Estimation of Seismic Attenuation (Q) from VSP Data

The aim of seismic processing is to obtain a high-resolution image of the subsurface. Many step effort to accomplish this goal. One of these steps that must be insisted is the compensation for the absorption of seismic energy in the earth. Seismic energy attenuation is linked to the degree of compaction of sediments, the presence of gas, the degree and type of fluid saturation. In this paper, the P-wave seismic attenuation is studied as Q factors using zero offset vertical seismic profiling (VSP) data from the Arvand oilfield, Iran. Q factor decreases as the attenuation increases. We use the spectral ratio method to calculate the interval attenuation. The analysis is carried out in frequency domain on down-going waves. The data is supposed to preserve from effect of source wavelet. The average velocity is picked from first arrivals and true amplitude is recovered by compensation for spherical divergence effect. The results have a good agreement with impedance log where the over pressure and hydrocarbon zones present.