The Method Research And Application Of Reservoir Fluid Identification In Time-Frequency Domain

Fluid identification is an important part of reservoir predication. With the development of oil-gas exploration and exploitation in our country, exploration areas transfer from structural hydrocarbon reservoir to lithologic hydrocarbon reservoir and subtle reservoir, how to identify fluid by effectively using the seismic information has become a hot research issue in geophysics circle. Because of the oil and gas reservoir researched by seismic exploration becoming more and more complicate, it's difficult to identify fluid only by little information or one method, and each method has some limitations, so it becomes important to use more seismic information and research different fluid identification method.This paper base on the spectral decomposition technique, explicitly introduce the principle and the advantages and disadvantages of time-frequency analysis method such as short-time fourier transform, wavelet transform, Wigner-Ville distribution, S transform and generalized S transform, and carry on numerical experiment by using synthetical simulation signal, directly contrast the effect of all the method, finally choosing the generalized S transform as the method of the spectral decomposition to provide a effective tool and means for carrying out the method research of reservoir fluid identification in time-frequency domain.The potential meaning and application value of the seismic low frequency information has been attached importance of the geophysics exploration circle. This paper introduced the definition of low frequency shadow and all kinds of factors that might result in low frequency shadow, and explicitly elaborate the research of all scholars to low frequency shadow based on the physical model and carry on numerical simulation of low frequency shadow by using viscous and diffusive wave equation, obtain the similar results compared to physical simulation, theoretically demonstrate the existence of low frequency shadow below the layer filled with fluid, meanwhile, extract the common frequency section by using the spectral decomposition technique to identify the low frequency shadow below the reservoir in the actual seismic data.Absorption parameter was regarded as one of the most sensitive and reliable indicators in oil and gas predication.This paper explicitly elaborate the mechanism of seismic wave absorption and attenuation, and introduce energy absorption analysis technique (EAA) and the technique developed from it called instantaneous wavelet absorption analysis. The technique proposed that the high absorption in the high frequency part of the instantaneous wavelet spectrum is in connection with the gas in the rock pore and the high absorption in the low frequency part may predict the water (oil) saturation. Obtaining the instantaneous seismic wavelet through the spectral decomposition to the seismic data, thus get the absorption coefficient by fitting the attenuation curve of low and high frequency part of the instantaneous wavelet spectrum to realize the reservoir fluid identification. This method applied in the actual seismic data and the effectiveness was showed in the result.Prestack seismic data contain ample stratigraphic information, especially when the reservoir filled with fluid, the information reflected by the different angle gather has much more difference in the place where filled with fluid and almost has no difference in the place where didn't fill with fluid. In AVO analysis, the affection of fluid was distinct in the far angle gather, further more, the amplitude contrast between oil sand and brine sand is higher at low frequencies. Based on the above phenomenon this paper porposed an instantaneous spectrum frequency difference analysis formula of prestack angle gather, and carried out the instantaneous spectral decomposition to the prestack different angle gather, highlight the anomaly information of fluid by using the instantaneous spectrum difference in low frequency of the different angle gather. The effectiveness was tested by the actual seismic data.