Abstract: A distributed acoustic system (DAS) method and system. The system may comprise an interrogator and an umbilical line comprising a first fiber optic cable and a second fiber optic cable attached at one end to the interrogator. The DAS may further include a downhole fiber attached to the umbilical line at the end opposite the interrogator and a light source disposed in the interrogator that is configured to emit a plurality of coherent light frequencies into the umbilical line and the downhole fiber. The method may include generating interferometric signals of the plurality of frequencies of backscattered light that have been received by the photo detector assembly and processing the interferometric signals with an information handling system.

Abstract: A distributed acoustic system (DAS) method and system. The system may comprise an interrogator and an umbilical line comprising a first fiber optic cable and a second fiber optic cable attached at one end to the interrogator. The DAS may further include a downhole fiber attached to the umbilical line at the end opposite the interrogator and a light source disposed in the interrogator that is configured to emit a plurality of coherent light frequencies into the umbilical line and the downhole fiber. The method may include generating interferometric signals of the plurality of frequencies of backscattered light that have been received by the photo detector assembly and processing the interferometric signals with an information handling system.

Abstract: A method of perforating a wellbore is provided. The method includes generating a shockwave that propagates throughout said wellbore by firing a perforation device at a perforating direction, and measuring the shockwave at a fiber optic cable in the wellbore using the fiber optic cable. The method further includes determining an orientation of the fiber optic cable relative to the perforating direction based on the shockwave and the perforating direction, and changing the perforating direction based on the orientation of said the optic cable for a subsequent perforation of the wellbore to minimize damage to the fiber optic cable during the subsequent perforation. The fiber optic cable is an existing cable that has been deployed before the method starts.

Abstract: A system for downhole measurements. The system may comprise a fiber optic cable that further comprises a transmission fiber and a return fiber. Additionally, the system may comprise a passive optical device optically connected to the transmission fiber and the return fiber, a first wavelength division multiplexer (WDM) optically connected to the transmission fiber, and a second WDM optically connected to the return fiber. The system may further comprise a transmitter and a first Raman pump optically connected to the first WDM and a receiver and a second Raman pump optically connected to the second WDM.

Abstract: A distributed acoustic system may comprise an interrogator which includes a single photon detector, an umbilical line comprising a first fiber optic cable and a second fiber optic cable attached at one end to the interrogator, and a downhole fiber attached to the umbilical line at the end opposite the interrogator. A method for optimizing a sampling frequency may comprise identifying a length of a fiber optic cable connected to an interrogator, identifying one or more regions on the fiber optic cable in which a backscatter is received, and optimizing a sampling frequency of a distributed acoustic system by identifying a minimum time interval that is between an emission of a light pulse such that at no point in time the backscatter arrives back at the interrogator that corresponds to more than one spatial location along a sensing portion of the fiber optic cable.

Abstract: A method of perforating a wellbore is provided. The method includes generating a shockwave that propagates throughout said wellbore by firing a perforation device at a perforating direction, and measuring the shockwave at a fiber optic cable in the wellbore using the fiber optic cable. The method further includes determining an orientation of the fiber optic cable relative to the perforating direction based on the shockwave and the perforating direction, and changing the perforating direction based on the orientation of said the optic cable for a subsequent perforation of the wellbore to minimize damage to the fiber optic cable during the subsequent perforation. The fiber optic cable is an existing cable that has been deployed before the method starts.

Abstract: Faded channels in a distributed acoustic sensing system can be mitigated using a phase modulator. A first pulse and a second pulse of an optical signal can be determined. A phase modulator can modulate the first pulse to have a different wavelength than the second pulse. The first pulse can be launched into a sensing fiber that extends into a wellbore. A first backscattered signal can be received from the sensing fiber in response to the first pulse being launched into the sensing fiber. The second pulse can be launched into the sensing fiber and a second backscattered signal can be received from the sensing fiber. Data about an environment of the wellbore can be determined by processing the first backscattered signal and the second backscattered signal to compensate for fading in the first backscattered signal or the second backscattered signal.

Abstract: A distributed acoustic system (DAS) method and system. The system may comprise an interrogator and an umbilical line comprising a first fiber optic cable and a second fiber optic cable attached at one end to the interrogator. The DAS may further include a downhole fiber attached to the umbilical line at the end opposite the interrogator and a light source disposed in the interrogator that is configured to emit a plurality of coherent light frequencies into the umbilical line and the downhole fiber. The method may include generating interferometric signals of the plurality of frequencies of backscattered light that have been received by the photo detector assembly and processing the interferometric signals with an information handling system.

Abstract: A distributed acoustic system (DAS) with an interrogator, an umbilical line attached at one end to the interrogator, and a downhole fiber attached to the umbilical line at the end opposite the interrogator. A method for optimizing a sampling frequency may begin with identifying a length of a fiber optic cable connected to an interrogator, identifying one or more regions on the fiber optic cable in which a backscatter is received, and optimizing a sampling frequency of a distributed acoustic system (DAS) by identifying a minimum time interval that is between an emission of a light pulse such that at no point in time the backscatter arrives back at the interrogator that corresponds to more than one spatial location along a sensing portion of the fiber optic cable.

Abstract: A distributed acoustic system may comprise an interrogator which includes a single photon detector, an umbilical line comprising a first fiber optic cable and a second fiber optic cable attached at one end to the interrogator, and a downhole fiber attached to the umbilical line at the end opposite the interrogator. A method for optimizing a sampling frequency may comprise identifying a length of a fiber optic cable connected to an interrogator, identifying one or more regions on the fiber optic cable in which a backscatter is received, and optimizing a sampling frequency of a distributed acoustic system by identifying a minimum time interval that is between an emission of a light pulse such that at no point in time the backscatter arrives back at the interrogator that corresponds to more than one spatial location along a sensing portion of the fiber optic cable.

Abstract: Distributed The disclosed embodiments include distributed acoustic sensing (DAS) systems, methods to improve DAS properties of optical fibers, and optical fibers having improved DAS properties. In one embodiment, the system includes an optoelectronic device operable to generate optical pulses. The system also includes an optical fiber having a first end and a second end. The optical fiber is formed from a material having a Rayleigh back-scattering coefficient, and is operable to transmit optical pulses from the first end towards the second end and to reflect a first portion of the optical pulses towards the first end. The system further includes perturbations that are selectively imprinted on the optical fiber, where the perturbations are compatible with a range of wavelengths and are operable to reflect a second portion of the optical pulses towards the first end of the optical fiber if a wavelength of the optical pulses is within the range.

Abstract: A distributed acoustic system (DAS) with an interrogator, an umbilical line attached at one end to the interrogator, and a downhole fiber attached to the umbilical line at the end opposite the interrogator. A method for optimizing a sampling frequency may begin with identifying a length of a fiber optic cable connected to an interrogator, identifying one or more regions on the fiber optic cable in which a backscatter is received, and optimizing a sampling frequency of a distributed acoustic system (DAS) by identifying a minimum time interval that is between an emission of a light pulse such that at no point in time the backscatter arrives back at the interrogator that corresponds to more than one spatial location along a sensing portion of the fiber optic cable.

Abstract: Faded channels in a distributed acoustic sensing system can be mitigated using a phase modulator. A first pulse and a second pulse of an optical signal can be determined. A phase modulator can modulate the first pulse to have a different wavelength than the second pulse. The first pulse can be launched into a sensing fiber that extends into a wellbore. A first backscattered signal can be received from the sensing fiber in response to the first pulse being launched into the sensing fiber. The second pulse can be launched into the sensing fiber and a second backscattered signal can be received from the sensing fiber. Data about an environment of the wellbore can be determined by processing the first backscattered signal and the second backscattered signal to compensate for fading in the first backscattered signal or the second backscattered signal.

Abstract: The disclosed embodiments include distributed acoustic sensing (DAS) systems, methods to improve DAS properties of optical fibers, and optical fibers having improved DAS properties. In one embodiment, the system includes an optoelectronic device operable to generate optical pulses. The system also includes an optical fiber having a first end and a second end. The optical fiber is formed from a material having a Rayleigh back-scattering coefficient, and is operable to transmit optical pulses from the first end towards the second end and to reflect a first portion of the optical pulses towards the first end. The system further includes perturbations that are selectively imprinted on the optical fiber, where the perturbations are compatible with a range of wavelengths and are operable to reflect a second portion of the optical pulses towards the first end of the optical fiber if a wavelength of the optical pulses is within said range.

Abstract: Systems and methods for distributed acoustic sensing based on coherent Rayleigh scattering are disclosed herein. A system comprises a pulse generator, an interferometer, a photo detector assembly, and an information handling system. The interferometer comprises a first and second optical switch each comprising a plurality of ports. The information handling system activates one port on each of the first and second optical switches so as to vary the optical path length of the interferometer. A method comprises splitting backscattered light from an optical pulse into a first portion and a second portion, activating one port of a first optical switch and one port of a second optical switch, sending the first portion into a first arm of an interferometer, sending the second portion into a second arm of the interferometer, combining the first and second portions to form an interferometric signal, and receiving the interferometric signal at a photodetector assembly.

Abstract: Systems and methods for distributed acoustic sensing based on coherent Rayleigh scattering are disclosed herein. A system comprises a pulse generator, an interferometer, a photo detector assembly, and an information handling system. The interferometer comprises a first and second optical switch each comprising a plurality of ports. The information handling system activates one port on each of the first and second optical switches so as to vary the optical path length of the interferometer. A method comprises splitting backscattered light from an optical pulse into a first portion and a second portion, activating one port of a first optical switch and one port of a second optical switch, sending the first portion into a first arm of an interferometer, sending the second portion into a second arm of the interferometer, combining the first and second portions to form an interferometric signal, and receiving the interferometric signal at a photodetector assembly.

Abstract: A method of measuring acceleration using an optical sensor. In the optical sensor, acceleration, acoustic velocity, or displacement (vibration) causes a corresponding shift in the center wavelength of the sensor output. The sensor can be coupled to a high-speed interferometric interrogator through an unbalanced fiber interferometer. The unbalanced interferometer functions to translate optical wavelength shift into phase shift, which is easily demodulated by the interrogator.

Abstract: An optical sensor in which acceleration, acoustic velocity, or displacement (vibration) causes a corresponding shift in the center wavelength of the sensor output. The sensor can be coupled to a high-speed interferometric interrogator through an unbalanced fiber interferometer. The unbalanced interferometer functions to translate optical wavelength shift into phase shift, which is easily demodulated by the interrogator. A method of measuring acceleration uses the sensor.

Abstract: An optical sensor in which acceleration, acoustic velocity, or displacement (vibration) causes a corresponding shift in the center wavelength of the sensor output. The sensor can be coupled to a high-speed interferometric interrogator through an unbalanced fiber interferometer. The unbalanced interferometer functions to translate optical wavelength shift into phase shift, which is easily demodulated by the interrogator. A method of measuring acceleration uses the sensor.

Abstract: A sensor apparatus combines an optical sensor in which acceleration, acoustic velocity, or displacement (vibration) causes a corresponding shift in the center wavelength of the sensor output, coupled to a high speed interferometric interrogator, through an unbalanced fiber interferometer. The unbalanced interferometer functions to translate optical wavelength shift into phase shift, which is easily demodulated by the interrogator.