Investigating the velocity‐depth ambiguity of reflection traveltimes

Geophysics ◽  
1994 ◽  
Vol 59 (11) ◽  
pp. 1763-1773 ◽  
Author(s):  
Hans J. Tieman
Keyword(s):  
Velocity Field ◽  
Seismic Data ◽  
Effective Width ◽  
Entire Space ◽  
Inversion Algorithm ◽  
Long Wavelength ◽  
Velocity Anomaly ◽  
Reflection Seismic ◽  
Frequency Components ◽  
The Difference

Reflection seismic data contain a long wavelength ambiguity making it difficult to separate traveltime information into velocity and reflector depth components. The existence of this velocity‐depth ambiguity is a feature of the geometry of the subsurface and is not caused by the particular inversion algorithm being used. Factors that control the occurrence of velocity‐depth ambiguities include the effective width of a potential velocity anomaly; i.e., its spatial wavelength, its height above a reflector, and its thickness. Factors that do not affect velocity‐depth ambiguities are the magnitude of the anomaly (the difference in velocity between it and the background) and the cable length with which data were recorded. A thin velocity anomaly induces an ambiguity at a wavelength approximately equal to 4.44 times the height of the anomaly above the reflector. A thick anomaly that spans the entire space from surface to reflector induces an ambiguity at a wavelength approximately equal to 2.57 the depth to the reflector. These are wavelengths that are significant in size, and therefore are of exploration interest. Through Fourier analysis, any subsurface velocity field can be decomposed into spatial frequency components. Thus the wavelength dependent velocity‐depth ambiguity adversely affects all velocity distributions.

Simultaneous inversion of prestack seismic data for rock properties using simulated annealing

Geophysics ◽  
2002 ◽  
Vol 67 (6) ◽  
pp. 1877-1885 ◽  
Author(s):  
Xin‐Quan Ma
Keyword(s):  
Simulated Annealing ◽  
Seismic Data ◽  
Low Frequency ◽  
Optimization Procedure ◽  
P Wave ◽  
Rock Properties ◽  
Inversion Method ◽  
Inversion Algorithm ◽  
Simultaneous Inversion ◽  
Reflection Seismic

A new prestack inversion algorithm has been developed to simultaneously estimate acoustic and shear impedances from P‐wave reflection seismic data. The algorithm uses a global optimization procedure in the form of simulated annealing. The goal of optimization is to find a global minimum of the objective function, which includes the misfit between synthetic and observed prestack seismic data. During the iterative inversion process, the acoustic and shear impedance models are randomly perturbed, and the synthetic seismic data are calculated and compared with the observed seismic data. To increase stability, constraints have been built into the inversion algorithm, using the low‐frequency impedance and background Vs/Vp models. The inversion method has been successfully applied to synthetic and field data examples to produce acoustic and shear impedances comparable to log data of similar bandwidth. The estimated acoustic and shear impedances can be combined to derive other elastic parameters, which may be used for identifying of lithology and fluid content of reservoirs.

Acoustic impedance estimation from combined harmonic reconstruction and interval velocity

Geophysics ◽  
2019 ◽  
Vol 84 (3) ◽  
pp. R385-R400
Author(s):  
Luca Bianchin ◽  
Emanuele Forte ◽  
Michele Pipan
Keyword(s):  
Velocity Field ◽  
Seismic Data ◽  
Acoustic Impedance ◽  
Low Frequency ◽  
Reconstruction Method ◽  
Well Log ◽  
Data Set ◽  
Low Frequencies ◽  
Interval Velocity ◽  
Frequency Components

Low-frequency components of reflection seismic data are of paramount importance for acoustic impedance (AI) inversion, but they typically suffer from a poor signal-to-noise ratio. The estimation of the low frequencies of AI can benefit from the combination of a harmonic reconstruction method (based on autoregressive [AR] models) and a seismic-derived interval velocity field. We have developed the construction of a convex cost function that accounts for the velocity field, together with geologic a priori information on AI and its uncertainty, during the AR reconstruction of the low frequencies. The minimization of this function allows one to reconstruct sensible estimates of low-frequency components of the subsurface reflectivity, which lead to an estimation of AI model via a recursive formulation. In particular, the method is suited for an initial and computationally inexpensive assessment of the absolute value of AI even when no well-log data are available. We first tested the method on layered synthetic models, then we analyzed its applicability and limitations on a real marine seismic data set that included tomographic velocity information. Despite a strong trace-to-trace variability in the results, which could partially be mitigated by multitrace inversion, the method demonstrates its capability to highlight lateral variations of AI that cannot be detected when the low frequencies only come from well-log information.

scholarly journals Using Very Fast Simulated Annealing in the Weighted AB Semblance method

2019 ◽  
Vol 37 (4) ◽  
Author(s):  
Marcelo Souza ◽  
Milton Porsani
Keyword(s):  
Simulated Annealing ◽  
Seismic Data ◽  
Real Data ◽  
Velocity Spectrum ◽  
Velocity Analysis ◽  
Inversion Algorithm ◽  
Coherence Measure ◽  
Reflection Seismic ◽  
Very Fast Simulated Annealing ◽  
Velocity Spectra

ABSTRACTThe conventional velocity analysis does not consider AVO effects in reflection seismic data. These conditions lead to obtaining of inadequate velocity fields, making it difficult to execute other steps in seismic processing. To overcome this problem, researchers developed the Weighted AB semblance method, a coherence measure which deals with AVO effects in velocity spectra. It is based on the application of two sigmoid weighting functions to AB semblance, which depend on four coefficients. The values of these coefficients directly influence the resolution of the resulting velocity spectrum. In this work, we apply the inversion algorithm Very Fast Simulated Annealing (VFSA) to obtain these values. Numerical experiments show that VFSA is a quite effective method, obtaining correct coefficient values and allowing the generation of the velocity spectrum with an excellent resolution for both synthetic and real data. Results also proved that Weighted AB semblance is an optimal coherence measure to be used in velocity spectrum, because it is insensitive to AVO effects and reversal polarity and presents considerably a better resolution than conventional semblance.Keywords: velocity analysis, AVO, high-resolution velocity spectra RESUMOA análise de velocidades convencional não considera efeitos de AVO em dados sísmicos de reflexão. Essas condições levam à obtenção de campos de velocidades inadequados, dificultando a execução de outras etapas do processamento sísmico. Para superar esse problema, pesquisadores desenvolveram o método AB semblance Ponderado, uma medida de coerência que lida com efeitos de AVO em espectros de velocidades. Ela ´e baseada na aplicação de duas funções sigmoides à AB semblance, que depende de quatro coeficientes. Os valores desses coeficientes influenciam diretamente a resolução do espectro de velocidade resultante. Nesse trabalho, n´os aplicamos o algoritmo de inversão Very Fast Simulated Annealing (VFSA) para obter esses valores. Experimentos numéricos mostram que VFSA é um método bastante eficaz, obtendo valores corretos dos coeficientes e permitindo a geração do espectro de velocidade com uma excelente resolução tanto para dados sintéticos quanto para dados reais. Resultados também provam que o AB semblance Ponderado ´e uma medida de coerência ótima para ser usada no espectro de velocidade, porque ela é insensível aos efeitos de AVO e apresenta resolução consideravelmente melhor do que a semblance convencional.Palavras-chave: análise de velocidades, AVO, espectro de velocidades de alta resolução.

A practical method for estimating effective parameters of anisotropy from reflection seismic data

Geophysics ◽  
2004 ◽  
Vol 69 (3) ◽  
pp. 681-689 ◽  
Author(s):  
J. Helen Isaac ◽  
Don C. Lawton
Keyword(s):  
Seismic Data ◽  
Multiple Solutions ◽  
Arrival Time ◽  
Symmetry Axis ◽  
P Wave ◽  
Model Parameters ◽  
Effective Parameters ◽  
Reflection Seismic ◽  
Special Cases ◽  
The Difference

The location of any event imaged by P‐wave reflection seismic data beneath a tilted transversely isotropic (TTI) overburden is shifted laterally if isotropic velocities are used during data processing. The magnitude of the shift depends on five independent parameters: overburden thickness, angle of tilt, symmetry‐axis velocity, and the Thomsen anisotropy parameters and δ. The shift also varies with source–receiver offset. We have developed a procedure to estimate these five parameters when the tilt of the symmetry axis from the vertical is equal to the dip of the TTI layer (except in the special cases transverse isotropy with vertical or horizontal axis of symmetry). We observe three attributes of seismic data processed using isotropic velocities: the zero‐offset arrival time of a selected reflection, the difference in arrival time between a near‐offset and a far‐offset arrival, and the difference in imaged location (smear) of this target event between the same offsets. We then perform a cascaded scan of the five parameters to determine those combinations of the five that result in calculated attributes equivalent to the observed attributes. The multiple solutions are averaged to give the parameter estimates. Application of this method to synthetic and physical model reflection data results in multiple solutions, which are constrained and averaged to obtain the effective imaging parameters. These effective parameters are close estimates of the true model parameters in both cases. For field seismic data this procedure requires that there be a suitable observable event below the TTI overburden and assumes that the measured times and shifts are reasonably accurate.

scholarly journals Multi-scale time-frequency domain full waveform inversion with a weighted local correlation-phase misfit function

2019 ◽  
Vol 16 (6) ◽  
pp. 1017-1031 ◽  
Author(s):  
Yong Hu ◽  
Liguo Han ◽  
Rushan Wu ◽  
Yongzhong Xu
Keyword(s):  
Frequency Domain ◽  
Seismic Data ◽  
Waveform Inversion ◽  
Low Frequency ◽  
Full Waveform Inversion ◽  
Local Correlation ◽  
Time Frequency ◽  
Model Dependence ◽  
Full Waveform ◽  
Frequency Components

Abstract Full Waveform Inversion (FWI) is based on the least squares algorithm to minimize the difference between the synthetic and observed data, which is a promising technique for high-resolution velocity inversion. However, the FWI method is characterized by strong model dependence, because the ultra-low-frequency components in the field seismic data are usually not available. In this work, to reduce the model dependence of the FWI method, we introduce a Weighted Local Correlation-phase based FWI method (WLCFWI), which emphasizes the correlation phase between the synthetic and observed data in the time-frequency domain. The local correlation-phase misfit function combines the advantages of phase and normalized correlation function, and has an enormous potential for reducing the model dependence and improving FWI results. Besides, in the correlation-phase misfit function, the amplitude information is treated as a weighting factor, which emphasizes the phase similarity between synthetic and observed data. Numerical examples and the analysis of the misfit function show that the WLCFWI method has a strong ability to reduce model dependence, even if the seismic data are devoid of low-frequency components and contain strong Gaussian noise.

Elastic inverse scattering for fluid variation with time-lapse seismic data

Geophysics ◽  
2015 ◽  
Vol 80 (2) ◽  
pp. WA61-WA67 ◽  
Author(s):  
Zhaoyun Zong ◽  
Xingyao Yin ◽  
Guochen Wu ◽  
Zhiping Wu
Keyword(s):  
Shear Modulus ◽  
Inverse Scattering ◽  
Seismic Data ◽  
Scattering Theory ◽  
Time Lapse ◽  
Monitoring Data ◽  
Prestack Inversion ◽  
Fluid Factor ◽  
Reference Medium ◽  
The Difference

Elastic inverse-scattering theory has been extended for fluid discrimination using the time-lapse seismic data. The fluid factor, shear modulus, and density are used to parameterize the reference medium and the monitoring medium, and the fluid factor works as the hydrocarbon indicator. The baseline medium is, in the conception of elastic scattering theory, the reference medium, and the monitoring medium is corresponding to the perturbed medium. The difference in the earth properties between the monitoring medium and the baseline medium is taken as the variation in the properties between the reference medium and perturbed medium. The baseline and monitoring data correspond to the background wavefields and measured full fields, respectively. And the variation between the baseline data and monitoring data is taken as the scattered wavefields. Under the above hypothesis, we derived a linearized and qualitative approximation of the reflectivity variation in terms of the changes of fluid factor, shear modulus, and density with the perturbation theory. Incorporating the effect of the wavelet into the reflectivity approximation as the forward solver, we determined a practical prestack inversion approach in a Bayesian scheme to estimate the fluid factor, shear modulus, and density changes directly with the time-lapse seismic data. We evaluated the examples revealing that the proposed approach rendered the estimation of the fluid factor, shear modulus, and density changes stably, even with moderate noise.

Near Surface Research and Excitation Horizon Prediction Based on Old River Course of Xiaoqing River in Shan Dong

2013 ◽  
Vol 664 ◽  
pp. 94-98
Author(s):  
Guang De Zhang
Keyword(s):  
Seismic Data ◽  
Practical Significance ◽  
Cone Penetration ◽  
Surface Deposition ◽  
Near Surface ◽  
Sedimentary Characteristics ◽  
The Difference ◽  
Exploration Area ◽  
Data Requirements ◽  
Static Cone Penetration Test

Following deepened exploration and development in Shengli exploration area, seismic data requirements are also getting higher and higher. However, in recent years the difference of Xiaoqing river on both sides have made us know that the importance of this problem. In view of the above, this task is aimed at quaternary shallow of old river course within Xiaoqing River. Our analysis of lithology and sedimentary characteristics are using static cone penetration test and rock core exploration method, and we want to reappear near surface deposition of old river course within Xiaoqing River. The research is close combined with the exploration demand and theoretical study, so it has important theoretical and practical significance.

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