Page 68 - Formation Damage during Improved Oil Recovery Fundamentals and Applications

50 David A. Wood and Bin Yuan

IOR method. From Eq. (2.1), it is clear that the capillary number can be
increased either by reducing the IFT(σ) or the contact angle (θ) (making
the system more water wet) or increasing μ. Altering either IFT or θ
involves inducing changes to the wettability of the crude oil-formation
water-porous rock-fluids system. For LSWF to be effective at increasing
oil recovery, a lowering of IFT or θ should be expected, although this
may be an effect of the processes at work rather than the driving mecha-
nism (Lager et al., 2008).
Barati-Harooni et al. (2016) conducted experiments and modeled the
relationships between temperature, pressure, and synthetic formation
water salinity and IFT of two carbonate oil reservoirs (Iran). Their results
showed that the IFT data of reservoir A increased as the temperature,
pressure, and salinity of synthetic formation water increased. On the
other hand, IFT data of reservoir B increased as the pressure and salinity
of synthetic formation water increased, but that IFT decreased as the
temperature increased.
Electrokinetic effects in porous media, such as streaming potential and
zeta potential (Fig. 2.1), are also related to its wettability (Jackson and
Vinogradov, 2012). These effects can therefore be used as direct indicators
to monitor changes in wettability throughout a reservoir or during IOR
projects. When fluids pass through porous media, they carry mobile
charges of double layers and an electric current is generated, which causes
a potential difference to build up in the system, referred to as the
“streaming potential”. The streaming potential can be measured to map
subsurface flow, detect subsurface flow patterns, and monitor wettability
in oil reservoirs (Sadeqi-Moqadam et al. 2016).
The closest plane to the porous rock surface at which flow occurs is
termed the shear plane or the slipping plane, and the electrical potential
at this plane is called the zeta potential (Thanh and Sprik, 2015). The
zeta potential depends upon several fluid and rock properties (e.g., elec-
trolyte concentrations; mineralogy) and influences the degree of coupling
between the electric flow and the fluid flow in porous media. The zeta
potential can be determined by measuring the streaming potential.
Sadeqi-Moqadam et al. (2016) performed experiments on sand packs
showing a spectrum of wetting conditions from completely water-wet to
completely oil-wet and determined the zeta potential and streaming
potential coupling coefficient. Their results showed good correlation
between these electrokinetic parameters and wettability states. They also
developed a bundle-of-tubes model to simulate and quantify wetting