiber 2 sensitive to deformation of the optical fiber 2 wound around the core 1 along a helix from external mechanical influences and from the effects of aggressive media, in the frequency of hydrogen, the penetration of which can lead to an increase in kilometer attenuation in fiber 2, this fiber 2 can be located inside mechanically connected with it a protective metal tube.

The fluid pressure sensor 6 inside the core 1 can be made in the form of a manometer, for example, with a pointer, which is connected to the internal volume of the core at the end of the sensor. You can also use other known methods for determining the internal pressure in the core 1.

An advantage of the claimed sensor is the possibility of its manufacture using known technologies. So, methods are already known (see prototype) for manufacturing a sensor in the form of a cylindrical core with a strain-sensitive optical fiber that is wound around the core in a helical line and mounted on it, with an additional temperature-sensitive optical fiber and an additional one located longitudinally sensitive to optical fiber deformation, which is mechanically connected to the core. The manufacture of a core in the form of a metal tube, for example, stainless steel, is possible (including a few kilometers long) on equipment for the manufacture of an optical lightning cable (see URL: http://nsw.com/Portals/0/Dokumente/NSW_Aerial% 20Cables% 20and% 20Systems.pdf accessed July 23, 2015) or phase wire (see RF Patent for Utility Model No. 124033, published January 10, 2013).

A traditional pressure gauge can be used as a fluid pressure sensor inside the core (see URL: https://ru.wikipedia.org/wiki/%D0%9C%D0%B0%D0%BD%D0%BE%D0%BC% D0% B5% D1% 82% D1% 80 (accessed July 23, 2015), located at the end of the sensor and connected to the internal volume of the core. As a device for controlling core pressure, a conventional gas or liquid pressure reducer can be used. Sealing the core tube from the ends, as well as connecting a pressure sensor (manometer) to it, pressure monitoring devices can be performed using standard hoses, tubes and high pressure fittings used in modern hydraulic systems (see, for example, URL: http: / /www.hydravia.ru/products/trubnye_soedineniya_ugol_konusa_24/, accessed 07.23.2015).

The manufacture of a strain-sensitive optical fiber located inside a protective metal tube mechanically connected to it is possible on equipment similar to that used for the production of known distributed strain sensors (see RF Patent Utility Model No. 124033, published January 10, 2013, see URL: http : //lscom.ru/smc_v4.html, accessed July 23, 2015).

The outer protective sheath of the sensor may be one of the traditional designs used for geophysical cables or optical communication cables and may contain, for example, a continuous sheath of polymer, armor, in the form of a wound from wires or in the form of corrugated metal tape. The outer protective sheath of the sensor can be performed on traditional equipment used in the production of geophysical cables or optical communication cables.

Claims (9)

1. Fiber optic pressure distribution sensor containing a cylindrical core and at least one deformation-sensitive optical fiber that is wound around the core in a helical line and fixed to the core, characterized in that the core is a sealed tube sealed from the ends and filled a given fluid under a given pressure, and the sensor contains a fluid pressure sensor inside the core. 2. The sensor according to claim 1, characterized in that the core is made of metal. 3. The sensor according to claim 1, characterized in that it contains at least one additional, temperature-sensitive optical fiber. 4. The sensor according to claim 1, characterized in that it contains at least one additional, located longitudinally sensitive to the deformation of the optical fiber, which is mechanically connected to the core. 5. The sensor according to claim 1, characterized in that it comprises a device for monitoring core pressure. 6. The sensor according to claim 1, characterized in that acetone, benzene, methyl alcohol, ethane, ammonia or nitrogen are used as the core filling fluid. 7. The sensor according to claim 1, characterized in that it contains an outer protective shell. 8. The sensor according to claim 1, characterized in that the optical fiber wound around the core in a helix sensitive to deformation is located inside a protective metal tube mechanically connected to it. 9. The sensor according to claim 1, characterized in that the fluid pressure sensor inside the core is a pressure gauge located at the end of the sensor and connected to the internal volume of the core.

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