Publication
Important properties of a crude oil, such as viscosity, are determined by the crude oil's chemical constituents. In particular, viscosity is highly dependent on the asphaltene content. Various processes that act on reservoir crude oils can alter chemical composition, such as aspahltene content, and therefore impact important crude oil properties. In many basins, such as the Llanos basin in Colombia, processes such as biodegradation, water washing, and multiple charging can contribute to asphaltene and viscosity variations. The considerable complexity of the problem requires a multidisciplinary workflow to understand the main factors that influence the quality of reservoir crude oils and their gradients. Here, we perform comprehensive two-dimensional gas chromatography with flame ionization detection and with mass spectrometry on samples of known provenance, combined with petroleum system modeling, to develop an understanding of the primary factors controlling asphaltene content and viscosity in a reservoir. The crude oils in our study show the impact of biodegradation, water washing, and multiple charging. Some variation of composition is observed laterally in the subsurface formation. These observations help constrain the petroleum system model; the timing of paleo-pasteurization appears to be key in establishing the quality of the oils.