Page 287 - Formation Damage during Improved Oil Recovery Fundamentals and Applications

258 Rouzbeh G. Moghanloo et al.

tubes. The rock permeability is then related to porosity (ϕ), tortuosity
(τ), and hydraulic pore radius (r h ) as follows:
r φ
2
k 5 h ; (6.5)
c τ
When effective hydraulic pore radius, r h is substituted by the surface
area per unit of grain volume ðS gv Þ, Eq. (6.5) can be rewritten as:
2
1 φ 1 φ
k 5 ; (6.6)
c τ S gv 12φ

6.5.1 Permeability reduction: effect of surface deposition and
pore plugging

Asphaltene deposition onto a rock surface may reduce porosity and per-
meability. Wang and Civan (2001) proposed that the instantaneous local
porosity due to deposition can be calculated from the difference between
the initial porosity, φ , and the fraction of asphaltene deposits, ε:
i
φ 5 φ 2 ε (6.7)
i
Further assuming that 1 2 φ 1 and considering constant tortuosity,
Eq. (6.6) can be modified to estimate permeability change as a function
of porosity (Civan, 2001; Kord et al., 2012):

3
k φ
5 ; (6.8)
k i φ i
However, connectivity loss (pore connectivity) has not been consid-
ered in Eq. (6.8) and permeability reduction is only attributed to pore
volume reduction.

6.5.2 Plugging and nonplugging parallel pathways model
Gruesbeck and Collins (1982) proposed a permeability model based on
porous media consisting of plugging and nonplugging parallel pathways.
Pores with relatively large diameter are considered “non-plugging” path-
ways where permeability reduction is only occurring due to surface depo-
sition of particles and thus pore volume shrinkage. The flow paths that
are tortuous and have diameter relatively close to particle size are consid-
ered “plugging pathways.” In the plugging pathways, pore throats will be
blocked through retainment of particles that will potentially lead to severe