Near-field strain in DAS-based microseismic observation

Microseismic monitoring with surface or downhole geophone arrays has been commonly used in tracking subsurface deformation and fracture networks during hydraulic fracturing operations. Recently, the use of fiber-optic DAS technology has improved microseismic acquisition to a new level with unprecedentedly high spatial resolution and low cost. Deploying fiber-optic cables in horizontal boreholes allows very close observation of these micro-sized earthquakes and captures their full wavefield details. We show that DAS-based microseismic profiles present a seldomly reported near-field strain signal between the P- and S-wave arrivals. This near-field signal shows monotonically increasing (or decreasing) temporal variation, which resembles the previously reported near-field observations of large earthquakes. To understand the near-field strain behavior, we provide a mathematical expression of the analytic normal strain solution that reveals the near-field, intermediate-near-field, intermediate-far-field, and far-field components. Synthetic DAS strain records of hydraulic-fracture-induced microseismic events can be generated using this analytic solution with the Brune source model. The polarity sign patterns of the near-field and far-field terms in these synthetics are linked to the corresponding source mechanism’s radiation patterns. These polarity sign patterns are demonstrated to be sensitive to the source orientations by rotating the moment tensor in different directions. A field data example is compared to the synthetic result and a qualitative match is shown. The microseismic near-field signals detected by DAS have potential value in hydraulic fracture monitoring by providing a means to better constrain microseismic source parameters that characterize the source magnitude, source orientation, and temporal source evolution, and therefore better reflect the geomechanical response of the hydraulically fractured environment in the unconventional reservoirs.

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Strain microseismics: Radiation patterns, synthetics, and moment tensor resolvability with distributed acoustic sensing in isotropic media

Geophysics ◽

10.1190/geo2019-0373.1 ◽

2020 ◽

Vol 85 (3) ◽

pp. KS101-KS114

Author(s):

Ismael Vera Rodriguez ◽

Andreas Wuestefeld

Keyword(s):

Moment Tensor ◽

Near Field ◽

Gauge Length ◽

P Wave ◽

Far Field ◽

S Wave ◽

Acoustic Sensing ◽

Moment Tensors ◽

Isotropic Media ◽

Distributed Acoustic Sensing

We have derived analytical formulations for the strain field produced by a moment tensor source in homogeneous isotropic media. Such formulations are important for microseismic projects that increasingly are monitored with fiber-optic distributed acoustic sensing (DAS) systems. We find that the spatial derivative of displacement produces new terms in strain proportional to [Formula: see text] with [Formula: see text]. In viscoelastic media, the derivative also produces an additional far-field term that is scaled by a frequency-dependent factor. When comparing with full wavefield synthetic data, we observe that the new terms proportional to [Formula: see text] can be considered part of a near-field in strain, similar to the practice with the displacement formulation. Analyses of moment tensor resolvability show that full moment tensors are resolvable with P-wave information from two or more noncoplanar vertical DAS cable geometries if intermediate- and far-field terms are considered and that S-wave information alone cannot constrain full moment tensors using only vertical wells. These results mirror previous observations made with displacement measurements. Furthermore, the addition of the new terms proportional to [Formula: see text] in strain improves the moment tensor resolvability but only in the case of a single vertical array. In the case of a single deviated/horizontal well, we can, in theory, resolve a full moment tensor but a case-by-case analysis is necessary to identify regions of full constraint around the well and the necessary noise conditions to guarantee reliable solutions. Real DAS measurements also are affected by the gauge length and interrogator details. In the case of the gauge length, we observe that this operator does not change the resolvability of the problem but it does affect inversion stability. The results derived here represent theoretical limits or in some cases specific examples. Practical implementations require analyses of conditioning, noise, coupling, and the effect of gauge length on a case-by-case basis.

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The waveform inversion of mainshock and aftershock data of the 2006 M6.3 Yogyakarta earthquake

Geoscience Letters ◽

10.1186/s40562-021-00176-w ◽

2021 ◽

Vol 8 (1) ◽

Author(s):

Hijrah Saputra ◽

Wahyudi Wahyudi ◽

Iman Suardi ◽

Ade Anggraini ◽

Wiwit Suryanto

Keyword(s):

Joint Inversion ◽

Body Wave ◽

Moment Tensor ◽

Near Field ◽

Source Parameters ◽

Waveform Inversion ◽

Moment Tensor Inversion ◽

Slip Distribution ◽

Aftershock Distribution ◽

Velocity Models

AbstractThis study comprehensively investigates the source mechanisms associated with the mainshock and aftershocks of the Mw = 6.3 Yogyakarta earthquake which occurred on May 27, 2006. The process involved using moment tensor inversion to determine the fault plane parameters and joint inversion which were further applied to understand the spatial and temporal slip distributions during the earthquake. Moreover, coseismal slip distribution was overlaid with the relocated aftershock distribution to determine the stress field variations around the tectonic area. Meanwhile, the moment tensor inversion made use of near-field data and its Green’s function was calculated using the extended reflectivity method while the joint inversion used near-field and teleseismic body wave data which were computed using the Kikuchi and Kanamori methods. These data were filtered through a trial-and-error method using a bandpass filter with frequency pairs and velocity models from several previous studies. Furthermore, the Akaike Bayesian Information Criterion (ABIC) method was applied to obtain more stable inversion results and different fault types were discovered. Strike–slip and dip-normal were recorded for the mainshock and similar types were recorded for the 8th aftershock while the 9th and 16th June were strike slips. However, the fault slip distribution from the joint inversion showed two asperities. The maximum slip was 0.78 m with the first asperity observed at 10 km south/north of the mainshock hypocenter. The source parameters discovered include total seismic moment M0 = 0.4311E + 19 (Nm) or Mw = 6.4 with a depth of 12 km and a duration of 28 s. The slip distribution overlaid with the aftershock distribution showed the tendency of the aftershock to occur around the asperities zone while a normal oblique focus mechanism was found using the joint inversion.

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Hydraulic Fracturing Diagnostics Utilizing Near and Far-Field Distributed Acoustic Sensing DAS Data Correspondences

10.2118/204205-ms ◽

2021 ◽

Author(s):

Yinghui Wu ◽

Robert Hull ◽

Andrew Tucker ◽

Craig Rice ◽

Peter Richter ◽

...

Keyword(s):

Hydraulic Fracture ◽

Near Field ◽

Fracture Propagation ◽

Cost Effective ◽

Hydraulic Fractures ◽

Far Field ◽

Distributed Temperature Sensing ◽

Acoustic Sensing ◽

Distributed Acoustic Sensing ◽

Multiple Fibers

Abstract Distributed fiber-optic sensing (DFOS) has been utilized in unconventional reservoirs for hydraulic fracture efficiency diagnostics for many years. Downhole fiber cables can be permanently installed external to the casing to monitor and measure the uniformity and efficiency of individual clusters and stages during the completion in the near-field wellbore environment. Ideally, a second fiber or multiple fibers can be deployed in offset well(s) to monitor and characterize fracture geometries recorded by fracture-driven interactions or frac-hits in the far-field. Fracture opening and closing, stress shadow creation and relaxation, along with stage isolation can be clearly identified. Most importantly, fracture propagation from the near to far-field can be better understood and correlated. With our current technology, we can deploy cost effective retrievable fibers to record these far-field data. Our objective here is to highlight key data that can be gathered with multiple fibers in a carefully planned well-spacing study and to evaluate and understand the correspondence between far-field and near-field Distributed Acoustic Sensing (DAS) data. In this paper, we present a case study of three adjacent horizontal wells equipped with fiber in the Permian basin. We can correlate the near-field fluid allocation across a stage down to the cluster level to far-field fracture driven interactions (FDIs) with their frac-hit strain intensity. With multiple fibers we can evaluate fracture geometry, the propagation of the hydraulic fractures, changes in the deformation related to completion designs, fracture complexity characterization and then integrate the results with other data to better understand the geomechanical processes between wells. Novel frac-hit corridor (FHC) is introduced to evaluate stage isolation, azimuth, and frac-hit intensity (FHI), which is measured in far-field. Frac design can be evaluated with the correlation from near-field allocation to far-field FHC and FHI. By analyzing multiple treatment and monitor wells, the correspondence can be further calibrated and examined. We observe the far-field FHC and FHI are directly related to the activities of near-field clusters and stages. A leaking plug may directly result in FHC overlapping, gaps and variations in FHI, which also can be correlated to cluster uniformity. A near-far field correspondence can be established to evaluate FHC and FHI behaviors. By utilizing various completion designs and related measurements (e.g. Distributed Temperature Sensing (DTS), gauges, microseismic etc.), optimization can be performed to change the frac design based on far-field and near-field DFOS data based on the Decision Tree Method (DTM). In summary, hydraulic fracture propagation can be better characterized, measured, and understood by deploying multiple fibers across a lease. The correspondence between the far-field measured FHC and FHI can be utilized for completion evaluation and diagnostics. As the observed strain is directly measured, completion engineering and geoscience teams can confidently optimize their understanding of the fracture designs in real-time.

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Far-field tsunami data assimilation for the 2015 Illapel earthquake

Geophysical Journal International ◽

10.1093/gji/ggz309 ◽

2019 ◽

Vol 219 (1) ◽

pp. 514-521 ◽

Cited By ~ 4

Author(s):

Y Wang ◽

K Satake ◽

R Cienfuegos ◽

M Quiroz ◽

P Navarrete

Keyword(s):

Data Assimilation ◽

Near Field ◽

Source Parameters ◽

Deep Ocean ◽

Seismic Source ◽

Far Field ◽

Complementary Method ◽

East Pacific ◽

2015 Illapel Earthquake ◽

Illapel Earthquake

SUMMARY The 2015 Illapel earthquake (Mw 8.3) occurred off central Chile on September 16, and generated a tsunami that propagated across the Pacific Ocean. The tsunami was recorded on tide gauges and Deep-ocean Assessment and Reporting of Tsunami (DART) tsunameters in east Pacific. Near-field and far-field tsunami forecasts were issued based on the estimation of seismic source parameters. In this study, we retroactively evaluate the potentiality of forecasting this tsunami in the far field based solely on tsunami data assimilation from DART tsunameters. Since there are limited number of DART buoys, virtual stations are assumed by interpolation to construct a more complete tsunami wavefront for data assimilation. The comparison between forecasted and observed tsunami waveforms suggests that our method accurately forecasts the tsunami amplitudes and arrival time in the east Pacific. This approach could be a complementary method of current tsunami warning systems based on seismic observations.

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Near-field strain observations of the October 2013 Ruisui, Taiwan, earthquake: source parameters and limits of very short-term strain detection

Earth Planets and Space ◽

10.1186/s40623-015-0284-1 ◽

2015 ◽

Vol 67 (1) ◽

Cited By ~ 15

Author(s):

Alexandre Canitano ◽

Ya-Ju Hsu ◽

Hsin-Ming Lee ◽

Alan T. Linde ◽

Selwyn Sacks

Keyword(s):

Near Field ◽

Source Parameters ◽

Earthquake Source ◽

Field Strain ◽

Short Term ◽

Earthquake Source Parameters ◽

Taiwan Earthquake ◽

Strain Detection

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Quick determination of earthquake source parameters from GPS measurements: a study of suitability for Taiwan

Geophysical Journal International ◽

10.1093/gji/ggz359 ◽

2019 ◽

Vol 219 (2) ◽

pp. 1148-1162

Author(s):

Jiun-Ting Lin ◽

Wu-Lung Chang ◽

Diego Melgar ◽

Amanda Thomas ◽

Chi-Yu Chiu

Keyword(s):

Rapid Determination ◽

Moment Tensor ◽

Near Field ◽

Source Parameters ◽

Early Warning Systems ◽

Earthquake Magnitude ◽

Observation System ◽

Earthquake Source Parameters ◽

Finite Fault

SUMMARY We test the feasibility of GPS-based rapid centroid moment tensor (GPS CMT) methods for Taiwan, one of the most earthquake prone areas in the world. In recent years, Taiwan has become a leading developer of seismometer-based earthquake early warning systems, which have successfully been applied to several large events. The rapid determination of earthquake magnitude and focal mechanism, important for a number of rapid response applications, including tsunami warning, is still challenging because of the limitations of near-field inertial recordings. This instrumental issue can be solved by an entirely different observation system: a GPS network. Taiwan is well posed to take advantage of GPS because in the last decade it has developed a very dense network. Thus, in this research, we explore the suitability of the GPS CMT inversion for Taiwan. We retrospectively investigate six moderate to large (Mw6.0 ∼ 7.0) earthquakes and propose a resolution test for our model, we find that the minimum resolvable earthquake magnitude of this system is ∼Mw5.5 (at 5 km depth). Our tests also suggest that the finite fault complexity, often challenging for the near-field methodology, can be ignored under such good station coverage and thus, can provide a fast and robust solution for large earthquake directly from the near field. Our findings help to understand and quantify how the proposed methodology could be implemented in real time and what its contributions could be to the overall earthquake monitoring system.

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Accuracy of the moment-tensor inversion of far-field P waves

Geophysical Journal International ◽

10.1093/gji/ggz446 ◽

2019 ◽

Vol 220 (1) ◽

pp. 248-256 ◽

Cited By ~ 1

Author(s):

Yue Kong ◽

Min Li ◽

Weimin Chen ◽

Boqi Kang

Keyword(s):

Moment Tensor ◽

Near Field ◽

Radial Component ◽

Moment Tensor Inversion ◽

Far Field ◽

Field Range ◽

P Waves ◽

Moment Tensors ◽

Nodal Lines ◽

The Moment

SUMMARY The far-field assumption is widely used and suitable for the moment-tensor inversion in which the source–receiver distance is quite long. However, the description of far field is uncertain and an explicit far-field range is missing. In this study, the explicit far-field range is determined and the errors of moment-tensor solutions produced by the far-field approximation are analysed. The distance, for which the far-field assumption is satisfied and the effect of the near-field term can be ignored, is directionally dependent. For the shear dislocation, in the directions near the nodal lines of the far-field P waves, the far-field distance is heavily dependent on the displacement component used to invert moment tensors. The radial component of displacement, which is parallel to the wave propagation direction, is recommended for the inversion and the corresponding far-field distance is quite short. In the directions far from the nodal lines, the selection of displacement components has little influence on the far-field distance. The maximum far-field distance appears in the directions of the pressure and tensile axes of the source and the value is about 30 wavelengths of radiated waves. Using more receivers (>6) in the moment-tensor inversion can shorten the far-field distance. The effect of the near-field term on the moment-tensor inversion for tensile dislocations and isotropic sources (explosion or implosion) can be ignored. The conclusions obtained in this study are helpful for determining the positions of receivers and evaluating the accuracy of moment-tensor solutions, with far-field assumption being applied in the inversion.

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Realtime Wellbore Digitalization for Stimulations Using Multi-Well Fiber Optics

10.2118/207710-ms ◽

2021 ◽

Author(s):

Xinyang Li ◽

Andres J. Chavarria ◽

Yassine Oukaci

Keyword(s):

Real Time ◽

Fiber Optics ◽

Near Field ◽

Fracture Propagation ◽

Field Strain ◽

Far Field ◽

Time Data ◽

Strain Measurements ◽

Well Stimulation ◽

Time Operation

Abstract Distributed Fiber-optic Sensing (DFOS) provides real-time data acquisition, monitoring and diagnostics for well stimulation and well spacing assessment. These include measurements of Distributed Acoustic Sensing (DAS) with high frequency acoustics in treatment wells, and low frequency strain/temperature sensing in offset monitor ones. The goal of this integrated study is to show the value of multi-well fiber sensing for real time fracturing diagnostics and stimulation optimization. By integrating near field injection to far field strain responses we assess overall reservoir development. The availability of fibers on both the treatment well and a nearby observation well allows us to investigate the near-wellbore injection profile and the far-field strain fracture propagation. Quantitative strain levels clearly respond to the effects of well distance, location and treatment well stimulation design. Monitoring well strain measurements of fracture density and triggered stimulated span were logged and compared to acoustic signals in the nearfield stage by stage. DAS interpretation was conducted during the treatment of each stage indicating the effectiveness and efficiency of the completion design. Results show that this is a very effective tool to better understand the performance of the fracturing treatment by digital transformation using DAS data. In addition, acoustic and strain measurements also validated its diagnostic capability for real-time operation monitoring. In this presentation we show how the near-field acoustic and far-field strain measurements allow for better understanding of the completion efficiency. This is by assessing the far field response to quantified DAS injected signals in the treatment. This analysis takes advantage of fiber installation on both the treatment and nearby monitor well. The fluid and proppant allocations in the near field were performed on the treatment well using relative acoustic intensities. Meanwhile, the fracture propagation induced strain change is recorded by the offset fiber well. Using this fiber data reveals dominant clusters and stage bias from near-field injection profile. Simultaneously the far-field identified fracture counts from strain further enable a geomechanical assessment of the stimulated reservoir and assess the effectiveness of the completion design. Multiple DAS fiber equipped wells not only provide single diagnostic tool for each of the fiber well, but also demonstrate significant integrated assessment of the stimulation effectiveness, completion efficiency, well interaction, and reservoir description. Availability of near and far field measurements constitutes an important tool to assess properties of the reservoir. Here we show how different vantage points can help illuminate a fracturing program in unconventional reservoirs.

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Calibration of MEMS Strain Sensors Fabricated on Silicon

10.1115/imece2001/mems-23856 ◽

2001 ◽

Author(s):

Li Cao ◽

Chuck Hautamaki ◽

Jia Zhou ◽

Tae Song Kim ◽

Sue Mantell

Keyword(s):

Silicon Wafer ◽

Near Field ◽

Strain Sensor ◽

Field Strain ◽

Sensor Calibration ◽

Far Field ◽

Calibration Technique ◽

Gage Factor ◽

Mems Sensor ◽

Aluminum Specimen

Abstract A calibration technique for measuring MEMS strain sensor performance is described. The sensor calibration technique entails developing a repeatable relationship (gage factor) between the change in sensor nominal resistance and the strain measured at the sensor. The calibration technique involves creating a “pseudo” strain sensor consisting of a strain gage mounted on a silicon wafer. Two identical test specimens are evaluated: the pseudo sensor mounted (with adhesive) on an aluminum specimen (or embedded in a specimen), and a MEMS strain sensor mounted on an aluminum specimen (or embedded in a specimen). The dimensions of the silicon wafer for both the pseudo sensor and MEMS sensor are identical. The specimens are loaded by tensile test. For the pseudo sensor specimen, a relationship is established between the strain applied to the specimen (far field strain) and the strain at the sensor (near field strain). Once the relationship between near field and far field strain is known, a relationship between near field strain and change in resistance of the uncalibrated MEMs sensor is established. This relationship between strain at the sensor and change in resistance is the gage factor. Two different MEMS strain sensor designs were fabricated by patterning polysilicon on a 500 micron thick silicon wafer: monofilament and membrane sensors. Gage factors for the MEMS sensors were determined following the calibration procedure. The results also lead to a conclusion that wafer geometry influences the strain transfer to the sensor.

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Expected impact of the 2016 central Italy earthquakes on the local gravity field

10.5194/egusphere-egu2020-7083 ◽

2020 ◽

Author(s):

Federica Riguzzi ◽

Hongbo Tan ◽

Chong-yang Shen

Keyword(s):

Gravity Field ◽

Half Space ◽

Near Field ◽

Source Parameters ◽

Central Italy ◽

Far Field ◽

Dislocation Theory ◽

Local Gravity ◽

Vertical Displacements ◽

Gnss Observations

We have modelled the surface volume and gravity changes caused by the three mainshocks (moment magnitudes Mw 6.0, 5.9, 6.5) occurred during the last seismic period started on 2016, August 24 in central Italy. Our calculations start from the source parameters estimated by the inversion of the largest dataset of InSAR and GNSS observations ever managed in Italy after earthquake occurrences, based on the half-space elastic dislocation theory. The vertical displacements modelled after the 2016 events allow to infer a substantial unbalance between the subsided and uplifted volumes. In particular, we detected ~106&#8729;106 m3 of hangingwall subsidence against ~37&#8729;106 m3 of footwall uplift, that accounts for ~74% of the total volume mobilization. From the ratio between the footwall and total deformed volumes, we have computed an average fault dip of ~47&#176;, in line with the values retrieved by seismological methods. The total gravity variations which affected the study area are of the order of ~1 &#956;Gal (1 &#956;Gal = 10&#8722;8 ms&#8722;2) in the far field, and ~170 &#956;Gal in the near field. The area affected within a gravity change of 1 &#956;Gal is ~140 km long and ~57 km wide, parallel to the Apennines chain. The larger contribution is given by positive variations which account for the tensional style of deformation and larger subsided area.

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