Fiber Optic Seismic Sensor Research Articles

Moho Imaging with Fiber Borehole Strainmeters Based on Ambient Noise Autocorrelation.

Moho tomography is important for studying the deep Earth structure and geodynamics, and fiber borehole strainmeters are broadband, low-noise, and attractive tools for seismic observation. Recently, many studies have shown that fiber optic seismic sensors can be used for subsurface structure imaging based on ambient noise cross-correlation, similar to conventional geophones. However, this array-dependent cross-correlation method is not suitable for fiber borehole strainmeters. Here, we developed a Moho imaging scheme for the characteristics of fiber borehole strainmeters based on ambient noise autocorrelation. S-wave reflection signals were extracted from the ambient noise through a series of processing steps, including phase autocorrelation (PAC), phase-weighted stacking (PWS), etc. Subsequently, the time-to-depth conversion crustal thickness beneath the station was calculated. We applied our scheme to continuous four-component recordings from four fiber borehole strainmeters in Lu'an, Anhui Province, China. The obtained Moho depth was consistent with the previous research results. Our work shows that this method is suitable for Moho imaging with fiber borehole strainmeters without relying on the number of stations.

Review on Low-Noise Broadband Fiber Optic Seismic Sensor and Its Applications

Fiber optic seismic sensors have important application prospects in the field of earthquake science research and underground structure detection, due to their strong adaptability in harsh environments such as deep wells, seabeds, and glaciers. It has always been one of the key problems to achieve ultra-low noise levels over a wide measurement frequency band for fiber optic seismic sensors. This article reviews two typical low-noise broadband fiber optic seismic sensing techniques, including narrow-linewidth laser frequency scanning and frequency locking sensing technique, laser interferometric phase interrogation technique. The principles are given. The measurement frequency band and noise level are tested and discussed. Recent progresses on crustal deformation observation, earthquake monitoring, water temperature solid tide detection and deep earth structure exploration based on fiber optic seismic sensors are introduced. Finally, the possible research trends are discussed.

Investigation into Fiber Optic Seismic Sensor incorporating Fiber Bragg Grating Array

This paper presents a theoretical investigation on a type of Fiber Optic Sensing system used for seismic monitoring which incorporates an array of Fiber Bragg Gratings (FBGs) in the sensing medium. An interferometry array contains a group of interferometry sub-arrays, every sub-array including a plurality of interferometry. Each interferometer in a sub-array is realized with a particular pair of fiber Bragg gratings and a sensing length of optical fiber located between the respective pair of fiber Bragg gratings. The fiber Bragg gratings in every respective couple of fiber Bragg gratings have a similar characteristic wavelength that is altered from the characteristic wavelength of every other couple of fiber Bragg gratings in the sub-array. The sub-arrays are interconnected to minimize the common-wavelength crosstalk among the sensors in the overall interferometry array. Our work focuses on investigating the selection of the optimum wavelength for use in the system. The study was performed using state-of-the-art simulation techniques for strain and temperature changes in the FBG sensor array. The cumulative results obtained can be used to help designers produce an optimized performance for similar fiber optic hydrophones in the future. It has been shown that the wavelength 1300nm region gives the best performance in this type of fiber optic hydrophone system.

Intelligent Microseismic Events Recognition in Fiber-Optic Microseismic Monitoring System Compared With Electronic One

Fiber-optic seismic sensor has become an emerging effective tool for microseismic monitoring, which is of importance for oil and gas production improvement. When processing the fiber-optic data, the recognition of microseismic events is the first crucial step, which is rarely reported due to the lack of such data. In this paper, based on the features of central data distribution, skewness, kurtosis, energy entropy, etc., the classification accuracy of microseismic (MS) events obtained by fiber-optic MS monitoring system and electronic one is compared using machine learning algorithm (e. g. SVM and KNN) for the first time. The results show that fiber-optic data has higher classification accuracy than electronic data when using the feature of central data distribution owing to the high signal-to-noise ratio of fiber-optic data. However, when choosing the features of energy entropy, zero-crossing rate and the energy proportion of specific frequency band, electronic data has higher classification accuracy than fiber-optic data benefiting from the longer events duration and the lower frequency components of electronic data. When using skewness and kurtosis, the classification performance in fiber-optic data is almost consistent with the electronic one. Moreover, the results indicate that the characteristics of MS signal itself have a greater impact on the discrimination ability of MS events than the applied machine learning classification algorithm.

Simulation and hardware implementation of demodulation for fiber optic seismic sensor with linear edge filtering method

Abstract The demodulation system is a very critical component of the seismic exploration, which determines the response speed and accuracy of data acquisition of the detection system. Here, we demonstrate a simulation and hardware implementation of demodulation system based on linear edge filtering method for fiber optic seismic sensor. The system is implemented mainly by an edge filter (long period fiber grating) with the linear slope of 1.368 dBm/nm and the sideband width of 6.05 nm, and a homemade circuit board. The results show that the system can be used to demodulate low-frequency (10 Hz–200 Hz) vibration signals, and the best signal-to-noise ratio is up to ~ 70 dB. Moreover, theoretically, the system could be used to demodulate higher frequency vibration and can be adapted to any vibration measurement, and suitable for engineering application due to the characteristics of simple structure, low cost, stable performance, fast response speed and high precision.

Seismic response of fiber optic seismic sensors

Fiber-optic seismic sensors (FOSS) consist of an optical fiber connected to an optical interrogator, which is electro-optic instrumentation that injects pulses of coherent light into the fiber and receives and demodulates the returned signals. The optical fiber is usually contained within a protective cable. Experiments were performed on a barrier island setting where several kilometers of cable had been buried at sub-meter depths. It has been hypothesized that seismic disturbances strain a segment of the optical fiber thus causing its optical path length to change. An array of eight 3 axis seismometers were buried alongside the cable at the same depth, with a spacing of 0.5 m, and with one axis parallel to the cable. An electromagnetic shaker, buried at the same depth and in different configurations with respect to the array and the FOSS, was excited with a 10-cycle tone burst varying in frequency from 10 to 200 Hz. The resulting seismic waves were simultaneously recorded with the seismometers and the FOSS. Signals recorded with the seismometer array were processed to calculate the average strain along the direction of the fiber. The presentation illustrates the comparison between the computed strain outputs of the seismometers and that of the FOSS.

In Search of Better Reservoir Imaging Using Fiber Optic Receivers Downhole

Seismic Receivers After nearly 4 decades of work, Bjorn Paulsson has created a system using fiber optic seismic receivers so sensitive that he said it will be able to create much more accurate, detailed seismic images with features too small to be seen now, detect the sounds of fracturing never heard before, and stand up to temperatures exceeding 300°C and pressures of more than 30,000 psi. But he needs USD 12 million from companies interested in using it in their wells, which is nearly equal to the financial backing he has received from the United States Department of Energy (DOE) to get to this stage. Paulsson and the DOE’s Research Partnership to Secure Energy for America (RPSEA) were organizing a meeting in late May seeking the support of oil companies to develop a full-scale version of the system he describes as “more than an order of magnitude better than what we can do now. This is not a small step up, it is a huge step.” The plan is to build a system that can place 200 fiber optic seismic sensors, each of which has three channels (3C) allowing it to detect the direction of incoming signals along three axes, deep in a 30,000-ft deep well. There would be a receiver every 50 ft covered by a metal housing capable of standing up to the extreme pressures found in wells in the ultradeepwater US Gulf of Mexico, and clamped tightly onto a drilling pipe that can deliver it to the end of a long horizontal well.

A Fiber Optic Borehole Seismic Vector Sensor System for High Resolution CCUS Site Characterization and Monitoring

Abstract Seismic techniques are the dominant geophysical techniques for the characterization of subsurface structures and stratigraphy. The seismic techniques also dominate the monitoring and mapping of reservoir injection and production processes. Borehole seismology, of all the seismic techniques, despite its current shortcomings, has been shown to provide the highest resolution characterization and most precise monitoring results because it generates higher signal to noise ratio and higher frequency data than surface seismic techniques. The operational environments for borehole seismic instruments are however much more demanding than for surface seismic instruments making both the instruments and the installation much more expensive. To address the critical site characterization and monitoring needs for CCUS programs, US Department of Energy (DOE) funded Paulsson, Inc. in 2010 to develop a fiber optic based ultra-large bandwidth clamped borehole seismic vector array capable of deploying up to one thousand 3C sensor pods suitable for deployment into high temperature and high pressure boreholes. Tests of the fiber optic seismic vector sensors developed on the DOE funding have shown that the new borehole seismic sensor technology is capable of generating outstanding high vector fidelity data with extremely large bandwidth: 0.01 – 6,000 Hz. Field tests have shown that the system can record events at magnitudes much smaller than M-2.6 at frequencies up to 2,000 Hz. The sensors have also proved to be about 100 times more sensitive than the regular coil geophones that are used in borehole seismic systems today. The fiber optic seismic sensors have furthermore been qualified to operate at temperatures over 300 °C (572 °F). Simultaneously with the fiber optic based seismic 3C vector sensors we are using the lead-in fiber to acquire Distributed Acoustic Sensor (DAS) data from the surface to the bottom the vector array. While the DAS data is of much lower quality than the vector sensor data it provides a 1 m spatial sampling of the downgoing wavefield which will be used to build the high resolution velocity model which is an essential component in high resolution imaging and monitoring.

MW2 concept of CO2 monitoring for offshore reservoirs in Japan

Abstract Most of the geological storage potentials of Japan are expected in the offshore saline aquifers. In this study, we intended to present a CO2 monitoring concept of offshore reservoirs for the future CCS in Japan. In the case of offshore potential reservoirs in Japan, a sole deviated injection well without any monitoring wells nearby is thought to be a probable well configuration for CO2 injection. We concentrated our study on the utilization of the injection well as a monitoring well, and permanent installation of various monitoring equipments to the well in behalf of well loggings was concluded to be the best option for it. The monitoring method through a series sensors properly placed on the injection well was devised and named “Monitoring without monitoring well (MW2)”, which is mainly comprised of time-lapse VSP by fiber optic seismic sensors and time-lapse VEMP by a magnetic sensor for detecting the CO2 plume along with pressure and temperature measurement and observation of injection profile of CO2.