Complex chemical EOR processes, such as in alkaline or surfactant flooding, are
typically optimized on their phase behavior and by core flood experiments. However,
the information from classical experiments are rather limited, because they do not
directly give insight the details of oil mobilization and displacements – in core floods,
typically oil production and differential pressure are measured, which are both 1D
data sets. The phase behavior is typically measured in test tubes and not under
realistic flow (mixing) conditions in porous media flow. Chemical EOR is changing
interactions between fluids and the porous medium and is therefore manifested on
the pore scale, where fluids are actually displaced. However, pore scale observations
are typically suffering from a limited field of view especially for multiphase flow
effects, which may not be representative for the overall system or the displacement.
In the frame of this study, we investigate displacements of crude oil by water and
alkali solutions in order to optimize injection-water compositions for tertiary recovery.
The study takes advantage of the high spatial and temporal resolution of microfluidics
in order to observe fluid phases in the pore space, their distribution and
displacements. Changes of the wetting state, breaking of oil clusters and the
formation of emulsion phases as characteristic for the displacements have been
observed. In order to overcome the limitation of the relatively small field of view, oil
clusters have been analyzed by statistical and topological means showing a
systematic change form water flooding to EOR.
The study shows that (a) cluster analysis can be used for EOR screening and – in the
present case – is more indicative with respect to EOR performance than production
data from the same experiment. The study might be a first step towards statistical
fingerprinting for optimizing EOR processes. (b) classical phase behavior
experiments do not reflect (or just partly) the phase behavior in the porous medium
under flow conditions. (c) the formation of (micro) emulsions in the pore space leads
to pinning effects and is therefore of disadvantage for the displacement.