FIBER OPTICS SENSOR FOR HYDROCABON AND CHEMICAL DETECTION

Abstract

Described is a fiber optic cable useful as a sensor for the detection of water or hydrocarbons. The fiber optic cable has sensor portions in line with fiber optic portions; the refractive index of the sensor portion changes when the sensor portion is placed in contact with water or hydrocarbons.

Claims

1. An optical conduit comprising at least one fiber optic portion and at least one sensor portion, whereby a light transmitted through the optical conduit passes through both the fiber optic portion and the sensor portion in a sequential manner, said sensor portion having a first refractive index and a first light transmissibility when in contact with air, and a second refractive index and a second light transmissibility when in contact with a substance other than air, wherein the first refractive index is similar or identical to the fiber optic cable refractive index and the first light transmissibility allows all or a significant portion of light of a desired wavelength therethrough, and wherein the second light transmissibility is different than the first light transmissibility or the second refractive index is different from the first refractive index.

2. The optical conduit of claim 1 wherein the at least one fiber optic portion comprises a plurality of fiber optic portions, and the at least one sensor portion comprises a plurality of sensor portions, wherein the optical conduit is configured so that each of the plurality of fiber optic portions alternate with each of the plurality of sensor portions.

3. The optical conduit of claim 1 wherein the substance other than air is an aqueous substance.

4. The optical conduit of claim 1 wherein the substance other than air is a hydrocarbon.

5. The optical conduit of claim 4 wherein the hydrocarbon is an oil.

6. The optical conduit of claim 1 wherein the sensor portion is made from a material having a first refractive index within 0.1 refractive index units of the fiber optic cable refractive index and an absorption coefficient of less than 0.1/mm.

7. The optical conduit of claim 1 wherein the sensor portion is made from a material selected from the group comprising silicone, polystyrene and polyvinyl acetate.

8. The optical conduit of claim 1 wherein each of the at least one fiber optic portion are between 1 m and 100 km in length, preferably between 1 m and 10 km in length, more preferably between 1 m and 2 km in length.

9. The optical conduit of claim 7 wherein each of the at least one fiber optic portion are between 30 and 50 m in length.

10. The optical conduit of claim 1 wherein each of the at least one sensor portion are between 5 and 1000 micrometers in length, preferably between 50 and 500 micrometers in length, most preferably about 250 micrometers in length.

11. A method of manufacturing an optical conduit of claim 1, comprising: a. Providing two lengths of fiber optic cable; b. Providing a ceramic ferrule with a polished endface to terminate each length of cable on both ends; c. Attaching a mating sleeve to one of the ferrules on one end of each of the two lengths of fiber optic cable; d. Mating the two lengths of fiber cable by inserting the other end of the each fiber cable into the mating adapter such as to leave a gap between the endfaces of the ferrules; e. Adding the sensor material to the gap between the ends in a manner that it fills the gap and adheres to the ends.

Description

BRIEF DESCRIPTION OF FIGURES

[0044] FIG. 1 is a schematic depiction of a fiber optic cable of the prior art.

[0045] FIG. 2 is a depiction of the light shift that occurs in a strained FBG sensor as understood in the prior art.

[0046] FIG. 3 is a schematic cross section of a fiber optic cable in a certain embodiment of the current invention.

[0047] FIG. 4 is a schematic cross section of a fiber optic cable in a further embodiment of the current invention.

[0048] FIG. 5 is a schematic cross section of a fiber optic cable in a further embodiment of the current invention.

[0049] FIG. 6 is a simplified general schematic of a fiber optic cable in certain embodiments of the present invention.

[0050] FIG. 7A is a schematic depiction a fiber optic cable of a certain embodiment of the present invention in the context of an oil leak in a hydrocarbon pipeline.

[0051] FIG. 7B and 7C are schematic depictions of fiber optic cables of various embodiments of the present invention in the context of an oil leak in an oil tank.

[0052] FIG. 8A-C and 9A-B show photographs of gap-connectors utilized in the making of the fiber optic cable of certain embodiments of the present invention.

[0053] FIG. 10 shows a photograph of a gap-connector covering and protecting a silicone “bead” between two sections of fiber optic cable.

[0054] FIG. 11 shows reflected power over the length of a fiber optic cable, as measured for a fiber optic cable sensor having a silicone bead at 3 m, in water, air, and oil.

[0055] FIG. 12A and 12B show gap peak power over time, and peak power over distance for various times, for a sensor of the present invention contacted with water (control) or oil.

[0056] FIG. 13 shows a schematic representation of a bundled fiber optic cable sensor of certain embodiments of the present invention, with staggered sensors.

[0057] FIG. 14 is a further depiction of a bundled fiber optic cable sensor of certain embodiments of the present invention.

DETAILED DESCRIPTION

[0058] Described is a new fiber optic sensor for oil leak detection. It can be used with, or without FBGs. The new fiber optic sensor comprises discrete lengths of fiber optic cable, connected together with a material which is generally transparent to light and with similar refractive index as the fiber optic cable, but having properties wherein the transparency and/or the refractive index of the material changes when the material comes into contact with a substance desired to be detected. In certain embodiments, and as exemplified herein, the material is a silicone “plug” or “bead” and the substance desired to be detected is a hydrocarbon, for example, an oil. The silicone is transparent to light and has a similar refractive index (RI) as the glass, around 1.45. Oil will soften and/or swell the silicone thereby changing the RI. The change in the RI of the silicone interferes with the light transmission through the core. This loss in the signal transmission at the silicone joint is reflected back using Optical Time Domain Reflectometry (OTDR), which can then determine the location of the triggered sensor by measuring the time delay for the return of reflected short pulses of light emitted at the entrance of the fiber.

[0059] OTDR is therefore able to detect the exact location of the “bead” that is affected.

[0060] See, for example, FIG. 3, which shows a schematic cross section of a fiber optic cable of the current invention. Fiber optic cable 200 comprises an inner core 22, a core/cladding interface 23, cladding 24, a buffer coating 26 and an outer protective sheath 27, as previously described. Interspersed along fiber optic cable 200 comprises one or more, in many embodiments a plurality, of what the inventor has termed “beads” 30 of silicone material. The beads may intersect the entire fiber optic cable (as shown in FIG. 3), may intersect only the inner core 22 (as shown in FIG. 4), or may intersect the core and cladding (as shown in FIG. 5) or any part of the cable, so long as the core 22 is intersected. All of these possibilities is shown in a more simplistic form, for the purposes of illustration, as one general schematic in FIG. 6.

[0061] Preferably, the silicone material is of a grade that has high optical clarity and a refractive index matching the fiber core. In this manner, light transmission loss at the joint can be minimised. There may be attenuation at the joint as the distance increases away from the OTDR, however these attenuated values are likely slight, and would in any event be part of the baseline when the entire system is deployed and calibrated. Changes resulting from the oil presence at a given sensor can be picked by measuring a light signal, and changes thereof, transmitted through the cable; if it is desired to determine the location of the oil presence, an OTDR may be used. The OTDR is a laser source that sends a short pulse of light and waits for an echo to return. If there is an interruption at any of the sensors, the echo will be reflected back. By timing the return, the OTDR can compute the distance of the sensor and pinpoint the location. If there was no splice and no silicone sensor in the fiber, meaning a normal intact fiber, there would still be slight decline in the transmission due to scattering from the molecules of the glass, referred to as the Rayleigh effect. The presence of silicone sensor would slightly increase the decline, however our measurements has shown this to be minimal.

[0062] FIG. 7A is a schematic illustration of a cable sensor of the present invention subjected to a hydrocarbon leak from an underground pipeline.

[0063] Fiber optic cable 200 containing silicone beads 30, 30A interspersed about 10 meter apart is run generally in parallel to and generally adjacent to an underground oil or gas pipeline 300. Fiber optic cable 200 is operably connected to an optical time domain reflectometer 36, which is typically (and as shown) located above ground, and is capable of sending a light signal through the fiber optic cable 200. The light signal continues along fiber optic cable 200 since the silicone beads 30 have high optical clarity and a refractive index generally matching the optical core. As illustrated, pipeline 30 has a crack or fracture 32, which leads to an oil leak 34 from the pipeline 30. A silicone bead 30A is in the path of the oil leak 34. When the silicone bead 30A comes into contact with the oil leak 34, it softens and swells, and its opacity and/or refractive index changes significantly. The silicone bead 30A is therefore no longer (or less) able to transmit light signal, and bounces some of that signal back to the optical time domain reflectometer 36. The bouncing back of signal is an indication that there is an oil leak 34 from the pipeline 300. The optical time domain reflectometer 36 can use the time difference between signal and bounce-back to determine the distance between it and the affected silicone bead 30A, which provides the user with both the knowledge that there is an oil leak, and the leak location along the fiber optic cable 200. The OTDR 36 can, in some exemplifications, transmit a signal to a second location, for example, wirelessly through the cloud to a monitoring station miles away, even anywhere in the world.

[0064] As would be readily evident, fiber optic cable 200 having silicone beads 30 interspersed about 1 km apart will be able to provide location information for a leak to a resolution of about 1 km. Fiber optic cable 200 can be made with silicone beads 30 interspersed at any interval, to provide the desired resolution. Alternatively, for example, multiple fiber optic cables 200 each with silicone beads 30 at 10 meters apart may be staggered to provide higher resolution. Such a system may be useful, for example, for use in oil gathering lines, which are typically less than or about 2 km in length and which connect oil wells to gathering stations, or from gathering stations to a main pipeline.

[0065] FIG. 7B is a schematic illustration of two cable sensors of the present invention, installed to detect hydrocarbon leaks from an oil tank.

[0066] Similarly to the application shown in FIG. 7A, a fiber optic cable 200 containing silicone beads 30 can be placed underneath an oil tank, for example an above ground, buried, or (as shown) partially buried oil tank 301. The fiber optic cable 200 is operably connected to an optical time domain reflectometer 36 which is typically (and as shown) located above ground, and is capable of sending a light signal through the fiber optic cable 200. The light signal continues along fiber optic cable 200 since the silicone beads 30 have high optical clarity and a refractive index generally matching the optical core. As illustrated, oil tank 301 has a crack or fracture 32, which leads to an oil leak 34 from the oil tank 301. A silicone bead 30A is in the path of the oil leak 34. When the silicone bead 30A comes into contact with the oil leak 34, it softens and swells, and its opacity and/or refractive index changes significantly. The silicone bead 30A is therefore no longer (or less) able to transmit light signal, and bounces some of that signal back to the optical time domain reflectometer 36. The bouncing back of signal is an indication that there is an oil leak 34 from the oil tank 301. The optical time domain reflectometer 36 can use the time difference between signal and bounce-back to determine the distance between it and the affected silicone bead 30A, which provides the user with both the knowledge that there is an oil leak, and the leak location along the fiber optic cable 200. The OTDR 36 can, in some exemplifications, transmit a signal to a second location, for example, wirelessly through the cloud to a monitoring station miles away.

[0067] As might be appreciated, for certain applications, such as small and discrete oil tanks, location information may not be as critical. As such, a much cheaper oil sensor can be implemented according to the invention, as also shown in a “dipstick” style sensor 201, also depicted in FIG. 7B. Dipstick sensor 201 also comprises fiber optic cable 200 and silicone bead 30B as previously described. However, in some embodiments, as little as one silicone bead 30B is sufficient (though more silicone beads can be interspersed as previously shown). The main difference between dipstick sensor 201 and other sensors of the present invention is that, since location information is not needed, the light source and measure does not need to be an OTDR. A much less expensive light source and detector 37 can be used, since the only measurement necessary is a change in the light signal. Thus dipstick sensors can be deployed very cheaply and effectively where point measurements or measurements without location information are desired.

[0068] Although the dipstick sensor 201 is shown with the silicone bead 30B having fiber optic cable on either side, it would be appreciated that a silicone bead 30C on the end of a fiber optic cable, as depicted in FIG. 7C, would also provide sensing of a hydrocarbon leak, and may be much less expensive to manufacture.

[0069] Although the examples herein are all shown with silicone beads, it would be understood that the beads can be made of any suitable material, and materials with different properties can be utilized depending on the substance one wishes to detect. Suitable materials are those which (1) are able to adhere or be adhered to the fiber optic core; (2) are optically clear enough to allow transmission of all or most of the light at the wavelength of the interrogation, or clear enough to allow at least some of the light through; (3) have a refractive index identical or similar enough to the fiber optic core to allow transmission of the light through the material with little or no bounce-back or signal loss; and (4) have optical properties (clarity and/or refractive index) which change when in the presence of the substance to be detected.

[0070] Where the substance to be detected is oil, silicone is an excellent material, as it has good optical properties, can have a refractive index which matches or nearly matches that of the inner core, has adhesive properties so that it can adhere to the fiber optic core, and changes properties when it comes into contact with hydrocarbon. Other suitable materials for the bead where the substance to be detected is oil may include certain polystyrenes. Where the substance to be detected is water, a suitable material for the bead may be polyvinyl acetate (PVA). Interestingly, the optical properties of polyvinyl acetate do not appear to change when in contact with oil, and the optical properties of silicone do not appear to change when in contact with water; accordingly, oil-specific sensors which do not react to water, and water-specific sensors which do not react to oil, are possible, and may be desirable in certain applications.

[0071] In certain applications, it may be desirable to bundle the two together, and/or to bundle these novel sensors with other, known, fiber optic sensors, such as those that are able to detect changes in temperature, pressure, or strain. Such multi-sensors may be within a single fiber optic bundle, or they may be separate fiber optic cables installed together. Bundling of cables in this manner may also help increase resolution, or distance, or both. An example of such a sensor fiber optic bundle can be seen (in two different schematic views) in FIGS. 13 and 14.

[0072] The design of packaging of the cables for leak detection is important for field deployment. There are several considerations that would dictate such design. One of key variables for the pipeline monitoring is the length of the pipeline and distance the light transmission has to travel through the fiber. The pipeline could be 10 km, 100 km or even 1000 km. For practical and economic reasons, one would want to minimize the control hubs for laser interrogator along the pipeline. In practice, there will be a limit to how many of the necklace sensors that can be installed on the fiber length, before the attenuation losses become problematic for measurements. With the FBG based leak detection fiber system, one could install around a dozen or so sensors for 140 nm bandwidth interrogator. Such interrogators could cost $50,000 to $100,000. This makes it commercially unviable to deploy such a system over longer distances. Our investigation has shown that with the necklace design system, there can be 100's of silicone joints before the signal attenuation could become a problem, a far superior system to the FBG design. In addition, relatively simple OTDR systems can be used, which are much less expensive than the interrogators used for FBG interrogation.

[0073] Using such a staggered sensors design, one could use dozens of fibers cables to obtain narrow spatial resolution, as the sensor could be located 1 m apart or 5 m apart as desired, without the problem of attenuation loss at the silicone joints. A single OTDR, costing $1000-$10,000 could be used to monitor multiple staggered fiber strands to cover tens or 100's of kilometer of pipeline using a multiplexing machine, such as a single mode optical fiber switch; for example, the Polatis 6000i (Viavi) has port counts up to 192×192 and switch times measured in the milliseconds. The fiber strands could be interrogated sequentially, on a time scale of seconds to a few minutes per total system scan.

[0074] It is desirable, in leak detection systems, to have multiple redundancies in the sensing system. Accordingly, it is often desirable to utilize multiple optical cables in the event that one of the fibers becomes non-functional. In the bundled configuration as described above, having the multiple fibers would provide the desired redundancy feature. An additional redundancy may be provided by having an interrogation system on both ends of the pipeline length to be monitored.

[0075] The protective outer jacket 47 shown in FIG. 14 would be permeable to hydrocarbon, for example jacket that is perforated or braided. It could also be a perforated conduit made from a metal such as steel or made from plastic. The bundle jacket may also be perforated, braided, or a mesh and that is placed inside a perforated conduit.

[0076] It can appreciated by someone skilled art, that one may incorporate fiber cores which act as control cores, or distributed sensors, such as DTS (distributed temperature sensor) or DAS (distributed acoustics sensor) that can traverse long distances. This would require a different interrogator, but such hybrid system could provide independent data of the presence of hydrocarbon as well the temperature and movement/vibration/acoustics that could all be incorporated into an AI system for a comprehensive data analysis and the event characterization.

[0077] It is envisaged that the necklace fiber system would be deployed alongside the pipeline, either strapped to outer pipe surface or placed in the vicinity of pipe, 1 cm to 100 cm away. The optimum location to place the cable directly underneath (the 6 o'clock position), since generally the spilt oil will have initial tendency to flow downwards and then usually sideways. Depending on the soil properties, at some point the soil will become saturated, and then the oil will move upwards. The cable could also be placed at higher positions around the pipe at say 3, 9 or 12 o'clock positions.

[0078] In one embodiment, for example, for detection of leaks along a 2 km pipeline, a necklace fiber system may comprise about 5-6 fiber optic cables, each 2 km long and running generally parallel to the pipeline, and each with about 80 sensor “beads”, generally equidistant to one another. The 5 fiber optic cables would be configured in a staggered configuration, much like as pictured in FIG. 13, so that the 80 beads would, in effect, provide the resolution of 400-480 beads (or sensor points) along the 2 km, therefore providing a resolution of about 4.2-5 meters.

[0079] While the initial aim of the development of the necklace design fiber optic system was for the detection of hydrocarbons, particular oil, it was discovered that the unique characteristics of the necklace design with the chemical sensitive “bead” in the joint would lend itself to detecting myriads of materials, liquids and gases. The key consideration in expanding the concept to other sensing materials in place of the silicone is the ability of the gap material to have optical properties and refractive index that would permit light transmission with acceptable signal attenuation, and that the gap material undergoes a significant change in RI upon contact with the targeted gas or liquid. In one example, the joint gap can be filled with polyvinyl alcohol (PVA) resin. PVA is susceptible to the presence of water, it softens and tends to dissolve in water. This would create big disruption of the signal at the joint. The RI of PVA is 1.4839. This is somewhat higher than the RI of glass at 1.4475. There are many techniques published that shows how to reduce the RI of PVA. One example is shown in “Miscibility studies of sodium alginate/polyvinyl alcohol blend in water by viscosity, ultrasonic, and refractive index methods”, Sateesh R. Prakash. In this paper, he teaches reducing the RI of PVA by mixing with a similar miscible polymer having lower melt index. In this experiment he uses a blend sodium alginate/polyvinyl alcohol. There is also possibility of adjusting the RI of core glass by various doping techniques.

EXAMPLE 1

[0080] A fiber optic cable having a single silicone bead was made, as follows. Splicing of glass core is routinely carried out in the industry, with negligible signal loss in the order of 1-2 db. We used standard splicing equipment to align two ends of two fiber optic cables. Silicone having a refractive index which closely matched the fiber optic cable was molded into a gap between the two aligned cable ends. We found that this provided a very stable and reliable connection, with a typical signal loss of less than 3 db, for example 1-3 db or even 0.3-1 db.

[0081] For example, commercially available gap-connectors were utilized and are shown in FIGS. 8A-C. Gap-connectors 40 comprise mating adapters 42, 44, which are commercially available multimode fiber-mating adapters (Fiber Instrument Sales, part number F18300SSC25) in which the multimode metal alignment sleeve was replaced by a single mode ceramic alignment split sleeve 50 (Fiber Instrument Sales, part number F18300SSC25). Sheathed fiber optic cables 52, 54 were each inserted into and fixed to one half of the mating adapter (42, 44, respectively) with ceramic sleeve 50 and two screws 46, 48 were used to secure them together in a precise alignment. A drop of silicone was injected into the 10 μm gap so that it flowed through the slot in the ceramic sleeve 50 and into the gap between the two connectors. Upon curing, the silicone bonded to the fiber cores, essentially re-forming a continuous fiber core for light transmission, with a very stable and secure connection. This method was essentially a molding process, inside the connector. FIG. 8A is a photograph of a side view of such a connector; FIG. 8B is the end view thereof. FIG. 8C shows the connector in an open state, connected to two fiber optic cables.

[0082] An alternate manufacturing method is shown in FIG. 9A-B. Here, similarly to the method shown in FIG. 8A-C, a commercially available gap connector 40 was used. However, instead of injecting silicone within a sleeve which covered the two fiber optic cores, a 0.25 mm thin metal plate 56 was inserted between the mating sleeves 42, 44 before the mating sleeve screws 46, 48 were fastened. The thin metal plate 56 has an aperture 58 into which silicone can be added; the silicone thus adheres to and forms an optical conduit with, the inner cores of fiber optic cables 52, 54. In certain embodiments, plate 56 can also contain screw apertures 60 and be therewith affixed to mating sleeves 42, 44; in other embodiments (not shown), plate 56 is of a size that it can fit between the screws and is friction fit in place; in such embodiments, the plate may be removed after the silicone has set, if desired. Though a plate 56 of 0.25 mm was used, a plate of different thickness, for example, anywhere from 5 to 500 micrometers, could be used to form sensor beads of such desired length.

[0083] FIG. 10 shows a connector, fully assembled, having a silicone bead between two cable inner cores, forming a continuous light conduit.

[0084] The metal connector described above is for illustration purposes only. Person skilled in art can design the packaging in many different ways to suit the application, the optical fiber deployment and manufacturing method. For example, the connectors could be made from ceramic or rigid plastic such as Nylon with a snap-fit design, so that the manufacturing can be automated. They could also be made in small cross-section instead of the large metal flanges shown in the illustration.

EXAMPLE 2: OIL SENSITIVE SENSOR AT 3 M

[0085] An optical fiber was constructed with a single silicone bead (sensor) utilizing the method of Example 1, and attached to an OTDR instrument. The optical fiber was configured such that there was a 3 meter line of fiber optic cable between the OTDR instrument and the bead.

[0086] The OTDR instrument measured reflected power as the silicone bead was subjected to three different environmental conditions: the silicone bead (and the portion of the sensor surrounding said silicone bead) was placed in water, air, and oil respectively, and the readings were measured. It was found that the reflected power for oil was 6.3 dB—significantly greater than that for water or air. The location of the sensor (3 m from the OTDR instrument) was also accurately determined. The results were shown in FIG. 11.

EXAMPLE 3: OIL SENSITIVE SENSOR AT 1.7 KM

[0087] The experiment of Example 2 was repeated, this time with 1.68 km of fiber optic cable between the OTDR instrument and the silicone bead. The first test was done with water applied to the sensor, which resulted in a signal in the 16-21 dB range at 1.7 km. When the sensor was immersed in light oil, the signal peak jumped to 25 dB after 60 minutes, and to 28 db after 65 minutes. It peaked to 31 dB after 70 minutes. The graph shown at FIG. 12A below ilustrates the rise in the power as the oil got absorbed into the sensor with time peaking at 31 dB after 70 minutes. This is significant, since in real situation, the oil could surround the sensor cable for hours or days with slow leak, and getting a response within hours or even days after the leak starting is extremely useful, in order to undertake remedial measures.

[0088] The data is depicted in FIG. 12B, which shows the peak power vs time with immersion in oil. There is delta of 10 dB in power shift as result of the oil contact. This is a very significant change, and easily decipherable.