Structural Modeling to Reduce Uncertainty, Eastern Cordillera Fold and Thrust Belt, Colombia
Uncertainty in modeling the extent of productive and prospective thrust sheets in the Piedemonte area of the Eastern Cordillera is high, owing to the difficult environment for seismic imaging. In spite of ample 2D and 3D seismic data and several iterations of reprocessing, imaging the productive and potential thrust sheets proves elusive, thus a rigorous structural modeling process is necessary to reduce uncertainty on trap sizes and extents. Reprocessed 3D seismic, along with new information from several recently drilled wells, provide the base for a refined 3D model of the area. The thrust-bounded packages each typically contain Paleogene Mirador, and sometimes Barco and Upper Cretaceous Guadalupe Formations. These units are low porosity sandstone reservoirs, but are strongly fractured. The productive and prospective thrust sheets underlie shallow to surface structures, notably the Nunchia syncline and the El Morro anticline. The shallow features are well imaged and combined with surface mapping constraints, provide important aids to interpretation of the deeper thrust sheets. The antiformal stack of thrust sheets extends for tens of kilometers along-strike, from the Recetor area, through Piedemonte and into the Niscota area. Individual thrust sheets also extend for tens of kilometers along strike, as supported by production history, pressure interactions and occasional tracer data. Wells aligned in the dip direction provide the best base for interpreting sections and understanding dip extent of the thrust sheets. Iterative balancing of sections using all wells yields sections where the cutoffs are best constrained. The shortening and stacking of the prospective thrust sheets must explain the translation and uplift of the Nunchia syncline and other shallow structural features. Changes in style and number of thrust sheets along strike are reflected in changes in the Nunchia syncline and other shallower features. Interpretation and balancing of sections that are constrained by the wells yield a fault network that accounts for all the structures. Carrying the interpretation through a network of sections provides an interpretation template for the 3D seismic volume. Further testing for balance in 3D yields a model with significantly reduced uncertainty. The refined model aids in evaluating potential reserves, extent and connections between the various thrust sheets and in defining targets for drilling, including untested thrust sheets with production potential.
AAPG Datapages/Search and Discovery Article #90193 © 2014 Rocky Mountain Section AAPG Annual Meeting, Denver, Colorado, July 20-22, 2014