Systems and methods are provided for generating a model for detection of seismic events. In this regard, one or more processors may receive from one or more stations located along an underwater optical route, one or more time series of polarization states of a detected light signal during a time period. The one or more processors may transform the one or more time series of polarization states into one or more spectrums in a frequency domain. Seismic activity data for the time period may be received by the one or more processors, where the seismic activity data include one or more seismic events detected in a region at least partially overlapping the underwater optical route. The one or more processors then generate a model for detecting seismic events based on the one or more spectrums and the seismic activity data.

Aspects of the present disclosure describe distributed optical fiber sensing systems, methods, and structures that advantageously employ point sensors that send sensory data/information over an attached, distributed optical fiber sensor without using a separate network or communications facility.

A method of detecting sand inflow into a wellbore is disclosed. The method can include obtaining a sample data set, detecting a broadband signal within the sample data set, comparing the broadband signal with a signal reference, determining that the broadband signal meets or exceeds the signal reference, and determining the presence of sand inflow into the wellbore based on determining that the broadband signal meets or exceeds the signal reference. The sample data set can be a sample of an acoustic signal originating within a wellbore including a fluid, and the broadband signal at least includes a portion of the sample data set at frequencies above 0.5 kHz.

Earthquake detection via fiber sensing is provided using using a supervisory path of submarine cables wherein the supervisory system/path of a submarine optical cable conveys portion(s) of an optical signal back to an origin location periodically—i.e., at every repeater location. Advantageously, since it is known where a returning signal is coming from, a resolution equivalent to an undersea span length may be determined—which is sufficient for wide area disturbances such as earthquakes. The returned signal is sufficiently strong such that the signal-to-noise ratio of a returned/received signal is not limited by the ASE noise of the amplifiers. The returned signal is much larger as compared to a normal distributed acoustic sensing (DAS) return signal since the return signal according to aspects of the present disclosure is directed backward via an optical coupler/reflector/circulator having a much larger coupling ratio as compared to normal Rayleigh back scattering utilized in DAS.

The present disclosure provides a method of processing data obtained from distributed optical fiber sensors to detect acoustic energy generated by a poroelastic effect of fractures in a structure, such as a rock formation. The sensing fiber of an optical fiber distributed sensing system may be deployed in the vicinity of the region where fracturing is occurring, for example, along a well that is offset from a treatment well undergoing hydraulic fracturing. The DAS data obtained from along the sensing fiber is processed to measure changes in the low-frequency strain caused by the poroelastic effects in the rock as the fractures open and close. This measured strain rate data is iteratively processed at each instant time to identify fracture opening features (characterised as compression-tension-compression) that are correlated with fracture closing features (characterised as tension-compression-tension) as a function of depth, to thereby identify and locate fracture hits in the vicinity of the sensing fiber.

A DAS VSP technique is used to determine the induced fracture height and fracture density of an induced fracture region. The DAS VSP technique obtains pre-hydraulic fracturing DAS VSP survey time-lapse data to establish a baseline reference for the direct acoustic wave travel time. The DAS VSP technique obtains one or more time-lapse data corresponding to the subsequent monitor surveys conducted after each hydraulic fracturing stage along the well. Forward modeling is used to determine a theoretical acoustic wave travel time difference. The forward modeling uses seismic anisotropy to describe the behavior of seismic waves traveling through the induced fracture regions. An inversion scheme is then used to invert for the induced fracture height and the fracture density using the forward modeling. The two extracted induced fracture characteristics may then be used to determine optimal hydraulic fracturing parameters.

A system can receive data that can indicate a flow rate with respect to perforations in a reference wellbore. The data can be received from a fiber optic cable in the reference wellbore in a geographic area of interest. The system can determine a uniformity index, which can indicate a uniformity of flow with respect to the perforations, based on the data. The system can generate a pressure-based model by training a model using the uniformity index for applying the pressure-based model to a target wellbore in the geographic area of interest to determine controls to rate and proppant with respect to the target wellbore.

A method for improving a signal-to-noise ratio of distributed acoustic sensing data may comprise transmitting an acoustic wave from an acoustic source into a subterranean formation, recording a first acoustic noise at a first time interval with a distributed acoustic sensing system, recording at least one acoustic wave and a second acoustic noise at a second time interval with the distributed acoustic sensing system, calculating a noise spectrum from the first time interval, calculating the noise spectrum in the second time interval, and removing the noise spectrum from acoustic data measured during the second time interval to identify acoustic data of the subterranean formation. A system may comprise an acoustic source, a distributed acoustic sensing system disposed within a well, and an information handling system.

Methods and systems for characterizing fractures in a subterranean formation are provided. The method includes introducing an encapsulated explosive unit into a casing located in a wellbore within the subterranean formation and maintaining the encapsulated explosive unit in a stage of the casing. The method also includes detonating the encapsulated explosive unit within the stage to generate a pressure wave that passes through a group of perforations and into the fractures and measuring a reflected pressure wave using a pressure sensor coupled to the bridge plug to produce a pressure measurement. The method further includes converting the pressure measurement into an acoustic signal correlated with the pressure measurement by an acoustic signal generator contained in the bridge plug and transmitting the acoustic signal to apply acoustic pressure on a fiber optic cable coupled to an exterior surface of the casing.

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.