Regional Study and Petroleum System Modeling of the Eastern Llanos Basin
Vayssaire, André1; Abdallah, Hussein; Hermoza, Wilber; and Figari Negri, Eduardo G.
The Llanos Basin is one of the most prolific and largest sedimentary basin in Colombia. Located along the western margin of the Guyana Shield it covers more than 200.000 km² bounded westward by the Andean Cordillera. During the last years the Geological Studies Group of REPSOL conducted a regional study of the area. The main challenge was not only to understand the geologic evolution of the basin and its remaining potential but also to create a consistent G&G framework. The variable quality of the seismic coming from different surveys, processes and reference datum, the lack of edited wells, and the heterogeneity in the stratigraphic criteria were the main hurdles to generate a coherent data base.
The principal milestones of the study were: seismic interpretation, well correlations, petrophysical analysis, reservoir facies mapping, structural restoration and 3D petroleum system modeling . The studied area includes part of the foothills for a better timing estimation since a significant part of the hydrocarbon was expulsed below it in the earliest stage due to the important overburden of this area. The Upper Cretaceous Gacheta source rock shows a Plio-Pleistocene expulsion pick. It reached the gas window in the South where expulsion started early Miocene. Hypothetical early Cretaceous source rock could have expulsed hydrocarbons since late Cretaceous but the migration may have been essentially westward, toward the Magdalena Valley.
Tertiary source rocks like Los Cuervos and Carbonera are also mature at present day along the Cordillera but expelled quantities could be much lower in comparison with Gacheta. It appears that petroleum expulsed in the very North of the basin have migration routes that focus toward Caño Limon. The most favorable places for long distance lateral migration are in the central part of the foreland basin where the Gacheta source is also the most prolific. The existence of a Paleozoic petroleum system remains unknown. Even though more than 150 wells have encountered Paleozoic rocks, most were suspended at the top of the Paleozoic section. The northern and southern parts of the basin show large compressive structures that require detailed studies and evaluation of their possible petroleum potential.
AAPG Search and Discovery Article #90166©2013 AAPG International Conference & Exhibition, Cartagena, Colombia, 8-11 September 2013