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Structural Analysis and Section Balancing to Reduce Uncertainty in Field Development in the Upper Magdalena Basin, Colombia

Abstract

The Neiva sub-basin of the Upper Magdalena basin in Colombia is a mature oil producing area, with prolific production from many fields. It is an intramontane basin limited on the west by the Central Cordillera and on the east by the Eastern Cordillera. The traps are primarily structural in this folded and thrusted area of extensive deformation. Production is typically from sandstones in the Cretaceous Montserrate, Caballos, and Tertiary Honda Formations. Increased coverage of 3D seismic, combined with the extensive well database, has allowed improved and more detailed mapping of the area, and has led to identification of additional opportunities in the area. The 3D seismic is of generally good quality in the deeper Cretaceous units, but in areas of structural complexity the imaging suffers and thus there is significant uncertainty in many parts of the basin. Structural modeling aids in defining opportunities and reducing uncertainty in the areas of greatest opportunity and interest. In addition, this basin has excellent unconventional potential from La Luna, Tetuan and possibly other formations, which will depend on detailed, tested structural mapping and definition as this aspect is explored in the future. The Neiva sub-basin was formed principally by compressive tectonics. In general, the Central Cordillera was thrust eastward (ESE) in the mid-Tertiary, and the thrusts extended into and through the stratigraphic section (Jurassic-Cretaceous-Paleogene) that floors the current basin. These thrusts generally verge east. The basin was a part of the uplifted, eroding fold and thrust belt on the east side of the Central Cordillera in the Eocene, and eventually was overlapped by a foreland/piggyback basin section before and during later episodes of ongoing compressional deformation, again showing eastward vergence in the sub-basin area. In mid-late Miocene, the Eastern Cordillera began significant uplift on generally west-verging thrusts, feeding sediments into the basin from the east side in this latest phase, as well as isolating the basin between the Cordilleras. The Arrayan field is an area that was identified with the expanded 3D coverage. It is a faulted anticline, deep in the basin, and it produces from Caballos Formation. Detailed structural analysis of wells, with structural balancing, illustrates the structural development in the context of the regional tectonics and reduces uncertainty on probable shape and extent of the field.