Quantitative Thickness Estimates Based On The Spectral Response Of AVO Measurements

With the difficulty of improving oil exploration, oil companies and geophysicists will increasingly focus on the study of thin interbedded reservoir.In China, thin interbedded reservoir is widely distributed in most lakes basin, land and sedimentary bodies of development potential. Research on thin interbedded reservoir have been decades of history, which is to study the seismic resolution technology of thin layer, identify amplitude response of a thin layer of meaning and thin, thin layer thickness estimates, thin reservoir delineation and lateral projections. How to determine the spatial distribution of thin and how to describe the response characteristics of the thin layer has become a hot and difficult project. However, studies of reservoir heterogeneity and complexity of seismic wave propagation in thin reservoir caused many obstacles and exploration success rate is low. AVO seismic technology as the most important methods of thin interbedded reservoir has been widely used. But most of the AVO technology are based on Zoeppritz equation and its derivation formula, these formulas are built on the assumption that the medium above and below of the interface exists in the elastic half-space, regardless of the reservoir sedimentary Effect of the thickness of the interlayer and the plurality of attenuation factors. AVO technology based on Zoeppritz equation cannot meet the requirements of studying thin interbedded reservoir.Over the past years, geophysicists use seismic data for problem solving TLC carried out extensive research, has made remarkable achievements.Due to the limited resolution of seismic data, such that each of the seismic wave is reflected by the seismic waves generated by a thin layer of mutual interference, superposition of the results, the use of such a thin layer of conventional seismic data interpretation is difficult. To solve the problem of thin reservoir prediction in recent years, geophysicists have to use a lot of new technology and methods for qualitatively and quantitatively description of thin reservoir characteristics.This paper firstly discusses the basic theory of seismic AVO technology, on the basis of the main factors affecting AVO forward modeling discussed. Then Point out the elements to impact the sub-wave AVO response, such as petro-physical parameters and reservoir thickness. The amplitude and frequency of earthquakes exists certain relationship, through the time-frequency transform, AVO analysis of seismic reflection wave in frequency domain, can improve the seismic resolution, which is more concerned with the production and research of the problem, comparing with interference, vertical resolution and other factors depends on the wavelength. Interference effects were thin on the theoretical study, indicating the formation mechanism of thin reservoir composite wave. Through the establishment of a wedge-shaped forward simulation model to study the seismic response characteristics of thin reservoir, drawn relationship between seismic reflection parameters and the thickness. That is larger than the thickness of a quarter of the local sub-wave can be long depending on the thickness of the amount to reflect the true thickness of the formation. The local layer thickness is less than a quarter of sub-wave length, then its apparent difference seismic response is substantially constant, does not vary with the true formation thickness, but within the range of peak-to-trough amplitude values are showing a regular change, so I can use some of the properties of quantitative parameters associated with the amplitude solving.Spectral analysis is the basis of seismic data processing, because the seismic signal is a complex non-stationary signal, suitable time-frequency analysis is key to ensure the quality of the time spectrum analysis of seismic data. Since when has the traditional method of frequency analysis method itself defects (short window Fourier transform window function is fixed, while the wavelet transform is not a real time spectrum), the paper quoted the S transform time-frequency analysis method. S transform can be derived, respectively, and the continuous wavelet transform short-time Fourier transform of the window, which combines the advantages of both transformations, while avoiding their disadvantages:it is the Fourier transform of a direct link with lossless reversible; with short window Fourier transform and wavelet transform, is a linear time-frequency representation, so the cross-term interference does not exist; S transform with a variety of resolutions, to overcome the lack of short-time Fourier transform of the window fixed resolution; additionly. Therefore, this study several basic time-frequency analysis method, based on a wedge-shaped model, discussed the basic principles of S transform and spectral analysis of the use of S transform theory of single-channel signal,TLC reflectance spectrum exists notch phenomenon notch period of time determined by the thickness of a single layer, and thin interbedded layers of interaction, reflection coefficient magnitude and polarity of the reflection coefficient of reflection coefficient sequence forms only affect the amplitude spectrum. With this cyclical characteristics, can quantified thin interbedded reservoir thickness.