Study on spatio-compositional variations and source facies for oils from the Central Wrench Corridor of the Oriente Basin (Ecuador). (January 2022) - Márquez, G.
Abstract: This research paper contains an integration of classical biomarker work with higher diamondoid examination to better characterize the petroleum systems in the north-central portion of the Sacha-Shushufindi Corridor in the Ecuadorian Oriente Basin. A set of crude oils, cuttings, and outcrop rock samples were analysed to address aspects such as source-rock lithology, paleo-depositional conditions, migration distances, as well as oil-oil and oil-source correlations. For this, gas chromatography-mass spectrometry (GC-MS), GC-triple-quadrupole MS (GC-MS/MS), and carbon isotope ratio mass spectrometry (IRMS) were performed on maltene fractions both from oils and rock extracts. GC-MS/MS analyses of oil-derived asphalthene hydrous pyrolysates were also included on the study. Classical biomarker results suggest mixing of pulses from distant siliciclastic and carbonate-rich Napo source rocks, with former oil charges being slightly biodegraded during the Paleogene and fresher Neogene pulses. These two types of Early-Late Cretaceous source rocks were deposited in shallow marine to nearshore and low-oxygen inner to middle neritic environments, respectively, with considerable and scarce contribution of land-plant material in both cases. Such differentiation of the two source facies types of the Napo Group is supported by results from quantitative extended diamondoid analysis (QEDA). Highlights: Study on oils from the Central Wrench Corridor of the Ecuadorian Oriente Basin. Evaluation of inter-field compositional changes in oil samples from north to south. Identification of contributions of carbonate and clay-rich Napo source rock facies.