Summary
The estimation of the quality factor is a important task to compensate the seismic energy dissipated during the acoustic/ elastic wave propagation in the earth. In this context, it is known in seismic processing stage, that the main goal of the Q-filtering is to improve the resolution of the seismic signal as well as to recover part of this energy dissipated by attenuation. In this work, we propose a way to improve the estimation of quality factor from seismic reflection data. Our methodology is based on the combination of the peak frequency-shift (PFS) method and the redatuming operator. The innovation in this work is in the way we correct travel times when the medium is consisted by many layers. In other words, the correction of traveltime table used in the PFS method is performed using the redatuming operator. This operation, which is performed iteratively, allows the estimation of the Q-factor layer by layer in a more accurate way. Application in synthetic and real (Viking Graben, North Sea, Norway) data sets demonstrates the feasibility of our analysis.
Introduction
When seismic waves propagate inside the earth, they suffer amplitude attenuation due to the inelasticity and the heterogeneities of the medium (Ricker, 1953; Futterman, 1962; White, 1983; Kneib and Shapiro, 1995). It is well know that attenuation causes a loss of high-frequency energy with increasing traveltime and time broadening of wavelet amplitude (dispersion). To estimate and compensate the absorption of seismic waves is a fundamental task in seismic processing and interpretation. These operations are important because it allows the improvement of the high-frequency (resolution) of seismic images, and consequentiality provides a better interpretation of the effects of AVO, obtaining also information on lithology, saturation, permeability and pore pressure (Best et al., 1994; Carcione et al., 2003; Carcione and Picotti, 2006).
Several methods have been developed for estimating the qualityfactor from reflection and transmission data. Dasgupta and Clark (1998) adapted the classic spectral ratio method (Bath, 1974) for determining the seismic quality factor Q from conventional common midpoint (CMP) gathers. Tonn (1991) using different numerical methods (among them spectral modeling and spectral ratio (Bath, 1974)) estimated the quality factor Q from VSP (vertical seismic profile) data. Blias (2012) also modified the spectral ratio method (Bath, 1974) for Q determination from near-offset VSP data. de Castro Nunesa et al. (2011) performed a comparative study to estimate the Q factor using different approaches, including the PFS method (Zhang and Ulrych, 2002) analyzed in this work.
