• 专利附录
  • 专利说明
  • 权利要求
  • 类似技术
  • 同族专利
  • 引用文献
  • 法律状态
  • 优先权
    • 专利摘要:
    fiber optics, fiber optic cable, distributed acoustic fiber optic sensor, use of an optical fiber, distributed fiber sensor, and a fiber optic cable. optical fiber cables with better performance are revealed for use in distributed detection, for example, in distributed acoustic sensors. in one embodiment, a fiber optic cable (210) comprises a core (208) and sheath (206) arranged within a cushioning material (202) and encased by a jacket (204) and arranged so that the core is displaced from the center of the cable. by displacing the core from the center of the jacket, any folding effect on the core can be maximized, compared to when the core is located in the center of the cable.
    公开号:BR112012011226B1
    申请号:R112012011226
    申请日:2010-11-11
    公开日:2020-01-21
    发明作者:John Hill David；Mcewen-King Magnus；Ian Crickmore Roger
    申请人:Optasense Holdings Ltd；
    IPC主号:
    专利说明:

    OPTICAL FIBER, FIBER OPTIC CABLE, AND, DISTRIBUTED ACOUSTIC FIBER OPTICAL SENSOR [001] The present invention relates to optical fibers and optical fiber cables suitable for use in distributed fiber optical detection, especially for use in optical fiber detection distributed acoustics and improvements in the design, application and manufacture of optical fiber and / or optical fiber cable for distributed fiber optical sensors.
    [002] Several sensors using optical fibers are known.
    Many such sensors are based on fiber optic point sensors or discrete reflection locations such as fiber Bragg networks or the like that are arranged along the length of an optical fiber. The returns from the spot sensors or discrete reflection locations can be analyzed to provide an indication of temperature, deformation and / or vibration in the vicinity of the discrete reflection or sensor locations.
    [003] Fully distributed fiber optic sensors are also known, in which the intrinsic dispersion of a continuous length of optical fiber is used. Such sensors allow the use of standard fiber optic cable without deliberately introducing reflection sites such as fiber Bragg networks or the like. Any optical fiber from which a backscattered signal can be detected can be used as part of the sensor. Time-splitting techniques are typically used to split the signal returns into numerous time boxes, with the returns in each time box corresponding to a different portion of the optical fiber. Such optical fiber sensors are referred to as distributed fiber optical sensors as the sensor options are completely distributed across the entire optical fiber. In the form used in this specification, the terms distributed optical fiber sensor will be used to mean a sensor in which the optical fiber itself constitutes the sensor and which is not based on the presence of specific point sensors or deliberately introduced reflection or interference locations,
    Petition 870190091694, of 9/13/2019, p. 9/39 / 28 which is an optical fiber intrinsic sensor.
    [004] U.S. patent 5,194,847 describes a distributed acoustic fiber optical sensor for intrusion detection. A continuous optical fiber with no specific spot sensors or reflection locations is used. Coherent light is released into the optical fiber and any light that undergoes Rayleigh backscattering within the optical fiber is detected and analyzed. A change in backscattered light in a time box is indicative of an acoustic or pressure wave incident on the relevant portion of the optical fiber. In this way, acoustic disturbances from any portion of the fiber can be detected.
    [005] The GB 2,444,745 patent specification describes a distributed acoustic fiber optical sensor system in which acoustic vibrations are detected by launching a plurality of pulse-modulated electromagnetic wave groups on a standard optical fiber. The frequency of one pulse within a group differs from the frequency of another pulse in the group. Rayleigh's backscattering of light from intrinsic reflection sites within the fiber is sampled and demodulated in the frequency difference between pulses in a group.
    [006] US patent 6,380,534 describes a distributed fiber optical deformation and temperature detection system that analyzes the Brillouin backscatter frequency distribution of light shed on the fiber to determine temperature and deformation over various portions of the detection by fiber, which can be embedded in a structure.
    [007] WO02 / 057805 describes the use of temperature, deformation and / or optical fiber acoustic sensors distributed in a variety of applications, including monitoring of flow line parameters in the oil and gas industry.
    [008] Optical distributed fiber detection or distributed acoustic detection (DAS) therefore provide suitable and convenient detection solutions that can monitor large lengths of optical fiber.
    Petition 870190091694, of 9/13/2019, p. 10/39 / 28
    Standard telecommunications fiber optics, for example, 125 pm optical fiber in a simple way, can be used, which means that fiber detection is relatively inexpensive and easily available and, in some cases, it may be possible to use existing optical fibers to acoustic monitoring, say. [009] In some cases, the use of standard telecommunications fiber optic cable may not provide optimal detection. It is, therefore, a goal of the present invention to provide fiber optics and improved fiber optic cables for use in distributed fiber optic detection.
    [0010] According to a first aspect of the present invention, an optical fiber comprising a core, a coating surrounding the core and a jacket surrounding the coating in which the core is displaced from the center of the optical fiber is provided.
    [0011] As those skilled in the art realize, an optical fiber comprises a core, which is optically transmissive in the operating wavelength, surrounded by coating material that has a different refractive index than the core, the core and the coating together cooperating to guide optical radiation within the fiber core. The coating is generally encased in a jacket material to protect the optical fiber. The jacket can include a cushioning material between the liner and the outer jacket. Standard optical fibers have the core at the center of the fiber and are generally symmetrical in section, within manufacturing tolerances.
    [0012] This aspect of the present invention provides an optical fiber in which the core is deliberately displaced from the center of the fiber, that is, in the section, the center of material of the core does not coincide with the center of the fiber (or, equivalently, the geometric center of the outer fiber envelope) as a whole. In other words, the optical fiber core is contained in the circumference of the jacket material, but is not concentric with it. Such an arrangement can be advantageous when the optical fiber is used in a distributed optical fiber sensor such as a distributed acoustic sensor.
    Petition 870190091694, of 9/13/2019, p. 11/39 / 28 [0013] In an optical acoustic fiber sensor distributed as described in GB2.442.745, optical radiation is transmitted in the optical fiber and any optical radiation undergoes Rayleigh backscattering within the optical fiber is detected. Any incident acoustic signal causes mechanical vibration of the fiber that changes the amount of Rayleigh backscatter in that part of the fiber. The variation in backscattering is related to the movement of the optical fiber, in other words, the amount of bending suffered by the optical fiber. Other distributed fiber optical vibration sensors are also based on the folding of the optical fiber which changes the amount of backscatter in relation to that portion of the optical fiber.
    [0014] Clearly, however, it is the folding of the core and the coating that is responsible for the difference in retrodispersion. In this present invention, by displacing the core from the center of the optical fiber, the amount of bending observed by the core can be maximized. Consider an optical fiber deployed on the ground running in a north-south direction. If an acoustic wave is incident on part of the fiber from the east, this will cause part of the relevant part of the fiber to vibrate, as a result of which the fiber will bend in an east-west direction. As the fiber folds to the west, the western side of the fiber will undergo a greater amount of folding. Similarly, as the fiber folds to the east, the eastern side of the fiber will undergo the greatest amount of folding. In a standard optical fiber, where the core is in the middle of the fiber, the core will undergo an optical change caused by the bending, but the amount of bending is less extreme than would be seen on either the eastern or western edges of the fiber. In a fiber of the present invention, the core is displaced from the center and is thus located closer to an edge of the optical fiber. If the optical fiber were deployed in such a way that the core was located along the eastern (or western) edge of the optical fiber, then, in the scenario described above, the core would suffer a greater amount of bending than if it were
    Petition 870190091694, of 9/13/2019, p. 12/39 / 28 located in the center of the same fiber. Thus, the optical fiber of the present invention can maximize the amount of bending suffered by the light that guides part of the fiber and consequently maximize the optical return because of incident vibrations.
    [0015] In certain modalities, it is useful to consider the distribution of strength and deformation limit in a fiber under bending. In a conventional axisymmetric fiber, the core is arranged along the centroidal axis, or neutral axis, and the limit of resistance and deformation increases with the distance of the neutral axis under bending. Modalities of the present invention are arranged in such a way that the center of the core is offset from the neutral axis of the optical fiber. In this way, the strength and deformation limits observed by the core can be increased, compared to a conventional fiber that undergoes equivalent bending. The displacement can be defined according to the predicted or desired bending and / or stresses and strains, and is desirably constant over an active fiber detection length.
    [0016] Preferably, therefore, the core is located on one side of the optical fiber. The core is surrounded by the coating (and therefore the coating is clearly displaced from the center of the fiber as well) and the core and the coating can have the same dimensions as a conventional optical fiber. However, the core and liner may be encased in a jacket and / or damping material, such that the core and liner are located on one edge of the damping material / liner.
    [0017] The material of the fiber optic jacket can be sufficiently large in such a way that the center of the optical fiber (in section) is not arranged in the core material. In one embodiment, the center of the optical fiber is not arranged either with the material of the coating, that is, the center of the fiber is arranged in the material of the jacket or in the damping material,
    Petition 870190091694, of 9/13/2019, p. 13/39 / 28 if present, and thus the core and the coating are located completely in the half of the optical fiber.
    [0018] It should be noted that the optical fiber can comprise several layers of shirt material.
    [0019] The optical fiber may comprise more than one damping material, at least part of the damping material being used as a filler material for the cable. At least part of the cushioning material can be gel. In one embodiment, the optical fiber comprises a gel cushion arranged in the center of the optical fiber, with the core and the coating on one side of the gel cushion. Alternatively, the core and the coating may be arranged within a gel-cushioning material, possibly with an inner jacket layer around the coating. In another embodiment, there may be a solid cushioning material in the center of the optical fiber, surrounded by a gel cushion, with the core and coating being arranged in the gel cushion. The present inventors have observed that optical fibers with gel cushioning show good response when used as fiber detection in distributed acoustic sensors. Gel damping is believed to be better at coupling acoustic waves to the optical fiber than solid dampers.
    [0020] The optical fiber can also comprise a plurality of layers of jackets and can comprise part of a fiber optic cable. In the form used herein, the terms optical fiber refer to a basic optical fiber with a core, coating and a jacket or coating material. The term fiber optic cable must mean an apparatus, which may comprise one or more optical fibers, and which has protective layers to protect the optical fiber (s) in use. A fiber optic cable can therefore comprise several layers of outer sheaths and / or reinforcement fibers. In some modalities, therefore, the optical fiber itself can comprise a
    Petition 870190091694, of 9/13/2019, p. 14/39 / 28 fiber optic cable, whereas, in other embodiments, the optical fiber may be part of a fiber optic cable.
    [0021] The optical fiber cable can thus comprise more than one optical fiber, for example, optical fibers intended for communication can be located on the same cable as the optical fiber intended for detection. Preferably, fiber optic detection is located towards the edge of the fiber optic cable edge. If the optical fiber detection is firmly attached inside the fiber optic cable, the same considerations discussed above apply, and the optical fiber detection will experience a greater bending effect if located towards the edge of the cable. Preferably, the optical fiber of detection is oriented within the optical fiber cable in such a way that the core of the optical fiber of detection is oriented with respect to the center of the optical fiber of detection in the same way that the optical fiber of detection is located with respect to the center of the cable. That is, if the optical fiber of detection is located facing the right side of the cable (that is, in a position of three hours), then the core of the fiber detection is also located to the right of the fiber detection (it has also a three o'clock position).
    [0022] In some modalities, the optical fiber of detection is located inside the fiber optic cable in a helical arrangement. As mentioned here, there may be benefits in locating the optical fiber away from the center of the cable. In some embodiments, it can be beneficial to ensure that the relative position of the optical fiber varies down the length of the cable so that the optical fiber describes a helix within the cable. This ensures that part of the fiber detection is always arranged towards the side of the cable from which the acoustic wave is incident. Additionally, a helical pattern can improve the quality of the beam pattern of the received signal. Also, the spatial resolution of the fiber detection portions in use is determined by the interrogation radiation used in the sensor. However, the resolution
    Petition 870190091694, of 9/13/2019, p. 15/39 / 28 sensor space actually also depends on the cable arrangement. If the fiber is used in a sensor that provides spatial detection portions that are 10 meters long, but the fiber itself is spiraled in an area that is only 5 m long, the actual spatial resolution of the fiber is 5 m. Thus, the final arrangement of the cable can influence spatial resolution. However, in some applications, it may be difficult to unfold a cable in any other way than generally straight. For example, in a downhole environment, the cable may be forced down the well along segments of the liner and unpacking a helical arrangement may not be possible. If, however, the cable itself contains a fiber wound in a desired helical arrangement, then the cable itself can be straight, but the available spatial resolution can be increased by a helical arrangement of the fiber within the cable. For example, the fiber can be wrapped around a central element.
    [0023] In use, the vibrations induced in the optical fiber can occur in a range of transverse directions and thus the alignment of the optical fiber or optical fiber cable may not be critical, simply the fact that the core of the optical fiber detection is decentralized location increases overall signal returns. However, in some modalities, you may want to basically detect acoustic signals in a particular plane and, in such a case, it can be beneficial to ensure that the core is displaced from the center of the optical fiber in that plane. Thus, to facilitate alignment, the outer jacket of the optical fiber can be provided with a visual indication, such as coloring or markings, indicating the side of the optical fiber on which the core is located.
    [0024] Additionally, or alternatively, the outer jacket of the optical fiber can be modeled to facilitate alignment. For example, in section, the optical fiber may have a slightly flat side that is designed to be the base side of the optical fiber. The fiber optic core would be located with
    Petition 870190091694, of 9/13/2019, p. 16/39 / 28 relation to the base side in a desired arrangement.
    [0025] The optical fiber of this aspect of the present invention therefore provides greater sensitivity, compared to the use of a similarly sized optical fiber where the core is located in the center of the fiber, since it maximizes the amount of optical disturbance observed by the fiber core.
    [0026] The principle of this aspect of the invention also applies to optical fiber cables in general. That is, if an optical fiber cable comprises a plurality of optical fibers and at least one of these fibers is to be used as a detection optical fiber, it can be beneficial to ensure that the fiber detection is an optical fiber that is located towards to the edge of the optical fiber cable, even if the optical fiber itself is a conventional optical fiber. Thus, in another aspect of the invention, a distributed optical acoustic fiber sensor is provided comprising an optical source coupled to a first optical fiber of a fiber optic cable to interrogate said first optical fiber with optical radiation and a detector coupled to said first optical fiber to detect radiation which is backscattered by said first optical fiber in which said optical fiber cable comprises a plurality of optical fibers and in which the first optical fiber is located towards the edge of the optical fiber cable. Desirably, the cross sectional alignment of the first optical fiber is controlled or maintained over an active sensing portion of the cable.
    [0027] In other words, in a fiber optic cable with a plurality of optical fibers, an optical fiber near the edge of the fiber optic cable, which is displaced from the center, is selected to be used as the fiber detection in order to maximize the amount of bending observed by the optical fiber detection. In general, this aspect of the present invention concerns the use of an optical fiber towards the edge of a fiber cable
    Petition 870190091694, of 9/13/2019, p. 17/39 / 28 optics such as fiber detection in a distributed fiber optic sensor. [0028] In another aspect of the invention, a distributed optical fiber sensor is provided comprising an optical source coupled to an optical fiber to transmit optical radiation to said fiber, a detector arranged to detect radiation backscattered by said fiber and a processor for processing the backscattered radiation to provide a plurality of discrete longitudinal detection portions of said fiber in which the optical source is coupled to said optical fiber in such a way that radiation transmitted on said fiber is displaced from the center of the optical fiber core.
    [0029] In this embodiment of the invention, optical radiation is coupled to the fiber core, that is, the light guide portion of the fiber, in such a way that the radiation is displaced from the center of the core. Conventionally, optical radiation can be coupled to the fiber by focusing the incident light in the center of the fiber core region for efficient coupling. However, in the present invention, the incident light is focused not on the center of the nucleus region, but towards the side of the nucleus region. For a fiber in a simple way, this means that the radiation will propagate with a greater light intensity towards the edge of the fiber core region than in the fiber side region. In a manner similar to that previously described, the edges of the core region will tend to have a greater variation in the amount of backscatter produced under vibration than the central part of the core region and, consequently, by the transmission of optical radiation across the edge of the region of core, the backscatter signal can be increased. This can increase the sensitivity of the distributed optical fiber sensor, compared to the coupling of interrogation radiation in the center of the optical fiber. Deliberately, it could be considered in general that the displacement of the incident radiation focal point outside the center of the optical fiber potentially reduces the efficiency of the coupling and thus should normally be avoided.
    Petition 870190091694, of 9/13/2019, p. 18/39 / 28 [0030] The end of the optical fiber can be provided with an optical fiber connector, and the optical fiber connector can be arranged to couple optical radiation at the input or output in the optical fiber. The fiber optic coupler may comprise a lens. The focal point of the fiber optic coupler can therefore be arranged to be displaced from the center of the fiber optic core region.
    [0031] In another aspect of the present invention, therefore, an optical fiber is provided comprising, at one end, a fiber optic coupler in which the fiber optic coupler is arranged to couple optical radiation at the entrance or exit of the core region fiber optics, where the focal point of the fiber optic coupler is displaced from the center of the fiber optic core region.
    [0032] As previously described, the use of an optical fiber with a gel damping material can improve the sensitivity of the optical fiber to acoustic vibrations, compared to an optical fiber without a gel damping. Thus, in another aspect of the present invention, a distributed optical acoustic fiber sensor is provided comprising an optical source coupled to an optical fiber cable to transmit optical radiation to said optical fiber cable, a detector arranged to detect backscattered radiation from Rayleigh by said fiber optic cable in which the fiber optic cable comprises at least one optical fiber and at least one region filled with gel.
    [0033] Fiber optic cables that use gel cushioning are known, but the present invention relates to the use of a gel-filled fiber optic cable in a distributed acoustic fiber optical sensor. It has been observed that fiber optic cables filled with gel have a good sensitivity to acoustic signals, since the optical fiber cable filled with gel couples well to incident acoustic signals. The optical fiber, that is, the optical fiber core and coating, can be arranged in the gel-filled region, or
    Petition 870190091694, of 9/13/2019, p. 19/39 / 28 can be arranged adjacent to the gel-filled region.
    [0034] The modes described above provide greater sensitivity when used in a distributed acoustic sensor, compared to the use of conventional optical fiber. In another embodiment, however, the present invention allows for additional detection functionality.
    [0035] Thus, according to a further aspect of the invention, an optical fiber is provided in which the optical fiber has a stiffness in a first transverse direction that is greater than the stiffness in a second transverse direction, the second transverse direction being different the first transverse direction.
    [0036] The optical fiber can be an optical fiber with varying stiffness or an optical fiber cable that includes an optical fiber.
    [0037] In this embodiment of the present invention, the optical fiber has a stiffness, ie flexural stiffness, which varies in the transverse direction, that is, perpendicular to the longitudinal axis of the fiber. In other words, the optical fiber will flex or bend in one direction more easily than it will flex or bend in the other direction. Preferably, the first transverse direction is orthogonal to the second transverse direction.
    [0038] As mentioned here, in relation to other aspects of the invention, distributed fiber optic sensors, such as distributed acoustic sensors, detect the change in backscattered radiation attributed to acoustic vibrations. Acoustic vibrations cause vibrations in the optical fiber that change the optical properties of the light guide portion of the optical fiber, thus varying the amount of backscattering. An optical fiber that flexes easily in one direction (the second direction) will therefore be sensitive to the acoustic signals that excite the fiber's vibration in that direction. However, if the optical fiber does not flex easily in a different direction (the first direction), then the acoustic waves that excite vibrations in that other direction will produce a limited response.
    Petition 870190091694, of 9/13/2019, p. 20/39 / 28 [0039] It can be seen, therefore, that, by drawing an optical fiber to flex preferably in the second direction, that is, with a bending stiffness that is greater in the first direction than in the second direction, a sensor which responds preferentially to acoustic signals with a particular component can be achieved.
    [0040] Imagine that the optical fiber has a very high stiffness in the first direction so that there is virtually no flexibility in that direction, but that it flexes easily in the second direction, and that the first and second directions are orthogonal to each other. If a cable like this were arranged vertically, say, in a vertical borehole, in such a way that the first direction was aligned in the north-south direction and then used in a distributed acoustic sensor, the sensor would easily respond to acoustic or seismic signals. which cause an east-west movement of the fiber optic cable, but would not easily respond to signals that cause a north-south movement of the fiber. A sensor like this therefore effectively resolves the component of the incident acoustic wave parallel to the east-west direction. Where a second optical fiber of the same construction (or a different part of the first optical fiber) is also deployed in the borehole, but this time with the first direction aligned in an east-west direction, the second optical fiber (or part different from the first optical fiber) would effectively resolve the components of any acoustic wave incident on the components in the north-south direction. Thus, it can be seen that two such optical fibers, or a judicious arrangement of a single optical fiber, allow the components of an incident acoustic wave to be determined in two dimensions.
    [0041] Preferably, therefore, the optical fiber has great rigidity in the first direction in such a way that the optical fiber does not flex easily in the first direction. Preferably, the stiffness in the second direction is such that the optical fiber flexes easily in the second direction.
    Petition 870190091694, of 9/13/2019, p. 21/39 / 28 [0042] In one embodiment, the optical fiber comprises at least one stiffening element, the at least one stiffening element with a stiffness that is greater in the first direction than in the second direction. For example, the stiffening element may have a thickness in the first direction that is significantly greater than the thickness in the second direction. In other words, the stiffening element is elongated in a transverse direction, for example, a plate-like element, and is arranged with its long edge along the first direction. Folding in the first direction requires folding a lot of material and is therefore difficult, whereas folding in the second direction involves folding only a relatively small amount of material and, consequently, is easier.
    [0043] Additionally, or alternatively, the at least one stiffening element may comprise a series of overlapping elements that can slide one apart from the other in the second direction, but cannot slide one apart from the other in the first direction.
    [0044] In some modalities, the optical fiber may have an asymmetric shape. For example, the optical fiber may have a cross section that is larger in the first direction than in the second direction. The optical fiber can, for example, have an elliptical-like cross section, with the longitudinal axis of the ellipse defining the first direction. Again, there is more material to bend in the first direction than in the second direction, leading to greater rigidity.
    [0045] In some embodiments, the fiber optic core and surrounding region are located towards the edge of the optical fiber in the second direction. As previously described in relation to the first aspect of the invention, locating the core region of an optical fiber towards the edge of an optical fiber can increase the detected signal of an optical fiber like this when used in a distributed optical fiber sensor.
    Petition 870190091694, of 9/13/2019, p. 22/39 / 28
    Clearly, in this modality, as the optical fiber is arranged to flex preferentially in the second direction, the core region must be located towards the edge of the optical fiber in the second direction to maximize the bending effects.
    [0046] As mentioned, the optical fiber of this aspect of the invention can be used in a distributed optical fiber sensor to resolve incident waves in the components in the first direction. Thus, there may be a distributed optical fiber sensor comprising a first optical fiber according to this aspect of the invention, an optical source coupled to transmit optical radiation to the first optical fiber, a detector coupled to the first optical fiber to detect back-dispersed optical radiation by first optical fiber and a processor arranged to process the detected backscattered radiation to provide a plurality of longitudinal detection portions of the first optical fiber. In one embodiment, the sensor may also comprise a second optical fiber in accordance with this aspect of the invention. The second fiber is coupled to an optical source, which may or may not be the same optical source used for the first optical fiber, and a detector. The detector can be a separate detector from the one used for the first optical fiber for ease of analysis, although the detector can be used for both optical fibers, using wavelength division and / or time or code multiplexing. The second optical fiber can be arranged in such a way that the first direction of the first optical fiber is substantially parallel to the second direction of the second optical fiber. The processor receives data corresponding to the backscattering detected by both optical fibers and can be arranged to determine the components of any disturbance incident in the first and second directions.
    [0047] This sensor can be particularly applicable for use in well drilling in the oil and gas industry and / or for seismic surveying, or the like. For example, during fracturing in
    Petition 870190091694, of 9/13/2019, p. 23/39 / 28 a well drilling, it is desirable to determine the location and density of the resulting fractures to provide more efficient extraction of the oil or gas. Being able to detect the pressure waves incident due to fracturing and resolve the components in two orthogonal environments allows mapping of the fracture density in at least two dimensions. At least a second pair of optical fibers can be deployed in a different location to provide two-dimensional mapping. Signal strength in various parts of the fiber detection and arrival time in different parts of the fiber can allow mapping in three dimensions. Alternatively, another pair of optical fibers arranged perpendicular to the longitudinal axis of the first pair of optical fibers would resolve the signals in three dimensions.
    [0048] In downhole uses, in particular, such as fracture mapping, as previously described, or condition / flow monitoring, or the like, the spatial length of the discrete detection portions of the optical fiber should preferably be relatively small, for example, on the order of a few tenths of an inch or possibly less. In an optical acoustic fiber sensor distributed as described in GB 2,442,745, spatial resolution is related to the duration of an interrogation pulse. A shorter interrogation pulse means that a shorter length of optical fiber is illuminated at the same time and thus the minimum effective size of the longitudinal detection portions is less than where a longer pulse has to be used.
    [0049] However, using shorter pulses means that less optical radiation is fed into the optical fiber. As experts in the art realize, the interrogation radiation must be below a non-linear threshold for the optical fiber and thus there is a limit to the optical power that can be transmitted in the fiber. Thus, with a lower interrogation pulse, there is less general light in the fiber, which means that there will be less backscattering
    Petition 870190091694, of 9/13/2019, p. 24/39 / 28 and the optical fiber range beyond which no usable signal is returned will be less. Only a small proportion of the optical radiation that is transmitted over an optical fiber is backscattered and not all the radiation that is backscattered is collected, some can be transmitted through the coating and absorbed by the jacket or damping material. The optical radiation that is directed back to the detector will also be attenuated on the return path and thus small signals can be completely attenuated before reaching the end of the optical fiber.
    [0050] It is therefore usual in optical detection of distributed fiber to use optical fiber with a core that has low attenuation. As a goal for most telecommunications fibers is low attenuation of transmitted signals, standard optical telecommunications fiber therefore meets this criterion. Distributed fiber optic sensors have therefore used conventional low-loss optical fiber, such as a standard 125-m optical fiber.
    [0051] The present inventors, however, realized that the use of fiber optics with greater attenuation can actually be beneficial in some cases. Thus, according to a further aspect of the invention, a distributed optical fiber sensor is provided comprising an optical source coupled to an optical fiber to transmit optical radiation to the optical fiber and a detector coupled to the optical fiber to detect back-scattered optical radiation by the fiber optics in which the optical fiber has a relatively high degree of heterogeneity and a relatively high numerical aperture.
    [0052] Relatively high means greater than 125 pm telecommunications optical fiber in a simple standard way.
    [0053] The present inventors realized that attenuation in an optical fiber is partially linked to the amount of heterogeneities in the optical fiber, but that a greater amount of heterogeneities can result in a greater amount of this retrodispersion. Typically versed in
    Petition 870190091694, of 9/13/2019, p. 25/39 / 28 technique would think that this benefit of greater backscattering would be outweighed by the detriment of greater attenuation - however, when together with the effect of a relatively high numerical aperture, most of the backscattered radiation is collected and the overall result is that a optical fiber like this provides a higher sensitivity than standard simple 125 pm optical fiber, at least for relatively small ranges of fiber detection. Higher sensitivity means that shorter pulses of interrogation radiation can be used, with a consequent reduction in the spatial length of each fiber detection portion.
    [0054] The present inventors observed that the existing 80 pm fiber each with the criteria of having a greater amount of heterogeneities, compared to the 125 pm optical fiber in a simple standard way. This leads to a higher degree of Rayleigh backscattering than for conventional 125 pm optical fiber. The amount of attenuation of backscattered radiation also increases, but this is offset by the fact that a higher proportion of backscattered radiation is also coupled to the optical fiber. The net result is that, compared to a standard 125 pm telecommunication fiber, a larger amount of backscattered radiation is detected for the same acoustic pulse and interrogation radiation.
    [0055] As previously mentioned, this effect is more pronounced for a fiber detection range of up to about 5 km. Preferably, therefore, the optical fiber has a detection length of the order of 5 km or less.
    [0056] This aspect of the present invention is therefore particularly suitable for downhole applications. Well drilling can typically be up to a few kilometers deep and the detection equipment can normally be located near the top of the well drilling. So a 5 km detection range or something like that is adequate
    Petition 870190091694, of 9/13/2019, p. 26/39 / 28 for many downhole applications. The ability to provide a distributed sensor with a continuous array of detection portions, each in the order of a few tenths of an inch in length, allows a large number of monitoring activities to be carried out.
    [0057] Thus, in general, this aspect of the present invention concerns the use of an 80 pm optical fiber distributed acoustic fiber optical sensor in downhole detection and / or monitoring applications. Experienced in the art they realize that an optical fiber of 80 pm is currently available by quality fiber optic producers. However, optical fibers could be produced to provide a relatively large amount of heterogeneities per unit length and a large numerical aperture with different dimensions.
    [0058] The invention extends to methods, apparatus and / or use in the manner substantially described herein with reference to the accompanying drawings.
    [0059] Any feature in one aspect of the invention can be applied to other aspects of the invention, in any appropriate combination. In particular, aspects of methods can be applied to aspects of apparatus, and vice versa.
    [0060] Preferred features of the present invention will now be described, purely by way of example, with reference to the accompanying drawings, in which:
    Figure 1 illustrates the basic components of a distributed fiber optic sensor;
    Figures 2a, 2b, 2c and 2d show optical fiber modalities in accordance with an aspect of the present invention;
    Figure 3 illustrates the bending suffered by an optical fiber in response to an incident acoustic wave;
    Figure 4 shows two modalities of an optical fiber according to another aspect of the invention;
    Petition 870190091694, of 9/13/2019, p. 27/39 / 28
    Figure 5 shows an additional embodiment of an optical fiber of the present invention; and
    Figures 6a and 6b illustrate a method for coupling optical radiation to an optical fiber displaced from the center of the fiber.
    [0061] Figure 1 shows a schematic of an optical fiber distributed detection arrangement. A fiber detection length 104 is connected at one end to an interrogator 106. The output of the interrogator 106 is passed to a signal processor 108, which can be colocalized with the interrogator, or can be remote from it, and optionally an interface of user / graphic display 10, which in practice can be performed by a duly specified PC. The user interface can be colocalized with the signal processor, or it can be remote from it.
    [0062] Fiber detection 104 can be many kilometers long and, in this example, is approximately 40 km long. Fiber detection is a standard unmodified single-mode optical fiber, as is routinely used in telecommunications applications. In conventional applications of distributed fiber optic sensors, fiber detection is at least partially contained in a medium to be monitored. For example, fiber 104 can be buried to provide monitoring of a perimeter or monitoring of a buried item such as piping or the like.
    [0063] The invention will be described in relation to a distributed acoustic sensor, although versed in the technique realize that the precept can be applied in general to any type of distributed optical fiber sensor.
    [0064] In operation, interrogator 106 releases electromagnetic interrogation radiation, which can, for example, comprise a series of optical pulses with a selected frequency pattern, in fiber detection. Optical pulses can have a frequency pattern described in the GB 2,442,745 patent specification whose contents are through
    Petition 870190091694, of 9/13/2019, p. 28/39 / 28 incorporated by reference. As described in GB 2,442,745, Rayleigh's backscattering phenomenon causes a certain fraction of the light to enter the fiber to be reflected back into the interrogator, where it is detected to provide an output signal that is representative of acoustic disturbances in the vicinity of the fiber. The interrogator, therefore, conveniently comprises at least one laser 112 and at least one optical modulator 114 to produce a plurality of optical pulses separated by a known optical frequency difference. The interrogator also comprises at least one photodetector 116 arranged to detect radiation that is backscattered at intrinsic dispersion sites within the fiber 104.
    [0065] The signal from the photodetector is processed by the signal processor 108. The signal processor conveniently demodulates the returned signal based on the frequency difference between the optical pulses as described in GB 2,442,745. The signal processor can also apply a phase unpacking algorithm as described in GB 2,442,745.
    [0066] The shape of the optical input and the detection method allow a single continuous fiber to be spatially resolved in discrete longitudinal detection portions. That is, the acoustic signal detected in a detection portion can be provided substantially independent of the signal detected in an adjacent portion. The spatial resolution of the optical fiber detection portions can, for example, be approximately 10 m, which, for a fiber length of 40 km, causes the interrogator's output to take the form of 4,000 independent data channels.
    [0067] In this way, the single fiber detection can provide detected data that are analogous to a multiplexed array of adjacent independent sensors arranged in a linear path.
    [0068] Conventional distributed fiber optic sensors use
    Petition 870190091694, of 9/13/2019, p. 29/39 / 28 standard telecommunications optical fiber. The present invention provides improvements in the design of fiber optic cable that improves the sensitivity or functionality of distributed fiber optic sensors.
    [0069] Figure 2 shows a cross section of an optical fiber 201 according to an embodiment of the invention. The optical fiber comprises an optical core 208 surrounded by a coating material 206 as is usual in the field of optical fibers. Core 208 and liner 206 may be produced by standard optical fiber production techniques and may, for example, comprise extruded silica glass. A cushioning material 202 is wrapped around the core, again as is usual in the manufacture of optical fibers. The damping material is coated in a liner material 204.
    [0070] Unlike conventional optical fibers, however, where the core and the sheath are located in the center of the optical fiber, in the modality shown in figure 1a, the core and sheath are displaced from the center of the optical fiber. The core and the sheath are located towards the edge of the optical fiber and, in the example shown, the center of the optical fiber falls neither in the core region nor in the sheath region.
    [0071] By the location of the optical fiber core facing the optical fiber side, that is, displacing the core from the fiber center, the signal coming from a fiber like this, when used as a distributed optical fiber sensor, can be maximized. As can be seen, in a distributed optical fiber sensor that responds to the mechanical movement of the optical fiber, it is the movement of the core and the coating parts of the optical fiber that leads to a change in the optical signal. For a distributed acoustic sensor as described in GB 2,442,745, the detected optical signal is radiation that has undergone Rayleigh backscattering within the optical fiber. The greater the intensity of the acoustic signal, the greater the change in the backscattered radiation detected.
    Petition 870190091694, of 9/13/2019, p. 30/39 / 28 [0072] Referring to figure 3, a standard 301 optical fiber is illustrated. The center of the fiber, which is where the core is normally located in a conventional optical fiber, is illustrated by the dotted line. The top drawings in figure 3 show the fiber arranged straight, as it can be unfolded in use. A mechanical vibration incident on the optical fiber can cause the optical fiber to vibrate, for example, oscillate in a transverse manner. Figure 3 shows the two ends of the movement of the optical fiber in a transverse direction. It will be apparent that it is the outer parts of the optical fiber that suffer the greatest bending. The actual degree of bending will depend on a number of factors including the fiber's elasticity in the longitudinal direction, but considering when the fiber was moved upwards (as shown on the page), it will be the top side of the fiber illustrated by the arrow 302 that suffers the greatest folding amount. The center of the fiber will also bend, but not to the edges of the fiber.
    [0073] Therefore, back to figure 2a, arranging the light guide portion 208 of the optical fiber towards the side of the optical fiber ensures that the bending effect to be observed by the core 208 and the coating 206 will be greater that where the core located in the center of the fiber. This will lead to a higher fiber signal return for a given incident mechanical disturbance and consequently the sensitivity of a distributed fiber optic sensor.
    [0074] Figure 2b shows another embodiment of an optical fiber according to the present invention. The optical fiber has a core and coating region, as previously described, located offset from the center of the fiber. The fiber also has a liner material 204. However, in this embodiment, the optical fiber has a first damping material 202 that surrounds the core and the sheath and a second damping material 210 disposed in the center of the optical fiber. At least one of the damping materials 202 and 210 can be gel. In one embodiment, the damping material 202 is a gel and the central material 210 is a
    Petition 870190091694, of 9/13/2019, p. 31/39 / 28 solid material to give the optical fiber a certain stiffness. In another embodiment, however, the core material 210 may be gel and the damping material 202 may be solid.
    [0075] The present inventors observed that optical fiber cable filled with gel provides better performance, when used in a distributed acoustic fiber optical sensor, than cables not filled with gel, since the presence of the gel helps to couple the acoustic signals in the core.
    [0076] Figure 2c shows another embodiment of the present invention. In this embodiment, a standard optical fiber 212, comprising a core, material, covering a damping material and a sheath, is arranged with a fiber optic cable 220. In this embodiment, the core of the optical fiber 21 is located in the center of the optical fiber , but the optical fiber itself is located towards the edge of the optical fiber cable as a whole. The fiber optic cable comprises a protective jacket 216 and a filler material 214. In some embodiments, the fiber optic cable may comprise more than one optical fiber 218. The additional optical fibers 218 can be used for optical communications via the optical fiber, while optical fiber 112 is used for optical detection in a distributed optical fiber sensor.
    [0077] In certain embodiments, such as those shown in figures 2a - 2c, the arrangement of the core in relation to the center of the cable is substantially constant along the cable.
    [0078] In other modalities, however, the optical fiber can be arranged in a helical pattern within the cable, that is, the position of the optical fiber within the cable varies along the length of the cable. Figure 2d illustrates the arrangement of the optical fiber inside the cable, with the cable jacket and damping material omitted for clarity. Where the cable has a solid core material, the optical fiber can be wrapped around the solid core.
    [0079] It will be clear that in the course of a few meters of cable a
    Petition 870190091694, of 9/13/2019, p. 32/39 / 28 helical winding will mean that the optical fiber is arranged on all sides of the center of the cable. Thus, it does not matter in which direction an acoustic wave is incident by at least part of the optical fiber will be subject to the maximum extent of the bending. A helical arrangement thus avoids the need to arrange the cable in a particular orientation.
    [0080] Additionally, the helix pitch can be chosen to provide a desired spatial resolution. In use, the fiber is interrogated with radiation pulses of particular duration and the pulse duration can define the length, in the fiber, of each detection portion. The minimum length of the detection portion can be partly determined by the length of the fiber being interrogated, as the interrogation pulses that define the size of the detection portion may need to be of a minimum duration to guarantee acceptable returns from the end of the fiber. . The spatial resolution of the sensor itself, however depends on how the fiber is arranged. Using a helical winding, a given cable length can correspond to a longer optical fiber length, thus improving the spatial resolution of the final sensor.
    [0081] Figures 6a and 6b show another embodiment of the present invention. In this embodiment, an optical fiber 601, which may be a conventional optical fiber, has, at one end, an optical fiber connector 602. Optical fiber connection devices are known to focus radiation on or from an optical fiber. In use, the optical fiber connector can be connected to a splitter or circulator to pass radiation to be transmitted to the fiber and direct backscattered radiation to the detector. In this embodiment, fiber optic connector 602 comprises a lens 603 and a housing 604 that holds the lens in place with respect to the end of the optical fiber 601.
    [0082] Conventionally, the lens is arranged to focus radiation in the center of the optical fiber, that is, the point 605 illustrated in the cross section of the
    Petition 870190091694, of 9/13/2019, p. 33/39 / 28 figure 6a. In the present invention, however, the fiber optic coupler is arranged to focus radiation on the optical fiber displaced from the center of the fiber, for example, at position 606. In this way, the radiation will be coupled to the optical fiber at the edge of the core region and the maximum light intensity with the core will be at the edge of the core. As previously described, the fold observed at the edge of the core will generally be greater than at the center of the core and consequently by coupling the radiation to the fiber in such a way that the maximum intensity is at the edges of the core, the amount of back dispersion can be maximized.
    [0083] Now back to figure 4, two modalities are shown according to a different aspect of the invention. An optical fiber 401 comprises an optical core region 402 and a coating region 403 as previously described. In each case, however, the optical fiber comprises one or more stiffening elements 404 that act to provide stiffness to the optical fiber in only one preferred direction. The rigidity elements comprise flat structures that are arranged along the entire length of the fiber and are arranged so that their thick edges are all aligned. In figure 4, the thick border of each element is shown being aligned horizontally. The rigidity element can comprise a thin strip of metal or plastic and acts to provide resistance to bending in one direction, in this case, the left to right horizontal direction, while allowing movement in the other direction, in this case, the direction vertical. It is realized that a thin strip-like element of a relatively flexible material oriented as shown in figure 4 can easily be folded up and down without much resistance, but it may not flex easily from side to side. Thus, the rigidity element acts to provide the optical fiber with a preferred direction of movement. The fiber can be flexed relatively easily in the vertical direction, but it will not be easily flexed in the vertical direction
    Petition 870190091694, of 9/13/2019, p. 34/39 / 28 horizontal.
    [0084] The modalities shown in figure 4 can therefore be used to respond preferentially to disturbances incident in the vertical direction. This can allow the components of an incident wave to be resolved in the vertical direction. For example, if a pressure wave is incident on any of the fibers shown in figure 4 from left to right, the wave can induce very little movement of the fibers and consequently there will be very little change in the back scattered radiation. A pressure wave on top or bottom will cause the fiber to vibrate (as shown in figure 3). This would result in a change in the amount of backscattered radiation that would be detected as a fiber disturbance. A pressure wave incident in a direction that is 45 ° with the vertical would cause a certain amount of vibration in the up and down direction because of the component of the incident wave in the up and down direction.
    [0085] Arranging two fibers in such a way that each responds preferentially in a single dimension, and arranging the preferred direction of movement to be orthogonal in each fiber, an incident disturbance, that is, an acoustic wave, can be resolved in two orthogonal components, as illustrated, in figure 5. Figure 5 shows another mode of fiber optic cable. Figure 5 shows two fiber optic cables 501 of identical designs. Each fiber optic cable has an optical fiber 502, which comprises an optical core and sheath and may optionally comprise at least one damping and / or at least one jacket material, as previously described. Wrapping the optical fiber is the cable material. The cable has a cross-sectional shape that is wider in one direction than the other, in this case an elliptical shape. Thus, each fiber will preferably bend in the direction of the smaller axis and will be resistant to bending in the direction of the longitudinal axis.
    Petition 870190091694, of 9/13/2019, p. 35/39 / 28 [0086] Optionally, the cable could comprise stiffening elements as previously described to prevent further movement in the direction of the longitudinal axis.
    [0087] The two fibers are arranged relatively close to each other and substantially parallel and are aligned so that the preferred direction of vibration of one fiber (illustrated by the arrows) is orthogonal to that of the other fiber. Any incident acoustic wave (which should mean any type of incident pressure wave, including seismic waves) that has a component perpendicular to the general axis along which the fibers extend thus will be resolved into orthogonal components by the two fibers. Such an arrangement may be suitable for seismic surveys and especially for downhole applications, for example, to detect and map fractures.
    [0088] Each feature disclosed in the description and, where appropriate, in the claims and drawings, may be provided independently or in any appropriate combination.
    权利要求:
    Claims (14)
    [1]
    1. Optical fiber (201) characterized by the fact that it comprises a core (208), a coating (206) surrounding the core and a jacket (204) surrounding the coating, further comprising at least one damping material (202, 210) filling the space between the liner (206) and the liner (204) in which the core (208) is displaced from the center of the optical fiber and in which the optical fiber is adapted to flex readily.
    [2]
    2. Optical fiber (201) according to claim 1, characterized by the fact that the core (208) is located on one side of the optical fiber.
    [3]
    Optical fiber (201) according to claim 1 or 2, characterized by the fact that the center of the optical fiber is not arranged in the core (208).
    [4]
    4. Optical fiber (201), according to claim 3, characterized by the fact that the center of the optical fiber is not within the coating.
    [5]
    Optical fiber (201) according to any one of claims 1 to 4, characterized in that it comprises more than one damping material (202, 210).
    [6]
    Optical fiber (201) according to any one of claims 1 to 5, characterized in that at least part of the damping material (202, 210) is a gel.
    [7]
    Optical fiber (201) according to any one of claims 1 to 6, characterized by the fact that it comprises a gel cushion arranged in the center of the optical fiber, with the core (208) and the coating (206) in one side of gel cushioning.
    [8]
    Optical fiber (201) according to any one of claims 1 to 7, characterized by the fact that the core (208) and the
    Petition 870190091694, of 9/13/2019, p. 37/39
    2/2 linings (206) are disposed within a gel cushioning material.
    [9]
    Optical fiber (201) according to any one of claims 1 to 8, characterized in that it comprises a solid damping material in the center of the optical fiber, surrounded by a gel damping, with the core (208) and the coating (206) being disposed in the gel cushion.
    [10]
    Optical fiber (201) according to any one of claims 1 to 9, characterized in that the core (208) describes a helix along the length of the fiber.
    [11]
    Optical fiber (201) according to any one of claims 1 to 10, characterized in that it comprises at least one stiffening member (404), the at least one stiffening member having a stiffness that is greater in one transverse direction than in a second transverse direction, so that the optical fiber flexes readily in the second direction and does not flex readily in the first direction, and in which the core (208) is displaced from the center of the optical fiber in the second transverse direction.
    [12]
    Fiber optic cable characterized by the fact that it comprises an optical fiber (201) as defined in any one of claims 1 to 11.
    [13]
    Fiber optic cable according to claim 12, characterized in that it comprises a plurality of optical fibers (201).
    [14]
    14. Distributed acoustic optical fiber sensor characterized by the fact that it comprises an optical fiber source coupled to an optical fiber (201) as defined in any one of claims 1 to 11 for interrogating the optical fiber (201) with optical radiation and a detector coupled to the optical fiber (201) to detect radiation that is backscattered from the optical fiber (201).
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    同族专利:
    公开号 | 公开日
    EA032731B1|2019-07-31|
    GB0919902D0|2009-12-30|
    EP2803957B1|2017-01-11|
    CA2780569A1|2011-05-19|
    EP2803957A2|2014-11-19|
    CA3051560A1|2011-05-19|
    EA201400829A1|2015-03-31|
    WO2011058314A1|2011-05-19|
    AU2010317792A1|2012-07-05|
    US11099085B2|2021-08-24|
    AU2010317792B2|2014-07-24|
    EP2499472A1|2012-09-19|
    CN102822645B|2018-07-27|
    CN108645430A|2018-10-12|
    EP2499472B1|2016-01-27|
    EA201290303A1|2012-12-28|
    EA029335B1|2018-03-30|
    US9677956B2|2017-06-13|
    CA3051561A1|2011-05-19|
    MY162097A|2017-05-31|
    BR112012011226A2|2018-03-27|
    CN102822645A|2012-12-12|
    EP2803957A3|2015-01-21|
    US20170343433A1|2017-11-30|
    CA2780569C|2019-09-24|
    US20120222487A1|2012-09-06|
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    法律状态:
    2019-01-08| B06F| Objections, documents and/or translations needed after an examination request according [chapter 6.6 patent gazette]|
    2019-07-16| B06T| Formal requirements before examination [chapter 6.20 patent gazette]|
    2019-12-03| B09A| Decision: intention to grant [chapter 9.1 patent gazette]|
    2020-01-21| B16A| Patent or certificate of addition of invention granted [chapter 16.1 patent gazette]|Free format text: PRAZO DE VALIDADE: 20 (VINTE) ANOS CONTADOS A PARTIR DE 11/11/2010, OBSERVADAS AS CONDICOES LEGAIS. |
    2021-09-08| B21F| Lapse acc. art. 78, item iv - on non-payment of the annual fees in time|Free format text: REFERENTE A 11A ANUIDADE. |
    2021-12-28| B24J| Lapse because of non-payment of annual fees (definitively: art 78 iv lpi, resolution 113/2013 art. 12)|Free format text: EM VIRTUDE DA EXTINCAO PUBLICADA NA RPI 2644 DE 08-09-2021 E CONSIDERANDO AUSENCIA DE MANIFESTACAO DENTRO DOS PRAZOS LEGAIS, INFORMO QUE CABE SER MANTIDA A EXTINCAO DA PATENTE E SEUS CERTIFICADOS, CONFORME O DISPOSTO NO ARTIGO 12, DA RESOLUCAO 113/2013. |
    优先权:
    申请号 | 申请日 | 专利标题
    GBGB0919902.7A|GB0919902D0|2009-11-13|2009-11-13|Improvements in fibre optic cables for distributed sensing|
    PCT/GB2010/002074|WO2011058314A1|2009-11-13|2010-11-11|Optic fibres and fibre optic sensing|
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