An optical system employs a method for measuring an acoustic signal in a wellbore. The optical system includes an optical interrogator and an optical fiber. The optical fiber has a plurality of nominal sites uniformly spaced apart along a longitudinal axis of the optical fiber. A plurality of gratings are formed in the optical fiber. Each of the plurality of gratings is associated with a nominal site and is separated from its associated nominal site by an offset distance. The offset distance is selected to reduce a destructive interference between reflections from the plurality of gratings. The optical interrogator transmits a light pulse into the optical fiber to measure the acoustic signal via a reflection of the light pulse from at least one of the plurality of gratings.

A method of detecting an event by: obtaining a first sample data set; determining a frequency domain feature(s) of the first sample data set over a first time period; determining a first threshold for the a frequency domain feature(s) using the first sample data set; determining that the frequency domain feature(s) matches the first threshold; determining the presence of an event during the first time period based on determining that the frequency domain feature(s) matches the first threshold; obtaining a second sample data set; determining a frequency domain feature(s) of the second sample data set over a second time period; determining a second threshold for the frequency domain feature(s) using the second sample data set; determining that the frequency domain feature(s) matches the second threshold; and determining the presence of the event during the second time period based on determining that the frequency domain feature(s) matches the second threshold.

An optical communication system that enables any deployed fiber-optic cable to function as an earthquake-detection sensor. In an example embodiment, a WDM optical transmitter of one network node operates to transmit a CW optical signal together with legacy data-carrying optical signals. At another network node, a low-complexity, low-latency coherent optical receiver is used to obtain time-resolved measurements of the Stokes parameters of the CW optical signal. The signal-processing chain of the optical receiver employs digital filtering to select frequency components of the measurements streams corresponding to seismic disturbances of the fiber-optical cable connecting the nodes. The selected frequency components are then used to compute values of an earthquake indicator, which are reported to a network controller. Based on such reports from three or more nodes, the network controller can determine the epicenter and magnitude of the earthquake and, if warranted, may generate a tsunami forecast.

A method includes collecting spectral data from fiber Bragg grating sensors distributed at locations along a fiber optic component positioned along a streamer; and analyzing the spectral data to produce measurements of bend of an axis of the streamer proximate the locations. A streamer monitoring system includes: a fiber optic component positioned along a streamer; a plurality of fiber Bragg grating sensors distributed at locations along the fiber optic component; a light source optically coupled to the fiber optic component and configured to interrogate the fiber Bragg grating sensors; a photodetector optically coupled to the fiber optic component and configured to collect spectral data from the interrogated fiber Bragg grating sensors; and a spectral analyzer in communication with the photodetector and configured to analyze the spectral data to produce measurements of bend of an axis of the streamer proximate the locations along the fiber optic component.

The invention relates to the use of distributed optical fiber sensors for distributed acoustic sensing, and in particular, modal analysis of distributed acoustic data obtained in-well to monitoring well integrity. By determining one or more acoustic modes corresponding to distributed speed of sound measurements within the wellbore, and analyzing variations in the distributed speed of sound measurement it is possible to derive information relating to a formation and/or fluid in the wellbore.

A data acquisition program, which includes core, image log, microseismic, DAS, DTS, and pressure data, is described. This program can be used in conjunction with a variety of techniques to accurately monitor and conduct well stimulation.

A distributed fiber optic acoustic detection device employs a novel distributed acoustic detection method using a phase noise cancelling distributed acoustic sensing (PNC-DAS) technique.

A distance of a water flow path and a velocity of the water flow is calculated using data obtained from both a pulsed neutron sensor and distributed acoustic sensors. The two distance and velocity values are compared to obtain a first calculated distance and velocity. The distance of the water flow path and the velocity of the water flow are calculated using the Doppler data obtained from distributed Doppler sensors. The distance and velocity values are compared with the first calculated distance and first calculated velocity to obtain a second calculated distance and velocity values. The distance of the water flow path and the velocity of the water flow are calculated using temperature data obtained from distributed temperature sensors. The distance and velocity values are compared with the second calculated distance and velocity to determine a distance of a cement interface, and a velocity of a water flow therein.

A workflow using techniques for improving signal-to-noise ratio and decreasing interferences for Low-Frequency Distributed Acoustic Sensing is described.

Embodiments disclosed herein include components, devices, systems, and operations and functions for generating a seismic profile. An optical signal is generated in an optical signal medium disposed in proximity to a formation. A seismic source induces seismic signals within the formation. A backscatter response corresponding to the seismic signals from the optical signal medium is detected and quadrature modulated to generate a quadrature trace. A seismic response is generated by determining phase differences in the backscatter response based on the quadrature modulated backscatter response. Portions of the seismic response above or below a response threshold are removed to generate a threshold seismic response. The threshold seismic response is correlated with at least one of the seismic signals to generate a correlated seismic response.