WO2022088512A1

WO2022088512A1 - Densely-wound optical fiber type ultra-sensitive oil well sensing optical cable

Info

Publication number: WO2022088512A1
Application number: PCT/CN2021/071275
Authority: WO
Inventors: 饶云江; 韩冰; 姚家珍; 栗鸣; 李强; 蒋新力; 曹珊珊; 吴明埝
Original assignee: 电子科技大学; 中天电力光缆有限公司; 江苏中天科技股份有限公司; 四川光盛物联科技有限公司
Priority date: 2020-10-30
Filing date: 2021-01-12
Publication date: 2022-05-05
Also published as: CN112504306A

Abstract

A densely-wound optical fiber type ultra-sensitive oil well sensing optical cable, comprising a tensile reinforcing member (6), an outer sheath (1), a curing layer (2), a sensing optical fiber (3), and an elastic sensitivity-enhancing structure (4). The sensing optical fiber (3) is wound on the elastic sensitivity-enhancing structure (4) and is fixed by the curing layer (2), and the sensing optical fiber (3) consists of a dense winding section and a non-dense winding section which are distributed in a staggered manner. The sensing optical fiber (3) comprises two single-mode optical fibers, and the two single-mode optical fibers are respectively used for measurement of sound waves and temperature. The acoustic pressure sensitivity and temperature sensitivity of the sensing optical cable are remarkably improved, and the sensing optical cable can be used for long-time high-sensitive exploration and development monitoring in a high-temperature environment in a well.

Description

Densely wound optical fiber type ultra-sensitive oil well sensing cable

technical field

The invention relates to the technical field of sensing optical cables, in particular to a densely wound optical fiber type ultra-sensitive oil well sensing optical cable.

Background technique

Traditional oil and gas exploration in wells uses electronic geophones for testing. A single electronic geophone can only measure single-point information in each measurement. The scheme of connecting multiple electronic geophones in series is expensive, and it is difficult to achieve a single shot covering the entire well. However, the optical fiber distributed sensing technology uses the sensing optical cable as the sensing medium, which can detect the information of each point on the optical fiber in the sensing optical cable, and the spatial resolution and cost performance are much higher. Therefore, when optical fiber distributed sensing technology is applied to oil and gas exploration and development in wells, the detection efficiency is significantly improved, the overall cost is greatly reduced, and it has huge social and economic benefits.

In practical applications of the existing optical fiber distributed sensing systems, the sensing fibers in the optical cable used are mostly vertical or wound around the central reinforcing member with a large pitch, and the sensitivity of the sensing optical cable is limited. At the same time, since most of the existing sensing optical cables only contain a single optical fiber, it is difficult to realize multi-parameter measurement when a single-wavelength signal light source is used. In addition, the existing ordinary sensing optical cables are mostly used in normal temperature environments such as ground monitoring or pipeline security monitoring, and it is difficult to meet the requirements for the sensing optical cables to have good high temperature resistance for oil and gas exploration and development in wells.

SUMMARY OF THE INVENTION

Based on the above technical problems, the present invention provides a densely wound optical fiber type ultra-sensitive oil well sensing optical cable. In view of the problem of low sensitivity of the existing sensing optical cable, the method of using the sensing optical fiber intermittently and tightly wound on the elastic sensitization structure can effectively The sensitivity of the sensing optical cable is improved, so that it can meet the requirements of high precision and high efficiency in oil and gas exploration and development in wells.

For solving the above technical problems, the technical scheme adopted in the present invention is as follows:

Densely wound optical fiber type ultra-sensitive oil well sensing optical cable, including outer sheath, solidified layer, sensing optical fiber, elastic sensitization structure and tensile strength member; the sensing fiber is wound on the elastic sensitized structure and fixed by the solidified layer. The sensing fiber consists of staggered densely wound sections and non-densely wound sections.

As a preferred way, the densely wound section of the sensing fiber is wound on the elastic sensitizing structure with a pitch of 100 μm to 1 mm; the non-densely wound section of the sensing fiber is wound on the elastic sensitization structure with a pitch of 1 mm to 1000 mm.

As a preferred manner, the sensing fiber includes a single-mode fiber, and the single-mode fiber passes through two optical signals of different wavelengths, so as to realize the simultaneous separation and measurement of the acoustic wave and the temperature.

As a preferred manner, the sensing fiber includes two single-mode fibers, and the two single-mode fibers are respectively used for the measurement of sound waves and temperature.

As a preferred manner, the outer sheath and the elastic sensitization structure are made of high temperature resistant material; the surface of the sensing optical fiber is coated with a high temperature resistant material coating.

As a preferred manner, the elasticity-sensitizing structure is a solid structure.

As a preferred manner, the elastic sensitization structure is a hollow structure composed of an elastic support layer and an air layer.

As a preferred manner, a metal support layer is provided between the elastic support layer and the air layer.

As a preferred manner, the outer surface of the elastic sensitization structure is coated with a metal sensitization layer.

As a preferred manner, the metal sensitization layer is made of copper.

Compared with the prior art, the beneficial effects of the present invention are:

(1) The sensing optical fiber of the present invention is tightly wound on the elastic sensitization structure by using the staggered densely wound section and non-densely wound section structure, which can ensure a longer sensing distance and make the winding part of the optical fiber per unit length. The actual length is longer, and the scattered light signal accumulated by external disturbance changes more strongly. Moreover, the deformation and temperature change of the elastic sensitizing structure under the influence of the external environment can further improve the deformation and temperature change of the sensing optical fiber, so that the sound pressure sensitivity and temperature sensitivity of the sensing optical cable can be improved by orders of magnitude.

(2) The present invention injects detection signal light of different wavelengths into the sensing optical fiber in the sensing optical fiber through the wavelength division multiplexing technology, and separates and demodulates the signal light of different wavelengths at the receiving end, which can realize the simultaneous multi-parameter synchronization of a single sensing optical fiber Measurement.

(3) The optical cable of the present invention is applied to the field of optical fiber distributed sensing technology. The outer sheath is made of materials such as high temperature resistant polyether ether ketone, and the sensing optical fiber is coated with high temperature resistant materials such as polyimide. Silicone rubber The elastic sensitization structure is made of high temperature resistant materials with low Young's modulus, so that the optical cable has the characteristics of high temperature resistance, making it more suitable for long-term monitoring in oil and gas wells in the high temperature environment of 200-300 °C.

(4) In the present invention, a metal sensitization layer is coated on the inner elastic sensitization structure of the sensing optical cable, while ensuring that the elastic sensitizing structure improves the sound pressure sensitivity of the sensing optical cable, the thermal conductivity of the elastic sensitizing structure is further improved, and the Sensing the temperature change of the optical fiber to improve the temperature sensitivity of the sensing optical cable.

Description of drawings

The present application will be further described by way of example embodiments, which will be described in detail with reference to the accompanying drawings, wherein:

1 is a schematic cross-sectional view of the present invention;

2 is a schematic diagram of the winding structure of the sensing optical fiber and the elastic sensitization structure of the present invention;

3 is a schematic diagram of the light intensity integral effect along the distance when the sensing optical fiber is not wound when the temperature changes according to the present invention;

4 is a schematic diagram of the light intensity integral effect along the distance when the sensing optical fiber is wound when the temperature changes according to the present invention;

5 is a schematic diagram of a hollow elastic sensitization structure of the present invention;

6 is a schematic diagram of an elastic sensitization structure containing a metal support layer of the present invention;

FIG. 7 is a schematic diagram of an elastic sensitization structure coated with a metal sensitization layer of the present invention.

Among them, 1 outer sheath, 2 cured layer, 3 sensing fiber, 4 elastic sensitization structure, 401 elastic support layer, 402 air layer, 403 metal support layer, 5 metal sensitization layer, 6 tensile strength member.

Detailed ways

In order to make the purpose, technical solutions and advantages of the embodiments of the present disclosure more clear, the technical solutions of the embodiments of the present disclosure will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present disclosure. Obviously, the described embodiments are some, but not all, embodiments of the present disclosure. Based on the described embodiments of the present disclosure, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the protection scope of the present disclosure.

Unless otherwise defined, technical or scientific terms used in this disclosure shall have the ordinary meaning as understood by one of ordinary skill in the art to which this disclosure belongs. As used in this disclosure, "first," "second," and similar terms do not denote any order, quantity, or importance, but are merely used to distinguish the various components. "Comprises" or "comprising" and similar words mean that the elements or things appearing before the word encompass the elements or things recited after the word and their equivalents, but do not exclude other elements or things. Words like "connected" or "connected" are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "Down", "Left", "Right", etc. are only used to represent the relative positional relationship, and when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

Figures 1-2 and Figures 5-7 are schematic structural diagrams of the densely wound optical fiber type ultra-sensitive oil well sensing cable according to some embodiments of the present application. Introduced around the fiber-optic ultra-sensitive oil well sensing cable. It should be noted that FIGS. 1 to 2 and FIGS. 5 to 7 are only examples, and do not limit the specific shape and structure of the densely wound optical fiber type ultra-sensitive oil well sensing cable.

Referring to FIGS. 1-2, in this embodiment, the densely wound optical fiber type ultra-sensitive oil well sensing optical cable includes an outer sheath 1, a cured layer 2, a sensing optical fiber 3, an elastic sensitization structure 4 and a tensile strength member 6; The sensing fiber 3 is wound on the elastic sensitizing structure 4 and fixed by the solidified layer 2, and the sensing fiber 3 is composed of densely wound sections and non-densely wound sections distributed in a staggered manner.

In this embodiment, the sensing optical fiber 3 is tightly wound on the elastic sensitizing structure 4 by means of staggered densely wound sections and non-densely wound section structures, which can ensure a longer sensing distance and make the winding part unit length. The actual length of the optical fiber is longer, and the scattered light signal accumulated by the external disturbance changes more strongly. Moreover, the deformation and temperature change of the elastic sensitizing structure 4 under the influence of the external environment can further enhance the deformation and temperature change of the sensing optical fiber 3, so that the sound pressure sensitivity and temperature sensitivity of the sensing optical cable can be improved by orders of magnitude.

Among them, the outer sheath 1 and the tensile strength member 6 are used to protect the sensing optical fiber 3 and the elastic sensitization structure 4 and enhance the overall strength of the optical cable. Specifically, the tensile strength member 6 is an armored structure formed by winding steel wires.

Specifically, the cured layer 2 is formed by curing glue. In addition to strengthening the connection between the sensing fiber 3 and the elastic sensitizing structure 4 , the cured layer 2 can also play a certain protective role on the sensing fiber 3 .

In some embodiments, the densely wound section of the sensing fiber 3 is wound on the elastic sensitization structure with a pitch of 100 μm˜1 mm; the non-densely wound section of the sensing fiber 3 is wound on the elastic sensitization structure 4 with a pitch of 1 mm to 1000 mm. superior.

In this embodiment, the winding method of the sensing optical fiber 3 is shown in FIG. 2 . A section of the sensing optical fiber 3 is wound on the elastic sensitization structure 4 with a certain prestress and a larger pitch of 1 mm to 1000 mm, and a section is close to the elastic sensitization structure 4 with no gap. It is wound laterally or wound on the elastic sensitization structure 4 with a smaller pitch of 100 μm to 1 mm, and so on. Among them, the densely wound section of the sensing optical fiber 3 is tightly wound on the elastomer sensitizing structure 4 to enhance the sound pressure and temperature sensitivity of the sensing optical cable, and the non-densely wound section of the sensing optical fiber 3 is wound on the elastic sensitizing structure 4 with a larger pitch. to prevent the fiber from breaking due to bending.

In some embodiments, the sensing fiber 3 includes a single-mode fiber, and the single-mode fiber has two optical signals of different wavelengths passing through it, so as to simultaneously realize the separate measurement of the acoustic wave and the temperature.

In this embodiment, the sensing optical fiber 3 transmits detection signal lights of two different wavelengths at the same time, and a single optical cable can measure multiple parameters at the same time through the wavelength division multiplexing technology, which greatly improves the measurement of the sensing optical fiber 3 efficiency. In addition, the temperature information detected by the system can not only monitor the changes of the external environment in real time, but also can be used to perform temperature compensation for the distributed acoustic wave sensing system.

In addition, for the sensing fiber 3, in some embodiments, a structure in which the sensing fiber includes two single-mode fibers can also be used, and the two single-mode fibers are respectively used for the measurement of sound waves and temperature.

Wherein, the principle of improving the sensitivity of the densely wound optical fiber type ultra-sensitive oil well sensing optical cable described in this embodiment is as follows:

First, the sound pressure sensitivity of an optical fiber refers to the ratio of the phase difference of the optical fiber caused by the acoustic signal to the free-field sound pressure at the center of the sound field:

in,

The phase change of the light beam transmitted in the sensing fiber 3 due to the effect of sound pressure can be divided into two parts, one part is the phase change caused by the sound pressure directly acting on the sensing fiber 3

The other part is that the deformation caused by the sound pressure acting on the elastic sensitizing structure 4 drives the sensing fiber 3 to produce a phase change.

can be expressed as:

where L is the effective sensing length of the fiber, β is the propagation constant in the fiber, n is the core refractive index of the fiber, D is the core diameter, V is the normalized frequency, and V is the normalized waveguide refractive index of the fiber. b has a certain corresponding relationship. ΔL ₁ is the change in length of the optical fiber directly under the action of external pressure, and ΔL ₂ is the change in the length of the optical fiber caused by the deformation of the elastic sensitizing structure 4 under the action of sound pressure.

By calculation, it can be seen that

Compare

Therefore, the sound pressure acts on the elastic sensitizing structure 4 to produce deformation, and the phase change of the light beam in the sensing fiber 3 is much larger than the light beam phase change caused by the sound pressure alone on the sensing fiber 3 . Therefore, the present invention adopts the structure in which the sensing optical fiber 3 is intermittently and tightly wound on the elastic sensitizing structure 4, which can significantly improve the sound pressure sensitivity of the sensing optical fiber cable.

Secondly, in the fiber, the Stokes photon number N _s and the anti-Stokes photon number N _a are:

where K _s and Ka are the coefficients related to the cross-section of Stokes light and anti-Stokes light, respectively, S is the backscattering factor, and v _s and v _a are Stokes and anti-Stokes _light , respectively frequency of Stokes light, α ₀ , α _s , α _a are the transmission losses of incident light, Stokes scattered light and anti-Stokes scattered light, respectively, z is the distance of the point to be measured, R _s (T) and R _a (T) are the coefficients related to the number of layouts on the low and high energy levels of the fiber molecule, respectively.

According to the known number of Stokes and anti-Stokes photons in the sensing fiber 3 at time T ₀ , the external temperature change can be sensed, and the relationship between the number of photons is:

The optical fiber distributed temperature sensing technology is to integrate the Raman scattered light intensity in the optical fiber within the system spatial resolution range to calculate and invert the external temperature. As shown in Figure 3, when the sensing fiber 3 is not wound, the Raman scattered light The intensity is only enhanced at the temperature change point. If the spatial resolution is greater than the thermal radiation range, there will be a measurement error between the calculated results of the system and the actual temperature field; however, as shown in Figure 4, the sensing fiber 3 is wound around the elastic sensitization structure 4 The actual length of the sensing fiber 3 per unit length can be increased, that is, when the external temperature field changes, even if the spatial resolution is greater than the thermal radiation range, the Raman scattered light intensity calculated by the DTS system integral in the unit length is still accurate, and the system precision and higher spatial resolution. In this embodiment, the spatial resolution of the DTS system is 20m, and the sensing fiber 3 is tightly wound on an elastic body with an outer diameter of 15mm, and the actual distance of winding the 20m sensing fiber 3 is 0.106m. According to the above formula, the received signal strength of DTS can be increased by 22.76dB at this time.

In some embodiments, the outer sheath 1 and the elastic sensitization structure 4 are made of high temperature resistant material; the surface of the sensing optical fiber 3 is coated with a high temperature resistant material coating.

Specifically, in this embodiment, the outer sheath 1 can be made of a high-temperature-resistant polyetheretherketone material, the sensing fiber 3 can be coated with a high-temperature-resistant material such as polyimide, and a low Young's modulus such as silicone rubber can be used. A large amount of high temperature resistant material is used to make the elastic sensitization structure 4, so that the optical cable has high temperature resistance characteristics, making it more suitable for long-term monitoring in oil and gas wells in a high temperature environment of 200-300 °C.

In some embodiments, the elasticity-sensitizing structure 4 is a solid structure. The elastic sensitization structure 4 of the solid structure has high mechanical strength, but has many consumables, and the overall weight of the optical cable is heavier.

Referring to FIG. 5 , in some embodiments, the elastic sensitization structure 4 is a hollow structure composed of an elastic support layer 401 and an air layer 402 .

In this embodiment, the sensitivity of the elastic sensitizing structure 4 of the hollow structure is higher than that of the solid structure, the total weight of the optical cable is lighter, the consumables are less, but the mechanical strength is slightly worse. Assume that the Young's modulus of the core of the sensing fiber 3 is 72GPa, the Poisson's ratio is 0.17, the Young's modulus of the elastic support layer 401 in the elastic sensitizing structure 4 is 500MPa, the Poisson's ratio is 0.465, and the outer diameter is 15mm , the inner diameter is 6mm, the sound pressure sensitivity of the sensing fiber 3 is -184.45dB re rad/μPa through calculation, and the sound pressure sensitivity of the sensing fiber 3 after being wound around the elastic sensitizing structure 4 is -155.39dB re rad/ μPa.

Referring to FIG. 6 , in some embodiments, a metal support layer 403 is disposed between the elastic support layer 401 and the air layer 402 . The metal support layer 403 can enhance the mechanical strength of the optical sensing cable, so as to overcome the problem of low mechanical strength of the elastic sensitizing structure 4 of the hollow structure while ensuring the sensitivity. Assuming that the parameters of the sensing fiber 3 and the elastic support layer 401 in the elastic sensitization structure 4 remain unchanged, the Young's modulus of the metal support layer 403 is 70.3 GPa, the Poisson's ratio is 0.345, the outer diameter is 8 mm, and the inner diameter is 6 mm. Then, the sound pressure sensitivity of the single-mode sensing fiber 301 after winding is -156.79dB re rad/μPa.

Referring to FIG. 7 , in some embodiments, the outer surface of the elastic sensitizing structure 4 is coated with a metal sensitizing layer 5 .

The elastic sensitization structure 4 is coated with a metal sensitization layer 5 to improve the temperature sensitivity of the sensing optical cable.

The temperature sensitivity of the Raman scattering-based DTS using the anti-Stokes Raman backscattering demodulation method can be expressed as:

Among them, h is the Planck coefficient, k is the Boltzmann constant, Δv is the fiber phonon frequency, T ₀ is the real-time fiber temperature, and T is the temperature change in a local area of the fiber. The thermal conductivity of SiO ₂ is about 7.6W/mK, and the thermal conductivity of metal is about 30-300W/mK. When the sensing fiber 3 in the present invention is intermittently and tightly wound on the elastic sensitizing structure 4 coated with the metal sensitizing layer 5, the local temperature change of the densely wound sensing fiber 3 is larger, and the optical fiber Raman scattering photons pass through. The larger the amount, the higher the temperature sensitivity.

Preferably, the metal sensitizing layer 5 is made of copper. Since copper has good thermal conductivity, the thermal conductivity of the elastic sensitization structure 4 can be improved, so as to improve the temperature sensitivity of the optical sensing cable.

Specifically, the diameter of the elastic sensitizing structure 4 is 0.5 cm˜2 cm.

The above is an embodiment of the present invention. The above examples and the specific parameters in the examples are only to clearly describe the verification process of the invention, not to limit the scope of patent protection of the present invention. The scope of patent protection of the present invention is still based on the claims. Equivalent structural changes made to the contents of the description and drawings shall be included within the protection scope of the present invention.

Claims

A densely wound optical fiber type ultra-sensitive oil well sensing optical cable, characterized in that it comprises a tensile strength member (6), an outer sheath (1), a cured layer (2), a sensing optical fiber (3) and an elastic sensitization structure (4) );

The sensing optical fiber (3) is wound on the elastic sensitization structure (4) and fixed by the solidified layer (2), and the sensing optical fiber (3) is composed of densely wound sections and non-densely wound sections distributed in a staggered manner.
The densely wound optical fiber type ultra-sensitive oil well sensing optical cable according to claim 1, is characterized in that:

The densely wound section of the sensing optical fiber (3) is wound on the elastic sensitization structure (4) with a pitch of 100 μm˜1 mm;

The non-densely wound section of the sensing optical fiber (3) is wound on the elastic sensitization structure (4) at a pitch of 1 mm to 1000 mm.
The densely wound optical fiber type ultra-sensitive oil well sensing optical cable according to claim 1, is characterized in that:

The sensing optical fiber (3) includes a single-mode optical fiber through which two optical signals of different wavelengths pass, so as to realize simultaneous separation and measurement of acoustic waves and temperature.
The densely wound optical fiber type ultra-sensitive oil well sensing optical cable according to claim 1, is characterized in that:

The sensing fiber (3) includes two single-mode fibers, and the two single-mode fibers are respectively used for the measurement of sound waves and temperature.
The densely wound optical fiber type ultra-sensitive oil well sensing optical cable according to claim 1, is characterized in that:

The outer sheath (1) and the elastic sensitization structure (4) are made of high temperature resistant materials;

The surface of the sensing fiber (3) is coated with a high temperature resistant material coating.
The densely wound optical fiber type ultra-sensitive oil well sensing optical cable according to claim 1, is characterized in that:

The elastic sensitization structure (4) is a solid structure.
The densely wound optical fiber type ultra-sensitive oil well sensing optical cable according to claim 1, is characterized in that:

The elastic sensitization structure (4) is a hollow structure composed of an elastic support layer (401) and an air layer (402).
The densely wound optical fiber type ultra-sensitive oil well sensing optical cable according to claim 7, is characterized in that:

A metal support layer (403) is arranged between the elastic support layer (401) and the air layer (402).
The densely wound optical fiber type ultra-sensitive oil well sensing optical cable according to claim 1, is characterized in that:

The outer surface of the elastic sensitization structure (4) is coated with a metal sensitization layer (5).
The densely wound optical fiber type ultra-sensitive oil well sensing optical cable according to claim 9, is characterized in that:

The metal sensitization layer (5) is composed of copper.