Rock physics, trend curves and flat-spots

Abstract

Seismic amplitudes and AVO have been used successfully in exploration worldwide. We present a general geologically-based methodology to characterize the expected amplitude and AVO behaviours of reservoirs and seal facies in a basin. We produce a rock physics model based on well data and consistent with the geological model for the basin. The result is summarized in a series of depth trend curves for rock properties and anticipated seismic responses, illustrated here with data from the West of Shetlands, UK, to predict amplitude and AVO responses throughout the basin. A by-product of the technique is the verification of the validity of the amplitude changes and flat-spots which can result from physical property changes across fluid interfaces. For example, seismic flat-spots cross-cutting dipping stratigraphy are commonly observed within the Triassic Mungaroo Formation of the Exmouth Plateau area of the North Carnarvon Basin. We show techniques for quantifying the consistency of flat-spots in 3D, assessing amplitude conformance with structure in map view and automatically determining fluid contact levels.