Abstract

The Top Khuff is a major regional seismic marker in Saudi Arabia with an apparent strong and consistent amplitude interpreted as a large impedance contrast between the Khuff carbonate and the overlying Sudair shale. However, the effective Top Khuff response is, in fact, a complex reflection of a stack of thin beds of highly contrasting impedance with significant lateral variations in reflectivity and thickness. Interference among these reflected waves disturbs the amplitude strength and effective reflection time of the Top Khuff and alters the phase and frequency bandwidth of the reflection wavelet. Variations in the Top Khuff amplitude and reflection wavelet were quantified using a Ricker wavelet and solved as an inverse problem with four model parameters: reflection coefficient, reflection time, phase, and frequency. These model parameters are interrelated, and the effective seismic response in a complex situation is a compromise among them. The fit of the Ricker wavelet with the Top Khuff amplitude revealed significant variations in these parameters and verified the Top Khuff is not a simple reflector and may not be a suitable reference horizon for seismic amplitude processing.

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