AAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Flexurally Driven Subsidence History of the Llanos Foreland Basin of Colombia: Implications for Hydrocarbon Exploration
(1) Jackson School of Geosciences, The University of Texas at Austin, Austin, TX.
(2) Department of Petroleum Engineering, University of Stavanger, Stavanger, Norway.
The Llanos basin of Colombia is located in the eastern side of the northern Andes and it is bounded to the north by the Merida Andes, to the east by the Guyana Shield, to the south by the Serrania de la Macarena and the Vaupes Arch, and to the west by the frontal thrust system of the Eastern Cordillera. This basin became a foreland since the Maastrichtian and shows a sudden and accelerated pulse of Middle Miocene subsidence recording the basin’s response to distant shallow subduction and collision events along the active Pacific margin of northwestern South America. Regional east-west shortening, driven in part by collision of the Panama arc along the Pacific margin of Colombia, has built the widest part of the northern Andes including a prominent arcuate thrust salient, the Cordillera Oriental, which overthrusts the Llanos foreland along a broad V-shaped tip projecting 40 km eastward into the Llanos basin. In this study we integrate 1200 km of 2D-seismic data, tied to 18 wells, and divided in four 300 to 400-km-long, regional transects spanning the basin. 2D flexural modeling using OSXFlex2D was carried out along all four transects to illustrate and understand the effect of tectonic and sedimentary subsidence. Sedimentary backstripping was applied to the observed structure maps of interpreted horizons in the foreland basin to remove sedimentary and water loading effects. Regional subsidence maps show an increase in the rate of tectonic subsidence in the salient area during the middle to late Miocene. Flexure models predict changes in the Middle Miocene to recent position of the eastern edge of the foreland basin as well as the changing locations and vertical relief of the flexurally-controlled forebulge. Most light oil fields in the thrust belt and foreland basin are located either south of the thrust salient (Cusiana-Cupiagua, Rubiales oilfields) or north of the salient (Guafita-Cano Limon, Arauca oilfields) but not directly adjacent to the salient where subsidence, source rock thicknesses and fracturing may be most favorable for hydrocarbons according to previous studies. There are no reported light oil accumulations on the present or past positions of the forebulge but comparisons of seismic data to model predictions show onlaps and wedges that could provide possible traps for hydrocarbons.