Amplitude decomposition of thin layer offset versus amplitude data



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The elastic characteristics of a lithologic interface will determine how the incident energy partitions at the interface for various angles of incidence. This phenomenon can be observed on common midpoint gathers as variations in the amplitude of the reflected signal obtained at different source and receiver offset distances. This information can be used for lithologic interpretations. At present, the majority of offset/amplitude research has been constrained to single interfaces where there is no interference from underlying reflections. This means that offset interpretations cannot be applied to cases exhibiting reflection interference such as thin layers. The objective of this dissertation was to find a means by which the thin single layer composite reflection could be decomposed into its interface offset responses. Two methods were approached to solve this problem. One approach attempted to measure the amount of wavelet interference within a thin layer using input thickness and wavelet estimates. The second approach attempted to relate the difference between the measured peaks and troughs of the thin layer reflection to the top and bottom interface responses. The combination of the two approaches produced a decomposition equation that could recover the interface responses from a thin layer reflection. The validity of the decomposition equation was tested with three types of data sets. A numerical data set was used to test if the general principles of the decomposition method could be successfully applied. A physical tank model was used to test the method in an environment more complex than the numerical methods could provide. The third data set was a field case that tested the application of this method as an interpretational tool. The significance of this new method is that it allows techniques for lithologic interpretations with offset to extend into the thin layer area. The other important contribution is that it can provide an additional technique to measure lateral thickness and lithologic variations within a thin layer.



Seismic reflection method