Modeling fault‐zone guided waves of microearthquakes in a geothermal reservoir

© 2015. American Geophysical Union. All Rights Reserved. Fault Zone Guided Waves (FZGWs) have been observed for the first time within New Zealand's transpressional continental plate boundary, the Alpine Fault, which is late in its typical seismic cycle. Ongoing study of these phases provides the opportunity to monitor interseismic conditions in the fault zone. Distinctive dispersive seismic codas (~7-35Hz) have been recorded on shallow borehole seismometers installed within 20m of the principal slip zone. Near the central Alpine Fault, known for low background seismicity, FZGW-generating microseismic events are located beyond the catchment-scale partitioning of the fault indicating lateral connectivity of the low-velocity zone immediately below the near-surface segmentation. Initial modeling of the low-velocity zone indicates a waveguide width of 60-200m with a 10-40% reduction in S wave velocity, similar to that inferred for the fault core of other mature plate boundary faults such as the San Andreas and North Anatolian Faults.

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Modeling guided waves to constrain the velocity structure of the oceanic crust in the subduction zone of eastern Alaska

10.5194/egusphere-egu2020-3268 ◽

2020 ◽

Author(s):

Xiaoyu Guan ◽

Yuanze Zhou ◽

Takashi Furumura

Keyword(s):

Subduction Zone ◽

Oceanic Crust ◽

High Frequency ◽

Subduction Zones ◽

Guided Waves ◽

Velocity Structure ◽

Guided Wave ◽

S Wave ◽

Arrival Times ◽

Velocity Models

Fitting subduction zone guided waves with synthetics is an ideal choice for studying the velocity structure of the oceanic crust. After an earthquake occurs in subduction zones, seismic waves can be trapped in the low-velocity oceanic crust and propagated as guided waves. The arrival time and frequency characteristics of the guided waves can be used to image the velocity structure of the oceanic crust. The analysis and modeling based on guided wave observations provide a rare opportunity to understand the velocity structure of the oceanic crust and the variations in oceanic crustal materials during the subduction process.High-frequency guided waves have been observed in the subduction zone of eastern Alaska. On several sections, observed seismograms recorded by seismic stations show low-frequency (<2Hz) onsets ahead of the main high-frequency (>2Hz) guided waves. Differences in the arrival times and dispersion characteristics of seismic phases are related to the velocity structure of the oceanic crust, and the characteristics of coda waves are related to the distribution of elongated scatters in the oceanic crust. Through fitting the observed broadband waveforms and synthetics modeled with the 2-D FDM (Finite Difference Method), we obtain the preferred oceanic crustal velocity models for several sections in the subduction zone of eastern Alaska. The preferred models can explain the seismic phase arrival times, dispersions, and coda characteristics in the observed waveforms. With the obtained P- and S- wave models of velocity structures on several sections, the material compositions they represent are deduced, and the variations of oceanic crustal materials during subducting can be understood. This provides new evidence for studying the details of the subduction process in the subduction zone of eastern Alaska.

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Microearthquake S-wave observations from 0 to 1 km in the Varian well at Parkfield, California

Bulletin of the Seismological Society of America ◽

10.1785/bssa0850061805 ◽

1995 ◽

Vol 85 (6) ◽

pp. 1805-1820

Author(s):

Denis Jongmans ◽

Peter E. Malin

Keyword(s):

Fault Zone ◽

Guided Waves ◽

Velocity Structure ◽

San Andreas Fault ◽

High Gain ◽

S Wave ◽

Lateral Velocity ◽

Wave Amplification ◽

S Waves ◽

San Andreas

Abstract High-gain three-component seismometers from 0- to 1-km deep along the Varian A-1 well at Parkfield, California, were used to record the waveforms of nearby microearthquakes. Despite being in the thick Tertiary sediments of the Parkfield Syncline, the S-wave amplification at this site is only about a factor of 3. The spectral content and spectral ratios of S waves along the well show that the average Qs in the top 1 km at this site is 37, with the Qs in different subintervals varying between 8 and 65. Based on initial S-wave polarizations, a complex S-wave velocity structure must exist at and below the Varian site. This structure appears to include position-dependent anisotropy as well as steep lateral velocity gradients. At a depth of 1 km, S-wave splitting parallel and normal to the San Andreas fault zone is consistently observed. This splitting scales at roughly 0.01 sec/km. Subsequent to the split S waves, the particle motion seems to be controlled by event focal mechanism. Above 1 km, the upgoing S waves attenuate and change directions of polarization, with a new splitting rate of 0.1 sec/km. Uniquely, for some events on the San Andreas fault immediately below the Varian site, large, post-S-wave signals with normal dispersion are present. We propose that these phases are fault-zone guided waves channeled from the San Andreas fault to the Varian site along the Gold Hill fault.

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Validating the origin of microseismic events in target reservoir using guided waves recorded by DAS

The Leading Edge ◽

10.1190/tle39110776.1 ◽

2020 ◽

Vol 39 (11) ◽

pp. 776-784

Author(s):

Owen Huff ◽

Ariel Lellouch ◽

Bin Luo ◽

Ge Jin ◽

Biondo Biondi

Keyword(s):

Wave Energy ◽

Guided Waves ◽

Velocity Structure ◽

Guided Wave ◽

Accurate Estimation ◽

Low Velocity ◽

Eagle Ford ◽

Low Velocity Layer ◽

Microseismic Events ◽

Velocity Layer

We develop a new algorithm that uses guided-wave energy in distributed acoustic sensing (DAS) records to identify microseismic events originating within or very close to a shale reservoir. Guided waves are dispersive waves that propagate in a low-velocity layer bounded by two high-velocity layers. This is a geologic structure that is seen for some shale reservoirs, most notably the Eagle Ford. Only microseismic events originating within or close to the low-velocity layer will excite significant guided-wave energy, which can be observed in DAS records. We confirm the relationship between guided-wave energy and event depth relative to the reservoir by using synthetic modeling. Given the known velocity structure, we can predict the dispersion curves for guided waves and use them to separate body and guided waves. We demonstrate a method to quantify the amplitude of guided waves in field DAS data recorded directly above the Eagle Ford Shale. Using this technique, we can separate events that originate within or close to the Eagle Ford from events that do not, thus circumventing the large depth uncertainty in a microseismic catalog derived from surface geophones. Our analysis shows that events classified as originating within or close to the Eagle Ford are horizontally closer to the stimulating well than non-Eagle Ford events. This is interpreted as representing different hydraulic fracture geometries in the Eagle Ford compared to its bounding formations, the Buda Limestone and Austin Chalk. The application of our method yields a new catalog that highlights the events relevant to stimulation and production in the target reservoir. It also provides a strong depth constraint that can improve relocation attempts using surface data, enabling a more accurate estimation of stimulated rock volume geometry.

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Fault Zone Guided Wave generation on the locked, late interseismic Alpine Fault, New Zealand

10.26686/wgtn.13818791 ◽

2021 ◽

Author(s):

JD Eccles ◽

AK Gulley ◽

PE Malin ◽

CM Boese ◽

John Townend ◽

...

Keyword(s):

Fault Zone ◽

Plate Boundary ◽

Guided Wave ◽

S Wave ◽

Low Velocity ◽

Catchment Scale ◽

Near Surface ◽

Low Velocity Zone ◽

Alpine Fault ◽

Velocity Zone

© 2015. American Geophysical Union. All Rights Reserved. Fault Zone Guided Waves (FZGWs) have been observed for the first time within New Zealand's transpressional continental plate boundary, the Alpine Fault, which is late in its typical seismic cycle. Ongoing study of these phases provides the opportunity to monitor interseismic conditions in the fault zone. Distinctive dispersive seismic codas (~7-35Hz) have been recorded on shallow borehole seismometers installed within 20m of the principal slip zone. Near the central Alpine Fault, known for low background seismicity, FZGW-generating microseismic events are located beyond the catchment-scale partitioning of the fault indicating lateral connectivity of the low-velocity zone immediately below the near-surface segmentation. Initial modeling of the low-velocity zone indicates a waveguide width of 60-200m with a 10-40% reduction in S wave velocity, similar to that inferred for the fault core of other mature plate boundary faults such as the San Andreas and North Anatolian Faults.

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Assessment of low-velocity impact damage in composites by the measure of second-harmonic guided waves with the phase-reversal approach

Science Progress ◽

10.1177/0036850419881079 ◽

2019 ◽

Vol 103 (1) ◽

pp. 003685041988107 ◽

Cited By ~ 2

Author(s):

Weibin Li ◽

Chang Jiang ◽

Xinlin Qing ◽

Liangbing Liu ◽

Mingxi Deng

Keyword(s):

Guided Waves ◽

Second Harmonic ◽

Impact Damage ◽

Guided Wave ◽

Second Order ◽

Low Velocity Impact ◽

Low Velocity ◽

Velocity Impact ◽

Phase Reversal ◽

The Impact

Structural strength and integrity of composites can be considerably affected by the low-velocity impact damage due to the unique characteristics of composites, such as layering bonded by adhesive and the weakness to impact. For such damage, there is an urgent need to develop advanced nondestructive testing approaches. Despite the fact that the second harmonics could provide information sensitive to the structural health condition, the diminutive amplitude of the measured second-order harmonic guided wave still limits the applications of the second-harmonic generation–based nonlinear guided wave approach. Herein, laminated composites suffered from low-velocity impact are characterized by use of nonlinear guided waves. An enhancement in the signal-to-noise ratio for the measure of second harmonics is achieved by a phase-reversal method. Results obtained indicate a monotonic correlation between the impact-induced damage in composites and the relative acoustic nonlinear indicator of guided waves. The experimental finding in this study shows that the measure of second-order harmonic guided waves with a phase-reversal method can be a promising indicator to impact damage rendering in an improved and reliable manner.

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Temperature Effects on Guided Wave Structural Damage Detection

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.47-50.129 ◽

2008 ◽

Vol 47-50 ◽

pp. 129-132 ◽

Cited By ~ 1

Author(s):

Chan Yik Park ◽

Seung Moon Jun

Keyword(s):

Damage Detection ◽

Structural Damage ◽

Guided Waves ◽

Guided Wave ◽

Low Velocity Impact ◽

Structural Damage Detection ◽

Low Velocity ◽

Simple Method ◽

Temperature Changes ◽

Health Monitoring Systems

Guided wave structural damage detection is one of promising candidates for the future aircraft structural health monitoring systems. There are several advantages of guided wave based damage detection: well established theoretical studies, simple sensor devices, large sensing areas, good sensitivity, etc. However, guided wave approaches are still vulnerable to false warnings of detecting damage due to temperature changes of the structures. Therefore, one of main challenges is to find an effective way of compensating temperature changes and to imply it to existing damage detect algorithms. In this paper, a simple method for applying guided waves to the problem of detecting damage in the presence of temperature changes is presented. In order to examine the effectiveness of the presented method, delaminations due to low-velocity impact on composite plate specimens are detected. The results show that the presented approach is simple but useful for detecting structural damage under the temperature variations.

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Transmission and detection of guided seismic waves in attenuating media

Geophysics ◽

10.1190/1.1444419 ◽

1998 ◽

Vol 63 (4) ◽

pp. 1190-1199 ◽

Cited By ~ 4

Author(s):

Jorge O. Parra ◽

Brian J. Zook ◽

Pei‐Cheng Xu ◽

Raymon L. Brown

Keyword(s):

Seismic Waves ◽

Guided Waves ◽

Test Site ◽

Guided Wave ◽

Leaky Mode ◽

Head Wave ◽

British Petroleum ◽

Low Velocity ◽

Time Frequency ◽

Shaly Sandstone

We can use guided seismic waves to map properties of reservoirs between wells, with the low‐velocity layers acting as waveguides. When guided waves are detected, they are an indication of the continuity of the bed examined. Guided waveforms are characterized by time‐frequency representations to study important physical properties of the beds acting as waveguides. We used full waveform seismic modeling in viscoelastic media to examine the required velocity contrasts and distances over which guided‐wave signals can be used. In one set of models, sandstones are the central waveguide lithology; in another set, shales. We applied these models, referred to here collectively as shaly sandstone waveguides, to a range of geological circumstances where either the sands or the shales represent the low‐velocity layers within a reservoir. To study the distances over which guided waves can be detected, we compared the amplitudes of the signals computed for the models, using a realistic source strength, to the signal levels determined from published borehole noise studies. In shaly sandstone waveguides, we find it is feasible to use particle velocity measurements to record guided waves above seismic noise levels in the frequency range of 60 to 800 Hz at well separations exceeding a distance of 800 m. However, pressure detectors such as hydrophones may only be useful up to distances of 400 m between wells. In addition to the issues of shaly sandstone waveguides and practical distances between wells, we present an application of guided waves using crosswell seismic data from the Gypsy test site in Oklahoma (a site originally established by British Petroleum). In this field example within a sandstone reservoir, we demonstrate the sensitivity of leaky mode amplitudes to source‐receiver location. Another telltale characteristic of continuity in the type of reservoir studied at the Gypsy test site, where there is a low shear velocity contrast between the host medium and the waveguide, is the head wave followed by the leaky mode.

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An application of induced event interferometry approach at The Geysers Geothermal Field, California, USA

10.5194/egusphere-egu21-8312 ◽

2021 ◽

Author(s):

Taghi Shirzad ◽

Stanisław Lasocki ◽

Beata Orlecka‐Sikora

Keyword(s):

Velocity Structure ◽

General Structure ◽

Clean Energy ◽

Velocity Model ◽

Geothermal Field ◽

Small Scale ◽

Low Velocity ◽

Study Region ◽

Resultant Velocity ◽

The Geysers

While the classical tomography approaches, e.g., P-, S-, and/or surface-wave traveltime tomography, provide a general structure of the Earth&#8217;s interior, new developments in signal processing of interferometry approaches are needed to obtain a high-resolution velocity structure. If the number of earthquakes is adequate, the virtual seismometer method may be a solution in regions with sparse instrumental coverage. Theoretically, the empirical Green&#8217;s functions between a pair of events can be retrieved using earthquake&#8217;s cross-correlations. Here, an event interferometry approach was used on a very small scale around Prati-9 and Prati-29 injection wells in the NW of The Geysers Geothermal Field. The study region experienced intense injection-induced seismicity. We selected all events with location uncertainties less than 50 m in a cuboid of the horizontal side ~1 &#215; ~2 km and the vertical edge at depths between 1.0 and 2.0 km. The cuboid was cut into 100m thick layers, and we applied to events from each layer criteria enabling a quasi 2D approach. After calculating the Rayleigh wave group velocity dispersion curves, further processing was performed at a 0.2s period, selected based on the sensitivity kernel criterion. Finally, the relative velocity model of each layer at the depth z was obtained by subtracting the velocity model of the just overlying layer (at the depth z-100m) from the model of this layer. Our resultant velocity model in the study area indicated four low-velocity anomalies. The first one can be linked by the two layers interface topography variation at the top of the cuboid (depth 1000 m). The secondary faults can cause the second low-velocity anomaly. The other two anomalies look to result from fluid injection into Prati-9 and Prati-29 wells.&#160; This work was supported under the S4CE: "Science for Clean Energy" project, which has received funding from the European Union&#8217;s Horizon 2020 research and innovation program, under grant agreement No 764810.

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Seismic inversion of shale reservoir properties using microseismic-induced guided waves recorded by distributed acoustic sensing (DAS)

Geophysics ◽

10.1190/geo2020-0607.1 ◽

2021 ◽

pp. 1-58

Author(s):

Bin Luo ◽

Ariel Lellouch ◽

Ge Jin ◽

Biondo Biondi ◽

James Simmons

Keyword(s):

Hydraulic Fracturing ◽

Guided Waves ◽

Wave Dispersion ◽

Seismic Inversion ◽

Dispersion Relations ◽

Guided Wave ◽

Low Velocity ◽

Propagator Matrix ◽

Shale Formation ◽

Shale Reservoir

Shale formation properties are crucial for the hydrocarbon production performance of unconventional reservoirs. Microseismic-induced guided waves, which propagate within the low-velocity shale formation, are an ideal candidate for accurate estimation of the shale thickness, velocity, and anisotropy. A DAS fiber deployed along the horizontal section of a monitor well can provide a high-resolution recording of guided waves excited by microseismic events during hydraulic fracturing operations. These guided waves manifest a highly dispersive behavior that allows for seismic inversion of the shale formation properties. An adaptation of the propagator matrix method is presented to estimate guided wave dispersion curves and its accuracy is validated by comparison to 3-D elastic wavefield simulations. The propagator matrix formulation holds for cases of vertical transverse isotropy (VTI) as well. A sensitivity analysis of the theoretical dispersion relations of the guided waves shows that they are mostly influenced by the thickness and S-wave velocity of the low-velocity shale reservoir. The VTI parameters of the formation are also shown to have an impact on the dispersion relations. These physical insights provide the foundation for a dispersion-based model inversion for a 1-D depth-dependent structure of the reservoir and its surroundings. The inversion procedure is validated in a synthetic case and applied to the field records collected in an Eagle Ford hydraulic fracturing project. The inverted structure agrees well with a sonic log acquired several hundred meters away from the monitor well. Seismic inversion using guided wave dispersion therefore shows promise to become a novel and cost-effective strategy for in-situ estimation of reservoir structure and properties, which complements microseismic-based interpretation and production-related information.

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