Estimation of Q from surface seismic reflection data

Geophysics ◽  
1998 ◽  
Vol 63 (6) ◽  
pp. 2120-2128 ◽  
Author(s):  
Rahul Dasgupta ◽  
Roger A. Clark
Keyword(s):  
Attenuation Factor ◽  
Spectral Ratio ◽  
Ratio Method ◽  
Amplitude Analysis ◽  
Gas Reservoir ◽  
Seismic Reflection Data ◽  
Reflection Data ◽  
Anelastic Attenuation ◽  
Zero Offset ◽  
Nmo Stretch

Reliable estimates of the anelastic attenuation factor, Q, are desirable for improved resolution through inverse Q deconvolution and to facilitate amplitude analysis. Q is a useful petrophysical parameter itself, yet Q is rarely measured. Estimates must currently be made from borehole seismology. This paper presents a simple technique for determining Q from conventional surface seismic common midpoint (CMP) gathers. It is essentially the classic spectral ratio method applied on a trace‐by‐trace basis to a designatured and NMO stretch‐corrected CMP gather. The variation of apparent Q versus offset (QVO) is extrapolated to give a zero‐offset Q estimate. Studies on synthetics suggest that, for reasonable data quality (S/N ratios better than 3:1, shallow (<5°) dips, and stacking velocity accuracy <5%), source‐to‐reflector average Q is recoverable to within some 3% and Q for a specific interval (depending on its two‐way time thickness and depth) is recoverable to 15–20%. Three case studies are reported. First, Q versus offset and vertical seismic profiling (VSP) Q estimates for a southern North Sea line were in close agreement, validating the method. For Chalk, Mushelkalk‐Keuper, and Bunter‐Zechstein, Q was estimated as 130 ± 15, 47 ± 8, and 156 ± 18, respectively. Next, two alternative lithological interpretations of a structure seen in a frontier area were discriminated between when Q estimates of 680 to 820 were obtained (compared to some 130–170 in the overlying units), favoring a metamorphic/crystalline lithology rather than (prospective) sediments. This was later confirmed by drilling. Third, a profile of Q estimates along a 200-ms-thick interval, known to include a gas reservoir, showed a clear and systematic reduction in Q to a low of 50 ± 11, coincident with the maximum reservoir thickness, from some 90–105 outside the reservoir. Q for the reservoir interval itself was estimated at 17 ± 7.

Another look at NMO stretch

Geophysics ◽  
1992 ◽  
Vol 57 (5) ◽  
pp. 749-751 ◽  
Author(s):  
Arthur E. Barnes
Keyword(s):  
Seismic Reflection ◽  
Qualitative Assessment ◽  
Seismic Reflection Data ◽  
Reflection Data ◽  
Amplitude Spectra ◽  
Nmo Correction ◽  
Zero Offset ◽  
Nmo Stretch ◽  
Dominant Frequencies

The normal moveout (NMO) correction is applied to seismic reflection data to transform traces recorded at non‐zero offset into traces that appear to have been recorded at zero offset; this introduces undesirable distortions called NMO stretch (Buchholtz, 1972). NMO stretch must be understood because it lengthens waveforms and thereby reduces resolution. Buchholtz (1972) gives a qualitative assessment of NMO stretch, Dunkin and Levin (1973) derive its effect on the amplitude spectra of narrow waveforms, while Yilmaz (1987, p. 160) considers its effect on dominant frequencies. These works are approximate and do not show how spectral distortions vary through time.

Accurate interval Q-factor estimation from VSP data

Geophysics ◽  
2012 ◽  
Vol 77 (3) ◽  
pp. WA149-WA156 ◽  
Author(s):  
E. Blias
Keyword(s):  
Real Data ◽  
Spectral Ratio ◽  
Ratio Method ◽  
Seismic Reflection Data ◽  
Reflection Data ◽  
Seismic Quality Factor ◽  
Vsp Data ◽  
Considerable Impact ◽  
The Difference ◽  
Factor Estimation

Inelastic attenuation, quantified by [Formula: see text], the seismic quality factor, has considerable impact on surface seismic reflection data. A new method for interval [Formula: see text]-factor estimation using near-offset VSP data was based on an objective function minimization measuring the difference between cumulative [Formula: see text] estimates and those calculated through interval [Formula: see text]. To calculate interval [Formula: see text], we used all receiver pairs that provided reasonable [Formula: see text] values. To estimate [Formula: see text] between two receiver levels, we used the equation that links amplitudes at different levels and could provide more accurate [Formula: see text] values than the spectral-ratio method. To improve interval [Formula: see text] estimates, which rely on traveltimes, we used a high-accuracy approach in the frequency domain to determine time shifts. Application of this method to real data demonstrated reasonable correspondence between [Formula: see text] estimates and log data.

Seismic anelastic attenuation estimation using prestack seismic gathers

Geophysics ◽  
2019 ◽  
Vol 84 (6) ◽  
pp. M37-M49
Author(s):  
Naihao Liu ◽  
Bo Zhang ◽  
Jinghuai Gao ◽  
Hao Wu ◽  
Shengjun Li
Keyword(s):  
Seismic Data ◽  
Seismic Waves ◽  
Synthetic Data ◽  
Spectral Ratio ◽  
Time Frequency ◽  
Anelastic Attenuation ◽  
Time Migration ◽  
Seismic Quality Factor ◽  
Zero Offset ◽  
Nmo Stretch

The seismic quality factor [Formula: see text] quantifies the anelastic attenuation of seismic waves in the subsurface and can be used in assisting reservoir characterization and as an indicator of hydrocarbons. Usually, the [Formula: see text]-factor is estimated by comparing the spectrum changes of vertical seismic profiles and poststack seismic data. However, seismic processing such as the normal moveout (NMO) stretch would distort the spectrum of the seismic data. Hence, we have estimated [Formula: see text] using prestack time migration gathers. To mitigate the NMO stretch effect, we compensate the NMO stretch of prestack seismic gathers in the time-frequency domain. Similar to the log spectral method, our method obtains the [Formula: see text] by measuring the log spectral ratio (LSR) of seismic events of the top and base of the reservoir at a zero-offset seismic trace. The LSR has a linear relationship with a new parameter [Formula: see text] by assuming that the source wavelet is a constant-phase wavelet. The parameters [Formula: see text] and LSR vary with the offset value (traveltime). We use the values of [Formula: see text] and LSR obtained from nonzero-offset seismic traces to simulate the values of [Formula: see text] and LSR at a zero-offset seismic trace. Finally, we obtain [Formula: see text] by applying the classic LSR method to the simulated [Formula: see text] and LSR. To demonstrate the validity and effectiveness of our method, we first apply it to noise-free and noisy synthetic data examples and then to real seismic data acquired over the Sichuan Basin, China. The synthetic and real seismic applications demonstrate the effectiveness of our method in highlighting high anelastic-attenuation zones.

scholarly journals Event couple spectral ratio Q method for earthquake clusters: application to North-West Bohemia

2018 ◽  
Author(s):  
Marius Kriegerowski ◽  
Simone Cesca ◽  
Matthias Ohrnberger ◽  
Torsten Dahm ◽  
Frank Krüger
Keyword(s):  
Wave Attenuation ◽  
Attenuation Factor ◽  
Source Region ◽  
Spectral Ratio ◽  
Ratio Method ◽  
Earthquake Swarms ◽  
North West ◽  
High Attenuation ◽  
West Bohemia ◽  
Spectral Ratio Method

Abstract. We develop an amplitude spectral ratio method for event couples from clustered earthquakes to estimate seismic wave attenuation (Q−1) in the source volume. The method allows to study attenuation within the source region of earthquake swarms or aftershocks at depth, independent of wave path and attenuation between source region and surface station. We exploit the high frequency slope of phase spectra using multitaper spectral estimates. The method is tested using simulated full wavefield seismograms affected by recorded noise and finite source rupture. The synthetic tests verify the approach and show that solutions are independent of focal mechanisms, but also show that seismic noise may broaden the scatter of results. We apply the event couple spectral ratio method to North-West Bohemia, Czech Republic, a region characterized by the persistent occurrence of earthquake swarms in a confined source region at mid-crustal depth. Our method indicates a strong anomaly of high attenuation in the source region of the swarm with an averaged attenuation factor of Qp 

Labeling long‐period multiple reflections

Geophysics ◽  
1989 ◽  
Vol 54 (1) ◽  
pp. 122-126 ◽  
Author(s):  
R. J. J. Hardy ◽  
M. R. Warner ◽  
R. W. Hobbs
Keyword(s):  
Seismic Reflection ◽  
High Amplitude ◽  
Data Sets ◽  
Multiple Reflections ◽  
Multiple Series ◽  
Seismic Reflection Data ◽  
Long Period ◽  
Reflection Data ◽  
Zero Offset ◽  
Marine Seismic

The many techniques that have been developed to remove multiple reflections from seismic data all leave remnant energy which can cause ambiguity in interpretation. The removal methods are mostly based on periodicity (e.g., Sinton et al., 1978) or the moveout difference between primary and multiple events (e.g., Schneider et al., 1965). They work on synthetic and selected field data sets but are rather unsatisfactory when applied to high‐amplitude, long‐period multiples in marine seismic reflection data acquired in moderately deep (700 m to 3 km) water. Differential moveout is often better than periodicity at discriminating between types of events because, while a multiple series may look periodic to the eye, it is only exactly so on zero‐offset reflections from horizontal layers. The technique of seismic event labeling described below works by returning offset information from CDP gathers to a stacked section by color coding, thereby discriminating between seismic reflection events by differential normal moveout. Events appear as a superposition of colors; the direction of color fringes indicates whether an event has been overcorrected or undercorrected for its hyperbolic normal moveout.

Measurements of attenuation from vertical seismic profiles by iterative modeling

Geophysics ◽  
1985 ◽  
Vol 50 (6) ◽  
pp. 931-949 ◽  
Author(s):  
Michel Dietrich ◽  
Michel Bouchon
Keyword(s):  
Velocity Dispersion ◽  
Synthetic Data ◽  
Layered Media ◽  
Spectral Ratio ◽  
Ratio Method ◽  
Seismic Profiles ◽  
Vertical Seismic Profiles ◽  
Anelastic Attenuation ◽  
Vsp Data ◽  
Intrinsic Dissipation

We present a numerical simulation of vertical seismic profiles (VSP) using the discrete horizontal wavenumber representation of seismic wave fields. The theoretical seismograms are computed in the acoustic case for flat layered media, and they include the effects of absorption and velocity dispersion. A study using the synthetic seismograms was conducted to investigate the accuracy and resolution of attenuation measurements from VSP data. It is shown that in finely layered media estimates of the anelastic attenuation obtained by use of the reduced spectral ratio method are usually inaccurate when the attenuation is measured over a small vertical extent. An iterative method is presented which improves the resolution of the measurements of intrinsic dissipation. This method allows determination for synthetic data of the quality factor over depth intervals of about one wavelength of the dominant seismic frequency.

AVO correction for scalar waves in the case of a thinly layered reflector overburden

Geophysics ◽  
1996 ◽  
Vol 61 (2) ◽  
pp. 520-528 ◽  
Author(s):  
Martin T. Widmaier ◽  
Sergei A. Shapiro ◽  
Peter Hubral
Keyword(s):  
Thin Layer ◽  
Transmission Loss ◽  
Thin Layers ◽  
Statistical Parameters ◽  
Medium Theory ◽  
Seismic Reflection Data ◽  
Amplitude Variation With Offset ◽  
Velocity Anisotropy ◽  
Reflection Data ◽  
Zero Offset

The reflection response of a seismic target is significantly affected by a thinly layered overburden, which creates velocity anisotropy and a transmission loss by scattering attenuation. These effects must be taken into account when imaging a target reflector and when inverting reflection coefficients. Describing scalar wave (i.e., acoustic wave or SH‐wave) propagation through a stack of thin layers by equivalent‐medium theory provides a simple generalized O’Doherty‐Anstey formula. This formulation is defined by a few statistical parameters that depend on the 1-D random fluctuations of the reflector overburden. The formula has been combined with well‐known target‐oriented and amplitude‐preserving migration/inversion algorithms and amplitude variation with offset (AVO) analysis procedures. The application of these combined procedures is demonstrated for SH‐waves in an elastic thinly‐layered medium. These techniques offer a suitable tool to compensate for the thin‐layer influence on traveltimes and amplitudes of seismic reflection data. The thin‐layer sensitive AVO parameters (zero‐offset amplitude and AVO gradient) of a target reflector can thus be better recovered.

Waveform-based estimation of Q and scattering properties for zero-offset vertical seismic profile data

Geophysics ◽  
2020 ◽  
Vol 85 (4) ◽  
pp. R365-R379
Author(s):  
Rie Nakata ◽  
David Lumley ◽  
Gary Hampson ◽  
Kurt Nihei ◽  
Nori Nakata
Keyword(s):  
Field Data ◽  
Estimation Method ◽  
Spectral Ratio ◽  
Seismic Profile ◽  
Ratio Method ◽  
Vsp Data ◽  
Spectral Ratio Method ◽  
Band Limited ◽  
Zero Offset ◽  
Negative Formula

Estimating [Formula: see text] using downgoing waves in zero-offset vertical seismic profiles (VSPs) can be challenging when scattered waves from near-borehole heterogeneities interfere with direct arrivals. In any [Formula: see text] estimation method that assumes a downgoing plane wave, constructive and destructive wave-mode interference can cause errors in the estimate. For example, in the spectral-ratio method, such interference modulates the amplitude spectra introducing significant variations and even nonphysical negative [Formula: see text] (amplification) estimates. We have investigated this phenomenon using synthetic and field data sets from offshore Australia and developed a two-step waveform-based method to characterize scattering anomalies and improve [Formula: see text] estimates. Waveform information is key to deal with closely spaced band-limited seismic events. First, we solve an inverse problem to locate and characterize scatterers by minimizing the traveltime and waveform misfits. Then, using the estimated parameters, we model the scatterers’ contribution to the VSP data and remove it from the observed waveforms. The resulting spectra resemble those that would have been acquired in the absence of the scatterers and are much more suitable for the spectral-ratio method. By assuming a 1D medium and a simple scatterer shape (i.e., circular), we parameterize a scattering heterogeneity using five parameters (depth, distance, size, velocity, and density) and seek a solution using a grid search to handle the nonuniqueness of the VSP inversion. Instead, adaptive subtraction is required to fine-tune the modeled interference to better fit the observation. We successfully use this method to characterize and mitigate the strongest wave interference in the field data. The final [Formula: see text] estimates contain milder variations and much less nonphysical negative [Formula: see text]. Our results demonstrate that the proposed method, readily extendible to multiple scatterer cases, can locate discrete scatterers, remove the effects of their interference, and thus significantly improve the [Formula: see text] estimates from VSP data.

scholarly journals Event couple spectral ratio <i>Q</i> method for earthquake clusters: application to northwest Bohemia

Solid Earth ◽  
2019 ◽  
Vol 10 (1) ◽  
pp. 317-328
Author(s):  
Marius Kriegerowski ◽  
Simone Cesca ◽  
Matthias Ohrnberger ◽  
Torsten Dahm ◽  
Frank Krüger
Keyword(s):  
Wave Attenuation ◽  
Attenuation Factor ◽  
Source Region ◽  
Spectral Ratio ◽  
Ratio Method ◽  
Earthquake Swarms ◽  
High Attenuation ◽  
Spectral Estimates ◽  
Wave Path ◽  
Spectral Ratio Method

Abstract. We develop an amplitude spectral ratio method for event couples from clustered earthquakes to estimate seismic wave attenuation (Q−1) in the source volume. The method allows to study attenuation within the source region of earthquake swarms or aftershocks at depth, independent of wave path and attenuation between source region and surface station. We exploit the high-frequency slope of phase spectra using multitaper spectral estimates. The method is tested using simulated full wave-field seismograms affected by recorded noise and finite source rupture. The synthetic tests verify the approach and show that solutions are independent of focal mechanisms but also show that seismic noise may broaden the scatter of results. We apply the event couple spectral ratio method to northwest Bohemia, Czech Republic, a region characterized by the persistent occurrence of earthquake swarms in a confined source region at mid-crustal depth. Our method indicates a strong anomaly of high attenuation in the source region of the swarm with an averaged attenuation factor of Qp<100. The application to S phases fails due to scattered P-phase energy interfering with S phases. The Qp anomaly supports the common hypothesis of highly fractured and fluid saturated rocks in the source region of the swarms in northwest Bohemia. However, high temperatures in a small volume around the swarms cannot be excluded to explain our observations.

Automatic NMO correction in anisotropic media and non-hyperbolic NMO velocity field estimation

2016 ◽  
Vol 56 (2) ◽  
pp. 592
Author(s):  
Mohamed Sedek ◽  
Lutz Gross
Keyword(s):  
Velocity Field ◽  
Seismic Reflection ◽  
Fast Method ◽  
Gas Field ◽  
Seismic Reflection Data ◽  
Anisotropic Effect ◽  
Reflection Data ◽  
Nmo Correction ◽  
Zero Offset ◽  
The One

The authors propose a new method to automatically normal move-out correct pre-stack seismic reflection data that is sorted by CDP gathers, and to estimate the normal move-out (NMO) velocity (Vnmo) as a full common depth point (CDP) velocity field that instantaneously varies with offsets/azimuths. The method is based on doing a pre-defined number of NMO velocity iterations using linear vertical interpolation of different NMO velocities at each seismic trace individually. At each iteration the seismic trace is shifted and multiplied by the zero offset trace followed by the summation of the product. Then, after all the iterations are done, the one with the maximum summation value is chosen, which is assumed to be the most suitable NMO velocity trace that accurately flattens seismic reflection events. The other traces follow the same process, and a final velocity field is then extracted. Another new, simple and fast method is also introduced to estimate the anisotropic effect from the extracted NMO velocity field. The method runs by calculating the spatial variation of the estimated NMO velocities at each arrival time and offset/azimuth, therefore instantaneously estimating the anisotropic effect. Isotropic and anisotropic synthetic geological models were built based on a ray-tracing algorithm to test the method. A range of synthetic background noise was applied, starting from 10–30%. The method has also been tested on Hess’s model and coal seam gas field data CDP examples. An Alaskan pre-stack seismic CDP field example has also been used.

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