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Compositional Simulation of Petroleum Vertical Migration and Evaporative Fractionation Processes

Luís Maurício Corrêa, Henrique L. de B. Penteado, and Laury M. Araújo
PETROBRAS/E&P Dept./Petroleum Systems Modeling, Rio de Janeiro, Brazil

Petroleum systems modeling allows the dynamic simulation of a series of physical and chemical processes during the geological history of a sedimentary basin. Among these processes, physical and chemical changes in petroleum associated with vertical migration are of utmost importance for the assessment of petroleum volumes and composition in an exploratory context. Evaporative fractionation is one of the processes related to petroleum migration which may cause alterations in the composition of an accumulation. Evaporative fractionation can be characterized by a quantitative analysis of chromatographic and PVT fluid data. This phenomenon can be simulated by coupling equations of multicomponent flow with equations of state in a petroleum systems simulator.

Several studies have confirmed, by the analyses of reservoirs fluid data and laboratory scale experiments, the occurrence of evaporative fractionation in basins. In order to verify whether a basin simulator is able to replicate the effects of evaporative fractionation during petroleum vertical migration, tests were performed using a synthetic geological model built in the PetroMod v.2011 software (IES/Schlumberger). A hybrid method of migration was used that combines multiphase Darcy flow (for lithologies with permeabilities less than 100 mD) and ray tracing (for carrier rocks), with petroleum composition based on a kinetic scheme with eleven compound classes, which is representative of the PVT properties of lacustrine oils from Brazilian marginal basins. PVT calculations (phase separation, physical and chemical properties of each phase) must be undertaken for each accumulation during the whole model history.

AAPG Search and Discovery Article #120098©2013 AAPG Hedberg Conference Petroleum Systems: Modeling the Past, Planning the Future, Nice, France, October 1-5, 2012