Application of Seismic Attributes and Fluvial Geomorphology of the Late Eocene- Oligocene of the Carbonera Formation in the Llanos Foreland Basin of Colombia

Torrado, Lucia¹; Mann, Paul; and Bhattacharya, Janok
¹[email protected]

Hydrocarbon exploration in the Llanos foreland basin of Colombia has been focused on the basis of structural entrapment; however, in the last decade the country's oil demand has generated an increased interest in exploration of stratigraphic traps. The study integrated 700 km² of 3D seismic data volumes with 9 wells in the eastern Casanare province, and additional 2D lines tied to 32 wells in a 17,168 km² area near the Rubiales field.

Interpretation of reservoir distribution includes multiple 3D attributes such as coherence, curvature, and spectral decomposition. The objective of the study is to assess the reservoir potential of the Late Eocene-Oligocene Carbonera Formation, a 400-1800m-thick reservoir unit of fluvial deposits with relatively unexplored stratigraphic traps, where distinguishing non-productive, mud-filled channels from productive sand-filled channels becomes crucial, since both channel types can appear similar on seismic sections.

Flattened time slices through coherence, frequency sub-bands, and curvature cubes respectively shows: 1)a meandering fluvial system with changes in the rivers’ paleoflow directions from southwest to northeast, and development of tributaries systems with a northwest to southeast orientation, 2) development of prospective sandy point bars, scrolls and sand bars deposits, not shown initially by coherence, and 3) most positive and most negative curvature shows ridges and channels based on differential compaction dependant of the channel's filling material, where some fluvial channels fills has been reinterpreted as non prospective mud plugs with good sealing attitude.

Finally, variations in accommodation and sediment supply conditioned the morphology of these fluvial deposits, where the channels exhibit: 1) moderate Width to Depth (W/D) ratio, moderate sinuosity with high avulsion frequency for the main drainage; 2) low W/D ratio, low sinuosity and high lateral accretion for the tributary channels in member Carbonera 1; 3) higher mud content in the Carbonera members 3 and 5; 4) wider channels with thicker floodplain deposits, localized sandstone bodies, and higher avulsion rates in Carbonera member 5 and 3; 5) fewer intra-formational seal development in the Eastern Llanos area, and 6) sand-prone channels deposits in the Carbonera member 7 with high lateral migration.

AAPG Search and Discovery Article #90166©2013 AAPG International Conference & Exhibition, Cartagena, Colombia, 8-11 September 2013