Page 67 - Formation Damage during Improved Oil Recovery Fundamentals and Applications

Low-Salinity Water Flooding: from Novel to Mature Technology 49

immiscible fluid (oil and water being the two immiscible fluids of interest
in IOR). The wetting properties determine the contact angle θ at which
the oil-water interface intersects the surface of the porous media
(Fig. 2.15), and that angle is used as the standard measure of wettability
(Cieplak and Robbins, 1990).
The contact angle is a function of the interfacial energies between
fluids and porous rock as defined by Eq. (2.16):
σ om 2 σ wm 5 σ ow cosθ (2.16)

where,
σ om 5 interfacial energy between oil and porous rock matrix (dyne/
cm);
σ wm 5 interfacial energy between formation water and porous rock
matrix (dyne/cm);
σ ow 5 IFT between oil and formation water (dyne/cm);
θ 5 contact angle at oil-formation water-porous rock interface mea-
sured through the water phase.
The IFT is the surface-free energy that exists between the two immis-
cible liquid phases (oil and formation water) in a crude oil-formation
water-porous rock system. The effect of capillary forces at play involved
in binding/trapping crude oil within the pores space of reservoir rocks
are influenced by the IFT and contact angle. Those capillary forces are
typically characterized by dimensionless number calculated as the capillary
number (Eq. (2.1)).
A significant increase in the capillary number (about four to six orders
of magnitude according to Ayirala and Rao, 2004) is required to signifi-
cantly reduce residual oil saturation (i.e., improve oil recovery) in any

Figure 2.15 Metrics used to quantify wettability states in oil reservoirs.