Processing for Preservation of Seismic Amplitudes
The rediscovery of the exploration significance of seismic event amplitudes was one of the important steps in recent progress toward direct detection of hydrocarbons. At the same time we appreciate that a closer look at amplitudes is of great importance particularly in search of stratigraphic objectives.
The figure which follows is adapted from Lindseth and notes the mechanisms which cause the seismogram to be generally weaker with increased reflection time. Against this background the amplitude distinction between a strong reflection and weak one as shown is a secondary matter.
In fact, we are not really speaking strictly of reflection amplitude which is a frequency dependent quantity. Amplitude as used in the present context refers to a gross measure of the peak of a reflection envelope and more correctly should be termed “reflection strength” or “reflection level”.
Divergence losses are, of course, a natural consequence of spreading wavefronts and would occur whether or not reflecting Interfaces or velocity gradients were present, though these govern the specific divergence behavior. Partial reflection losses (or transmission losses), on the other hand, occur only because partially reflecting interfaces are present. The more Interfaces that are present, the greater these losses will be. Hence, transmission loss effects can be greater or less than divergence losses, depending upon the reflective distribution.
Attenuation losses are least well understood of all these mechanisms. They Are bound up both with the absorptive process which turns seismic energy into heat, and scattering by material inhomogeneities which makes a seismic signal lose
Figures & Tables
Stratigraphic interpretation of seismic data requires that the seismic information be expressed in geological terms. The strictly geological view of the earth is developed from surface observations, guiding principles of geological evolution and subsurface information from bore holes. Seismic measurements on the other hand, define in some sense the subsurface geometry and give estimates of the acoustic impedance which is related to the rock velocities and densities. This publication contains eight chapters on: relating seismic data to stratigraphy; information content and resolution potential of seismic data; processing for preservation of seismic amplitudes; the role of seismic wavelets and wavelet processing; contributions of geoseismic modeling; qualitative stratigraphic correlations; quantitative stratigraphic correlations; and conversion of seismic data to log-like displays.