Perhaps the most important unconstrained aspect of petroleum systems analysis concerns the charging and emplacement of petroleum to a structure or prospect. Petroleum charge rates, leakage, and spill control petroleum residence time in a reservoir, which is fundamental for prediction of biodegration rates, seal integrity (failure), and oil quality, all of which are affected by fluid mixing processes. While forward models can estimate plausible charge rates based on thermal histories, there are no field data proxies for the charge rates that are necessary to constrain migration and charge models. To solve this problem, we are coupling high resolution, full physics reservoir simulation protocols to full 4D basin models such that gradients in petroleum compositions from models and from chemical analysis can be used to constrain charges rates. This new generation of hybrid reservoir simulator/basin models necessitates rapid high resolution fluid mixing solvers and multicomponent fluids.

This paper deals with the development of compositional fluid mixing simulators that can be coupled with basin modeling. These simulators will enable the forward simulation of detailed reservoir charging and fluid property evolution, coupling the effects of advection, diffusion, gravity segregation, and biodegration to predict the development of compositional gradients in petroleum columns that can be used to constrain reservoir charging and alteration processes. In this paper the effects of advection, diffusion, and gravity segregation are particularly studied. The traditional simulator for solving the isothermal gravity/chemical equilibrium problem is deduced as a special example of the simulators presented here. Numerical experiments to show these effects are given.

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