The value and utility of 3d seismic post-stack post processing in a structurally complex environment: A ncs case study
|Location||International Geological Congress,oslo 2008|
|Author||Spencer, Paul۱; Fisher, Gaynor۲; Henderson, Jonathan۲|
|Holding Date||15 September 2008|
A case study is presented which demonstrates how 3D seismic post-stack post-processing techniques have proved to be an essential step in both the verification of existing structural interpretations and the further delineation of play fairways in a complex hangingwall developed above a linked arcuate ramp-flat fault system. Several local wells have drilled in footwall degradation slump complexes, proving hydrocarbons at several levels. Further prospectivity is recognised in Brent reservoirs trapped in accommodation structures above ramp-flat segments and within the syn-tectonic Upper Jurassic packages that appear to both erode and infill the evolving topography.
Understanding the geometry of the controlling bounding fault system is hampered by noise in the vintage input data: A range of 3D seismic post-stack post-processing techniques are widely available which can substantially aid interpretation in such circumstances. These post-processing techniques can be used for both conditioning the input data for specific interpretation tasks and highlighting or delineating features associated with specific elements of the imaged geology.
In this study the primary objective was to provide increased confidence in defining fault trajectories and the accurate delineation of the syn-tectonic Upper Jurassic section. This was addressed by a two-stage directed image-processing workflow. The output from this workflow is a set of seismic volumes that are now utilised within the 3D interpretation workflow by the partnership.
Improved structural imaging was attained through the iterative application of adaptive noise-attenuation filters. The techniques applied in this study permit the user to define a set of parameters that control the applied filters in order to address the specific interpretation objectives. In this study maximising the clarity of features associated with the larger scale faulting was deemed to override the need to retain very small scale discontinuities and faults.
In order to improve the imaging of the syn-tectonic Upper Jurassic fairway, spectral whitening was applied to the Noise Cancelled data. This resulted in enhanced vertical resolution without increasing the noise level in the data and improved imaging of the internal seismic character which, when coupled with improved continuity of the data, allowed more confident mapping of this important exploration upside.
Although these post-processing techniques do not give a definitive answer regarding the imaged sub-surface geology, they do provide additional and valuable information that enables the interpreter to develop a more robust model of the imaged sub-surface geology and therefore better quantify the associated uncertainties. The added value is that an exploration team is empowered to begin constructive interpretation on an otherwise sub-optimal dataset whilst awaiting a new seismic dataset to be acquired.