Model parameterization and amplitude variation with angle and azimuth inversion for orthotropic parameters

2019 ◽  
Author(s):  
Lixiang Ji ◽  
Zhaoyun Zong
Keyword(s):  
Amplitude Variation ◽  
Model Parameterization ◽  
Amplitude Variation With Angle

Model parameterization and amplitude variation with angle and azimuthal inversion in orthotropic media

Geophysics ◽  
2020 ◽  
Vol 86 (1) ◽  
pp. R1-R14
Author(s):  
Zhaoyun Zong ◽  
Lixiang Ji
Keyword(s):  
Parameter Estimation ◽  
Seismic Data ◽  
Inversion Method ◽  
Initial Model ◽  
Amplitude Variation ◽  
Inversion Result ◽  
Model Parameterization ◽  
Orthotropic Media ◽  
The Stability ◽  
Amplitude Variation With Angle

Horizontal layered formations with a suite of vertical or near-vertical fractures are usually assumed to be an approximate orthotropic medium and are more suitable for estimating fracture properties with wide-azimuth prestack seismic data in shale reservoirs. However, the small contribution of anisotropic parameters to the reflection coefficients highly reduces the stability of anisotropic parameter estimation by using seismic inversion approaches. Therefore, a novel model parameterization approach for the reflectivity and a pragmatic inversion method are proposed to enhance the stability of the inversion for orthotropic media. Previous attempts to characterize orthotropic media properties required using four or five independent parameters. However, we have derived a novel formulation that reduces the number of parameters to three. The inversion process is better conditioned with fewer degrees of freedom. An accuracy comparison of our formula with the previous ones indicates that our approach is sufficiently precise for reasonable parameter estimation. Furthermore, a Bayesian inversion method is developed that uses the amplitude variation with angle and azimuth (AVAZ) of the seismic data. Smooth background constraints reduce the similarity between the inversion result and the initial model, thereby reducing the sensitivity of the initial model to the inversion result. Cauchy and Gaussian probability distributions are used as prior constraints on the model parameters and the likelihood function, respectively. These ensure that the results are within the range of plausibility. Synthetic examples demonstrate that the adopted orthotropic AVAZ inversion method is feasible for estimating the anisotropic parameters even with moderate noise. The field data example illustrates the inversion robustness and stability of the adopted method in a fractured reservoir with a single well control.

Case study: Phase-component amplitude variation with angle

Geophysics ◽  
2019 ◽  
Vol 84 (4) ◽  
pp. B285-B297
Author(s):  
Elita Selmara De Abreu ◽  
John Patrick Castagna ◽  
Gabriel Gil
Keyword(s):  
Thin Layer ◽  
Thin Layers ◽  
Phase Response ◽  
Study Phase ◽  
Phase Decomposition ◽  
Seismic Modeling ◽  
Phase Component ◽  
Amplitude Variation ◽  
High Impedance ◽  
Amplitude Variation With Angle

In detectable and isolated thin layers below seismic resolution, phase decomposition can theoretically be used to discriminate relatively high-impedance thin-layer responses from low-impedance reservoir responses. Phase decomposition can be used to isolate seismic amplitudes with a particular phase response or to decompose the seismic trace into symmetrical and antisymmetrical phase components. These components sum to form the original trace. Assuming zero-phase seismic data and normal American polarity, seismically thin layers that are high impedance relative to overlying and underlying half-spaces are seen on the [Formula: see text] phase component, whereas a relatively low-impedance thin layer will appear on the [Formula: see text] phase component. When such phase decomposition is applied to prestack attributes on a 2D line across a thin, 8 m thick, gas-saturated reservoir in the Western Canadian Sedimentary Basin of Alberta, Canada, amplitude-variation-with-angle is magnified on the [Formula: see text] phase component. The [Formula: see text] far-offset component allows the lateral extent of the reservoir to be better delineated. This amplification is also seen on the [Formula: see text] phase component of the gradient attribute. These results are corroborated by seismic modeling that indicates the same phase-component relationships for near- and far-angle stacks as are observed on the real data. Fluid substitution and seismic modeling indicate that, relative to full-phase data, the mixed-phase response observed in this study exhibits variations in fluid effects that are magnified and better observed at far angles on the [Formula: see text] phase component.

Amplitude‐variation‐with‐angle behavior of self‐similar interfaces

Geophysics ◽  
1999 ◽  
Vol 64 (6) ◽  
pp. 1928-1938 ◽  
Author(s):  
Kees Wapenaar
Keyword(s):  
Normal Incidence ◽  
Reflection And Transmission Coefficients ◽  
Well Logs ◽  
Amplitude Variation ◽  
Reflection And Transmission ◽  
Velocity Function ◽  
Transmission Coefficients ◽  
Step Functions ◽  
Self Similar ◽  
Amplitude Variation With Angle

Amplitude‐variation‐with‐angle (AVA) analysis is generally based on the assumption that the medium parameters behave as step functions of the depth coordinate z, at least in a finite region around the interface. However, outliers observed in well logs often behave quite differently from step functions. In this paper, outliers in the acoustic propagation velocity are parameterized by functions of the form [Formula: see text]. The wavelet transform of this function reveals properties similar to those of several outliers in real well logs. Moreover, this function is self‐similar, according to [Formula: see text], for β > 0. Analytical expressions are derived for the acoustic normal incidence reflection and transmission coefficients for this type of velocity function. For oblique incidence, no explicit solutions are available. However, by exploiting the self‐similarity property of the velocity function, it turns out that the acoustic angle‐dependent and frequency‐dependent reflection and transmission coefficients are self‐similar as well. To be more specific, these coefficients appear to be constant along curves described by [Formula: see text], where p is the raypath parameter and ω the angular frequency. The singularity exponent α that is reflected in these curves may prove to be a useful indicator in seismic characterization.

scholarly journals Distribution of melt along the East Pacific Rise from 9°30′ to 10°N from an amplitude variation with angle of incidence (AVA) technique

2015 ◽  
Vol 203 (1) ◽  
pp. 1-21 ◽  
Author(s):  
Milena Marjanović ◽  
Hélène Carton ◽  
Suzanne M. Carbotte ◽  
Mladen R. Nedimović ◽  
John C. Mutter ◽  
...  
Keyword(s):  
East Pacific Rise ◽  
Angle Of Incidence ◽  
Amplitude Variation ◽  
East Pacific ◽  
Amplitude Variation With Angle

Integration of well data into geostatistical seismic amplitude variation with angle inversion for facies estimation

Geophysics ◽  
2015 ◽  
Vol 80 (6) ◽  
pp. M113-M128 ◽  
Author(s):  
Leonardo Azevedo ◽  
Ruben Nunes ◽  
Amílcar Soares ◽  
Evaldo C. Mundin ◽  
Guenther Schwedersky Neto
Keyword(s):  
Amplitude Variation ◽  
Seismic Amplitude ◽  
Well Data ◽  
Amplitude Variation With Angle

scholarly journals Approximations to seismic AVA responses: Validity and potential in glaciological applications

Geophysics ◽  
2016 ◽  
Vol 81 (1) ◽  
pp. WA1-WA11 ◽  
Author(s):  
Adam D. Booth ◽  
Ezgi Emir ◽  
Anja Diez
Keyword(s):  
Incident Angle ◽  
P Wave ◽  
Curve Matching ◽  
Weak Interface ◽  
Amplitude Variation ◽  
Seismic Properties ◽  
The Future ◽  
Transverse Isotropic ◽  
Comparable Accuracy ◽  
Amplitude Variation With Angle

Amplitude-variation-with-angle (AVA) methods establish the seismic properties of material either side of a reflective interface, and their use is growing in glaciology. The AVA response of an interface is defined by the complex Knott-Zoeppritz (K-Z) equations, numerous approximations to which we typically assume weak interface contrasts and isotropic propagation, inconsistent with the strong contrasts at glacier beds and the vertically transverse isotropic (VTI) fabrics were associated with englacial reflectivity. We considered the validity of a suite of approximate K-Z equations for the exact P-wave reflectivity [Formula: see text] of ice overlying bedrock, sediment and water, and englacial interfaces between isotropic and VTI ice. We found that the approximations of Aki-Richards, Shuey, and Fatti match exact glacier bed reflectivity to within [Formula: see text], smaller than the uncertainty in typical glaciological AVA analyses, but only for maximum incident angle [Formula: see text] limited to 30°. A stricter limit of [Formula: see text] offered comparable accuracy to a hydrocarbon benchmark case of shale overlying gas-charged sand. The VTI-compliant Rüger approximation accurately described englacial reflectivity, to within [Formula: see text], and it can be modified to give a quadratic expression in [Formula: see text] suitable for curve-matching operations. Having shown the circumstances under which AVA approximations were valid for glaciological applications, we have suggested that their interpretative advantages can be exploited in the future AVA interpretations.

Sign in / Sign up

Export Citation Format

Share Document