Influence of Small-Scale Lateral Heterogeneity on Seismic Velocity Analysis and Time-to-Depth Conversion

2014 ◽  
Author(s):  
Mamoru Takanashi
Keyword(s):  
Seismic Velocity ◽  
Small Scale ◽  
Velocity Analysis ◽  
Lateral Heterogeneity

Migration velocity analysis for TI media in the presence of quadratic lateral velocity variation

Geophysics ◽  
2012 ◽  
Vol 77 (6) ◽  
pp. U87-U96 ◽  
Author(s):  
Mamoru Takanashi ◽  
Ilya Tsvankin
Keyword(s):  
Migration Velocity ◽  
P Wave ◽  
Velocity Variation ◽  
Small Scale ◽  
Velocity Analysis ◽  
Lateral Heterogeneity ◽  
Lateral Velocity ◽  
Symmetry Direction ◽  
Migration Velocity Analysis ◽  
Ti Media

One of the most serious problems in anisotropic velocity analysis is the trade-off between anisotropy and lateral heterogeneity, especially if velocity varies on a scale smaller than the maximum offset. We have developed a P-wave MVA (migration velocity analysis) algorithm for transversely isotropic (TI) models that include layers with small-scale lateral heterogeneity. Each layer is described by constant Thomsen parameters [Formula: see text] and [Formula: see text] and the symmetry-direction velocity [Formula: see text] that varies as a quadratic function of the distance along the layer boundaries. For tilted TI media (TTI), the symmetry axis is taken orthogonal to the reflectors. We analyzed the influence of lateral heterogeneity on image gathers obtained after prestack depth migration and found that quadratic lateral velocity variation in the overburden can significantly distort the moveout of the target reflection. Consequently, medium parameters beneath the heterogeneous layer(s) are estimated with substantial error, even when borehole information (e.g., check shots or sonic logs) is available. Because residual moveout in the image gathers is highly sensitive to lateral heterogeneity in the overburden, our algorithm simultaneously inverts for the interval parameters of all layers. Synthetic tests for models with a gently dipping overburden demonstrate that if the vertical profile of the symmetry-direction velocity [Formula: see text] is known at one location, the algorithm can reconstruct the other relevant parameters of TI models. The proposed approach helps increase the robustness of anisotropic velocity model-building and enhance image quality in the presence of small-scale lateral heterogeneity in the overburden.

High-resolution seismic velocity analysis by sign-based weighted semblance

Geophysics ◽  
2021 ◽  
pp. 1-35
Author(s):  
M. Javad Khoshnavaz
Keyword(s):  
Seismic Velocity ◽  
Resolution Enhancement ◽  
Synthetic Data ◽  
Correlation Coefficients ◽  
Velocity Model ◽  
Seismic Attenuation ◽  
Velocity Analysis ◽  
Velocity Models ◽  
Amplitude Versus Offset ◽  
Amplitude Versus

Building an accurate velocity model plays a vital role in routine seismic imaging workflows. Normal-moveout-based seismic velocity analysis is a popular method to make the velocity models. However, traditional velocity analysis methodologies are not generally capable of handling amplitude variations across moveout curves, specifically polarity reversals caused by amplitude-versus-offset anomalies. I present a normal-moveout-based velocity analysis approach that circumvents this shortcoming by modifying the conventional semblance function to include polarity and amplitude correction terms computed using correlation coefficients of seismic traces in the velocity analysis scanning window with a reference trace. Thus, the proposed workflow is suitable for any class of amplitude-versus-offset effects. The approach is demonstrated to four synthetic data examples of different conditions and a field data consisting a common-midpoint gather. Lateral resolution enhancement using the proposed workflow is evaluated by comparison between the results from the workflow and the results obtained by the application of conventional semblance and three semblance-based velocity analysis algorithms developed to circumvent the challenges associated with amplitude variations across moveout curves, caused by seismic attenuation and class II amplitude-versus-offset anomalies. According to the obtained results, the proposed workflow is superior to all the presented workflows in handling such anomalies.

scholarly journals Effect of centimetric freezing of the near subsurface on Rayleigh and Love wave velocity in ambient seismic noise correlations

2020 ◽  
Vol 224 (1) ◽  
pp. 626-636
Author(s):  
René Steinmann ◽  
Céline Hadziioannou ◽  
Eric Larose
Keyword(s):  
Surface Wave ◽  
Wave Velocity ◽  
Love Wave ◽  
Ambient Noise ◽  
Seismic Velocity ◽  
Environmental Parameters ◽  
Velocity Variation ◽  
Small Scale ◽  
Apparent Velocity ◽  
Velocity Variations

SUMMARY About a decade ago, noise-based monitoring became a key tool in seismology. One of the tools is passive image interferometry (PII), which uses noise correlation functions (NCF) to retrieve seismic velocity variations. Most studies apply PII to vertical components recording oceanic low-frequent ambient noise ( < 1 Hz). In this work, PII is applied to high-frequent urban ambient noise ( > 1 Hz) on three three-component sensors. With environmental sensors inside the subsurface and in the air, we are able to connect observed velocity variations with environmental parameters. Temperatures below 0 °C correlate well with strong shear wave velocity increases. The temperature sensors inside the ground suggest that a frozen layer of less than 5 cm thickness causes apparent velocity increases above 2  % , depending on the channel pair. The observations indicate that the different velocity variation retrieved from the different channel pairs are due to different surface wave responses inherent in the channel pairs. With dispersion curve modelling in a 1-D medium we can verify that surfaces waves of several tens of metres wavelength experience a velocity increase of several percent due to a centimetres thick frozen layer. Moreover, the model verifies that Love waves show larger velocity increases than Rayleigh waves. The findings of this study provide new insights for monitoring with PII. A few days with temperature below 0 °C can already mask other potential targets (e.g. faults or storage sites). Here, we suggest to use vertical components, which is less sensitive to the frozen layer at the surface. If the target is the seasonal freezing, like in permafrost studies, we suggest to use three-component sensors in order to retrieve the Love wave response. This opens the possibility to study other small-scale processes at the shallow subsurface with surface wave responses.

scholarly journals Continuous active-source seismic monitoring of C O2 injection in a brine aquifer

Geophysics ◽  
2007 ◽  
Vol 72 (5) ◽  
pp. A57-A61 ◽  
Author(s):  
Thomas M. Daley ◽  
Ray D. Solbau ◽  
Jonathan B. Ajo-Franklin ◽  
Sally M. Benson
Keyword(s):  
Seismic Velocity ◽  
Seismic Monitoring ◽  
Small Scale ◽  
Saline Aquifer ◽  
Observation Well ◽  
Velocity Change ◽  
Seismic Velocity Change ◽  
Fluid Sampling ◽  
Brine Aquifer

Continuous crosswell seismic monitoring of a small-scale [Formula: see text] injection was accomplished with the development of a novel tubing-deployed piezoelectric borehole source. This piezotube source was deployed on the [Formula: see text] injection tubing, near the top of the saline aquifer reservoir at [Formula: see text] depth, and allowed acquisition of crosswell recordings at [Formula: see text] intervals during the multiday injection. The change in traveltime recorded at various depths in a nearby observation well allowed hour-by-hour monitoring of the growing [Formula: see text] plume via the induced seismic velocity change. Traveltime changes of [Formula: see text] (up to 8%) were observed, with no change seen at control sensors placed above the reservoir. The traveltime measurements indicate that the [Formula: see text] plume reached the top of the reservoir sand before reaching the observation well, where regular fluid sampling was occuring during the injection, thus providing information about the in situ buoyancy of [Formula: see text].

Poststack velocity analysis by separation and imaging of seismic diffractions

Geophysics ◽  
2007 ◽  
Vol 72 (6) ◽  
pp. U89-U94 ◽  
Author(s):  
Sergey Fomel ◽  
Evgeny Landa ◽  
M. Turhan Taner
Keyword(s):  
High Resolution ◽  
Seismic Data ◽  
Field Data ◽  
Small Scale ◽  
Velocity Analysis ◽  
High Resolution Imaging ◽  
Diffracted Waves ◽  
Resolution Imaging ◽  
Seismic Reflections ◽  
Optimal Focusing

Small geologic features manifest themselves in seismic data in the form of diffracted waves, which are fundamentally different from seismic reflections. Using two field-data examples and one synthetic example, we demonstrate the possibility of separating seismic diffractions in the data and imaging them with optimally chosen migration velocities. Our criteria for separating reflection and diffraction events are the smoothness and continuity of local event slopes that correspond to reflection events. For optimal focusing, we develop the local varimax measure. The objectives of this work are velocity analysis implemented in the poststack domain and high-resolution imaging of small-scale heterogeneities. Our examples demonstrate the effectiveness of the proposed method for high-resolution imaging of such geologic features as faults, channels, and salt boundaries.

Seismic mapping of on-shore sediments at Andøya, Norway, deposited prior to the North Atlantic rifting

2020 ◽  
Vol 8 (4) ◽  
pp. SQ105-SQ114
Author(s):  
Tor Arne Johansen ◽  
Bent Ole Ruud ◽  
Tormod Henningsen ◽  
Marco Brönner
Keyword(s):  
North Atlantic ◽  
Seismic Velocity ◽  
Traffic Noise ◽  
Seismic Exploration ◽  
Small Scale ◽  
Near Surface ◽  
The North ◽  
Seismic Surveying ◽  
The North Atlantic ◽  
Seismic Velocity Contrasts

Andøya is an island in the north of Norway. On its eastern side, it contains a local downfaulted basin of Mesozoic sediments sheltered from erosion during subsequent periods of Pleistocene glaciation. The sediments were deposited before the North Atlantic rifting and partly overlie weathered basement. We have recently carried out seismic surveying to better understand the geometry and seismic responses of the basin system. Extensive civil infrastructure and wet mire made the study area challenging for seismic exploration. We shot the survey lines at wet mire with detonating cord during winter when the mire was frozen. In the summer, we conducted seismic surveying along road shoulders with a small-scale vibrator. The seismic processing was particularly challenging due to the influence of traffic noise, heterogeneous near-surface conditions, and large seismic velocity contrasts. We interpreted the seismic lines in integration with other geophysical data and well logs to obtain a consistent and best possible seismic model of the basin. Our interpretation indicates a reorganization of the regional paleostress regime that took place during the continental breakup in the Eocene. In spite of severe obstacles for seismic surveying of the area, our results honor the robustness of the seismic method for subsurface imaging.

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