Abstract

Spectral decomposition analyses seismic reflectivity data in the frequency domain, providing images of the subsurface that complement conventional seismic interpretation. It is a highly visual tool that allows additional value to be extracted from seismic data, to aid in the identification of geological information and to be used in conjunction with more traditional methods such as amplitude extraction and attribute analysis. The methods of spectral decomposition chosen utilized a top reservoir seismic reflection surface, with the selected dominant frequency volumes coloured and recombined in a spatial context to produce various red–green–blue (RGB) blends. Application of spectral decomposition to the Laggan and Tormore fields revealed the varied distribution of turbiditic sands, as well as extensive east–west faults that have previously been inferred from seismic reflection data. These enhanced images of the reservoir provide a more detailed interpretation of the field architecture and have been captured in DONG E&P UK Ltd's own fault and reservoir models, leading to a greater understanding of potential field development outcomes and future well placement decisions. Attempts to distinguish hydrocarbon effects using spectral decomposition proved difficult, although interesting frequency variations around a known gas–oil contact (GOC) were noted.