1. Unconventional Gas Research Institute, China University of Petroleum(Beijing), Beijing 102249, China; 2. State Key Laboratory of Petroleum Resource and Prospecting, China University of Petroleum(Beijing), Beijing 102249, China; 3. State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Chengdu University of Technology, Chengdu, Sichuan 610059, China; 4. The First Exploitation Factory, Huabei Oilfield Company, PetroChina, Renqiu, Hebei 062552, China
Abstract:The essence of time-frequency analysis is windowed Fourier transform which is performed by multiplying seismic data by a window function before Fourier transform on this windowed signal.Therefore,the time-frequency spectra contain frequency response of the window function,which contaminates wavelet spectrums and consequently makes the relationship between spectral ratio and frequency in the classical spectral ratio method becomes nonlinear.To overcome this problem,we propose a new spectral ratio formula in the generalized-S domain.In our new Q estimation formula,we define a new parameter γ that relates to the window shape controlled parameters λ and p.What is interesting is that the spectral ratio happens to have linear relationships with γ.In this case,we should perform linear fitting between spectral ratio and γ during Q estimation,and the reciprocal of the slope of the fitting line equals to Q.Synthetic and field data tests allow us to obtain the following understandings:①The time-frequency instantaneous amplitude spectra in the generalized S domain are different from conventional Fourier spectra,which is caused by the amplitude distortion induced by high amplitude property of Gauss window function at high frequency end; ②The spectral ratio calculated by instantaneous amplitude spectra in the generalized S domain has obvious nonlinear relationship with frequency,which does not correspond to the classical Futterman attenuation mechanism.Interestingly,there is a linear relationship between spectral ratio and new defined parameter γ.We detect the hydrocarbon abnormal of a reef reservoir in South China Sea using our proposed Q estimation method,low Q value abnormal obtained in this area indicates the presence of oil reservoirs.
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