Study on spatio-compositional variations and source facies for oils from the Central Wrench Corridor of the Oriente Basin (Ecuador)

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).