We study the dynamics of a water-oil meniscus moving from a smaller
to a larger pore. The process is characterised by an abrupt change
in the configuration, yielding a sudden energy release. A theoretic
study for static conditions provides analytical solutions of the
surface energy content of the system. Although the configuration
after the sudden energy release is energetically more convenient,
an energy barrier must be overcome before the process can happen
spontaneously. The energy barrier depends on the system geometry
and on the flow parameters. The analytical results are compared to
numerical simulations that solve the full Navier-Stokes equation
in the pore space and employ the Volume Of Fluid (VOF) method to
track the evolution of the interface. First, the numerical simulations
of a quasi-static process are validated by comparison with the analytical
solutions for a static meniscus, then numerical simulations with
varying injection velocity are used to investigate dynamic effects
on the configuration change. During the sudden energy jump the system
exhibits an oscillatory behaviour. Extension to more complex geometries
might elucidate the mechanisms leading to a dynamic capillary pressure
and to bifurcations in final distributions of fluid phases in porous