TECHNIQUES IN SUBSURFACE MAPPING USING SPECTRAL DECOMPOSITION AND WELL LOG CHARACTER: CASE STUDY OF CENOZOIC FLUVIAL & MARGINAL MARINE RESERVOIRS OF LLANOS FOOTHILLS, COLOMBIA

An exploration workflow is proposed which involves the use of spectral decomposition of 3D seismic data integrated with well log character. The new spectral decomposition analysis techniques are demonstrated with the identification and mapping of complex subsurface potential fluvial reservoirs south of the giant Cusiana oil field, Llanos Foothills, Colombia. Gamma ray well logs are normalized to capture the sedimentological character and improve the interpretation of cyclicity and depositional settings of well log displays and cross-sections while spectral decomposition detects the subtle stratigraphic features undetectable in the time domain seismic data. The observed geomorphological changes in fluvial system geometries in the Cenozoic formations revolutionize depositional models that predict changes in slope gradient, sediment source, and tectonic activity of the present day Eastern Cordillera. From the perspective of potential plays, spectral decomposition interpretations reveal low frequency shadows that may be direct indicators of gas accumulations associated with overbank and channel fill. The workflow described here can be replicated in other areas establishing powerful interpretive subsurface mapping techniques for the generation of exploration and production depositional models.