Heavy Oil Occurrence in the Putumayo Foothils, Topoyaco Block, Southwestern Colombia

Porras, Luis R.¹; Lugo, Jairo M.; and Talukdar, Suhas
¹[email protected]

Recent exploration efforts in the Topoyaco Block have resulted in the discovery of heavy oil accumulations in both, the folded thrust sheets and in the sub-thrust of the northern structures of the Andean foothills in Putumayo. Geochemical analysis from the oil found in the sub-thrust, suggest a Late Cretaceous source rock, while gas chromatography points to a mixture of moderately and heavily biodegraded oil, that indicates two possible phases of migration and biodegradation of the oil into the reservoir. The thermal maturity of the oil based on sterane maturity ratios suggests an original API quality of the oil of 30o prior to migration, which is similar to oils found in fields south west of the Topoyaco block. We interpret that the initial biodegradation occurred prior to trap formation, and that further biodegradation occurred due to fresh water percolation into the reservoirs via fault surfaces or exposed carrier beds. Further exploration in the area requires a thorough understanding of the timing and synchronization between source rock maturation, oil migration and trap generation. Along with timing, trap integrity and mechanisms of fresh water migration into the reservoirs, is also of supreme importance to reduce the petroleum system uncertainty in this region.

AAPG Search and Discovery Article #90166©2013 AAPG International Conference & Exhibition, Cartagena, Colombia, 8-11 September 2013