Date of Award

Spring 2020

Document Type

Open Access Dissertation

Department

Earth and Ocean Sciences

First Advisor

James Kellogg

Abstract

The Parrando and Guavio anticlines are located in the Llanos foothills on the eastern flank of the Eastern Cordillera of Colombia. This study presents new 3D horizon maps, seismic and stratigraphic interpretations, and 1D burial models based on a 3D seismic volume, 2D seismic lines, and well logs. The Guavio anticline was formed by overlapping Miocene-Pliocene fault-bend folds and inversion of the Guaicaramo normal fault. Unlike previous models, the basement fold is interpreted as formed by a ramp from pre-Cretaceous basement to a double wedge fault probably preceded by a thin-skinned bedding plane thrust fault. A new 1D burial model predicts that source rocks began to expel oil at 18 Ma, 10 Myr before trap formation. The Parrando anticline is a thin-skinned fault-bend fold southeast of the Guavio anticline with a forelimb break through fault.

Previous studies of fractures in the Foothills relied on surface geologic studies or downhole imager logs. In this study, attribute analysis and ant-tracking algorithms on a 3D seismic volume were used to produce curvature and fracture network maps for the Parrando anticline. Two prominent fracture systems were observed, NE-SW and NW-SE. The major fracture strike azimuth is NE-SW, parallel to the structural trend of the Foothills, concentrated in folded rocks of the Parrando anticline. Several NE-SW fractures show extensional displacement consistent with folding or an elastic plate subjected to pure bending. NE-SW fractures in the Late Cretaceous source rocks may have been inherited from Early Cretaceous rifting, while those in the Oligocene Carbonera Fm may have been early folding or bending of the lithosphere before the advancing mountain front. The secondary fracture strike azimuth is NW-SE perpendicular to the structural trend of the Foothills. NW-SE fractures are found in strata from 21 to 6 Ma and are most intense in mid-Miocene (14 Ma). These may be inherited from earlier initial folding and thrusting on the Guaicaramo fault. This method permits the mapping of fracture systems in rock volumes between wells, and in areas where no well borehole imagery logs are available.

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