JPH0727955A - Optical fiber cable for measuring temperature of geothermal well - Google Patents

Abstract

PURPOSE:To prevent damage of metallic pipes and an increase in transmission loss by previously specifying the length of optical fibers at a service environmental temp. to the length of the metallic pipes at the same temp. or below specifying a difference between both to a difference between the inside lengths of the metallic pipes or above. CONSTITUTION:The optical fibers are previously provided with surplus lengths and are housed slightly long in the metallic pipes at the time of producing the metallic pipe optical fibers. The lengths of the optical fibers 2 at the time of use are specified to the length of the metallic pipes 1 or below to avert stagnating of the optical fibers in the lower part and generating fine bends therein even at the time of perpendicular laying and to avert generating of tension which arises from a difference in the lengths along the inside of the metallic pipes with the positions in the pipe due to spiral disposition of the metallic pipes 1 in formation into a cable of a twisted structure in such a case. The difference between the length along the centers of the metallic pipes 1 and the length along the inside of the metallic pipes 1 when the optical fibers 2 are nearest the central (center of a spiral shape) side of the cable section is confined to the difference between the inside lengths of the metallic pipes.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of an optical fiber cable used for measuring the temperature of a well such as a geothermal well.

[0002]

2. Description of the Related Art Raman backscattered light generated in an optical fiber is temporally sampled and measured by injecting pulsed light from one end of the optical fiber, and the obtained data is subjected to arithmetic processing so that the data along the optical fiber Devices for measuring temperature distribution have already been put to practical use.

The optical fiber used for such a purpose is desired to have as little coating as possible so that the external temperature is easily transmitted to itself. On the other hand, it is necessary to protect the optical fiber itself from external force and moisture. Therefore, an optical fiber cable (metal tube optical fiber) having a structure in which an optical fiber element wire is housed in a metal tube has been used.

When measuring the temperature of a well (geothermal well) of a geothermal power plant, a temperature measuring element such as a thermistor is housed in a corrosion-resistant metal tube to protect it from corrosive hot water in the mine. Another method is to gradually lower the geothermal well with a weight.

[0005]

By the way, in such an application, the elongation of the metal tube is larger due to the difference in coefficient of linear expansion between the metal tube and the optical fiber element wire, so that tensile tension is not applied to the optical fiber element wire. It is practiced to store an optical fiber longer than a metal tube in advance during manufacturing. However, since it is necessary to lay the optical fiber cable vertically or almost vertically, the optical fiber element wire gradually falls under its own weight inside the metal tube and bends finely below the metal tube to remain, causing an increase in transmission loss. was there.

Further, since the inside of the geothermal well is filled with high temperature corrosive hot water, and especially the deepest part is under high water pressure and high temperature, the metal tube is sealed and the strength of the optical fiber is deteriorated due to hot water infiltration. Need to be prevented. Since this sealing is performed after forming a cable of a metal tube optical fiber or a composite of other materials into a cable, it is usually applied to the end of the metal tube. On the other hand, in order to insert an optical fiber cable into a well, a weight of several tens of kilograms must be attached to its end. However, since the end portion of the optical fiber cable is sealed as described above, there is a problem that if the metal tube is crushed or bent when the weight is attached, the metal tube is damaged such as cracked.

[0007]

The present invention has been made in order to solve such a problem, and the first feature thereof is as follows.
The optical fiber cable has a stranded wire structure including a metal tube optical fiber so as to cancel out the difference in length between the optical fiber element wire and the metal tube due to temperature change. That is, the length of the optical fiber strand at the use environment temperature is set to be equal to or less than the length of the metal tube at the same temperature, and the difference between the two is set to be equal to or more than the difference between the internal lengths of the metal tubes spirally arranged. Although the end of this metal tube is sealed, the end of the metal tube is sealed with a long metal body with a convex end so that it is easy to attach a weight when lowering the cable in the geothermal well. Is desirable. In such a cable, the metal tube optical fibers may be twisted together, or the metal tube optical fiber and the metal wire may be twisted together. That is, it is sufficient that at least one metal tube optical fiber is used for twisting, and the number of wire rods forming the twisted wire is not limited. The second feature is that the optical fiber fixing portions are discretely provided in the metal tube optical fiber tube in order to prevent the optical fiber from dropping due to its own weight.

[0008]

First, the operation relating to the first characteristic will be described.
It has already been stated that when manufacturing the metal tube optical fiber, an extra length is previously stored in the optical fiber to store the optical fiber in a longer length. However, since the elongation due to the temperature rise is larger in the metal tube than in the optical fiber, depending on the extra length of the optical fiber, the metal tube may be longer in use or vice versa. When using by vertical installation, there is no problem if the optical fiber strand is shorter, but if it is long, it will drop by its own weight and stay finely bent downward. Also, when installed vertically, both the metal tube and the optical fiber are arranged in a substantially straight line, and due to the difference in the coefficient of linear expansion, there is a difference in elongation between the two, causing friction between the optical fiber element wire and the inner surface of the metal tube, and Tensile tension is applied to the wire. The present invention, the length of the optical fiber strand at the time of use and less than the length of the metal tube,
It prevents the optical fiber from staying downward and causing a slight bend even when installed vertically, and the metal pipe is arranged in a spiral by using a cable with a stranded wire structure, and the length along the inside of the metal pipe is located inside the pipe. The generation of tension was avoided by varying the

When the metal tube is made into a spiral shape, it can be considered that it is located along the center of the metal tube if the positions of the optical fiber strands in the tube are averaged. Therefore, in this case, the length along the center of the metal tube is The difference between the length of the optical fiber element and the length along the inside of the metal pipe when the optical fiber is closest to the center of the cross section of the cable (the center of the spiral shape) is defined as the difference in the inner length of the metal pipe.

Here, if the difference between the expansion length of the optical fiber strand and the expansion length of the metal pipe is equal to or less than the difference in the internal length of the metal pipe, when the metal pipe extends, the optical fiber strand receives tensile tension. The tension can be prevented because the components can be offset by moving the components toward the center side of the cable cross section inside the metal tube.

Further, when the optical fiber wire is shorter than the metal tube in use and the difference in length between the two is equal to or more than the difference in internal length of the metal tube, the optical fiber wire is inside the metal tube as described above. Even if it moves to the center side of the cable cross section, no extra length is generated. In practice, it is naturally preferable that the optical fiber is inserted up to the end of the metal tube, and it is better to align the optical fiber and the end of the metal tube during manufacturing. In other words, the lengths of the optical fiber and the metal tube are equal, so the ends are aligned, or even if the optical fiber is longer, the ends are aligned because they are housed in a corrugated inside the metal pipe. .

Considering the above, it is preferable to design the length of the optical fiber strand in the following relationship. Actual length of metal tube during manufacturing: LM (m) Actual length of optical fiber strand during manufacturing: LF (m) Linear expansion coefficient of metal: αM Linear expansion coefficient of optical fiber: αF Expected rise during use Temperature: T (℃) Extra length ratio of optical fiber that can be offset in the metal tube by the twisted wire structure (ratio of difference in internal length of metal tube to length along center of metal tube): β (%), used at temperature T In this case, the condition that tension is not applied to the optical fiber is that the difference between the expansion length of the metal tube and the expansion length of the optical fiber that occurs when the temperature rises by T can be canceled by the twisted wire structure, and is expressed by the following formula. . LM × (αM−αF) × T ≦ β × LF ... Formula Further, the condition that the optical fiber does not remain in the used state is expressed by the following formula. LM × (1 + αM × T) ≧ LF × (1 + αF × T) + β
XLF ... Equation From the above equation, the ideal ratio of the length of the optical fiber at the time of manufacture to the length of the metal tube is obtained, and LF / LM = (αM−αF) × T / β. However, the actual operating environment temperature is generally unknown and non-uniform, and in actual cable design, the operating environment temperature is estimated, and the above concept is applied according to the distribution form to determine LF or β. Need to decide.

Further, according to the present invention, the end of the metal tube optical fiber is sealed with a metal elongated body having a convex end to prevent the intrusion of hot water or the like. At this time, since the weight can be attached to the metal elongated body instead of the metal tube for sealing the optical fiber, the metal tube is not damaged.

Next, the operation relating to the second feature will be described. Conventionally, the resin has been filled over the entire length of the metal tube for the purpose of preventing water infiltration, but when used in a high temperature environment such as a geothermal well, thermal deterioration of the resin itself may adversely affect the transmission loss of the optical fiber. However, the force when the metal tube is stretched is applied to the optical fiber, which is not preferable. The present invention prevents the optical fiber strand from dropping downward by its own weight even when the cable is installed vertically by providing the fixing portion of the optical fiber strand inside the metal tube in a discrete manner. The adverse effects of deterioration are also minimized.
Therefore, the optical fiber does not bend more finely than necessary in the metal tube and does not cause an increase in transmission loss. Further, according to this configuration, the optical fiber element wire can be stored longer than the metal tube at the time of manufacturing within a range where the transmission loss does not increase.

[0015]

EXAMPLES Examples of the present invention will be described below. (Embodiment 1) FIG. 1 is a sectional view of a cable of the present invention, which is SUS316.
・ Three kinds of metal tubes 1 of Hastelloy and Incoloy, in which the optical fiber wire 2 is housed, and 3 galvanized steel wires 3
Shows that the wire is twisted around the SUS316 wire 4. The material of the metal tube 1 is not particularly limited, but SUS304 or
Stainless steel such as SUS316, Hastelloy Inconel,
In addition to an alloy mainly composed of nickel called incoloy or the like, a corrosion resistant metal such as titanium is preferable. The diameter of the metal tube 1 may be selected depending on the use conditions such as crushing strength and tensile strength and the manufacturing conditions. For example, inner diameter: 0.7 to 3.6.
mm, outer diameter: 1.0 to 4.0 mm, wall thickness: 0.1 to 0.
The thing about 3 mm is mentioned. In this example, the outer diameter of the metal tube 1 and the metal wires 3 and 4 is 2 mm, and the inner diameter of the metal tube 1 is 1.
A 6 mm one was used. On the other hand, the material and structure of the optical fiber element wire 2 housed in the metal tube are not particularly limited. Any size can be used as long as it can be stored in the metal tube, and it may be selected according to the application. Here, an optical fiber made of silica glass having a core diameter of 50 μm and a cladding diameter of 125 μm and having an outer diameter of 210 μm with a heat-resistant resin coating around it was used.

In this example, the stranded wire pitch is 120 mm, and when the optical fiber element wire 2 is located in the center of the metal tube due to the relationship between the diameter of the metal tube and the optical fiber, and in the center of the cable cross section inside the metal tube. When the difference in length from the case where the position is located (difference in internal length of the metal pipe) is obtained, the result is as follows. When located at the center of the metal tube 1, the center of the optical fiber is 2 mm from the center of the cable cross section, so the length L1 of the optical fiber when traveling one pitch is L1 = √ (120 ² + (2 × 2 × π ) ² ) = 120.6
56. When located on the center side of the cable cross section, the center of the optical fiber is 1.305 m from the center of the cable cross section.
Since it is m, the length L of the optical fiber when traveling one pitch
2 is L2 = √ (120 ² + (2 × 1.305 × π) ² ) = 1
It becomes 20.280. Therefore, the ratio of the difference δL in the internal length of the metal pipe to L1 = the extra length ratio β is β = (δL / L1) × 100 = 0.31%.

Meanwhile, considering the metal tube Hastelloy, the temperature rise during use because the linear expansion coefficient of the optical fiber with respect to the linear expansion coefficient of 13 × 10 ^-6 of Hastelloy degree 1.1 × 10 ^-6 is If the temperature is 260 ° C., the difference between the two elongation amounts is 0.31% according to the following calculation. (13 × 10 ⁻⁶ −1.1 × 10 ⁻⁶ ) × 260 × 100 =
0.31 (%) Therefore, considering the above β results, assuming that the entire cable is used in an environment with an elevated temperature of 260 ° C, the length of the optical fiber and the metal tube at the time of manufacture If the lengths are made equal, no tension is applied to the optical fiber strand.

The sealed portion of this cable will be described with reference to FIG. The figure (A) shows the cable 7 pulled out from the laying drum 5 with the weight 6 attached to the tip, and the figure (B) shows (A).
The circled portion in the figure is enlarged, and the figure (C) shows the sealed portion in the figure (B) further enlarged. (C) As shown in the figure, the metal tube 1 containing the optical fiber element 2 and the empty metal tube 9 (only the optical fiber is not included, the metal tube optical Same as fiber: length 2
m) was welded and sealed with a YAG laser. The outer diameter (1.5 mm) of the convex portions at both ends of the plug 8 is substantially equal to the inner diameter of the metal tubes 1 and 9, and the outer diameter of the central portion is equal to the outer diameter of the metal tubes 1 and 9. The outer diameters of the convex portions at both ends are made slightly smaller than the inner diameters of the metal pipes 1 and 9 in order to facilitate insertion into the metal pipes.

The projections on both ends of the plug 8 are 5 m each.
m and the central portion also have a length of 5 mm, but there is no particular limitation as long as the length is sufficient for welding. By making the convex portions on both ends longer than the length required for welding, it is possible to prevent the stress from concentrating on the weld portion when the metal pipe is bent during use after welding. With such a structure, since the weight can be attached to the empty metal tube, the metal tube that seals the optical fiber element wire is not damaged when the weight is attached. Actually, the empty metal tube weighs 10k
When a cable was laid in the geothermal well with the g weight suspended, it could be used normally without any problems.

Further, there is a structure shown in FIG. 3 as a structure having a function similar to this. What is shown in FIG. (A) is a plug formed by forming one end of a metal wire 10 into a convex shape, and what is shown in (B) is a plug 8 similar to the plug shown in FIG. Instead of the pipe 9, a metal wire 11 is welded.

(Embodiment 2) Next, an example in which an optical fiber fixing portion is provided will be described with reference to FIG. This shows a cross section of a metal tube optical fiber.
Fixing part that prevents movement of the optical fiber strand 2 at intervals of 00 m
12 are provided. In this example, the two-part mixed curing type silicone rubber is used as the fixing portion 12, but it is not particularly limited as long as it does not adversely affect the loss increase of the optical fiber.

The optical fiber wire 2 is stored 0.31% longer than the length of the metal tube 1, and even if the temperature rises by 260 ° C., the elongation of the metal tube is increased by 0.31% as compared with the length of the metal tube 1. No tension is applied to the fiber strand. Further, even if this cable is laid vertically, the optical fiber fixing portion is provided, so that the optical fiber does not stay downward and bend finely due to its own weight. The distance between the fixing portions 12 may be determined in consideration of the inner diameter of the metal tube 1, the temperature range used, the extra length of the optical fiber wire at the time of manufacture, and is not limited to 100 m.

[0023]

As described above, according to the cable of the present invention, even when the cable is hung and vertically laid, the optical fiber moves by its own weight and bends finely and stays downward, resulting in transmission loss. Can be prevented from increasing.
Further, the optical fiber can be securely sealed in the metal tube, and the metal tube can be prevented from being damaged due to the attachment of the weight. Therefore, the deterioration of the optical fiber due to the intrusion of water can be prevented. Therefore, it is convenient to use for temperature measurement in geothermal wells of geothermal power plants.

[Brief description of drawings]

FIG. 1 is a sectional view of a cable of the present invention.

2A and 2B are explanatory views of a sealed portion of a cable of the present invention, in which FIG. 2A is a cable pulled out from a laying drum with a weight attached to its tip, and FIG. 2B is an enlarged view of a circled portion in FIG. ,
(C) shows an enlarged view of the sealed portion in (B).

FIG. 3 is a cross-sectional view showing a sealed portion of the cable of the present invention, (A)
Is a plug formed by forming one end of a metal wire into a convex shape, (B)
Indicates a metal wire welded to a plug having convex ends.

FIG. 4 is a cross-sectional view of a cable of the present invention in which an optical fiber fixing portion is provided inside a metal tube.

[Explanation of symbols]

 1,9 Metal tube 2 Optical fiber element wire 3 Galvanized steel wire 4 SUS316 wire 5 Laying drum 6 Weight 7 Cable 8 Plug 10,11 Metal wire 12 Fixed part

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Kenji Watanabe 2-82 Watanabe-dori, Chuo-ku, Fukuoka City Kyushu Electric Power Co., Inc. (72) Koichi Yasuga 2-82-1 Watanabe-dori, Chuo-ku, Fukuoka No. Kyushu Electric Power Co., Inc. (72) Inventor Yasuhiro Ogata 1-282 Watanabe-dori, Chuo-ku, Fukuoka City Kyushu Electric Power Co., Ltd.

Claims (3)

[Claims] 1. A stranded optical fiber cable including a metal tube optical fiber in which an optical fiber element wire is housed in a metal tube, wherein the length of the optical fiber element wire at the ambient temperature is the metal tube at the same temperature. Is less than or equal to the length, and the difference between them is greater than or equal to the difference in the internal length of the metal pipe arranged in a spiral shape, and the end of the metal pipe is sealed. . 2. An optical fiber cable for geothermal well temperature measurement according to claim 1, wherein the end of the metal tube is sealed with a metal elongated body having a convex end. 3. An optical fiber cable for geothermal well temperature measurement, which is an optical fiber cable in which an optical fiber element wire is housed in a metal tube, and optical fiber fixing portions are discretely provided inside the metal tube.