A New Approach to Seismic Interpretation in Challenging Imaging Environments
C. Edward Helsing and David C. Berman
ExxonMobil Exploration Company, Houston, TX
A seismic image adjacent to a complex velocity anomaly such as a salt body comprises reflections resulting from multiple ray path types. Despite application of multipathing algorithms such as Wave Equation PSDM, the full stack seismic data generally exhibits low signal to noise ratios allowing for multiple valid structural interpretations. We present a new approach to this common interpretation problem.
Recent advances in computing now allow commercial production of Wave Equation PSDM subsurface angle gathers which are used for residual velocity updates. Taking the next step and stacking subsurface angle gathers provides the interpreter with a new way of viewing seismic data, in which partial stacks are defined as a function of subsurface angle rather than the familiar surface offset or angle. This distinction is important because subsurface angle stacks more often efficiently separate signal from noise compared to surface offset or angle stacks. The reason for this is, given a point in the volume, a dip and a reflection angle, the ray paths from a given source and receiver to the image point are uniquely defined. This is not true for surface offset data in a multipathing situation.
Using subsalt examples from the Gulf of Mexico we describe a technique that allows the interpreter to integrate subsurface angle stacks with seismic and non seismic datasets to discriminate between valid alternative structural interpretations.
Additional applications of this technique include imaging beneath velocity anomalies related to shallow gas, large discovered gas fields or anomalous channel fill within the overburden.