Robust prestack Q-determination using surface seismic data: Part 2 — 3D case study

Abstract

In part one of this paper, we introduced a novel method of measuring seismic attenuation from prestack surface seismic data. This prestack Q-inversion (PSQI) employed methods to reduce the presence of spectral interference and then minimize the influence of interference that remains. By changing the domain of operation, angle-dependent effects in the overburden were eliminated when a locally 1D medium was assumed. To demonstrate the suitability of the PSQI method, we applied it to a 3D seismic survey from Western Canada. Preprocessing of the data was carried out to reduce noise, regularize amplitudes, and transform the seismic gathers into the [Formula: see text]-p domain prior to attenuation measurements. In addition to the seismic gathers, we also incorporated velocity data and zero-offset traveltime information. The result was that we were able to generate a map of 1/Q values which showed coherent patterns that could be explained by the presence of top gas in the reservoir. These measurements were correlated to independent amplitude attributes. We performed a number of other analyses to establish the appropriateness of the attenuation measurements. We compared 1/Q measurements with the predecessor QVO method, and showed that the PSQI measurements were less influenced by artifacts and were more robust to changes in the bandwidth of analysis. We also analyzed a VSP survey in the same geological setting and showed that the resulting measurement (1/Q = 0.0271) is very close to the mean PSQI value for the 3D survey (1/Q = 0.0312). This case study thus showed how the described PSQI method overcame many of the difficulties associated with obtaining accurate attenuation measurements from surface seismic data.