Chemometric Identification of Geochemically Distinct Oil Tribes as a Tool to Advance Understanding of the Petroleum Systems in the Middle Magdalena Valley, Colombia

Abstract

The Middle Magdalena Valley (MMV) is an intermontane basin and petroleum province in northwestern Colombia that, along with the Eastern Cordillera and Llanos, has acted as a regional sedimentary basin from the Triassic well 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. 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.

Chemometric analysis of 73 oil samples, employing hierarchical cluster analysis and principal 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. Tribes 1 through 4 are likely related to the primary regional source rock, the La Luna Formation. However, biomarker ratios and alternating least squares analysis are used to observe regional differences in character and thermal maturity of the La Luna oil as well as mixing. The northernmost Tribe in the MMV, Tribe 5, likely originates from the middle Cretaceous Tablazo or Rosablanca Formations. 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. Finally, diamondoid analysis shows the presence of secondary cracking in the Tribe 6 oil, while also suggesting input from a deeply buried and cracked source in the central MMV that may be the middle Cretaceous Tablazo Formation.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018