A Discussion on Factors Affecting the Results of Thin Bed Thickness Determination Using Spectral Inversion

Abstract

Layer thickness is regarded as the basis for other steps of reservoir evaluation and simulation. This makes it highly important in oil exploration and production, motivating researchers to establish several methods to determine it. Having a migrated zero-offset seismic section, it is usually easy to evaluate the thickness of a layer from the distance between the top and the base of the layer in a peak-to-peak or trough manner. However, in locations wherein the layer thickness is not sufficient to yield two distinct peaks/troughs from its top and base-that is, when the layer thickness is below the tuning thickness-this simple method may not be useful. Hence, other methods need to be developed for this case. Spectral inversion is a method that uses spectral decomposition to improve images of layers whose thicknesses are below the tuning thickness. In this method, a procedure is formulated to invert the frequency spectra of the layer thickness, which is then applied to synthetic data using a complex spectral analysis. Layer thicknesses significantly below the seismic tuning thickness can be accurately determined in this manner without amplitude calibration. In this article, the spectral inversion method is applied to symmetric and asymmetric wedge models and the result is evaluated by changing different parameters to investigate their effects. It is concluded that the approach not only guarantees the effectiveness of spectral inversion but makes it fast enough to be practical in use for a short frequency band of the lowest available frequencies together with short enough investigation intervals for layer thickness (T) and even component of reflectivity series squared minus odd component of reflectivity series squared, k D r 2 e r 2 o .