Resolution of Thin Villeta Formation Arena N Reservoirs in the Platanillo Area of the Putumayo Basin Using Sparse-Layer Inversion

Wardle, John; Bueno, Edgar; Castagna, John P.; Gil, Gabriel D.; and Moreno, Carlos¹
[email protected]

The Arena N reservoirs of the Cretaceous Villeta Formation in the Platanillo Area of the Putumayo foreland basin in Southern Colombia are typically below seismic resolution. As these sands are laterally discontinuous and not seismically resolvable, there is significant exploration potential in the area that is limited by the risk of absent or inadequate reservoir rock. Improved seismic resolution could mitigate this problem and would also make it easier to find subtle stratigraphic traps that are known to occur in the area. Sparse-layer inversion is a method similar to sparse-spike inversion that better resolves thin layers. Significantly, it does not require a starting model derived from well logs, and thus handles lateral discontinuity better than conventional model-based seismic inversion techniques. The purpose of this study was to ascertain if sparse-layer inversion could improve drilling results in this area. Application of sparse-layer inversion to a Platanillo 3D seismic dataset resulted in a better than 2-fold improvement in resolution as compared to conventional seismic methods, with sands as thin as 8 meters being readily resolved. Predicted impedance sections matched existing wells and successfully distinguished wells encountering good reservoir quality from poor producers. Four wells were drilled after the inversion project was completed with 100% prediction success. On conventional data, seismic modeling shows that these high impedance sandstones have a composite seismic response with the Arena N formation top in the well corresponding to a trough on the seismic data; thereby making mapping problematical. The association of a seismic trough with a high impedance formation top on conventional seismic data is a result of the complex interference pattern resulting from closely spaced seismic reflectors. After inversion, the high impedance reservoirs are readily tied to a positive seismic reflection at their top and a trough at their base. Multiattribute analysis using the sparse layer inversion as input resulted in prediction of reservoir properties sufficiently adequate to be useful in well location and prediction of well performance.

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