Optical fiber cable, optical fiber cable monitoring system and well monitoring method

Abstract

An optical cable (10, 10a) comprises: an optical fiber (1) for sensing deformation of a hydrocarbon absorbing resin (2) having a property of swelling by absorbing hydrocarbons in oil; a strand (20) arranged in a manner surrounding the outer periphery of the optical fiber (1); and a hydrocarbon absorbing resin (2) filling a space between the optical fiber (1) and the strand (20). The optical cable (10, 10a) constructed as described above is installed in the entire range of a well (100) as a measurement target in the depth direction thereof, and a backscattered light frequency shift signal from the optical fiber (1) is measured by a backscattered light measuring device (40) to detect the presence / absence of oil leaking from the well (100) in the entire range in the depth direction of the well (100).

Description

Technical Field

[0001] The present application relates to an optical cable, an optical cable monitoring system and a well monitoring method. Background Art

[0002] Conventionally, after the service life of an oil well ends, the casing as the structure of the oil well is cut at a certain depth (about 50m) where there is an oil well outlet, which is defined with reference to the surface (in the case of the ground) or the seabed (in the case of the ocean) without affecting the ground construction, etc., and a steel cover provided at the uppermost end of the casing is welded to seal the oil well outlet. Then, the space around the casing is filled with sand. Therefore, the oil well at the end of its service life is abandoned.

[0003] This abandonment method was established about 80 years ago and to date, about 50,000 wells a year, totaling about 4 million wells or more, have been abandoned using this method.

[0004] However, for example, in California, the United States, cooking water contamination believed to be caused by abandoned oil wells (hereinafter referred to as abandoned oil wells) has been found, which has an impact on daily life. Therefore, stricter disposal methods are required.

[0005] In addition, among the oil wells on the seabed near the coast of Malaysia, there are increasing oil leaks from waste oil wells (abandoned oil wells), so the problem of marine pollution cannot be ignored.

[0006] Therefore, now that about 100 years have passed since the large-scale development of oil, the treatment of abandoned oil wells and the like has become increasingly important due to the increase in the number of oil wells and the increase in offshore oil development.

[0007] On the other hand, in the past, there were few examples of research on the treatment of abandoned oil wells as described above. In most cases, the treatment was not conducted on the abandoned oil well itself, but on some related elements, for example, as shown in the following invention, an excavation temporary filling material used in oil well excavation for extracting oil, natural gas, etc. (for example, see Patent Document 1) or an invention related to the treatment of accompanying water (fracture water) generated while extracting oil or natural gas from an oil well or a natural gas well (for example, see Patent Document 2).

[0008] Citation List

[0009] Patent Documents

[0010] Patent Document 1: International Publication No. 2015 / 072317

[0011] Patent Document 2: Japanese Patent Publication No. 2018-43221

[0012] Patent Document 3: International Publication No. 2014 / 181617

[0013] Non-patent documents

[0014] Non-patent document 1: Wu, Qian et al., titled “Advanced Distributed Fiber Optic Sensors for Monitoring Poor Zonal Isolation with Hydrocarbon Migration in Cemented Annui”, Society of Petroleum Engineers, September 14, 2016, doi:10.2118 / 180329-MS Summary of the invention

[0015] Problems to be solved by the present invention

[0016] Therefore, in order to further clarify the problem to be solved by this application, Fig.14 The principle of oil leakage from abandoned oil wells is explained. Fig.14 This diagram explains the principle of oil leakage from abandoned oil wells.

[0017] like Fig.14 As shown, in the casing or cement surrounding the casing of a well formed underground or on the seabed, cracks between the casing surface and the cement surface (upper part) and cracks inside the cement (lower part) are caused by underground carbon dioxide (CO 2 ), oxygen (O 2 ) and hydrogen sulfide (H 2 S) and other components, thereby also causing outer casing corrosion. In addition, the appearance of such cracks is caused by the stress of geological movement. Therefore, the cracks that appear around the well will expand over time, forming a channel from the oil-bearing layer to the underground drinking water layer or seawater, leading to leakage accidents. As another reason, in the case of an internal corrosion hole formed in the casing from the inside of the well, for example, leakage may occur due to the connection between the internal corrosion hole and the crack.

[0018] In the case of California, the United States, water containing radioactive isotopes was injected from the ground into an abandoned oil well, and then, when radiation was detected in the groundwater, it was determined that the oil well had a leak. In this case in California, if it is determined by some method that the casing has corroded and broken, and the determined portion is the upper portion of the oil well, that portion is repaired through construction work.

[0019] In cases where the leak path can be specified, the following methods can be used: Fig.15As shown, a specific portion of the corresponding casing is drilled using an inexpensive and effective repair means inner well tool, and a filler grout as a special adhesive is injected through the hole into the gap where the crack causing the leakage occurs, thereby repairing. Fig.15 In FIG. 1 , the dashed line S1 indicates the moving path of the inner well tool, and the front end of the arrow indicates a specific part of the casing. The part repaired by the filler grouting is the range S2 surrounded by the trapezoidal dashed line, and is the part where cracks have occurred in the cement outside the oil well, and there is a crack that has occurred on the side closest to the oil well. However, in this method, it is difficult to confirm the effect of the repair, that is, it is difficult to confirm that no leakage occurs. Note that P represents the surface of the ground or the sea.

[0020] Recently, it has been published that a special outer coating is applied to an optical fiber, and the outer coating selectively absorbs hydrocarbons (HC) in oil and swells, and the presence of hydrocarbons can be indicated by sensing the deformation of the outer coating using an optical fiber (for example, see Non-Patent Document 1). In addition, when hydrocarbons disappear, the swelling deformation may disappear, thus indicating the possibility of confirming the effect after the leakage path is disconnected. However, a method for confirming the repair effect has not yet been solved.

[0021] In addition, recently, the scale of oil wells has become larger and larger, which has caused two major problems. The first problem is that the corrosion resistance of the steel or cement used initially was not fully understood, and the carbon dioxide (CO 2 ) concentration reaches 77% or more. The second problem is that it is impossible to solve such a problem at the cost of developing oil wells.

[0022] As mentioned above, although the possibility of detection through optical fiber has been confirmed, there is currently no method that has been verified to be implemented in oil wells.

[0023] The present application is proposed to solve the above-mentioned problems. The purpose of the present invention is to provide an optical cable, an optical cable monitoring system and a well monitoring method, wherein while promoting the standardization and popularization of petroleum technology taking into account corrosion resistance, the leakage path of the oil well is detected, thereby specifying the leakage path, thereby being able to verify the effectiveness of the oil well repair method and enable long-term monitoring of the oil well.

[0024] Solution to the problem

[0025] The optical cable according to the present application includes: an optical fiber; a strand, which includes a plurality of cables arranged along the radial direction of the optical fiber, the plurality of cables being twisted to surround the outer circumference of the optical fiber and arranged in a ring shape; and a hydrocarbon absorbing resin (hydrocarbon absorbing resin) configured to absorb hydrocarbons (hydrocarbons) and fill the gap between the optical fiber and the strand.

[0026] Another optical cable according to the present application includes: an optical fiber; a strand, which includes a plurality of cables arranged in a radial direction of the optical fiber, the plurality of cables are twisted to surround the outer circumference of the optical fiber and are arranged in a ring shape; a second strand, which includes a plurality of cables arranged in a radial direction of the optical fiber, the plurality of cables are twisted to surround the outer circumference of the strand and are arranged in a ring shape, and the plurality of cables have an outer diameter larger than that of the cables of the strand; a physical quantity measuring optical fiber, which is provided as a cable replacing the second strand and is configured to measure temperature, strain or pressure as a physical quantity of a measurement target; a third strand, which includes a plurality of cables arranged in a radial direction of the optical fiber, the plurality of cables are twisted to surround the outer circumference of the second strand and are arranged in a ring shape, and the plurality of cables have an outer diameter larger than that of the cables of the second strand; and a hydrocarbon absorbing resin, which is configured to absorb hydrocarbons and fill gaps between the optical fiber, the strand, the second strand, and the third strand.

[0027] Effects of the Invention

[0028] The optical cable, the optical cable monitoring system and the well monitoring method using the optical cable according to the present application can achieve remarkable effects, that is, an optical cable, an optical cable monitoring system and a well monitoring method can be provided, wherein, while promoting the standardization and popularization of petroleum technology taking into account corrosion resistance, the leakage path of the oil well is detected, thereby specifying the leakage path, thereby being able to verify the effectiveness of the oil well repair method and enabling long-term monitoring of the oil well. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 : is a diagram showing an example of the optical cable monitoring system according to Embodiment 1.

[0030] Figure 2 : is a diagram showing an example of a basic structure of an optical fiber cable according to Embodiment 1.

[0031] Figure 3 is with Figure 2 A schematic cross-sectional view of the optical cable in a direction perpendicular to the axis thereof is shown.

[0032] Figure 4 is a diagram showing another example of the basic structure of the optical fiber cable according to Embodiment 1.

[0033] Figure 5 is with Figure 4 A schematic cross-sectional view of the optical cable in a direction perpendicular to the axis thereof is shown.

[0034] Figure 6 This is a schematic diagram of the structure of an oil immersion test device for optical cables used in the optical cable monitoring system according to Example 1.

[0035] Figure 7 Yes means Figure 6 Illustration of the fiber optic cable sample used in the oil immersion test shown.

[0036] Figure 8 is a table showing the Figure 6 Shown are the specifications of the equipment for making quantitative measurements of optical cables used in oil immersion tests.

[0037] Fig. 9 express Figure 8 An example of the center frequency characteristics of an optical cable sample in a characteristic measurement test is shown.

[0038] Fig.10 Indicated in Figure 6 Shown is an example of the measurement of strain distribution of two fiber optic cable samples during an oil immersion test.

[0039] Fig.11 express Figure 6 An example of strain distribution over time for a fiber optic cable sample during an oil immersion test is shown.

[0040] Fig.12 Indicated in Figure 6 Shown is the filling effect measured on the strain distribution of the optical cable sample during the oil immersion test.

[0041] Fig.13 FIG. 1 is a schematic diagram showing an example of monitoring data of the optical cable monitoring system according to Embodiment 1. FIG.

[0042] Fig.14 is a diagram illustrating the problems of the optical cable monitoring system.

[0043] Fig.15 is a diagram showing an example of a conventional optical cable monitoring system. DETAILED DESCRIPTION

[0044] Hereinafter, embodiments of the present application will be described with reference to the accompanying drawings.

[0045] Example 1

[0046] Figure 1 is a diagram showing an example of an optical cable monitoring system 50 according to Embodiment 1.

[0047] like Figure 1 As shown, in order to monitor the well 100 installed on the seabed, the monitoring center 110 is provided with a hybrid backscattered light measuring device 40, which uses both Brillouin scattering and Rayleigh scattering for processing the signal from the optical fiber. In addition, the optical cable 10 including the optical fiber having the function of detecting hydrocarbons is arranged to extend from the monitoring center 110 along the seabed to the location where the well 100 is installed, and after reaching the installation location of the well 100 (the uppermost part of the well 100), it further extends along the periphery of the well 100 to reach the bottom (lowest part) of the well 100. Note that in Figure 1 , Q represents the sea surface.

[0048] In this case, the backscattered light measuring device 40 and the optical cable 10 having a hydrocarbon detection function are connected to each other to form an optical cable monitoring system 50, in which the backscattered light measuring device 40 measures the frequency shift of scattered light related to the placement position of the optical cable, and detects the position of oil leakage from the well based on the measured value. That is, the optical cable monitoring system 50 includes the optical cable 10 and the backscattered light measuring device 40 as main components.

[0049] By installing the optical cable monitoring system 50 as described above, it is possible to perform long-term monitoring of the presence or absence of leakage of oil or the like as a monitoring object for 50 years or more within a range from a height position corresponding to the seabed (i.e., from the highest position of the well 100 to the lowest position of the well 100). Hereinafter, the details of the optical cable monitoring system 50 will be described, with an emphasis on the optical cable used in the optical cable monitoring system 50.

[0050] First, the optical cable 10 used in the optical cable monitoring system 50 will be described with reference to the drawings.

[0051] Figure 2 and Figure 3 1 is a diagram showing an example of a basic structure of an optical cable 10 that can be used in the optical cable monitoring system according to Embodiment 1. More specifically, Figure 2 1 is a schematic diagram showing the structure of the optical cable 10, and shows the structure of the optical cable in three dimensions. Figure 3 It is a cross-sectional view showing a direction perpendicular to the axis of the optical cable.

[0052] like Figure 2 and Figure 3 As shown, the optical fiber 1 is arranged at the central axis portion of a strand 20 composed of a plurality of twisted steel wires 3 arranged in a ring shape. The surrounding area of ​​the optical fiber 1 is filled with a hydrocarbon absorbing resin 2a as a resin that absorbs hydrocarbons. On the outside of the strand 20, a second strand 21 is arranged, which is formed by a plurality of steel wires 4 having an outer diameter greater than that of the steel wires 3, and the plurality of steel wires 4 are twisted in the opposite direction to the strand 20 and arranged in a ring shape.

[0053] Note that the strand 20 and the second strand 21 are generally formed of an armored cable, and by disposing optical fibers therein, they can be used for so-called general purposes such as communication or data transmission.

[0054] In the optical cable 10 according to the first embodiment, the strand 20 (composed of Figure 2 and Figure 3The gap between the optical fiber 1, the strand 20 and the second strand 21 is filled with a hydrocarbon absorbing resin 2b similar to the above-mentioned resin. Note that, generally, after the optical fiber 1, the strand 20 and the second strand 21 are bonded to each other, the gap between them is filled with the hydrocarbon absorbing resin 2, thereby manufacturing the optical cable 10.

[0055] The hydrocarbon absorbing resin 2 is provided to completely fill the gap, and the optical cable 10 is generally manufactured to have a long size of 3 km or more.

[0056] Note that the hydrocarbon absorbing resin 2 may also be provided intermittently along the axial direction of the optical cable 10, in which case the pitch of the positions where the hydrocarbon absorbing resin 2 is provided is determined based on the accuracy of position detection of oil leakage or the like.

[0057] In general, the hydrocarbon absorbing resin 2 has a property of expanding in triaxial directions (three-dimensional axial directions) when absorbing hydrocarbons, and unless the resin is constrained, strain caused by tensile stress is generated in the optical fiber due to the influence of the resin that has absorbed hydrocarbons (for example, see Non-Patent Document 1). However, the optical cable 10 according to the present embodiment is different in that when the hydrocarbon absorbing resin 2 has absorbed hydrocarbons, the deformation of the hydrocarbon absorbing resin 2 is restricted by, for example, the presence of the strands 20, with the result that compressive strain (strain caused by compressive stress) occurs in the optical fiber 1.

[0058] In the above description, the optical cable 10 has been described in which a double (two-layer) strand is formed outside the optical fiber 1. However, without being limited thereto, the optical cable may be formed only of the optical fiber 1 and the strand 20 disposed outside the optical fiber 1, thereby obtaining the same effect.

[0059] Regarding the relationship between the strand twisting direction and the second strand twisting direction, an optical cable having a structure in which the second strand twisting direction is opposite to the strand twisting direction is formed, such as in Example 1. Figure 2 As shown, it is optimal to prevent fraying of the strands.

[0060] Example 2

[0061] In the optical cable monitoring system 50 according to the present embodiment 2, the structure of the optical cable 10 used in the above-mentioned embodiment 1 is modified to adopt an optical cable that can extract only a signal purely based on hydrocarbons contained in the oil well by compensating for the influence of temperature, strain, pressure, etc. Hereinafter, an optical cable 10a obtained by modifying the structure of the optical cable 10 will be described.

[0062] In the optical cable 10a according to the present embodiment 2, the steel wire 4 forming the second strand 21 of the optical cable 10 is partially changed, so that an optical fiber sensor for sensing temperature, strain, pressure, etc. is provided in combination. By providing an optical fiber sensor capable of sensing temperature, strain, pressure, etc. according to the purpose, a signal based only on the influence of the absorption of hydrocarbons can be extracted from the optical fiber 1, and the influence of temperature, strain, pressure, etc. can be compensated by the measurement result obtained by using the optical fiber sensor as described above.

[0063] That is, in the case where it is necessary to use a cable having a DPATS (abbreviation for distributed pressure, tone, temperature and strain sensing) function, the optical cable 10a according to the present embodiment 2 can be used. That is, if temperature compensation is required, another optical fiber for measuring temperature can be prepared, if strain compensation is required, another optical fiber for measuring strain can be prepared, and if pressure compensation is required, another optical fiber for measuring pressure can be prepared.

[0064] Hereinafter, specific examples of an optical cable having a DPATS function will be described with reference to the accompanying drawings. Figure 4 is a diagram showing an example of a basic structure of an optical cable 10 a including a physical quantity measuring optical fiber 6 for measuring a physical quantity of a measurement target. Figure 5 is with Figure 4 The optical cable 10a is shown in a schematic cross-sectional view in a direction perpendicular to its axis.

[0065] like Figure 4 and Figure 5 As shown, the optical cable 10a has the following features, in which a third strand 22 composed of a plurality of steel wires 5 is newly provided at a position corresponding to the outermost peripheral portion corresponding to the outer side of the optical cable 10 described in Embodiment 1, and a physical quantity measuring optical fiber 6 for measuring the temperature, strain, pressure, etc. of the measurement target is newly provided inside the third strand 22 to replace a part of the second strand 21. Note that, as in the case of the above-mentioned optical cable 10, the gaps between the optical fiber 1, the strand 20, the second strand 21, and the third strand 22 are filled with a hydrocarbon absorbing resin 2. Oil will enter the area filled with the hydrocarbon absorbing resin 2.

[0066] The reason for the above configuration is as follows. Generally, in an optical cable having multiple layers (multi-path) of strands, even if the physical quantity measuring optical fiber 6 (particularly the temperature measuring optical fiber here) is located inside to some extent, the external temperature is transferred there, so that detection thereof is possible. In addition, arranging the physical quantity measuring optical fiber 6 inside has the advantage of protecting the physical quantity measuring optical fiber 6 itself. It should be noted that the optical cable itself cannot become an oil leakage channel.

[0067] Note that, generally, in a multilayer optical cable, the gap between the outer layer and the inner layer of the optical cable is filled with a protective material, etc. Therefore, a cable wire for the purpose of detecting oil leakage, etc., can also be arranged at the outermost periphery of the optical cable, which is advantageous in terms of improving detection performance.

[0068] In the above description, the optical cable is manufactured so that the hydrocarbon absorbing resin 2 fills the gaps between the optical fiber 1, the strand 20, and the second strand 21, or fills the gaps between the optical fiber 1, the strand 20, the second strand 21, and the third strand 22. However, without being limited thereto, an optical cable manufactured so that an outer coating is provided on the surface of the optical fiber 1 may be used, whereby the same effect can be obtained.

[0069] The optical cable filled with the hydrocarbon absorbing resin 2 has a life of at least fifty years in an environment of 200° C. It should be noted that when the optical cable is used in an environment of low temperature and shallow depth, its life is expected to be semi-permanent.

[0070] Next, the verification experiment conducted for the hydrocarbon detection function of the above optical cable and the results thereof are described with reference to the accompanying drawings. Here, in particular, the verification was conducted using an optical cable having a structure formed only of an optical fiber and an innermost layer (one layer) of strands located immediately outside the optical fiber, and as described in the above-mentioned embodiment 1, it is a basic structure for confirming the operation and effect in the case of providing a resin for detecting hydrocarbons.

[0071] Figure 6 A schematic configuration of the experimental equipment used in the verification experiment is shown. A sample cable (optical fiber cable with hydrocarbon detection function) is immersed in each of two light oil containers, and the shift of backscattered light occurring when each cable absorbs hydrocarbons in the light oil is measured by a hybrid backscattered light measurement device DTSS (abbreviation for distributed temperature and strain sensing), which is connected to these cables and is capable of measuring two frequency shifts with one device.

[0072] Here, the two frequency shifts are analyzed by pulsed pre-pumped Brillouin optical time domain analysis (PPP-BOTDA) for Brillouin scattered light and by a technique called tunable wavelength coherent optical time domain reflectometry (TW-COTDR) for Rayleigh scattered light. Therefore, even when temperature and strain change simultaneously, the changes in both can be analyzed.

[0073] Figure 7 Detailed specifications of each sample cable used in the verification experiment are shown. An optical fiber having a sensing portion in which a surrounding area of ​​the optical fiber is filled with a resin having a hydrocarbon detection function is held within the armored cable. Figure 7 The portion with a length of 9 cm shown in “Sensing portion” is a sensing portion for detecting hydrocarbons.

[0074] The cross-sectional view of the sensing portion at position AA is represented as a cross-sectional view below the sensing portion. As shown in the cross-sectional view, the surrounding area of ​​the optical fiber disposed at the center portion is filled with a resin having a hydrocarbon detection function, which is indicated by a multi-dot pattern. In addition, the cross-sectional view of the armored cable at position BB is shown as a cross-sectional view BB on the left side of cross-sectional view AA. As shown in the cross-sectional view, at position BB, the surrounding area of ​​the optical fiber is not filled with the above-mentioned resin having a hydrocarbon detection function. As described above, the sensing portion is filled with a resin having a hydrocarbon detection function, and the portion of the armored cable other than the sensing portion is not filled with a resin having a hydrocarbon detection function.

[0075] Furthermore, reference optical fibers (non-armored cable form) having a length of 1 m were connected to both ends of the optical fibers, respectively. The sample cable constructed as described above was held by immersing the entire armored cable portion in a container (containing hydrocarbons) storing light oil therein.

[0076] As described above, the length of the sensing portion is short compared to the other portions. Therefore, it is considered that the strain change due to temperature change and / or pressure change is small and negligible compared to the strain change due to absorption of hydrocarbon components.

[0077] Figure 8 : is a table showing the specifications of the hybrid backscattered light measuring device. Since its measurement functions include the two main functions of PPP-BOTDA and TW-COTDR mentioned above, the specifications are shown for each of the two functions. As shown in the table, the two functions are the same in terms of distance range, distance resolution, etc., but are very different in frequency characteristics.

[0078] then, Fig. 9 The center frequency distribution in the constituent parts of the two sample cables described above is shown when the frequency shift analysis of these sample cables is performed by PPP-BOTDA.

[0079] This figure shows the characteristics of the sample cable before it was immersed in light oil. The center frequency of the armored cable section under test was found to be about 11.1 GHz, while the center frequency of the reference fiber section was about 10.8 GHz.

[0080] Next, Fig.10 An example of measurement of strain distribution of two sample cables is shown. For both samples, occurrence of strain is recognized, which is considered to be caused by absorption of hydrocarbons by immersion in light oil (the center portion of the strain distribution of each sample is concave).

[0081] then, Fig.11Shown is a temporal change in strain distribution in the case where the strain distribution is measured for sample cable #2 over a period of about 1 month. Fig.11 The numerical values ​​representing the data in the figure indicate the date when the strain distribution was measured.

[0082] like Fig.11 As shown in Figure 2, the strain distribution changes greatly. It is believed that this change is caused by the gradual increase in the hydrocarbon content in the filler.

[0083] at last, Fig.12 The horizontal axis represents the measurement date, and shows the time change of the strain distribution when a filler as a resin having a hydrocarbon detection function is provided and when no filler is provided. Fig.12 In FIG. 1 , the downward arrows (two in total) indicate the time when the sample cable was immersed in the light oil, and the upward arrows (two in total) indicate the time when the sample cable immersed in the light oil was extracted therefrom. Note that the interval Ts indicated by the double arrow is the time period during which the measurement is stopped. As a result, it was found that since the sample cable (with the filler) was immersed in the light oil, the filler absorbed hydrocarbons, and thus a strain change occurred significantly.

[0084] Next, we will refer to Figure 1 and Fig.13 A case where the optical fiber cable 10 or 10a is used for long-term (approximately fifty years) monitoring of oil wells or the like will be described.

[0085] In monitoring, the presence or absence of leakage of oil or the like is determined by whether hydrocarbons, which are the main components of oil, are detected by the optical cable 10. Figure 1 The uppermost position of the well 100 shown (corresponding to Figure 1 The height of the seafloor in Fig.13 , the position where the point depth value is 0 (zero) represents the height position corresponding to the seafloor) to the lowest position of the well 100 (corresponding to Fig.13 If hydrocarbons are detected in the resin provided in the optical cable 10 at some parts of the height position of the depth value 1, the scattered light offset at the detection part is used as a representation of the difference between the detected part and the other parts (reference Fig.13 ) of the offset. The location (depth position) indicating the above different outputs is the part where the oil leak occurs. Fig.13 In the present invention, it is found that the leakage signal is detected only after the oil well is installed for fifty years. In addition, it is found that the leakage position is slightly lower than the center height position of the well 100.

[0086] Here, it is considered that the scattered light offset amount that changes due to the absorption of hydrocarbons by the resin is not affected by the position in the depth direction of the well 100, and changes only according to the absorption amount of hydrocarbons, while temperature, pressure, strain, etc. are likely to change according to the position in the depth direction. In the case where these influences are large, it is necessary to correct the scattered light offset amount caused thereby. In this case, the optical cable 10a having the above-mentioned DPATS function can be used.

[0087] As described above, in the optical cable monitoring system 50 using the optical cable 10 or 10a, the depth position of the oil leak or the like in the well to be inspected is detected, and therefore, the well can be repaired by performing local repair at the location where the leak is detected, thereby extending the service life of the well without abandoning the entire well.

[0088] Furthermore, after the partial repair, the presence / absence of the leakage signal in the optical cable monitoring system 50 is checked, and if no leakage signal is detected, it can be confirmed that the effect of repairing the leakage has been obtained.

[0089] Although the present application is described above with respect to various exemplary embodiments and implementations, it should be understood that the various features, aspects, and functions described in one or more individual embodiments are not limited to their applicability to the specific embodiments describing the above features, aspects, and functions, but may be applicable to one or more embodiments of the present disclosure alone or in various combinations.

[0090] Therefore, it is understood that many modifications that are not illustrated can be designed without departing from the scope of the present application. For example, at least one constituent element can be modified, added or eliminated. At least one of the constituent elements mentioned in at least one preferred embodiment can be selected and combined with the constituent elements mentioned in another preferred embodiment.

[0091] Description of Reference Numerals

[0092] 1. Fiber Optic

[0093] 2,2a,2b Hydrocarbon Absorbent Resins

[0094] 3,4,5 Steel Wire

[0095] 6 Physical quantity measurement optical fiber

[0096] 10,10a optical cable

[0097] 20 strands

[0098] 21 Second strand

[0099] 22 Third strand

[0100] 40 Backscattered light measurement equipment

[0101] 50 Optical Cable Monitoring System

[0102] 100 Wells

Claims

1. An optical cable comprising: optical fiber; a strand including a plurality of cables disposed in a radial direction of the optical fiber, the plurality of cables being twisted to surround an outer circumference of the optical fiber and arranged in a ring shape; a second strand including a plurality of cables disposed in a radial direction of the optical fiber, the plurality of cables being twisted to surround an outer circumference of the strand and arranged in a ring shape, the plurality of cables having an outer diameter greater than that of the cables of the strand; a physical quantity measuring optical fiber provided to replace one of the cables of the second strand and configured to measure temperature, strain, or pressure as a physical quantity of a measurement target; a third strand including a plurality of cables disposed in a radial direction of the optical fiber, the plurality of cables being twisted to surround an outer circumference of the second strand and arranged in a ring shape, the plurality of cables having a larger outer diameter than the cables of the second strand; as well as a hydrocarbon absorbing resin configured to absorb hydrocarbons and fill gaps between the optical fiber, the strand, the second strand, and the third strand; wherein the physical quantity measuring optical fiber is isolated from the hydrocarbon absorbing resin so that a measurement result obtained by the physical quantity measuring optical fiber is not affected by expansion of the hydrocarbon absorbing resin caused by absorption of hydrocarbons, The measurement result obtained by the physical quantity measuring optical fiber, which is only affected by the temperature, strain or pressure changes of the measurement target and not affected by the expansion of the hydrocarbon absorbing resin, is used to compensate for the influence of temperature, strain or pressure on the signal generated by the optical fiber, so that the corrected signal is only affected by the expansion of the hydrocarbon absorbing resin caused by the absorption of hydrocarbons.

2. The optical cable according to claim 1, wherein The hydrocarbon absorbing resin is intermittently provided along the longitudinal direction of the strand.

3. An optical cable monitoring system, comprising: The optical cable according to claim 1 or 2; as well as A backscattered light measurement device configured to measure the frequency shift of Brillouin scattered light and Rayleigh scattered light, wherein: The frequency shift change of the optical fiber caused by the absorption of hydrocarbons contained in the measurement target by the hydrocarbon absorbing resin and the frequency shift change of the optical fiber caused by the change of pressure, strain or temperature as the physical quantity of the measurement target are measured in a differentiated manner.

4. The optical cable monitoring system according to claim 3, wherein: The frequency shift change of the optical fiber due to absorption of hydrocarbons contained in the measurement target, which is measured in a manner distinguished from the frequency shift change of the optical fiber caused by changes in pressure, strain or temperature as a physical quantity of the measurement target, and the occurrence position in the optical fiber where the frequency shift change of the optical fiber due to absorption of hydrocarbons contained in the measurement target occurs are measured so as to be associated with each other.

5. A well monitoring method for monitoring oil leakage from a well, using the optical cable monitoring system according to claim 4, wherein: An optical fiber for detecting hydrocarbons is installed outside the well in the depth direction. The well monitoring method comprises: Recording the time variation of a leakage signal at a location in the well, the leakage signal being a signal in which the shift of scattered light caused by hydrocarbons detected by the optical fiber is different from the shift of scattered light at other locations caused by oil leakage; and At the location where the leakage signal is detected, the well is repaired, and the presence / absence of the leakage signal detection is confirmed after the repair to determine whether the repair of the well has been properly performed.

Images