Metallic tube optical fiber cable

Abstract

To suppress a falling of an amount of reflection attenuation of an optical fiber by maintaining slack of the optical fiber.SOLUTION: A metal tube optical fiber cable according to the present invention comprises: a sensor-purpose optical fiber; an inner tube that has the optical fiber arranged in a tube; and an outer tube that has the inner tube arranged in the tube. A tip end side of the outer tube is closed, and a gas inflow port is formed on a base end side of the outer tube. A tip end side of the inner tube is located on the base end side of the outer tube relative to a tip end thereof, and communicated with the inner tube of the outer tube. A gas emission port is formed on a base end side of the inner pipe and a tip end of the optical fiber is located on a base end side of the inner tube relative to a tip end thereof.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a structure of a metal conduit optical fiber cable that uses an optical fiber as a sensor. [Background technology]

[0002] Metal-tube optical fiber cables are known that are used in high-temperature, high-pressure environments such as geothermal logging, and have a heat- and pressure-resistant barrier layer around the optical fiber. The optical fiber itself acts as a distributed acoustic sensor (DAS) or distributed temperature sensor (DTS) to detect vibration and temperature.

[0003] In such high-temperature and high-pressure environments, hydrogen gas can penetrate the metal used in metal-tube optical fiber cables. Hydrogen gas can also be generated by metal corrosion. This hydrogen gas can increase optical fiber loss at specific wavelengths, potentially affecting strain, pressure, and temperature detection. This issue can occur not only due to hydrogen gas penetration and metal corrosion, but also when metal-tube optical fiber cables are used in environments with high hydrogen concentrations. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 2992191 [Patent Document 2] Japanese Patent Application Publication No. 6-59169 Summary of the Invention [Problem to be solved by the invention]

[0005] In view of the above-mentioned problems, for example, Patent Documents 1 and 2 disclose a metal-tube optical fiber cable structure in which an optical fiber is doubly covered with an inner tube and an outer tube. In this structure, a gas supply mechanism is provided on the base end side of the inner tube, and the tip end side is connected to the inside of the outer tube, and the tip end side of the outer tube is sealed. In this state, by flowing in an inert gas from the base end side of the inner tube, the optical fiber is constantly placed in an environment filled with inert gas, and the effects of hydrogen gas are mitigated. The inert gas flowing into the inner tube passes through the outer tube and is discharged from the base end side of the outer tube. In addition, in Patent Document 2, the base end of the inner tube is sealed with a sealing material, a hole is drilled near the base end of the inner tube to provide a gas filling inlet, the space between the outer tube and the inner tube is sealed with a sealing material at the base end of the outer tube, and a hole is drilled near the base end of the outer tube to provide a gas exhaust outlet.

[0006] However, when inert gas is introduced into the base end of the inner tube, the optical fiber in the inner tube is constantly exposed to the inert gas flow from the base end to the tip end of the inner tube. The optical fiber is arranged inside the inner tube with a certain amount of slack, but this slack is stretched by the gas flow and gravity, and there is a risk that the tip will come into contact with the barrier layer or the like. If the tip of the optical fiber comes into contact with the barrier layer or the like, the reflection state will deteriorate, which may affect the detection of strain, pressure, and temperature. In particular, it is considered important to keep the return loss at the tip of the optical fiber low for measurements using modern DAS. In addition, it is necessary to seal the gap between the outer and inner tubes and the ends of the tubes to prevent the enclosed gas from escaping. In Patent Document 1, a branch tube is attached to the base end of the inner tube and sealed, but the inner tube is first cut and then attached to the branch tube, which requires a step of cutting the inner tube and poses a risk of damaging the exposed optical fiber. In Patent Document 2, the base end of the inner tube and the gap between the outer and inner tubes are sealed with a sealant, and holes are drilled near the base ends of the inner and outer tubes as gas inlet and outlet ports, which requires processing time and poses a risk of damaging the optical fiber inside the inner tube.

[0007] Therefore, the present invention proposes a metal tube optical fiber cable structure that can prevent a decrease in the return loss of the optical fiber due to maintaining slack in the optical fiber and can easily provide a gas filling inlet and exhaust outlet. [Means for solving the problem]

[0008] The metal-tube optical fiber cable of the present invention is a metal-tube optical fiber cable comprising an optical fiber for a sensor, an inner tube in which the optical fiber is disposed, and an outer tube in which the inner tube is disposed, wherein the tip side of the outer tube is closed, a gas inlet is formed at the base end side of the outer tube, the tip side of the inner tube is positioned more base end than the tip of the outer tube and is connected to the inside of the outer tube, a gas outlet is formed at the base end side of the inner tube, and the tip of the optical fiber is positioned more base end than the tip of the inner tube. As a result, the inert gas that flows into the tube from the gas inlet on the base end side of the outer tube flows into the inner tube from the tip side of the outer tube, and then flows from the tip side of the inner tube toward the gas outlet on the base end side.

[0009] The metal-tube optical fiber cable also includes a joint portion in which the base end of the outer tube is positioned closer to the tip than the base end of the inner tube, and which has an outer tube insertion hole that holds the inserted outer tube, an inner tube insertion hole that holds the inserted inner tube, a gas supply hole, and an inlet path that connects the gas supply hole to the gas inlet of the outer tube. As a result, the gas exhaust port of the inner pipe inserted into the inner pipe insertion hole is located outside the joint part, and the gas inlet port of the outer pipe inserted into the outer pipe insertion hole is located in the inlet path inside the joint part. [Effects of the Invention]

[0010] According to the present invention, it is possible to prevent a decrease in return loss of an optical fiber caused by maintaining slack in the optical fiber. Furthermore, by using the joint part, even if some kind of malfunction occurs in the device after installation, no large-scale installation equipment is required, and the joint part can be easily attached to the metal-tube optical fiber cable at the installation site to restore it, thereby reducing labor costs. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a diagram showing a schematic diagram of a configuration example of a metal conduit optical fiber cable according to an embodiment of the present invention; [Figure 2] 1A and 1B are diagrams illustrating a configuration example of a cable portion according to the present embodiment; [Figure 3] 2 is a diagram schematically showing a cross section of a region P of the cable portion of the present embodiment. FIG. [Figure 4] FIG. 2 is a diagram schematically illustrating a cross section of a joint portion according to the present embodiment. [Figure 5] FIG. 10 is a diagram schematically illustrating a cross section of a tip end side of a cable portion of a comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, an embodiment will be described with reference to FIGS. The configurations shown in the drawings referred to in the description of the present embodiment are only intended to illustrate the essential parts and their peripheral configurations required to realize the present embodiment. The drawings are schematic and may be modified in various ways depending on the design, etc., without departing from the technical concept of the present invention.

[0013] In this embodiment, a metal conduit optical fiber cable 1 for detecting vibrations and temperatures inside by being lowered (inserted) into an observation well 100 such as a geothermal well as shown in FIG. 1 will be described. In this disclosure, the direction in which the metal-conduit optical fiber cable 1 is inserted into a detection target such as an observation well 100 is referred to as the distal direction, and the direction opposite to the distal direction is referred to as the proximal direction. In this case, the distal end of each member constituting the metal-conduit optical fiber cable 1 is referred to as the distal end, and the proximal end is referred to as the proximal end.

[0014] The metal-tube optical fiber cable 1 includes a cable portion 2 and a joint portion 3. The base end of the cable portion 2 is connected to the joint portion 3, and the inert gas GS supplied from the joint portion 3 flows into the cable portion 2. This fills the inside of the cable portion 2 with the inert gas GS. The inert gas GS protects the optical fiber 4, which will be described later, and may be, for example, nitrogen, argon, or helium. The arrows in each drawing indicate the direction in which the inert gas GS flows.

[0015] As shown in Fig. 2, the cable section 2 includes an optical fiber 4, an inner tube 5, and an outer tube 6. The inner tube 5 and the outer tube 6 are metal tubes that function as heat-resistant and pressure-resistant barrier layers to protect the optical fiber 4. The inner tube 5 and the outer tube 6 are filled with an inert gas GS to prevent hydrogen gas generated by factors such as metal corrosion and permeation from the outer tube 6 from coming into contact with the optical fiber 4. Hydrogen gas increases loss at specific wavelengths in the optical fiber 4, which may affect the detection of vibrations and temperatures. Therefore, the tube is filled with an inert gas GS to prevent hydrogen gas from coming into contact with the optical fiber 4.

[0016] The optical fiber 4 functions as a sensor for detecting strain, pressure, and temperature, and its outer surface is covered with a heat insulating material. The tip of the cable portion 2 is inserted into the observation well 100 to detect vibration and temperature.

[0017] The optical fiber 4 is inserted into the inner tube 5, and the inner tube 5 is inserted into the outer tube 6. For example, the inner tube 5 has an inner diameter of about 0.7 to 3.0 mm, and the outer tube 6 has an inner diameter larger than that of the inner tube 5.

[0018] FIG. 3 is a diagram showing a schematic cross section of a region P at the tip of the cable portion 2. As shown in FIG. 3, a pressure-resistant barrier layer 7 that seals (blocks) the tip of the outer tube 6 is provided at the tip of the outer tube 6. The pressure-resistant barrier layer 7 is formed by driving a cap 8 into the outer tube 6 and sealing the gap between the outer tube 6 and the cap 8 with a sealing material such as silver solder 30.

[0019] 4, a gas inlet 9 is provided on the base end side of the outer tube 6. For example, an opening at the tip of the outer tube 6 is formed as the gas inlet 9. An inert gas GS supplied from a gas supply hole 16 of the joint part 3, which will be described later, flows into the gas inlet 9.

[0020] The tip side of the inner pipe 5 is in communication with the interior of the outer pipe 6. In FIG. 3, the tip of the inner pipe 5 is formed as an open end 10. The open end 10 of the inner pipe 5 is located closer to the base end than the sealed surface 12 at the tip of the inner pipe of the outer pipe 6, thereby communicating the interiors of the inner pipe 5 and outer pipe 6. Therefore, the inert gas GS that has flowed into the outer pipe 6 flows into the inner pipe 5.

[0021] Furthermore, slack is provided in the optical fiber 4 inserted into the inner tube 5, and when the cable portion 2 is lowered (inserted) in the direction of gravity (towards the bottom of the observation well 100) as shown in Figure 1, the tip 13 of the optical fiber 4 is located closer to the base end than the open end 10 of the inner tube 5. In a stretched state with no slack, the optical fiber 4 may come into contact with the sealing surface 12 of the outer tube 6, but by providing slack, the tip 13 maintains a position closer to the base end than the open end 10.

[0022] 1, a gas outlet 11 is provided on the base end side of the inner pipe 5. For example, an opening at the base end of the inner pipe 5 is formed as the gas outlet 11. The inert gas GS flowing in from the gas inlet 9 fills the inner pipe 5 and the outer pipe 6, and the pushed-out inert gas GS is discharged from the gas outlet 11. Since the base end of the outer pipe 6 is located closer to the tip than the base end of the inner pipe 5, the gas inlet 9 of the outer pipe 6 is located closer to the tip than the gas outlet 11 of the inner pipe 5.

[0023] The optical fiber 4 extending from the gas outlet 11 of the inner tube 5 to the base end side is connected to a measuring instrument 22 via an excess length storage body 21 of a termination box 20. The measuring instrument 22 measures strain, pressure, and temperature based on detection from the optical fiber 4.

[0024] 4, the joint part 3 has an outer pipe insertion hole 14, an inner pipe insertion hole 15, a gas supply hole 16, and an inflow path 17. The outer pipe insertion hole 14, the inner pipe insertion hole 15, and the gas supply hole 16 are in communication with each other via the inflow path 17.

[0025] The outer tube 6 is inserted into and held in the outer tube insertion hole 14. When inserted into the outer tube insertion hole 14, the outer tube 6 is sealed and fixed by the outer tube retaining portion 18. The outer tube retaining portion 18 is, for example, a nut, and by screwing the nut in place, the ferrule 23 is compressed, thereby sealing and fixing the outer tube 6 to the outer tube insertion hole 14. At this time, the gas inlet 9 of the outer tube 6 is located inside the inlet channel 17 and is in communication with the inlet channel 17.

[0026] The inner tube insertion hole 15 is formed closer to the base end than the outer tube insertion hole 14, and the inner tube 5 extending from the gas inlet 9 of the outer tube 6 is inserted into and held in the inner tube insertion hole 15. The inner tube 5 is sealed and fixed in place by an inner tube retaining portion 19 while inserted into the inner tube insertion hole 15. The inner tube retaining portion 19 is, for example, a nut, and by screwing the nut in place, the ferrule 24 is compressed, sealing and fixing the inner tube 5 to the inner tube insertion hole 15. Since the inner pipe 5 is inserted through the inner pipe insertion hole 15, the inner diameter of the inner pipe insertion hole 15 is smaller than the inner diameter of the outer pipe insertion hole 14 through which the outer pipe 6 is inserted.

[0027] An inert gas GS is supplied to the gas supply hole 16 from a gas supply mechanism (not shown). Here, the flow path of the inert gas GS in the metal-conduit optical fiber cable 1 will be described.

[0028] As shown in Figure 4, when an inert gas GS is supplied to the gas supply hole 16 of the joint portion 3, the supplied inert gas GS flows into the gas inlet 9 of the outer tube 6 via the inlet path 17 because the inner tube insertion hole 15 is sealed.

[0029] The inert gas GS that flows into the outer tube 6 from the gas inlet 9 flows toward the tip end of the outer tube 6 and, as shown in Figure 3, flows into the open end 10 of the inner tube 5 at the tip of the outer tube 6. The inert gas GS that flows into the inner tube 5 from the open end 10 flows from the tip end side to the base end side of the inner tube 5. As a result, the inner tube 5 and the outer tube 6 are filled with the inert gas GS.

[0030] When the inert gas GS is filled inside the inner tube 5 and the outer tube 6, as the inert gas GS flows into the gas inlet 9, the inert gas GS filled inside the tubes is pushed out toward the base end of the inner tube 5 and discharged from the gas outlet 11 shown in Figure 1.

[0031] Here, the optical fiber 4 inserted into the inner tube 5 is constantly subjected to the influence of gravity when the cable portion 2 is inserted in the direction of gravity (toward the bottom of the observation well 100) as shown in Figure 1. As a result, the slack in the optical fiber 4 is stretched over time, and there is a risk that the tip 13 of the optical fiber 4 may come into contact with the sealing surface 12. If the tip 13 of the optical fiber 4 comes into contact with the sealing surface 12, the reflectivity of the optical fiber 4 will deteriorate, adversely affecting the detection of vibration and temperature.

[0032] 5, when the inert gas GS is introduced from the base end side of the inner tube 5A, the optical fiber 4A inside the inner tube 5A is constantly exposed to a gas flow of the inert gas GS flowing from the base end side to the tip end side of the inner tube 5A. This gas flow may actually promote the extension of the slack in the optical fiber 4A.

[0033] On the other hand, in this embodiment, as shown in Figure 3, a gas inlet 9 is formed at the base end of the outer tube 6 and a gas outlet 11 is formed at the base end of the inner tube 5, so that the inert gas GS that flows toward the tip end of the outer tube 6 flows from the tip end of the inner tube 5 toward the base end through the open end 10 of the inner tube 5.

[0034] In this way, the inert gas GS flowing from the tip side to the base end side of the inner tube 5 generates a gas flow that flows in the opposite direction to gravity inside the inner tube 5. This gas flow always pushes the optical fiber 4 slightly toward the base end during measurement, making it possible to prevent the slack in the optical fiber 4 from extending due to gravity.

[0035] Therefore, according to this embodiment, it is possible to maintain the slack of the optical fiber 4 during measurement, and it is possible to prevent transmission loss caused by the slack of the optical fiber 4 being stretched and the tip 13 of the optical fiber 4 coming into contact with the sealing surface 12.

[0036] To maintain high measurement quality during use, it is desirable to constantly supply inert gas GS through the gas supply hole 16 in the joint 3. However, during the lowering (insertion) and lifting of the cable 2 during logging, the drum around which the cable 2 is wound rotates, making it difficult to supply the inert gas GS. Therefore, by supplying inert gas GS before logging (before the cable 2 is lowered) and filling the inner and outer tubes 5 and 6 with inert gas GS, the residual pressure in the tubes can be prevented from decreasing even when the cable 2 is lowered. By subsequently supplying inert gas GS during logging and again after lifting, the tubes can be constantly filled with inert gas GS, thereby preventing damage to the optical fiber 4. This further extends the life of the metal-tube optical fiber cable 1.

[0037] According to the present embodiment described above, the cable portion 2 of the metal-tube optical fiber cable 1 includes an optical fiber 4 for a sensor, an inner tube 5 in which the optical fiber 4 is disposed, and an outer tube 6 in which the inner tube 5 is disposed (see Figure 2). At this time, the tip of the optical fiber 4 is positioned closer to the base end than the tip of the inner tube 5. The tip side of the outer tube 6 is closed, and a gas inlet 9 is formed on the base end side of the outer tube 6. Furthermore, the tip side of the inner tube 5 is positioned closer to the base end than the tip of the outer tube 6 and is connected to the inside of the outer tube 6, and a gas outlet 11 is formed on the base end side of the inner tube 5 (see Figures 1, 3 and 4).

[0038] As a result, the inert gas GS that flows into the tube from the gas inlet 9 on the base end side of the outer tube 6 flows from the tip side of the outer tube 6 into the inner tube 5, and flows from the tip side of the inner tube 5 toward the gas outlet 11 on the base end side. Therefore, as described above, the gas flow of the inert gas GS flowing from the tip side to the base side of the inner tube 5 suppresses the extension of slack in the optical fiber 4, and prevents transmission loss due to the tip 13 of the optical fiber 4 coming into contact with the sealing surface 12. This makes it possible to improve the quality and extend the life of the metal-tube optical fiber cable 1.

[0039] In this embodiment, the opening at the base end of the outer tube 6 is formed as the gas inlet 9, and the opening at the base end of the inner tube 5 is formed as the gas outlet 11 (see FIGS. 1 and 4). By forming the openings of each tube as the gas inlet 9 and the gas outlet 11, respectively, it is no longer necessary to drill holes in each tube or cut the inner tube to expose the optical fiber in order to provide the gas inlet 9 or the gas outlet 11. This reduces the number of steps and also prevents the optical fiber 4 inside the tube from being damaged during the process of drilling holes in each tube or cutting the inner tube.

[0040] In this embodiment, the joint portion 3 of the metal tube optical fiber cable 1 is provided with an outer tube insertion hole 14 that holds the inserted outer tube 6, an inner tube insertion hole 15 that holds the inserted inner tube 5, a gas supply hole 16 through which the supplied inert gas GS flows in, and an inlet path 17 that connects the gas supply hole 16 to the gas inlet 9 of the outer tube 6 (see Figure 4).

[0041] As a result, the gas outlet 11 of the inner pipe 5 inserted into the inner pipe insertion hole 15 is located outside the joint part 3, and the gas inlet 9 of the outer pipe 6 inserted into the outer pipe insertion hole 14 is located in the inlet channel 17 inside the joint part 3. In other words, the positional relationship between the gas inlet 9 of the outer pipe 6 and the gas outlet 11 of the inner pipe 5 can be easily determined and fixed by the joint part 3.

[0042] Furthermore, in the joint portion 3, by inserting the outer pipe 6 into the outer pipe insertion hole 14, the inert gas GS supplied from the gas supply hole 16 can be made to flow into the gas inlet 9 of the outer pipe 6 via the inlet path 17. Therefore, by inserting the outer pipe 6 into the outer pipe insertion hole 14, the inert gas GS can be supplied without having to drill a separate hole in the outer pipe 6 for supplying the inert gas GS. In other words, simply inserting the outer pipe 6 into the outer pipe insertion hole 14 not only determines the positional relationship with the inner pipe 5, but also reduces the labor required for drilling a hole for supplying the inert gas GS.

[0043] Furthermore, with the joint portion 3, the outer pipe 6 inserted into the outer pipe insertion hole 14 can be easily sealed and fixed by the outer pipe retaining portion 18, and the inner pipe 5 inserted into the inner pipe insertion hole 15 can be easily sealed and fixed by the inner pipe retaining portion 19. The joint part 3 is usually attached to the metal-tube optical fiber cable 1 at a factory or the like before shipping and installing it in an observation well such as a geothermal well. However, even if some kind of equipment malfunction occurs after installation, the joint part 3 can be easily attached to the metal-tube optical fiber cable 1 at the installation site without the need for large-scale installation equipment, and the cable can be reconditioned, thereby reducing labor costs.

[0044] Finally, the effects described in this disclosure are examples and are not intended to be limiting, and other effects may be achieved, or a part of the effects described in this disclosure may be achieved. Furthermore, not all of the combinations of configurations described in the embodiments are necessarily essential to solving the problems. [Explanation of symbols]

[0045] 1. Metal-tube fiber optic cable 2 Cable section 3 Joint 4. Optical Fiber 5 Inner tube 6 outer tube 9 Gas inlet 11 Gas outlet 14 Outer tube insertion hole 15 Inner pipe insertion hole 16 Gas supply hole 17 Inflow channel

Claims

1. A metal-tube optical fiber cable comprising an optical fiber for a sensor, an inner tube in which the optical fiber is disposed, and an outer tube in which the inner tube is disposed, a distal end side of the outer tube is closed, and a gas inlet is formed on a proximal end side of the outer tube; a distal end side of the inner tube is located closer to the base end than the distal end of the outer tube and communicates with the interior of the outer tube, and a gas exhaust port is formed on the base end side of the inner tube; The tip of the optical fiber is located closer to the base end than the tip of the inner tube. Metal tube fiber optic cable.

2. The proximal end of the outer tube is located closer to the distal end than the proximal end of the inner tube, The gas supply port is provided with a joint portion having an outer pipe insertion hole for holding the inserted outer pipe, an inner pipe insertion hole for holding the inserted inner pipe, a gas supply hole, and an inflow path for communicating the gas supply hole with a gas inlet of the outer pipe. The metal conduit optical fiber cable according to claim 1 .

3. the outer tube is inserted into the outer tube insertion hole and sealed and fixed therein; The inner pipe is sealed and fixed in a state where it is inserted into the inner pipe insertion hole. The metal conduit optical fiber cable according to claim 2 .

4. The inner tube is connected to the outer tube through an opening at the tip thereof. The metal conduit optical fiber cable according to any one of claims 1 to 3.

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