Journal of Petroleum Geology, Vol. 41(2), April 2018, pp 113-134
GEOCHEMICAL EVALUATION OF CRUDE OILS
FROM THE CARACARA AND TIPLE AREAS,
EASTERN LLANOS BASIN, COLOMBIA:
PALAEO BIODEGRADATION AND OIL MIXING
, G. Márquez
, A. Permanyer
and J.R. Gallego
This study presents an organic geochemical characterization of heavy and liquid oils from
Cretaceous and Cenozoic reservoir rocks in the Tiple and Caracara blocks in the eastern
Llanos Basin, Colombia. Samples of heavy oil were recovered from the Upper Eocene Mirador
Formation and the C7 interval of the Oligocene – Miocene Carbonera Formation; the liquid
oils came from these intervals and from the Cretaceous Guadalupe, Une and Gachetá
Formations. The heavy oil and most of the liquid oils probably originated from multiple source
rocks or source facies, and showed evidence of biodegradation as suggested by the coexistence
of n-alkanes and 25-norhopanes. The results indicate a close genetic relationship between
the samples in the Carbonera (C7 interval), Mirador and Guadalupe Formation reservoirs.
These petroleums are interpreted to result from at least two separate oil charges. An early
charge (Oligocene to Early Miocene) was derived from marine carbonate and transitional
siliciclastic Cretaceous source rocks as indicated by biomarker analysis using GC/MS. This
initial oil charge was biodegraded in the reservoir, and was mixed with a later charge (or
charges) of fresh oil during the Late Miocene to Pliocene. A relatively high proportion of
the unaltered oil charge was recorded for heavy oil samples from the Melero-1 well in the
Tiple block, and is inferred to originate from Cenozoic carbonaceous shale or coaly source
rocks. Geochemical parameters suggest that oils from the Gachetá and Une Formations
are similar and that they originated from a source different to that of the other oil samples.
These two oils do not correlate well with extracts from transitional siliciclastic source rock
from the Upper Cretaceous Gachetá Formation in the Ramiriqui-1 well, located in the LLA
22 block to the north. By contrast, one or more organofacies of the Gachetá Formation may
have generated the heavy oil and most of the liquid oil samples. The results suggest that the
heavy oils may have formed as a result of biodegradation at the palaeo oil-water contact,
although deasphalting cannot entirely be dismissed.
Center for Research in Sustainable Chemistry,
Universidad de Huelva, 21007 Huelva, Spain.
Depart. of Mineralogy, Petrology and Applied Geology,
Universitat de Barcelona, 08028 Barcelona, Spain.
Department of Exploration and Mining Prospecting,
Universidad de Oviedo, 33600 Mieres, Asturias, Spain.
*corresponding author, email:
Key words: Colombia, Llanos Basin, Cretaceous,
Cenozoic, heavy oil, biodegradation, mixed oil, reservoir
geochemistry, organic geochemistry.
© 2018 The Authors. Journal of Petroleum Geology © 2018 Scientic Press Ltd
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