Thin‐bed AVO: Compensating for the effects of NMO on reflectivity sequences

Geophysics ◽  
2001 ◽  
Vol 66 (6) ◽  
pp. 1714-1720 ◽  
Author(s):  
Alessandro Castoro ◽  
Roy E. White ◽  
Rhodri D. Thomas
Keyword(s):  
Normal Incidence ◽  
Wavelet Estimation ◽  
Avo Analysis ◽  
Seismic Wavelet ◽  
Amplitude Versus Offset ◽  
Nmo Correction ◽  
Fourier Spectra ◽  
Nmo Stretch ◽  
Amplitude Versus

Estimating the amplitude versus offset (AVO) gradient for thin beds is problematic because of offset‐dependent tuning and NMO stretch. When AVO analysis is carried out before NMO correction, the nonparallel nature of the NMO hyperbolas results in differential interference conditions at each offset and complicates AVO interpretation. If AVO analysis is carried out after NMO correction, the data bandwidth is distorted and corrections must be made to recover the true AVO response. A correction for NMO stretch can be applied to Fourier spectra obtained after windowing the NMO‐corrected prestack data. This approach requires knowledge of the seismic wavelet but seems to be relatively insensitive to noise in the data or uncertainties in the wavelet estimation. The technique allows the interference conditions to be made independent of offset and the correct AVO gradient relative to the normal incidence amplitude to be recovered.

Amplitude preservation of Radon-based multiple-removal filters

Geophysics ◽  
2006 ◽  
Vol 71 (5) ◽  
pp. V123-V126 ◽  
Author(s):  
Ethan J. Nowak ◽  
Matthias G. Imhof
Keyword(s):  
Radon Transform ◽  
Seismic Data ◽  
Transform Domain ◽  
Multiple Reflections ◽  
Avo Analysis ◽  
Amplitude Versus Offset ◽  
Amplitude Preservation ◽  
Amplitude Versus

This study examines the effect of filtering in the Radon transform domain on reflection amplitudes. Radon filters are often used for removal of multiple reflections from normal moveout-corrected seismic data. The unweighted solution to the Radon transform reduces reflection amplitudes at both near and far offsets due to a truncation effect. However, the weighted solutions to the transform produce localized events in the transform domain, which minimizes this truncation effect. Synthetic examples suggest that filters designed in the Radon domain based on a weighted solution to the linear, parabolic, or hyperbolic transforms preserve the near- and far-offset reflection amplitudes while removing the multiples; whereas the unweighted solutions diminish reflection amplitudes which may distort subsequent amplitude-versus-offset (AVO) analysis.

Amplitude‐versus‐offset variations in gas sands

Geophysics ◽  
1989 ◽  
Vol 54 (6) ◽  
pp. 680-688 ◽  
Author(s):  
Steven R. Rutherford ◽  
Robert H. Williams
Keyword(s):  
Gulf Of Mexico ◽  
Normal Incidence ◽  
Arkoma Basin ◽  
Offshore Area ◽  
Amplitude Versus Offset ◽  
Wide Range ◽  
Class 1 ◽  
Two Factors ◽  
Seismic Reflections ◽  
Amplitude Versus

Seismic reflections from gas sands exhibit a wide range of amplitude‐versus‐offset (AVO) characteristics. The two factors that most strongly determine the AVO behavior of a gas‐sand reflection are the normal incidence reflection coefficient [Formula: see text] and the contrast in Poisson’s ratio at the reflector. Of these two factors, [Formula: see text] is the least constrained. Based on their AVO characteristics, gas‐sand reflectors can be grouped into three classes defined in terms of [Formula: see text] at the top of the gas sand. Class 1 gas sands have higher impedance than the encasing shale with relatively large positive values for [Formula: see text]. Class 2 gas sands have nearly the same impedance as the encasing shale and are characterized by values of [Formula: see text] near zero. Class 3 sands have lower impedance than the encasing shale with negative, large magnitude values for [Formula: see text]. Each of these sand classes has a distinct AVO characteristic. An example of a gas sand from each of the three classes is presented in the paper. The Class 1 example involves a Hartshorn channel sand from the Arkoma Basin. The Class 2 example considers a Miocene gas sand from the Brazos offshore area of the Gulf of Mexico. The Class 3 example is a Pliocene gas sand from the High Island offshore area of the Gulf of Mexico.

scholarly journals Identification of Sandstone Reservoir Saturated by Oil Using Low Frequency Analysis with base on CWT and AVO Analysis

2016 ◽  
Vol 4 (01) ◽  
pp. 55
Author(s):  
Sudarmaji S ◽  
Budi Eka Nurcahya
Keyword(s):  
Wavelet Transform ◽  
Frequency Analysis ◽  
Low Frequency ◽  
Class Iii ◽  
Porous Rock ◽  
Avo Analysis ◽  
Reflection Seismic ◽  
Amplitude Versus Offset ◽  
Sandstone Reservoir ◽  
Amplitude Versus

<span>Identification of sandstone resevoir saturated by oil has been conducted by mean low <span>frequency and amplitude versus offset (AVO) analysis. Low Frequency analysis was has been <span>conducted among 3D and 2D seismic data of PSTM gather using continuose wavelet transform <span>(CWT) around 15hz. Low frequency analysis was done by calculating attribute gradient time <span>frequency of instantaneous amplitude using continuous wavelet transform (CWT) around <span>15hz for detecting the existing diffusive wave from reflection seismic. Diffusive wave is a <span>wave that appears due to fluid movement in porous rock, especially fluid of hydrocarbon with <span>certain viscosity and permeability. While amplitude versus offset (AVO) analysis was done <span>for detecting the impedance character of sandstone reservoir that related to porous rock. <span>Amplitude versus offset (AVO) analysis was done by calculating gradient*intercept and <span>observing the curve of wave reflectivity as a function of offset. The positive value of <span>gradient*intercept and curve of reflectivity as a function of offset could be identified as AVO<br /><span>class III and correlated to sandstone reservoir with low impedance and good porosity.</span></span></span></span></span></span></span></span></span></span></span></span><br /></span>

Poroelastic analysis of frequency-dependent amplitude-versus-offset variations

Geophysics ◽  
2011 ◽  
Vol 76 (3) ◽  
pp. C31-C40 ◽  
Author(s):  
Lanfeng Liu ◽  
Siyuan Cao ◽  
Lu Wang
Keyword(s):  
Frequency Domain ◽  
Incident Angle ◽  
Normal Incidence ◽  
Frequency Dependent ◽  
Phase Reversal ◽  
Hard Rocks ◽  
Amplitude Versus Offset ◽  
Nondispersive Medium ◽  
Domain Phase ◽  
Amplitude Versus

Using analytic equations and numerical modeling, we have investigated characteristics of the frequency-dependent amplitude versus incident angle at an interface between a nondispersive medium and a patchy-saturated dispersive medium. For acoustically hard rocks, at normal incidence and smaller incident angles, the reflection magnitude increases when frequency increases, whereas in the amplitude versus incident-angle domain, the amplitude decreases with increasing incident angle (offset). For acoustically moderate to slightly hard rocks, phase reversal may occur when frequency increases from low to high. This type of response can happen in traditional amplitude-versus-offset class I and II reservoirs, but the frequency-domain phase reversal will be in different incident-angle ranges. For acoustically soft reservoirs, in amplitude versus incident-angle domain, the reflection magnitude increases with increasing incident angle. However, in amplitude-versus-frequency domain, the reflection magnitude increases when frequency decreases, which occurs in all investigated frequencies.

Incomplete AVO near salt structures

Geophysics ◽  
1992 ◽  
Vol 57 (4) ◽  
pp. 543-553 ◽  
Author(s):  
Christopher P. Ross
Keyword(s):  
Seismic Profiles ◽  
Spectral Modeling ◽  
Signal Degradation ◽  
Amplitude Versus Offset ◽  
Bright Spots ◽  
Close Proximity ◽  
Pseudo Spectral ◽  
Amplitude Versus ◽  
Structure Class ◽  
Made In

Amplitude versus offset (AVO) measurements for deep hydrocarbon‐bearing sands can be compromised when made in close proximity to a shallow salt piercement structure. Anomalous responses are observed, particularly on low acoustic impedance bright spots. CMP data from key seismic profiles traversing the bright spots do not show the expected Class 3 offset responses. On these CMPs, significant decrease of far trace energy is observed. CMP data from other seismic profiles off‐structure do exhibit the Class 3 offset responses, implying that structural complications may be interfering with the offset response. A synthetic AVO gather was generated using well log data, which supports the off‐structure Class 3 responses, further reinforcing the concept of structurally‐biased AVO responses. Acoustic, pseudo‐spectral modeling of the structure substantiates the misleading AVO response. Pseudo‐spectral modeling results suggest that signal degradation observed on the far offsets is caused by wavefield refraction—a shadow zone, where the known hydrocarbon‐bearing sands are not completely illuminated. Such shadow zones obscure the correct AVO response, which may have bearing on exploration and development.

Inversion of normal incidence seismograms

Geophysics ◽  
1982 ◽  
Vol 47 (5) ◽  
pp. 757-770 ◽  
Author(s):  
A. Bamberger ◽  
G. Chavent ◽  
Ch. Hemon ◽  
P. Lailly
Keyword(s):  
Simulated Data ◽  
Normal Incidence ◽  
State Equation ◽  
Inversion Algorithm ◽  
Multiple Reflections ◽  
Common Depth Point ◽  
Adjoint State ◽  
Nmo Correction ◽  
The One ◽  
Practical Feasibility

The well‐known instability of Kunetz’s (1963) inversion algorithm can be explained by the progressive manner in which the calculations are done (descending from the surface) and by the fact that completely different impedances can yield indistinguishable synthetic seismograms. Those difficulties can be overcome by using an iterative algorithm for the inversion of the one‐dimensional (1-D) wave equation, together with a stabilizing constraint on the sums of the jumps of the desired impedance. For computational efficiency, the synthetic seismogram is computed by the method of characteristics, and the gradient of the error criterion is computed by optimal control techniques (adjoint state equation). The numerical results on simulated data confirm the expected stability of the algorithm in the presence of measurement noise (tests include noise levels of 50 percent). The inversion of two field sections demonstrates the practical feasibility of the method and the importance of taking into account all internal as well as external multiple reflections. Reflection coefficients obtained by this method show an excellent agreement with well‐log data in a case where standard estimation techniques [deconvolution of common‐depth‐point (CDP) stacked and normal‐moveout (NMO) correction section] failed.

scholarly journals Crosswell Seismic Amplitude-Versus-Offset for Detailed Imaging of Facies and Fluid Distribution within Carbonate Oil Reservoirs

2008 ◽  
Author(s):  
Wayne Pennington ◽  
Mohamed Ibrahim ◽  
Roger Turpening ◽  
Sean Trisch ◽  
Josh Richardson ◽  
...  
Keyword(s):  
Oil Reservoirs ◽  
Fluid Distribution ◽  
Seismic Amplitude ◽  
Amplitude Versus Offset ◽  
Detailed Imaging ◽  
Amplitude Versus

scholarly journals QVOA Techniques for Estimation of Fracture Directions

2018 ◽  
Vol 2018 ◽  
pp. 1-11
Author(s):  
Vladimir Sabinin
Keyword(s):  
Quality Factor ◽  
Symmetry Axis ◽  
Factor Versus ◽  
Synthetic Data ◽  
Computational Techniques ◽  
High Quality ◽  
Amplitude Versus Offset ◽  
Target Layer ◽  
Analysis Quality ◽  
Amplitude Versus

Some new computational techniques are suggested for estimating symmetry axis azimuth of fractures in the viscoelastic anisotropic target layer in the framework of QVOA analysis (Quality factor Versus Offset and Azimuth). The different QVOA techniques are compared using synthetic viscoelastic surface reflected data with and without noise. I calculated errors for these techniques which depend on different sets of azimuths and intervals of offsets. Superiority of the high-order “enhanced general” and “cubic” techniques is shown. The high-quality QVOA techniques are compared with one of the high-quality AVOA techniques (Amplitude Versus Offset and Azimuth) in the synthetic data with noise and attenuation. Results are comparable.

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