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Seismic Attributes for Reservoir Characterization in Deepwater Settings - Offshore Colombia (Guajira Basin)

Abstract

The uncertainties associated with reservoir identification during the exploration process are reduced through the use of methods such as seismic attributes and inversion. These techniques provide interpreters with a powerful tool to enhance the subsurface information, resulting in more accurate geologic models for play and prospect definition. Gas was discovered in a well drilled in 2014, confirming the hydrocarbon potential in the Guajira offshore basin. Given the high amplitude of target horizons and correlations with onshore outcrops, initial interpretation considered a carbonate hosted reservoir. Instead, the gas was hosted in an Eocene/Oligocene siliciclastic reservoir. After this discovery and the integration of the results into the regional framework, a search was made for an effective approach to avoid seismic misinterpretations related to lithological identification. Using reservoir petrophysical properties, the characterization of the turbidite deposits was made through seismic attribute analysis and inversion, calibrating the well data with the seismic expression in 1,500 km2 of reflection data (pre-stack time migration). A chronostratigraphic marker horizon, used to define the limits of extensional sedimentation undeformed by Late Miocene–Pliocene subduction (Mantilla et al., 2013), was the basis of this assessment. This included geometry and distribution, as well as seismic response and relations between seismic facies, seismic attributes, and petrophysical properties. The seismic methods applied in this study allowed the extension of borehole reservoir properties, specifically acoustic impedance, beyond the well into the seismic cube, even in the presence of a highly laminated reservoir. The resulting workflow is an effective tool to reduce the time taken for reservoir mapping and modeling, providing an easier routine to update subsurface models for future drilling and development plans, and to reduce interpretation uncertainty.