AAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Look Within Your Wavelet: 3-D Seismic Analysis Workflows to Investigate Subtle Stratigraphy
(1) ffA, Houston, TX.
(2) ffA, Aberdeen, United Kingdom.
Stratigraphic features such as pinch outs, internal bedding geometries and clinoforms often fall below the level of seismic resolution. Seismic analysis workflows can help improve vertical resolution and identify thin beds on seismic reflection data, which can in turn lead to more accurate stratigraphic interpretation. We present a workflow that combines Spectral Enhancement, Color Blending, and Terrace and Bedform attributes to enhance the vertical resolution of 3D seismic data. Examples from several 3D data sets from different geologic settings illustrate the wide applicability of this workflow.
High frequency reflections are attenuated by the earth, so their influence in reflectivity data is reduced with depth, resulting in poor definition of thin beds. Enhancement of frequency in many cases also leads to an increase in noise levels, along with the increase in resolution. We present a unique approach that selectively enhances the remaining high frequency signal by applying frequency-dependent, structurally-oriented noise filters in order to enhance signal but not noise. This results in improved vertical resolution of the data, and thus better imaging of thin beds.
The frequency decomposition process presented here outputs a number of bandpass, magnitude and phase volumes generated at discrete frequencies. Using a Color Blending tool, three magnitude volumes can be combined and viewed simultaneously to reveal the interplay between the responses at three different frequencies. This can reveal a wealth of information about stratigraphic facies and facies boundaries. And by viewing the Color Blend on a horizon, the interpreter can view high-resolution stratigraphic information at and around a specific geological event. A Color Blend can also highlight subtle and previously unseen faulting.
Two attributes have been found to be particularly effective at delineating thin beds. The Terrace attribute is a wavelet blocking attribute that assigns the maximum amplitude to segments of a seismic trace between points of curvature. This results in the separation of wavelet doublets, allowing interpretation of previously unresolved events. The Bedform attribute extracts lineations along peaks and troughs based on phase, rather than amplitude, revealing stratal relationships more clearly. When calculated from spectrally enhanced (and conditioned) data, the Terrace and Bedform attributes can reveal subtle stratigraphic details, such as clinoforms and pinch outs.