Waterflooding has
been an effective and relatively inexpensive process of improving recovery
beyond the primary natural drive. In carbonate reservoirs, which are alwaysmixed/strongly oil-wet, waterflooding seems ineffective as water cut escalatesleaving behind high residual oil saturation (ROS). In such case, rock
wettability do not favour the optimal condition for oil displacement by the
injection water.
Through the
centuries in a reservoir, a thermodynamic equilibrium has existed between the
brine, oil and the rock and there is no doubt that injecting different brine
would considerably change this equilibrium. This is a major reason why the
brine injected during convectional waterflooding is usually selected based its compatibility
with existing formation brine. This change is linked with the interaction
between the injected brine and the rock surface. However, decades of research
has confirmed that the change is more positive towards improving oil recovery.
The brine-rock interaction has been observed to be prompted by the reactivity
of the ions in the injected water, which is crucial in creating a surface
charge alteration.
Furthermore,
during smart waterflooding, it is predicted that as the injected water displaces
the oil ahead, rock wettability is favourably altered along the way. Therefore,
waterflooding is termed smart when the injected water’s ionic composition and
salinity are manipulated – selective addition or removal of certain ions. Read more............
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