Anisotropic Pre-Stack Depth Migration in the Cusiana and Cupiagua Sur Fields

The eastern foothills of Colombian western Cordillera is a region with a complex structural history that involves an early shortening parallel to bedding and a folding phase prior to the Andean Orogeny. This was followed by in-sequence thrusting that produced the main structures and finally a phase of out-ofsequence thrusting. Seismic imaging of the BP operated Cusiana and Cupiagua Sur fields has been a big challenge since the exploration phase and as the depletion of the fields continues, the need for accurate event positioning and focusing becomes more and more critical in order to optimize infill wells location and reservoir management in general. Imaging in complex foothills areas requires PSDM in order to account for strong lateral variation of velocities. However, it has been recognized that ignoring anisotropy leads to positioning and focusing problems. A complete seismic volume was depth migrated taken into consideration the anisotropy introduced by the thick shale section of the Carbonera Formation. In absence of direct measurements of anisotropy parameters, a tomography approach was used in order to determine the best anisotropic parameters. The quality of the well tie was used as a driver in the tomography process, which converged to a valid solution after two iterations. Additional scans were performed in order to refine the delta and epsilon fields, based on the quality of the imaging. Overall, the quality of the depth migrated volume with anisotropy allowed better definition of the fault planes and produced a more focused image compared to the previous dataset. In addition to this, a significant lateral displacement of the structures at target level was observed.