Finding Additional Oil Volumes by Structural Analysis, Section Balancing and 3-D Restorations in the Upper Magdalena Basin, Colombia

Abstract

Structures in the Neiva sub-basin of the Upper Magdalena basin in Colombia were formed during two episodes of compressive deformation, during the Eocene-Oligocene and Miocene-present. The Central Cordillera was thrust eastward in mid-Tertiary, and the east-vergent thrust system extended into and through the stratigraphic section (Jurassic-Cretaceous-Paleogene) that floors the current basin. The basin was a part of an uplifted, eroding fold and thrust belt on the east side of the Central Cordillera in the Eocene-Oligocene. This first episode of deformation is capped above a strong angular unconformity by a Miocene-present foreland/piggyback basin sequence. The second deformation episode was active during deposition of this sequence, reactivating earlier thrusts. In late Miocene, the Eastern Cordillera began additional significant uplift on generally west-verging thrusts, feeding sediments into the basin from the east side in this latest phase, as well as further isolating the basin between the Cordilleras.

The area is a mature oil producing area, with prolific production from many fields. The traps are primarily structural, and production is from sandstones in the Cretaceous Monserrate, Caballos, and Miocene Honda Formations. Increased coverage of 3D seismic, combined with the well database, has allowed improved 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 on certain structures in the basin.

A process of iterative structural interpretation and balancing of sections in the northern portion of the sub-basin yielded a viable fault network and a template for interpretation in 3D. Equally, iterative interpretation of the 3D seismic and 3D map-view restoration highlighted areas of unrecognized potential volumes. The independently determined volumes from the structural modeling fit well with material balance determinations based on well production in certain fields. Previous interpretations, based only on the seismic image and wells, without taking into account the structural system, yielded much lower volumes that are not supported by the production data. In this structural complex area, the structural balancing defines potential oil volume that was previously unrecognized, while reducing uncertainty on geometry and extent of fields.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018