Vertical resolution and seismic data interpretation

Abstract

　Understanding and comprehension of vertical resolution of reflection seismic profiles are important for the interpretation of underground structures. When considering vertical resolution, we need to take account of separability which indicates the ability of the separation of two wavelets, and of visibility which comprehends thickness of the thin layer from amplitude. For the separability, the one-quarter wavelength law is applicable, and two wavelets are independently recognized. Visibility depends on the signal-to-noise (S/N) ratio, and the thickness of one thirties of wavelength can be detected in the outstanding S/N case. The theory of the separability can be formulated using Ricker or sinc wavelets, but the basic wavelet of the actual seismic section is not always simple. So, we have to manually interpret predominant frequency from the seismic section. Predominant frequency varies depending on the depth of the target. Regarding the source, smaller the size of source, higher the predominant frequency, but penetration of the energy degrades. Selection of the optimum source size for each target is essential. During the seismic interpretation, understanding of the geological setting is also important, which determines the difference of seismic anomaly and actual layer extents, for example. In the case of thin layer, we have to consider the apparent alteration of the wavelet shape and AVO effects. And when integrating core, log and seismic data, we need to consider the adjustment of the vertical resolution of them. When we interpret more complex actual seismic sections, consideration of specific underground condition and parameters of data acquisition/ processing is necessary in addition to the resolution basics discussed in this paper.