Petroleum generation and migration in the putumayo basin, Colombia: insights from an organic geochemistry and basin modeling study in the foothills

摘要

This paper discusses the results of 1D modeling and geochemical analyses of rock, oil and gas samples performed in the foothills of the Putumayo Basin, Colombia. A multivariate statistical assessment of biomarker data points to the existence of three oil groups, two of the them similar to oil families reported in previous studies and related to the Villeta Formation source rocks, and a novel one tentatively associated with the Caballos Formation source rocks. Geochemical data of oil and gas samples points to a complex reservoir filling history in the foothills, with at least two migration pulses with distinct maturity levels. Vitrinite reflectance data together with modeling results shows that the source rock is practically immature in the Putumayo foothills, even in the footwall of large thrust faults. The thermal and burial reconstruction of a pseudo well located in the present cordillera area suggests that the source rocks have started petroleum generation and expulsion during the Late Oligocene/Miocene. The oil and gas expelled during such a period have migrated over 80 km, reaching the present foreland area. Subsequent tectonic burial and/or higher heat flows related to the Late Miocene/Pliocene Andean Paroxysm is thought to account for a second pulse of migration of thermally evolved hydrocarbons limited to the foothills area.