Spectral Analysis of Outcrop-Based Synthetic Seismic Data; an Example from the San Fernando Slope Channel System, Baja, California

Turbidite channels are important hydrocarbon reservoir types but difficult to predict due to their complex internal architectures and highly variable facies. The well-exposed, late Cretaceous San Fernando slope channel system in Baja California, Mexico, provides a good opportunity to analyze the internal architecture and lithofacies variation at unprecedented scales. Forward seismic modelling of outcrops incorporates outcrop scale details into the interpretation of conventional seismic data. Spectral decomposition methods provide the possibility to detect features of the various architectural channel complex elements and lithofacies associations which are typically below seismic resolution.

The San Fernando slope channel system is a conglomeratic, Deepwater channel-levee system that trends oblique to the slope, and consists of at least four channel complex sets each bounded by an erosional surface, where axial parts are controlled by a contemporaneous fault. Comprehensive outcrop data were utilized to construct a detailed geological model that includes lateral and vertical architecture and lithology changes. The geological model is 250m in vertical scale and 2500m in the horizontal - substantially larger than any previously reported in literature.

The synthetic seismograms presented are generated through finite-difference elastic modeling; they illustrate seismic responses of different typical slope channel lithofacies associations, and the effect of physical property variation on seismic expression. The marginal parts of channels present strong reflections, while axial amalgamated channels correspond to weak and pulled-up reflections due to hard acoustic impedance and similar internal lithofacies association, which would likely been misinterpreted as marginal parts. Spectral analysis of synthetics shows that thin, non-amalgamated channels are detectable at low frequencies and channels' discontinuity shows up at high frequencies, the axial amalgamated channels are not revealed at any frequencies. The effects of lithology, thickness and internal architecture on spectral features were tested. Lithofacies assemblages have impact mainly on amplitude; frequency change is mainly determined by thickness. Among different sub-seismic internal architectures only the inclined surfaces are detectable at high frequencies. The results highlight how this approach has the potential to aid the interpretation of architectural elements in conventional seismic data.

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California