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Prospective Trends in the Putumayo Foothills of Southern Colombia from Integrated Data Analysis

Abstract

The Putumayo Basin is one of the most prolific basins in Colombia; however the foothills area of the basin is poorly explored despite the recognized potential for new discoveries. Gran Tierra Energy Colombia has led the exploration for hydrocarbons in the basin with important discoveries, including the first foothills field. One of the keys of successful exploration is understanding the structural evolution of the basin. As the prospective structures are result of a complex tectonic history, and tend to be hidden by the Andean orogeny thrusts, an integrated study was done using surface and subsurface data. For this study historical 2D seismic lines from different areas along the Putumayo Foothills were interpreted. The interpretation was constrained by wells; integrating the lithology descriptions and logs including dip and image data. The results were correlated with the surface geology and remote sensing analysis to determinate the link between the surface trends and the subsurface structures. Based on the remote sensing images and the surface geology, several different regional trends were identified along the fold and thrust belt, changing from E-W to NE-SW direction. These trends are consequence of previous configuration of the basin and the position of older faults reactivated with preferential orientations. The seismic data reveals significant changes in the subsurface configuration of the regional trends; the examples presented in this paper demonstrate changes in the angle of the leading thrust fault separating the foothills and the relatively undisturbed foreland area. When the subsurface and surface data are compared it is apparent there is a relationship between the direction of the trends and the angles of the leading thrust faults as a consequence of the orientation of the stress tensor configuration. This produces thrust faults with lower angles in areas where the direction of the main component of the tensor is perpendicular while in other areas the angle of the faults is higher and a dextral component is present. Based on the described changes, this work establishes a division between regions of differing structural characters and different configurations of the leading thrust fault, related with the shortening and deformation of the previous structures. An understanding of the relationship between the present day thrust faults and the stress configuration is critical to reduce the exploratory risk.