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Chemometric Identification and 1-D Modeling of Geochemically Distinct Oil Tribes, an Integrated Approach to Petroleum System Analysis in the Middle Magdalenca Valley, Colombia


The Middle Magdalena Valley (MMV) is an intermontane basin and petroleum province in northwestern Colombia that, along with the Eastern Cordillera and Llanos Basin, has acted as a regional sedimentary basin from the Triassic into the late Neogene. During the Cretaceous, restricted marine conditions within a broad foreland basin resulted mainly in the deposition of organic-rich carbonate and siliciclastic sediments in the area of the modern MMV (Cooper et al., 1995). While the Upper Cretaceous La Luna Formation is the primary regional source rock, the Cretaceous Tablazo and Umir Formations may also contribute within the basin. Despite over a century of petroleum exploration, the complex burial and variable exhumation history associated with the Andean orogeny add uncertainty to the evaluation of petroleum systems in the MMV by impacting the distribution, quality, and thermal maturity of the Cretaceous succession of organic-rich source rocks. This study utilizes the multivariate statistical analysis of source- related biomarker and isotopic ratios from oil samples to establish distinct oil ‘tribes’ and then infer the differences in source rock depositional environment, lithology, and thermal maturity between them. 1D basin modeling is employed to integrate tribes into the MMV basin history by exploring differences in distribution, maturity, and source over time.

Chemometric analysis of 73 oil samples, employing hierarchical cluster and principle component analysis, defines six geochemically distinct oil tribes that may originate from different source rocks or organofacies of the same source rock within the MMV (Peters et al., 2007). The tribes in this study show systematic distribution by both map location and reservoir age. 1D basin modeling demonstrates that Tribes 1 through 4 are likely related to the primary regional source rock, the La Luna Formation while the northernmost tribe in the MMV, Tribe 5, likely originates from the middle Cretaceous Tablazo Formation. Tribe 6, in the southern MMV, is the sole terrigenous oil identified in the study, suggesting a non-marine source in the western flank of the Eastern Cordillera or an extension of the Cretaceous Umir Formation. Biomarker ratios and alternating least squares analysis are used to observe regional differences in character and thermal maturity between tribes as well as mixing. Finally, diamondoid analysis shows the presence of secondary cracking in the Tribe 6 oil while also suggesting, in corroboration to modeling results, input from a deeply buried and cracked source in the central MMV that may be the middle Cretaceous Tablazo Formation.