scholarly journals Focal mechanism determination of induced microearthquakes in an oil field using full waveforms from shallow and deep seismic networks

Geophysics ◽  
2011 ◽  
Vol 76 (6) ◽  
pp. WC87-WC101 ◽  
Author(s):  
Junlun Li ◽  
H. Sadi Kuleli ◽  
Haijiang Zhang ◽  
M. Nafi Toksöz
Keyword(s):  
Current Knowledge ◽  
Waveform Inversion ◽  
Local Stress ◽  
Focal Mechanisms ◽  
Oil Field ◽  
P Wave ◽  
Stress Regime ◽  
Direction Parallel ◽  
Near Surface ◽  
Seismic Networks

A new, relatively high frequency, full waveform matching method was used to study the focal mechanisms of small, local earthquakes induced in an oil field, which are monitored by a sparse near-surface network and a deep borehole network. The determined source properties are helpful for understanding the local stress regime in this field. During the waveform inversion, we maximize both the phase and amplitude matching between the observed and modeled waveforms. We also use the polarities of the first P-wave arrivals and the average S/P amplitude ratios to better constrain the matching. An objective function is constructed to include all four criteria. For different hypocenters and source types, comprehensive synthetic tests showed that our method is robust enough to determine the focal mechanisms under the current array geometries, even when there is considerable velocity inaccuracy. The application to several tens of induced microseismic events showed satisfactory waveform matching between modeled and observed seismograms. Most of the events have a strike direction parallel with the major northeast-southwest faults in the region, and some events trend parallel with the northwest-southeast conjugate faults. The results are consistent with the in situ well breakout measurements and the current knowledge on the stress direction of this region. The source mechanisms of the studied events, together with the hypocenter distribution, indicate that the microearthquakes are caused by the reactivation of preexisting faults. We observed that the faulting mechanism varies with depth, from strike-slip dominance at shallower depth to normal faulting dominance at greater depth.

scholarly journals Near-surface attenuation estimation using wave-propagation modeling

Geophysics ◽  
2008 ◽  
Vol 73 (6) ◽  
pp. U27-U37 ◽  
Author(s):  
Nizare El Yadari ◽  
Fabian Ernst ◽  
Wim Mulder
Keyword(s):  
Wave Attenuation ◽  
Waveform Inversion ◽  
Real Data ◽  
P Wave ◽  
Surface Model ◽  
Near Surface ◽  
Propagation Modeling ◽  
Static Corrections ◽  
Starting Model ◽  
Wave Propagation Modeling

The effect of the near surface on seismic land data can be so severe that static corrections are insufficient. Full-waveform inversion followed by redatuming may be an alternative, but inversion will work only if the starting model is sufficiently close to the true model. As a first step toward determining a viscoelastic near-surface model, we assume that existing methods can provide a horizontally layered velocity and density model. Because near-surface attenuation is strongest, we propose a method to estimate the P-wave attenuation based on viscoacoustic finite-difference modeling. We compare energy decay along traveltime curves of reflection and refraction events in the modeled and observed seismic data for a range of attenuation parameters. The best match provides an estimate of the attenuation. First, we estimate only the attenuation of the top layer and study the sensitivity to depth and velocity perturbations. Then, we consider multiple layers. We apply the method to synthetic and real data and investigate the effect of source wavelet and topography. The method is robust against depth and velocity perturbations smaller than 10%. The results are sensitive to the source wavelet. Incorporating the surface topography in the computed traveltimes reduces the uncertainty of the attenuation estimates, especially for deeper layers.

Challenges in shallow targets reconstruction by 3D elastic full-waveform inversion — Which initial model?

Geophysics ◽  
2021 ◽  
pp. 1-91
Author(s):  
Daniela Teodor ◽  
Cesare Cesare ◽  
Farbod Khosro Anjom ◽  
Romain Brossier ◽  
Valentina Socco Laura ◽  
...  
Keyword(s):  
Field Data ◽  
Weighting Function ◽  
Waveform Inversion ◽  
P Wave ◽  
Full Waveform Inversion ◽  
Initial Model ◽  
Near Surface ◽  
Velocity Models ◽  
Full Waveform ◽  
3D Acquisition

Elastic full-waveform inversion (FWI) is a powerful tool for high-resolution subsurface multi-parameter characterization. However, 3D FWI applied to land data for near-surface applications is particularly challenging, since the seismograms are dominated by highly energetic, dispersive, and complex-scattered surface waves (SWs). In these conditions, a successful deterministic FWI scheme requires an accurate initial model. This study, primarily focused on field data analysis for 3D applications, aims at enhancing the resolution in the imaging of complex shallow targets, by integrating devoted SW analysis techniques with a 3D spectral-element-based elastic FWI. From dispersion curves (DCs), extracted from seismic data recorded over a sharp-interface shallow target, we built different initial S-wave (VS) and P-wave (VP) velocity models (laterally homogeneous and laterally variable), using a specific data-transform. Starting from these models, we carry out 3D FWI tests on synthetic and field data, using a relatively straightforward inversion scheme. The field data processing before FWI consists of bandpass filtering and muting of noisy traces. During FWI, a weighting function is applied to the far-offset traces. We test both 2D and 3D acquisition layouts, with different positions of the sources and variable offsets. The 3D FWI workflow enriched the overall content of the initial models, allowing a reliable reconstruction of the shallow target, especially when using laterally variable initial models. Moreover, a 3D acquisition layout guaranteed a better reconstruction of the target’s shape and lateral extension. In addition, the integration of model-oriented (preliminary monoparametric FWI) and data-oriented (time-windowing) strategies into the main optimization scheme has granted further improvement of the FWI results.

Seismic reprocessing and interpretation of a fractured-basement play: Texas Panhandle

2017 ◽  
Vol 5 (3) ◽  
pp. SK179-SK187 ◽  
Author(s):  
Thang Ha ◽  
Kurt Marfurt
Keyword(s):  
Horizontal Stress ◽  
Wave Impedance ◽  
Azimuthal Anisotropy ◽  
Oil Field ◽  
P Wave ◽  
Coherent Noise ◽  
Seismic Attribute ◽  
Gas Field ◽  
Direction Parallel ◽  
Head Waves

The Panhandle-Hugoton field, of Texas, Oklahoma, and Kansas, is a giant oil field and is the largest conventional gas field in North America. Most hydrocarbon production in this field comes from the Wichita Uplift area, where the basement is the most shallow. Although the field has been extensively produced, many local hydrocarbon accumulations have not been fully exploited. Recent drilling activity in the survey indicates that some wells produce directly from basement fractures, suggesting a new play type for the area. Because the target is shallow, the seismic data are heavily contaminated by coherent noise, such as ground roll and head waves, creating challenges for seismic processing. To improve the seismic interpretation, we carefully reprocessed the field gathers resulting in improved correlation within the sedimentary and the basement sections. Correlating well control to seismic attribute volumes indicates that a fractured basement gives rise to lower P-wave impedance and strong amplitude versus azimuth anomalies. The azimuthal anisotropy is strongest in a direction parallel to the regional maximum horizontal stress, suggesting that these fractures are open. Coherence anomalies indicate a rugose basement surface, whereas curvature shows two lineament sets, consistent with the weathering and fractured exposure of basement in the Wichita Mountains to the southeast.

scholarly journals Seismotectonics and 1-D velocity model of the Greater Geneva Basin, France–Switzerland

2020 ◽  
Vol 221 (3) ◽  
pp. 2026-2047 ◽  
Author(s):  
Verónica Antunes ◽  
Thomas Planès ◽  
Jiří Zahradník ◽  
Anne Obermann ◽  
Celso Alvizuri ◽  
...  
Keyword(s):  
Large Scale ◽  
Waveform Inversion ◽  
Broad Band ◽  
Velocity Model ◽  
Strike Slip ◽  
P Wave ◽  
Tectonic Structures ◽  
Stress Regime ◽  
Geothermal Exploration ◽  
Velocity Models

SUMMARY The Greater Geneva Basin (GGB), located in southwestern Switzerland and neighboring France, is enclosed by the rotating northwestern edge of the Alpine front and the Jura mountains chain. Recently, this basin has received increasing attention as a target for geothermal exploration. Historical and instrumental seismicity suggest that faults affecting the basin may still be active. Moderate-magnitude earthquakes have been located along the Vuache fault, a major strike-slip structure crossing the basin. Before geothermal exploration starts, it is key to evaluate the seismic rate in the region and identify possible seismogenic areas. In this context, we deployed a temporary seismic network of 20 broad-band stations (from September 2016 to January 2018) to investigate the ongoing seismic activity, its relationship with local tectonic structures, and the large-scale kinematics of the area. Our network lowered the magnitude of completeness of the permanent Swiss and French networks from 2.0 to a theoretical value of 0.5. Using a new coherence-based detector (LASSIE - particularly effective to detect microseismicity in noisy environments), we recorded scarce seismicity in the basin with local magnitudes ranging from 0.7 to 2.1 ML. No earthquakes were found in the Canton of Geneva where geothermal activities will take place. We constructed a local ’minimum 1-D P-wave velocity model’ adapted to the GGB using earthquakes from surrounding regions. We relocated the events of our catalogue obtaining deeper hypocentres compared to the locations obtained using the available regional velocity models. We also retrieved eight new focal mechanisms using a combination of polarities and waveform inversion techniques (CSPS). The stress inversion shows a pure strike-slip stress regime, which is in agreement with structural and geological data. Combining the background seismicity with our catalogue, we identified seismogenic areas offsetting the basin.

scholarly journals Sicily and southern Calabria focal mechanism database: a valuable tool for local and regional stress-field determination

2013 ◽  
Vol 56 (1) ◽  
Author(s):  
Luciano Scarfì ◽  
Alfio Messina ◽  
Carmelo Cassisi
Keyword(s):  
Focal Mechanisms ◽  
P Wave ◽  
Stress Fields ◽  
Fault Plane Solutions ◽  
Stress Regime ◽  
Seismogenic Structures ◽  
Different Depths ◽  
Tectonic Lineament ◽  
Regional Tectonics

<p>In this work, we present a new catalog of focal mechanisms calculated for earthquakes recorded in Sicily and southern Calabria. It comprises about 300 solutions, for events with magnitudes ranging from 2.7 to 4.8 that occurred from 1999 to 2011. We used P-wave polarities to compute the fault-plane solutions. Two main goals are achieved. For the first, the catalog allows the stress regime and kinematics characterizing the studied area to be depicted at a regional and more local scale. In particular, moving along the tectonic lineament that extends from the Aeolian Islands to the Ionian Sea, there is a change from a regime characterized by sub-horizontal P-axes, ca. NW-SE directed, to an extensive one in the Calabro-Peloritan Arc, where T-axes striking in a NW-SE direction prevail. Our results also show that part of the seismicity is clustered along the main active seismogenic structures, of which the focal mechanisms indicate the kinematics. Finally, in the Etna volcano area, different stress fields act at different depths due to the combination of the regional tectonics, the strong pressurization of the deep magmatic system, and the dynamics of the shallower portion of the volcano. As a second goal, we highlight that the catalog also represents a valuable tool, through the data distribution on the internet, for further studies directed towards improving our understanding of the geodynamic complexity of the region, and for a better characterization of the seismogenic sources.</p>

Detecting a known near-surface target through application of frequency-dependent traveltime tomography and full-waveform inversion to P- and SH-wave seismic refraction data

Geophysics ◽  
2017 ◽  
Vol 82 (1) ◽  
pp. R1-R17 ◽  
Author(s):  
Jianxiong Chen ◽  
Colin A. Zelt ◽  
Priyank Jaiswal
Keyword(s):  
Waveform Inversion ◽  
P Wave ◽  
Sh Wave ◽  
Void Space ◽  
Near Surface ◽  
Traveltime Tomography ◽  
Velocity Anomaly ◽  
Velocity Models ◽  
Full Waveform ◽  
Wave Models

We have applied a combined workflow of frequency-dependent traveltime tomography (FDTT) and full-waveform inversion (FWI) to 2D near-surface P- and SH-wave seismic data to detect a known target consisting of a buried tunnel with concrete walls and a void space inside. FDTT inverted the P- and SH-wave picked traveltimes at 250 Hz to provide long-wavelength background velocity models as the starting models for FWI. FWI inverted 18–54 Hz P-wave data and 16–50 Hz SH-wave data to produce velocity models with subwavelength- and wavelength-scale features allowing for direct interpretation of the velocity models as is usually carried out in conventional imaging using seismic reflection data. The P- and SH-wave models image the top part of the tunnel at the correct location at a depth of 1.6 m as a high-velocity anomaly. The P-wave models also image the air in the void space of the tunnel as a low-velocity anomaly. The inverted models were assessed by synthetic tests, the consistency of the inverted sources, and the fit between the predicted and observed data. As a comparison, conventional ray-theory infinite-frequency traveltime tomography (IFTT) was also applied in a combined workflow with FWI. The comparisons of the inverted models favor the use of FDTT over IFTT because (1) The FDTT models better recover the magnitude of the velocity anomalies and (2) the FDTT model serves as a better starting model for FWI, which results in a more accurate FWI velocity estimation with better recovery of the magnitude and location of the key features. FDTT will not provide significant benefits over IFTT in all studies, particularly those in which ray theory is valid.

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