Page 50 - Formation Damage during Improved Oil Recovery Fundamentals and Applications

32 David A. Wood and Bin Yuan

by the blocking of pore throats with fines and swelled clays are both forms
of formation damage that could be of benefit regarding EOR. However,
these mechanisms work in subtly different ways, which seem to impact
their potential IOR benefits that may vary from formation to formation.

2.5 SALINITY THRESHOLDS AND RESERVOIR
HETEROGENEITY INFLUENCES ON PARTICLE
DETACHMENT
The CSC and critical rate of salinity decrease (CRSD) (Khilar et al.,
1983) are significant in terms of particle detachment thresholds in porous
rocks. CSC is the salinity threshold below which fine particles, particularly
clays, are released from matrix surfaces (pore linings). Khilar and Fogler
(1984) identified that CSCs differ from sediment to sediment and are
dependent on valence and size of the dissolved solubilized salt cations in
the formation water. Blume et al. (2005) found that particle detachment in
heterogeneous formations could be quite different from those observed
in relatively clean quartz sandstones. They found that the quantity of particles
released and the CSC could be an order of magnitude higher for hetero-
geneous formations, and significant particle detachment could also occur
above the CSC in such formations. These findings bring into question
the concept of all formations displaying a sharp CSC. This highlights the
complex interactions between formation fluid salinity, cations present in
those fluids, hydrodynamic forces, potentially-mobile-particle availability
at the pore linings, and clay mineralogy of the particles on the matrix sur-
faces. All of these factors are likely to have an impact on particle release,
and their relative impacts are difficult to distinguish in specific formations.

2.6 EXPLOITING PORE PLUGGING TO PREFERENTIALLY
ENHANCE OIL RECOVERY
2.6.1 Quantifying and modeling fines migration and
pore plugging
Fine particles in porous formations tend to exist in mechanical equilib-
rium balancing the drag, lift, electrostatic, and gravitational forces acting