Optical frequency domain reflectometry based fiber optic crude oil storage tank interface monitoring device and method

Abstract

The application provides a kind of based on optical frequency domain reflection's optical fiber crude oil storage tank interface monitoring device and method, device includes measurement component, measurement cable, host computer and heating component;Measurement component at least includes optical component and signal processing component;The first end of measurement cable is located in the tank mouth of crude oil storage tank, and the second end is located in the tank bottom of crude oil storage tank;Optical component and the first end of measurement cable are connected, and signal processing component and the first end of measurement cable are connected;Optical component is used to generate the light beam of incident measurement cable;Signal processing component is used to obtain the temperature data associated with the backscattering Rayleigh scattering light generated by measurement cable, temperature data characterizes the temperature information of each position of measurement cable, and backscattering Rayleigh scattering light is related to the temperature of each position of measurement cable;Heating component heats measurement cable to specified temperature;Host computer determines the position of the interface of different medium in crude oil storage tank according to temperature data in the process that measurement cable starts to cool from specified temperature.

Description

Technical Field

[0001] This invention relates to the field of crude oil storage tank interface monitoring technology, and in particular to a fiber optic crude oil storage tank interface monitoring device and method based on optical frequency domain reflection. Background Technology

[0002] Crude oil produced from oilfield wells typically has a high water content, generally between 70% and 90%. Therefore, the extracted crude oil needs to undergo multiple processes, including demulsification, dehydration, degassing, settling, impurity removal, oil-water separation, and oil-gas separation, to obtain petroleum that meets refining standards. During the settling process in crude oil storage tanks (referred to as oil tanks), the various media such as gas, oil, and water, due to their different densities, are distributed in different areas of the tank. Therefore, from top to bottom, the tank can be divided into a gas layer, a foam layer, an oil layer, an emulsion layer, and a water layer. In actual oil production, it is necessary to periodically drain the crude oil to reduce its water content. Therefore, accurately measuring the locations of the interfaces between the layers within the oil tank helps to achieve precise control over the drainage volume, thereby reducing energy consumption, saving costs, and improving production automation.

[0003] One existing method for monitoring the interface inside an oil tank involves using a guiding optical fiber installed inside the tank to guide an optical signal from the gas inside the tank to the liquid, thereby generating a strong reflection peak at the gas-liquid interface. The location of the gas-liquid interface is determined by locating the position of the strong reflection peak.

[0004] The problem with this approach is that it cannot monitor other interfaces within the tank (such as the interface between the oil layer and the emulsion layer, and the interface between the emulsion layer and the water layer), making it difficult to accurately control the drainage volume. Summary of the Invention

[0005] To address the shortcomings of the prior art, this invention provides a fiber optic crude oil storage tank interface monitoring device and method based on optical frequency domain reflection, in order to monitor the interface of multiple media within the oil tank.

[0006] The first aspect of this application provides a fiber optic crude oil storage tank interface monitoring device based on optical frequency domain reflection, comprising: a measurement component, a measurement optical cable, a host computer, and a heating component;

[0007] The measurement components include at least optical components and signal processing components;

[0008] The first end of the measuring optical cable is located at the mouth of the crude oil storage tank, and the second end is located at the bottom of the crude oil storage tank.

[0009] The optical component is connected to the first end of the measuring optical cable, and the signal processing component is connected to the optical component;

[0010] The optical components are used to generate a light beam incident on the measuring optical cable;

[0011] The signal processing component is used to obtain temperature data associated with the backscattered Rayleigh light generated by the measuring optical cable. The temperature data characterizes the temperature information at various locations of the measuring optical cable, and the backscattered Rayleigh light is related to the temperature at various locations of the measuring optical cable.

[0012] The heating assembly includes at least a heating sleeve and a steam generator;

[0013] The measuring optical cable is installed inside the heating sleeve;

[0014] The steam generator is used to supply steam into the heating sleeve to heat the measuring optical cable;

[0015] The host computer is used to determine the location of the interface between different media in the crude oil storage tank based on the temperature data during the cooling process of the measuring optical cable from the specified temperature.

[0016] A second aspect of this application provides a fiber optic crude oil tank interface monitoring method based on optical frequency domain reflection, applied to a fiber optic crude oil tank interface monitoring device including a measuring optical cable, wherein a first end of the measuring optical cable is located at the tank opening of the crude oil tank, and a second end is located at the bottom of the crude oil tank, the method comprising:

[0017] Steam at a specified temperature is supplied into the heating sleeve containing the measuring optical cable, so that the measuring optical cable is heated to the specified temperature;

[0018] During the cooling process of the measuring optical cable from the specified temperature, temperature data associated with the backscattered Rayleigh light generated by the measuring optical cable is obtained. The temperature data characterizes the temperature information at various locations of the measuring optical cable. The backscattered Rayleigh light is related to the temperature at various locations of the measuring optical cable. The backscattered Rayleigh light is generated after the light beam enters the measuring optical cable.

[0019] The location of the interface between different media inside the crude oil storage tank is determined based on the temperature data.

[0020] The beneficial effects of this plan are as follows:

[0021] Based on the backscattered Rayleigh light generated when the beam is incident on the measuring optical cable, temperature data at various locations are obtained when the measuring optical cable cools down throughout the crude oil storage tank. The location of the interface between different media in the crude oil storage tank is determined based on the temperature data. Compared with the existing scheme, this scheme can obtain the temperature data of the measuring optical cable at each interface, thus determining the location of multiple interfaces in the crude oil storage tank (such as the interface between the oil layer and the emulsion layer, and the interface between the emulsion layer and the water layer), which is beneficial for more accurate control of the drainage of the crude oil storage tank. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0023] Figure 1 A schematic diagram of the structure of a fiber optic crude oil storage tank interface monitoring device based on optical frequency domain reflection provided in an embodiment of this application;

[0024] Figure 2 A schematic diagram illustrating the positional relationship between a measuring optical cable and a heating sleeve, provided as an embodiment of this application;

[0025] Figure 3 This application provides a schematic diagram of the structure of an optical component and a signal processing component according to an embodiment of the present application.

[0026] Figure 4 A schematic diagram of an FPGA digital signal processing unit and a host computer provided for embodiments of this application;

[0027] Figure 5 A flowchart illustrating a fiber optic crude oil storage tank interface monitoring method based on optical frequency domain reflection, provided for embodiments of this application;

[0028] Figure 6 A flowchart illustrating a cross-correlation demodulation method provided in this application embodiment;

[0029] Figure 7 This application provides a curve showing the change of temperature data with distance from the tank opening. Detailed Implementation

[0030] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] To facilitate understanding of the technical solution of this embodiment, some terms that may be involved in this embodiment will be explained first.

[0032] Optical Frequency Domain Reflectometry (OFDR) is an optical signal monitoring technology. A monitoring system based on this technology is called an OFDR system. In this system, a linearly swept laser emits swept light that is transmitted to a reference arm and a signal arm. The backscattered Rayleigh light returning from each position on the signal arm beats with the light in the reference arm. The frequency and intensity of the received interference signal are used to locate events, and strain and temperature changes are calculated based on the spectral shift.

[0033] Spatial resolution. In distributed fiber optic sensing, spatial resolution characterizes the length of fiber represented by a single sensing point. It involves dividing a single fiber into continuous segments of equal length, with the smallest segment serving as a sensing unit, known as the spatial resolution. The spatial resolution of an OFDR system can reach the centimeter (cm) to millimeter (mm) level.

[0034] Backscattering. Rayleigh scattering is caused by the difference in refractive index of optical fibers, and the scattering occurs throughout the entire fiber. Rayleigh scattering disperses the optical signal in all directions, and the scattered light that returns along the original path of the fiber is called backscattered Rayleigh light.

[0035] Beat frequency interference effect. In an OFDR system, after the linearly swept beam passes through the signal arm and the reference arm respectively, the two beams interfere with each other, which is called the beat frequency interference effect.

[0036] Specific heat capacity. The ratio of the heat absorbed (or released) by a given mass of a substance when its temperature rises (or falls) to the product of its mass and the temperature rise (or fall) is called the specific heat capacity of that substance. Specific heat capacity is represented by c, and the unit is joules per kilogram per degree Celsius (J / kg·℃).

[0037] One existing method for monitoring the interface inside an oil tank involves connecting an optical frequency domain reflectometer (OFDR) to one end of a sensing fiber optic cable, and the other end of the sensing fiber optic cable to a guide fiber optic cable. The OFDR transmits optical signals to the sensing fiber optic cable, which then travels along the sensing fiber optic cable to the guide fiber optic cable. One end of the guide fiber optic cable connected to the sensing fiber optic cable is in the air, while the other end is immersed in the liquid inside the crude oil storage tank. The optical signal passes through the air-liquid interface in the guide fiber optic cable, generating a strong reflection peak at the air-liquid interface. The OFDR measurement system can locate the position of the strong reflection peak, thereby determining the location of the air-liquid interface.

[0038] The drawback of the above solution is that it is only applicable to the detection of air-liquid interfaces and is difficult to detect multiple interfaces between various media in crude oil storage tanks.

[0039] Another existing solution for monitoring interfaces within oil tanks involves a heating power control component that uses an optical fiber to penetrate the liquid inside the crude oil storage tank. The oil-water interface processor responds to a power-on command and uses the optical fiber to obtain multiple current-moment temperature-sensitive characteristic data points. Based on this data, the processor analyzes the location of each interface. The oil-water interface processor is the main unit of a distributed temperature sensing (DTS) system.

[0040] The drawback of the above solution is that it uses DTS temperature measurement technology to detect the oil-water interface. However, the spatial resolution of DTS technology is at the meter level, while the thickness of some media layers (such as emulsion layers and foam layers) inside crude oil storage tanks is usually at the centimeter or millimeter level. Therefore, DTS technology cannot identify emulsion layers and foam layers, making it difficult to accurately estimate the interface between these layers and other media layers, and thus making it impossible to accurately control the drainage volume.

[0041] To address the shortcomings of the existing solutions, this application provides a fiber optic crude oil storage tank interface monitoring device and corresponding monitoring method based on optical frequency domain reflection.

[0042] The structure of the fiber optic crude oil tank interface monitoring device based on optical frequency domain reflection can be found in [reference needed]. Figure 1 .

[0043] The device may include: a heating component, a measuring component 1, a measuring optical cable 31, and a host computer 5.

[0044] The measurement components may include optical components and signal processing components;

[0045] The first end of the measuring optical cable is located at the mouth of the crude oil storage tank, and the second end is located at the bottom of the crude oil storage tank; that is to say, the measuring optical cable runs through the liquid substance stored inside the crude oil storage tank.

[0046] The optical component is connected to the first end of the measurement optical cable, and the signal processing component is connected to the optical component. Specifically, the dual-channel photodetector of the signal processing component can be connected to the fourth and fifth fiber optic couplers of the optical component.

[0047] Optical components are used to generate a beam of light incident on the measurement optical cable;

[0048] The signal processing component is used to obtain temperature data associated with the backscattered Rayleigh light generated by the measurement optical cable. The temperature data characterizes the temperature information at various locations of the measurement optical cable, and the backscattered Rayleigh light is related to the temperature at various locations of the measurement optical cable.

[0049] The heating assembly may include at least a heating sleeve 33 and a steam generator 4.

[0050] The measuring optical cable is placed inside the heating sleeve, and the steam generator is used to supply steam into the heating sleeve to heat the measuring optical cable;

[0051] The host computer is used to determine the location of the interface between different media in the crude oil storage tank based on temperature data during the process of measuring the optical cable cooling down from a specified temperature.

[0052] Please see Figure 1 One end of the heating sleeve is located Figure 1 The heating sleeve is located at the opening of crude oil storage tank 2, and the other end of the heating sleeve can contact the bottom of crude oil storage tank 2.

[0053] In some alternative embodiments, crude oil storage tank 2 may also be replaced with a crude oil storage tank interface simulation component for simulating crude oil storage tanks.

[0054] Crude oil storage tanks can contain multiple media in layers, such as... Figure 1 The tank may include, from the opening to the bottom, an air layer 221, a foam layer 222, an oil layer 223, an emulsion layer 224, and a water layer 225. These media are distributed from top to bottom due to their different densities.

[0055] The steam generator can output steam at a specific temperature. The steam output port of the steam generator can be directly connected to the end of the heating sleeve located at the tank opening. The output steam directly enters the heating sleeve to heat the measuring optical cable.

[0056] Alternatively, to facilitate the installation of the steam generator, the heating assembly may also include Figure 1 The steam transmission pipe 34 shown has one end connected to the steam output port of the steam generator, and the other end extending into the heating jacket. Thus, steam output from the steam generator can be transmitted into the heating jacket through the steam transmission pipe.

[0057] Heating sleeves can be fixed to crude oil storage tanks in a variety of ways.

[0058] As an example, the crude oil storage tank has a tank measuring instrument connection flange 21 and a measuring component connection flange 32 at the tank opening. The former forms an integral structure with the crude oil storage tank, while the latter is welded to the heating sleeve. The heating sleeve and the crude oil storage tank are connected through these two flanges.

[0059] For measuring the positional relationship between the optical cable, heating sleeve, and steam transmission pipe, please refer to... Figure 2 (1). As can be seen, the heating sleeve surrounds the measuring optical cable, and a cavity capable of accommodating high-temperature steam is formed between the inner wall of the heating sleeve and the outer surface of the measuring optical cable. The other end of the steam transmission pipe extends into the cavity inside the heating sleeve, and the high-temperature steam generated by the steam generator is input into the cavity, thereby heating the measuring optical cable located inside the heating sleeve.

[0060] The measurement optical cable may include a protective sheath and at least one measurement optical fiber encased within the protective sheath, for example, it may include... Figure 2 The first and second measuring optical fibers are shown in the cross-sectional view of (2);

[0061] Correspondingly, when the optical components generate a beam of light incident on the measurement optical cable, they can generate a beam of light incident on the first measurement optical fiber and the second measurement optical fiber.

[0062] Backscattered Rayleigh light can be generated after the light beam is incident on the first and second measuring optical fibers. The temperature data obtained by the signal processing component can be temperature data associated with the first and second backscattered Rayleigh light, wherein the first backscattered Rayleigh light is generated by the first measuring optical fiber and the second backscattered Rayleigh light is generated by the second measuring optical fiber.

[0063] Optional, please see Figure 3 The optical components may specifically include a linearly swept frequency light source, an optical isolator, a first circulator, a second circulator, a first reference fiber, a second reference fiber, a first fiber coupler, a second fiber coupler, a third fiber coupler, a fourth fiber coupler, and a fifth fiber coupler.

[0064] The second fiber coupler and the fourth fiber coupler may include a first circulator, which can be connected to the first sensing fiber and the first sensing fiber can be connected to the first measuring fiber.

[0065] A second circulator may be included between the third fiber coupler and the fifth fiber coupler. The second circulator may be connected to the second sensing fiber and the second sensing fiber may be connected to the second measurement fiber.

[0066] The linear sweep frequency light source is connected to the first fiber optic coupler through an optical isolator. Thus, the beam generated by the linear sweep frequency light source can enter the first fiber optic coupler through the optical isolator. The optical isolator can prevent the reflected light from damaging the light source.

[0067] The first fiber coupler is used to split the beam provided by the linear sweep frequency source into a first beam and a second beam.

[0068] The second fiber coupler is used to pass a portion of the first beam through the first circulator into the first measuring fiber, and to pass another portion of the first beam into the first reference fiber.

[0069] The third fiber coupler is used to pass a portion of the second beam through the second circulator into the second measuring fiber, and to pass another portion of the second beam into the second reference fiber.

[0070] The fourth fiber coupler is used to obtain the first beat frequency interference light signal and the second beat frequency interference light signal at different times based on the beams of the first back-scattered Rayleigh light and the first reference fiber.

[0071] The fifth fiber coupler is used to obtain the third and fourth beat frequency interference signals at different times based on the beams of the second back-scattered Rayleigh light and the second reference fiber.

[0072] The signal processing component is used to obtain temperature data associated with the first and second backscattered Rayleigh light, including:

[0073] The signal processing component is used to obtain temperature data based on the first beat frequency interference optical signal, the second beat frequency interference optical signal, the third beat frequency interference optical signal and the fourth beat frequency interference optical signal.

[0074] like Figure 3 As shown, the signal processing component may include a dual-channel photodetector, a dual-channel AD acquisition module, and an FPGA digital signal processing unit.

[0075] When the measurement component is operating, the beam output from the linearly swept frequency light source passes through the optical isolator and enters the first fiber coupler. The first fiber coupler can split the incident beam into two beams at a certain splitting ratio, which are then incident on the second and third fiber couplers respectively. The splitting ratio of the first fiber coupler can be 50%:50%, meaning that the first fiber coupler can split the beam output from the light source into two beams of equal intensity, which are then incident on the second and third fiber couplers respectively.

[0076] The input end of the second fiber coupler and one output end of the first fiber coupler are connected by an optical fiber. After the beam split from the first fiber coupler enters the second fiber coupler, the second fiber coupler can split the incident beam into two beams with a splitting ratio of 99%:1%. The beam with 99% intensity enters the first sensing fiber through the first circulator and enters the first measuring fiber along the first sensing fiber. The beam with 1% intensity enters the fourth fiber coupler through the first reference fiber.

[0077] The input end of the third fiber coupler and the other output end of the first fiber coupler are connected by an optical fiber. After the beam split from the first fiber coupler enters the third fiber coupler, the third fiber coupler can split the incident beam into two beams with a splitting ratio of 99%:1%. The beam with 99% intensity enters the second sensing fiber through the second circulator and enters the second measuring fiber along the second sensing fiber. The beam with 1% intensity enters the fifth fiber coupler through the second reference fiber.

[0078] The first backscattered Rayleigh light generated by the first measuring fiber can return to the fourth fiber coupler through the first circulator, and the second backscattered Rayleigh light generated by the second measuring fiber can return to the fifth fiber coupler through the second circulator.

[0079] The first backscattered Rayleigh light and 1% of the beam in the first reference fiber can generate a beat frequency interference effect in the fourth fiber coupler, thereby generating a beat frequency interference optical signal. The fourth fiber coupler can transmit the first beat frequency interference optical signal and the second beat frequency interference optical signal generated at different times to the first channel of the dual-channel photodetector through the optical fiber.

[0080] The second backscattered Rayleigh beam and 1% of the beam in the second reference fiber can generate a beat frequency interference effect in the fifth fiber coupler, thereby generating a beat frequency interference optical signal. The fifth fiber coupler can transmit the third and fourth beat frequency interference optical signals generated at different times to the second channel of the dual-channel photodetector through the optical fiber.

[0081] Among them, the first beat frequency interference optical signal and the third beat frequency interference optical signal are optical signals generated at the same time, for example, both are optical signals generated at time t1, and the second beat frequency interference optical signal and the fourth beat frequency interference optical signal are optical signals generated at the same time, for example, both are optical signals generated at time t2.

[0082] The dual-channel photodetector can convert the two optical signals output from the fourth and fifth fiber couplers into corresponding beat frequency interference electrical signals; the dual-channel AD acquisition module can convert the beat frequency interference electrical signals provided by the dual-channel photodetector into corresponding digital interference signals; and the FPGA digital signal processing unit can process the digital interference signals into temperature data characterizing the temperature at different locations on the optical cable.

[0083] Please see below. Figure 4 The FPGA digital signal processing unit may include an OFDR backscattering demodulation module and a cross-sensitivity cancellation module. The OFDR backscattering demodulation module can perform temperature and strain demodulation operations on digital interference signals at different times, while the cross-sensitivity cancellation module is used for cross-sensitivity cancellation operations.

[0084] Temperature data obtained by the FPGA digital signal processing unit can be uploaded to a host computer via Ethernet or serial port. This host computer can be a personal computer or other electronic device with similar data processing capabilities. Based on the temperature data and the differences in specific heat capacity of different media, the host computer can determine the precise location of the interface between different media layers within the crude oil storage tank.

[0085] In some alternative embodiments, the first and second measuring optical fibers can be directly connected to the measuring component, and the beam output by the measuring component can directly enter the measuring optical fibers.

[0086] In some alternative embodiments, the monitoring device of this embodiment may further include Figure 1 The sensing optical cable 35 shown includes a first sensing optical fiber and a second sensing optical fiber.

[0087] The first measuring optical fiber is connected to the first circulator via the first sensing optical fiber, and the first circulator is connected to the second optical fiber coupler.

[0088] The second measuring fiber is connected to the second circulator via the second sensing fiber, and the second circulator is connected to the third fiber coupler.

[0089] In this case, the light beam output by the light source of the measuring component can be transmitted along the first sensing fiber to the first measuring fiber, and along the second sensing fiber to the second measuring fiber.

[0090] The beneficial effects of this embodiment are as follows:

[0091] Based on the backscattered Rayleigh light generated when the beam is incident on the measuring optical cable, temperature data at various locations are obtained when the measuring optical cable cools down throughout the crude oil storage tank. The location of the interface between different media in the crude oil storage tank is determined based on the temperature data. Compared with the existing scheme, this scheme can obtain the temperature data of the measuring optical cable at each interface, thus determining the location of multiple interfaces in the crude oil storage tank (such as the interface between the oil layer and the emulsion layer, and the interface between the emulsion layer and the water layer), which is beneficial for more accurate control of the drainage of the crude oil storage tank.

[0092] This application also provides a fiber optic crude oil tank interface monitoring method based on optical frequency domain reflection. This method can be applied to a fiber optic crude oil tank interface monitoring device based on optical frequency domain reflection, which includes a measuring optical cable. The structure and working principle of the device can be found in the foregoing embodiments.

[0093] Please see Figure 5 Here is a flowchart of the above method, which may include the following steps.

[0094] S501 delivers steam at a specified temperature into the heating sleeve containing the measuring optical cable, thereby heating the measuring optical cable to the specified temperature.

[0095] In step S501, the steam generator can generate high-temperature steam at a specified temperature, such as 100 degrees Celsius, under the control of the host computer, and input the steam into the heating jacket through the steam transmission pipe.

[0096] The host computer can control the steam generator to continuously supply high-temperature steam to the heating jacket for a certain duration, thereby ensuring that all positions of the measuring optical cable in the crude oil storage tank are heated to the specified temperature. For example, the host computer can control the steam generator to continuously supply 100-degree high-temperature steam to the heating jacket for 10 minutes to ensure that all positions of the measuring optical cable in the crude oil storage tank are heated to 100 degrees Celsius.

[0097] S502, during the cooling process of the measuring optical cable from a specified temperature, obtain temperature data associated with the back Rayleigh scattering light generated by the measuring optical cable. The temperature data characterizes the temperature information at various locations of the measuring optical cable. The back Rayleigh scattering light is related to the temperature at various locations of the measuring optical cable and is generated after the beam enters the measuring optical cable.

[0098] Step S502 may include:

[0099] Receive the first back Rayleigh scattered light generated by the first measuring fiber in the measuring optical cable, and the second back Rayleigh scattered light generated by the second measuring fiber in the measuring optical cable;

[0100] Temperature data were obtained based on the first and second backscattered Rayleigh light.

[0101] The temperature data obtained based on the first and second backscattered Rayleigh light may include:

[0102] At different times, a first beat frequency interference light signal and a second beat frequency interference light signal are obtained based on the first backscattered Rayleigh light and the first reference light;

[0103] The third and fourth beat frequency interference signals are obtained at different times based on the second backscattered Rayleigh light and the second reference light.

[0104] Temperature data is obtained based on the first, second, third, and fourth beat frequency interference optical signals.

[0105] Specifically, after confirming that all parts of the measuring optical cable have been heated to the specified temperature, the host computer can control the steam generator to stop supplying steam, at which point the measuring optical cable will begin to cool down from the specified temperature.

[0106] After the steam generator stops supplying steam, the host computer can control the optical components to continuously generate a beam of light directed toward the measurement optical cable. At different times, the signal processing components can measure the backscattered Rayleigh light generated after the beam is incident on the measurement optical cable. For example, a measurement can be performed at time t1 after the steam supply stops, and another measurement can be performed at time t2 after the steam supply stops, so as to obtain the beat frequency interference light signals at the two times.

[0107] After the beam enters the first measuring fiber, the first measuring fiber returns a first back Rayleigh scattered light carrying temperature and strain information at various locations on the first measuring fiber. The first back Rayleigh scattered light generates a beat frequency interference signal with the first reference beam in the fourth fiber coupler. After the beam enters the second measuring fiber, the second measuring fiber returns a second back Rayleigh scattered light carrying temperature and strain information at various locations on the second measuring fiber. The second back Rayleigh scattered light generates a beat frequency interference signal with the second reference beam in the fifth fiber coupler.

[0108] The first reference beam refers to the beam with 1% intensity that enters the fourth fiber coupler through the first reference fiber; the second reference beam refers to the beam with 1% intensity that enters the fifth fiber coupler through the second reference fiber.

[0109] Since the light source of the optical component outputs beams at two different times, the signal processing component can obtain the first beat frequency interference light signal, the second beat frequency interference light signal, the third beat frequency interference light signal and the fourth beat frequency interference light signal generated by the two fiber couplers (the fourth fiber coupler and the fifth fiber coupler) at two different times, and then obtain temperature data based on these beat frequency interference light signals.

[0110] S503 determines the location of the interface between different media inside the crude oil storage tank based on temperature data.

[0111] The beneficial effects of this embodiment can be found in the beneficial effects of the corresponding devices in the foregoing embodiments, and will not be repeated here.

[0112] The signal processing component may obtain temperature data from the beat frequency interference optical signal in the following ways:

[0113] The first wavelength shift is obtained by processing the first beat frequency interference optical signal and the second beat frequency interference optical signal using the cross-correlation demodulation method.

[0114] The second wavelength shift was obtained by processing the third and fourth beat frequency interference optical signals using the cross-correlation demodulation method.

[0115] Based on the first wavelength drift, the second wavelength drift, the temperature sensitivity coefficient and strain sensitivity coefficient of the first measuring fiber, and the temperature sensitivity coefficient and strain sensitivity coefficient of the second measuring fiber, the temperature data at each location of the measuring optical cable are determined.

[0116] Specifically, the first beat frequency interference light signal output by the fourth fiber coupler at time t1 is processed by a dual-channel photodetector and a dual-channel AD acquisition module to obtain the corresponding first digital interference signal P11. The second beat frequency interference light signal output by the fourth fiber coupler at time t2 is processed by a signal processing component to obtain the corresponding second digital interference signal P12. The OFDR backscattering demodulation module can demodulate the first and second digital interference signals to obtain the wavelength drift that characterizes the temperature and strain changes at various positions of the first measuring fiber during the time interval from t1 to t2.

[0117] The third beat frequency interference light signal output by the fifth fiber coupler at time t1 is processed by a dual-channel photodetector and a dual-channel AD acquisition module to obtain the corresponding third digital interference signal P21. The fourth beat frequency interference light signal output by the fifth fiber coupler at time t2 is processed by a signal processing component to obtain the corresponding fourth digital interference signal P22. The OFDR back Rayleigh scattering demodulation module can demodulate the third and fourth digital interference signals to obtain the wavelength drift that characterizes the temperature and strain changes at various positions of the second measuring fiber during the time interval from t1 to t2.

[0118] Then, the two sets of wavelength drift values ​​are input into the cross-sensitivity elimination module. The cross-sensitivity elimination module uses the pre-set temperature sensitivity coefficient and strain sensitivity coefficient of the two measuring optical fibers, combined with the wavelength drift values, to establish a set of wavelength drift equations based on the sensitivity matrix, eliminate strain changes in the measuring optical fibers, and obtain temperature data characterizing the temperature changes at various locations of the measuring optical cable.

[0119] Temperature data can be expressed in ΔT i The expression represents the position of the optical fiber being measured, where i represents the i-th position of the optical fiber, and the upper limit of the value of i is related to the spatial resolution of the OFDR system. ΔT i This indicates the temperature change at this location during the time interval from t1 to t2.

[0120] The demodulation method used in the OFDR back Rayleigh scattering demodulation module can be as follows: Figure 6 The cross-correlation demodulation method shown can also be other OFDR system demodulation methods. For details, please refer to relevant technical documents. This embodiment does not limit the demodulation method used.

[0121] After demodulation by the OFDR backscattering demodulation module, the wavelength shift Δλ at each position of the first measurement fiber during the time interval t1 to t2 can be obtained. 1i And the wavelength shift Δλ at each position of the second measuring fiber during the time interval t1 to t2. 2i .

[0122] After the light beam enters the optical fiber, the wavelength shift of the back Rayleigh scattered light generated by the optical fiber can be expressed by the following formula (1).

[0123]

[0124] Among them, K T and K ε Let ΔT and Δε represent the temperature sensitivity coefficient and strain sensitivity coefficient of the optical fiber, respectively, where ΔT represents the temperature change, Δε represents the strain change, and λ0 is the initial wavelength of the incident light. Assume the wavelength shifts of the two demodulated signals are Δλ and Δε, respectively. 1i and Δλ 2i Let the temperature and strain changes experienced by the optical cable at position i be ΔT and ΔT, respectively. i and Δε i The temperature sensitivity coefficient of the first measuring optical fiber is K. T1 The strain sensitivity coefficient is K ε1 The temperature sensitivity coefficient of the second measuring fiber is K. T2 The strain sensitivity coefficient is K ε2 The wavelength shift at each position of the first and second measuring fibers can be expressed by the following formula (2).

[0125]

[0126] Formula (2) can be transformed into the following formula (3).

[0127]

[0128] Based on the wavelength drift equations (3) based on the sensitivity matrix, substituting the wavelength drift of the first and second measuring fibers at various positions eliminates the cross-sensitivity effect and yields the temperature data ΔT characterizing the temperature change amplitude at each position of the measuring optical cable. i .

[0129] After obtaining the temperature data, the location of each interface can be determined as follows.

[0130] After heating of the optical cable is stopped, the temperature changes of different media layers vary within the same time frame due to differences in their specific heat capacities. Water has a specific heat capacity of 4.2 kJ / (kg·℃), crude oil 1.7–2.0 kJ / (kg·℃), and air 1.007 kJ / (kg·℃), while the specific heat capacities of the emulsion and foam layers fall between those of water, crude oil, and crude oil / air. Therefore, the temperature decreases at different rates within the same time frame. After obtaining temperature data at various locations within the optical cable, the temperature distribution can be determined based on this data. Figure 7The curve showing the location-temperature change inside the crude oil storage tank has the horizontal axis representing the distance to the tank opening (in meters) and the vertical axis representing the temperature change of the measuring optical cable during the time interval t1 to t2 at the corresponding location. The slope of the curve can be considered to depend on the specific heat capacity of the medium at the corresponding location. Therefore, the location of the slope change in the curve can be determined as the location of the interface between different media.

[0131] Finally, it should be noted that in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0132] It should be noted that the concepts of "first" and "second" mentioned in this invention are only used to distinguish different systems, modules or units, and are not used to limit the order of functions performed by these systems, modules or units or their interdependencies.

[0133] Those skilled in the art will be able to implement or use this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A fiber optic crude oil storage tank interface monitoring device based on optical frequency domain reflection, characterized in that, include: Measurement components, measurement optical cables, host computer, and heating components; The measurement components include at least optical components and signal processing components; The first end of the measuring optical cable is located at the mouth of the crude oil storage tank, and the second end is located at the bottom of the crude oil storage tank. The optical component is connected to the first end of the measuring optical cable, and the signal processing component is connected to the optical component; The optical components are used to generate a light beam incident on the measuring optical cable; The signal processing component is used to obtain temperature data associated with the backscattered Rayleigh light generated by the measuring optical cable. The temperature data characterizes the temperature information at various locations of the measuring optical cable, and the backscattered Rayleigh light is related to the temperature at various locations of the measuring optical cable. The heating assembly includes at least a heating sleeve and a steam generator; The measuring optical cable is disposed inside the heating sleeve; the heating sleeve surrounds the measuring optical cable, and a cavity capable of accommodating high-temperature steam is formed between the inner wall of the heating sleeve and the outer surface of the measuring optical cable. One end of the steam transmission pipe is connected to the steam output port of the steam generator, and the other end of the steam transmission pipe extends into the cavity inside the heating sleeve; The steam generator is used to supply steam to the heating sleeve through the steam transmission pipe to heat the measuring optical cable; The host computer is used to determine the location of the interface between different media in the crude oil storage tank based on the temperature data during the cooling process of the measuring optical cable from the specified temperature.

2. The apparatus according to claim 1, characterized in that, The measuring optical cable includes a protective sleeve, a first measuring optical fiber, and a second measuring optical fiber; Both the first measuring optical fiber and the second measuring optical fiber are located inside the protective sleeve; The optical components are used to generate a light beam incident on the measuring optical cable, including: The optical components are used to generate a light beam incident on the first measuring fiber and the second measuring fiber; The signal processing component is used to obtain temperature data associated with the backscattered Rayleigh light generated by the measuring optical cable, including: The signal processing component is used to obtain temperature data associated with a first backscattered Rayleigh light and a second backscattered Rayleigh light, wherein the first backscattered Rayleigh light is generated by the first measuring fiber and the second backscattered Rayleigh light is generated by the second measuring fiber.

3. The apparatus according to claim 2, characterized in that, The optical components include a linearly swept frequency light source, an optical isolator, a first reference fiber, a second reference fiber, a first circulator, a second circulator, a first fiber coupler, a second fiber coupler, a third fiber coupler, a fourth fiber coupler, and a fifth fiber coupler. The beam generated by the linear sweep frequency light source enters the first fiber coupler through the optical isolator; The first fiber coupler is used to split the light beam generated by the linearly swept frequency light source into a first beam and a second beam; The second fiber coupler is used to pass a portion of the first beam through the first circulator into the first measuring fiber, and to pass another portion of the first beam into the first reference fiber. The third fiber coupler is used to pass a portion of the second beam through the second circulator into the second measuring fiber, and to pass another portion of the second beam into the second reference fiber; The fourth fiber coupler is used to obtain a first beat frequency interference light signal and a second beat frequency interference light signal at different times based on the beams of the first back-scattered Rayleigh light and the first reference fiber. The fifth fiber coupler is used to obtain the third beat frequency interference light signal and the fourth beat frequency interference light signal at different times based on the beams of the second back-scattered Rayleigh light and the second reference fiber. The signal processing component is used to obtain temperature data associated with the first and second backscattered Rayleigh light, including: The signal processing component is used to obtain temperature data based on the first beat frequency interference optical signal, the second beat frequency interference optical signal, the third beat frequency interference optical signal, and the fourth beat frequency interference optical signal.

4. The apparatus according to claim 3, characterized in that, It also includes a first sensing fiber and a second sensing fiber; The first measuring optical fiber is connected to the first circulator via the first sensing optical fiber, and the first circulator is connected to the second optical fiber coupler. The second measuring fiber is connected to the second circulator via the second sensing fiber, and the second circulator is connected to the third fiber coupler.

5. A fiber optic method for monitoring the interface of crude oil storage tanks based on optical frequency domain reflection, characterized in that, An optical fiber crude oil storage tank interface monitoring device based on optical frequency domain reflection, comprising a measuring optical cable, wherein the first end of the measuring optical cable is located at the tank opening of the crude oil storage tank and the second end is located at the tank bottom of the crude oil storage tank, the method comprising: Steam at a specified temperature is supplied to the heating sleeve containing the measuring optical cable through a steam transmission pipe, thereby heating the measuring optical cable to the specified temperature. The heating sleeve surrounds the measuring optical cable, and a cavity capable of accommodating high-temperature steam is formed between the inner wall of the heating sleeve and the outer surface of the measuring optical cable. One end of the steam transmission pipe is connected to the steam output port of the steam generator, and the other end of the steam transmission pipe extends into the cavity inside the heating sleeve. During the cooling process of the measuring optical cable from the specified temperature, temperature data associated with the backscattered Rayleigh light generated by the measuring optical cable is obtained. The temperature data characterizes the temperature information at various locations of the measuring optical cable. The backscattered Rayleigh light is related to the temperature at various locations of the measuring optical cable. The backscattered Rayleigh light is generated after the light beam enters the measuring optical cable. The location of the interface between different media inside the crude oil storage tank is determined based on the temperature data.

6. The method according to claim 5, characterized in that, The acquisition of temperature data associated with the backscattered Rayleigh light generated by the measuring optical cable includes: Receive the first back Rayleigh scattered light generated by the first measuring fiber in the measuring optical cable, and the second back Rayleigh scattered light generated by the second measuring fiber in the measuring optical cable; Temperature data is obtained based on the first backscattered Rayleigh light and the second backscattered Rayleigh light.

7. The method according to claim 6, characterized in that, The step of obtaining temperature data based on the first backscattered Rayleigh light and the second backscattered Rayleigh light includes: At different times, a first beat frequency interference light signal and a second beat frequency interference light signal are obtained based on the beams of the first back-scattered Rayleigh light and the first reference fiber. At different times, the third beat frequency interference light signal and the fourth beat frequency interference light signal are obtained based on the beams of the second back-scattered Rayleigh light and the second reference fiber. Temperature data is obtained based on the first beat frequency interference optical signal, the second beat frequency interference optical signal, the third beat frequency interference optical signal, and the fourth beat frequency interference optical signal.

8. The method according to claim 7, characterized in that, The step of obtaining temperature data based on the first beat frequency interference optical signal, the second beat frequency interference optical signal, the third beat frequency interference optical signal, and the fourth beat frequency interference optical signal includes: The first wavelength shift is obtained by processing the first beat frequency interference optical signal and the second beat frequency interference optical signal using the cross-correlation demodulation method. The second wavelength shift is obtained by processing the third beat frequency interference optical signal and the fourth beat frequency interference optical signal using the cross-correlation demodulation method. Based on the first wavelength drift, the second wavelength drift, the temperature sensitivity coefficient and strain sensitivity coefficient of the first measuring optical fiber, and the temperature sensitivity coefficient and strain sensitivity coefficient of the second measuring optical fiber, the temperature data at each location of the measuring optical cable are determined.

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