Siyuan Cao

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

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 ...

Phase scanning method for detuning in thin bed

﹟＋ ﹟ ＋ Summary Thin bed response is one of key concerns in seismic amplitude interpretation, owing to tuning effect that depends on both thickness and offset. We propose a methodology to remove tuning effect in order to obtain true amplitude. Traditional detuning methods can’t handle nonzero phase wavelet and can’t effectively remove tuning effects of thin layer with thickness above /8 λ when the tuning effect is most severe. In this study we proposed a new method, called phase scanning, that has potential to solve this problem. The synthetic study shows that our method is effective to any kind of wavelets, noise tolerant, and applicable to a wide range of thickness of the thin-bed.

Frequency‐dependent AVA variations in thinly layered porous media

Amplitude-Versus-Offset (AVO) technology has successfully helped to detect hydrocarbon reservoir for more than two decades. However, the Zoeppritz equation only considers the elastic properties of the media, the nonelastic behaviors are ignored. There are still some problems that the traditional AVO technology doesn’t handle adequately. Although the frequency-dependent AVO technology has been brought forward, a theory is lacking to guide it. Based on White’s patchy saturation model, we have investigated characteristics of the frequency dependent Amplitude Versus incident-Angle (AVA) at an interface between a non-dispersive medium and a patchysaturated dispersive medium. And then, numerical modeling based on Biot’s poroelastic wave theory was performed on three selected reservoir models. The numerical modeling results confirmed our analytical analysis. These variations could provide insight for frequency-dependent AVO analysis.

True Amplitude Extraction Technology and Its Application in Pre-Stack Seismic Data

Common-reflection-point (CRP) gather is a bridge that connects seismic data and petrophysical parameters. Pre-stack attributes extraction and pre-stack inversion, both of them are important means of reservoir prediction. Quality of CRP gather usually has great impact on the accuracy of seismic exploration. Therefore, pre-stack CRP gathers noise suppression technology becomes a major research direction. Based on the vector decomposition principle, here we propose a method to suppress noise. This method estimates optimal unit vectors by searching in various directions and then suppresses noise through vector angle smoothing and restriction. Model tests indicate that the proposed method can separate effective signal from noise very well and suppress random noise effectively in single wavenumber case. Application of our method to real data shows that the method can recover effective signal with good amplitude preserved from pre-stack noisy seismic data even in the case of low signal to noise ratio (SNR).

Wide-band B-spline Wavelet With Four Parameters

Summary Based on the wavelet decomposition theory of seismic pulse and its reconstruction, we proposed one method to make of wide-band wavelet. A series of seismic wavelets can be made in this way. In virtue of complex frequency Bspline wavelet, we formed the wide-band B-spline wavelet with four parameters and deduced its analytic expression both in the time domain and in the frequency domain. The numbers and energy of side lobes of the new wide-band Bspline wavelet with four parameters can be easily adjusted through its parameters. In comparison with the Ricker wavelet and wide-band Ricker wavelet in the condition of same main lobe equivalent frequency, the wide-band Bspline wavelet with four parameters not only has smaller side lobe but also has shorter time length. The synthetic result of wedge model indicated that the wide-band b-spline wavelet with four parameters has higher resolution. Finally, we also discussed its parameters adjustment in the practical application. Therefore, the seismic data processors and interpreters may have more seismic wavelet selections conveniently.