Eugenio Vaz dos Santos2
(1) Ecopetrol, Santafe de Bogota, Colombia
(2) Petrobras, Rio de Janeiro, Brazil
Abstract: Geochemical characterization of oils in the Colombian basins with commercial production
Based on geochemical information of 300 oil samples from the Colombian basins with commercial production (Putumayo, Upper Magdalena, Middle Magdalena and Lower Magdalena Valley, Catatumbo and Llanos) an evaluation about oil quality, age and depositional environment of the source rocks as well as level of biodegradation and thermal evolution was made. The quality of the Colombian oils varies largely with API Gravities between 5° and 55° , low concentrations of sulfur, vanadium and nickel and a percentage of saturates hydrocarbon with up to 40% in most cases. In relation to the depositional environments and age of the source rocks, it is concluded that Cretaceous organic facies are predominant and these are deposited in three main environments: marine anoxic with carbonatic influence, marine siliciclastic anoxic to suboxic and marine deltaic suboxic. Only in the Lower Magdalena Valley and Llanos Foothills, oils from Tertiary source rocks, deposited in marine deltaic environments were identified. Oils with higher levels of thermal maturity, corresponding to a late generation phase, are located in the Catatumbo basin. Lower Magdalena Valley and Llanos foothills, while oils with lower maturity level, corresponding to an early generation, are located in the Upper Magdalena Valley. Strong biodegradation processes have left their print in many oils affecting their quality. The most biodegraded oils are located in fields like Rubiales and Castilla, in the Llanos Basin, Teca and Cocorna in the Middle Magdalena Valley and Dina in the Upper Magdalena Valley. Biodegradation processes have been working all along the trap filling history, mixing intensively biodegraded oils with "fresh" hydrocarbons, improving in many cases the oil quality in the reservoirs, but difficulting the geochemical and geological interpretation.
AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana