Applying High-resolution Sequence Stratigraphy to Identify New Oil Traps, Northern Llanos Basin, Colombia

The main oil reservoirs in the northern Llanos basin of Colombia are laterally extensive and thick (~400 ft) stacked paralic (marginal marine) sandstones of the Oligocene Carbonera Formation. Typically, the internal heterogeneity and complexity of paralic deposits are responsible for entrapment of hydrocarbons in thin, laterally restricted sandstones that cannot be easily followed by lithostratigraphic correlations and that are out of the range of seismic resolution. A new approach of correlating and applying high-resolution sequence stratigraphic methods using the existing electric well logs allowed for a better understanding of the internal architecture of the paralic deposits of the Carbonera Formation. We recognized a succession of two 40-ft-thick, 4th-order progradational, shoaling-upward parasequences within the Guafita Member. These parasequences are bounded by laterally extensive marine mudstones (flooding surfaces) and look well-preserved in wells drilled in the Cano Rondon and Caricare fields. Correlation of parasequences and electrofacies analysis, coupled with an understanding of the depositional model using modern analogs and paleogeographic information, enabled identification of untapped channelized reservoirs within the lowest parasequence. These newly recognized reservoirs were tested, resulting in the production of atypically light oil (40° API) and in the recovery of reserves that would otherwise have been left behind pipe.