f Characterization of the Ciénaga de Oro Formation in the Saman Block, Lower Magdalena Basin, Colombia, using 3D Seismic Inversion and Facies Analysis

3D seismic-based lithologic characterization of the Oligo-Miocene Cienaga de Oro Formation (COF) was performed in a ~500 sqkm area (Saman) of the Lower Madgalena Basin, Colombia. Facies variations and discontinuities of the COF make the reservoir distribution and quality the critical exploration risk in the basin. The study integrates seismic attributes, facies analysis and inversion (P-impedance), calibrated to 7 wells. The COF overlies an igneous-metamorphic basement, which forms a high amplitude seismic reflector. Both the top and the internal character of the COF present variations across the area. These reflect lithologic changes that can be recognized to some extent with amplitude and other seismic attributes from the pstm volume. However, a significant improvement in the characterization of the COF was obtained with 3D acoustic inversion and seismic facies analysis. The P-impedance volume allowed for an improved discrimination of different depositional events, interpreted as transgressive deposits advancing SE-wards. The basal section, with a very high P-impedance response, is restricted to the northern area and correlates with immature, coarse-grained deposits with poor reservoir properties. The upper section shows a discontinuous distribution of sandstones (exploration target) and shales, with the sand-prone facies correlating to moderate-high P-impedance and the shales to lowest values. Seismic facies analysis, where the variations of the wave form between top and base of the COF were subdivided into eight discrete responses, was performed both in unsupervised mode and constrained by wells. This helped further discriminating prospective (sand-prone) and non-prospective zones (shales or tight sands / conglomerates).