Page 286 - Formation Damage during Improved Oil Recovery Fundamentals and Applications

Formation Damage by Organic Deposition 257

where, σ is the deposition constant; R refers to the ratio of particle size
to pore throat size, R c refers to the critical ratio of particle size to pore
throat size. Basically, according to Eq. (6.4) pore throat plugging occurs at
conditions where the critical pore throat diameter is greater than the
average pore throat diameter.
Surface deposition, entrainment, and pore throat plugging are the three
mechanisms contributing to asphaltene damage in porous media. There is
however a postulated forth parameter, the Deep Bed Filtration (DBF) model
by Wang and Civan (2001) and Wang (2000). DBF refers to the retention
process of particles which occurs when the particulate suspension flow
through a porous medium causes a separation between the solid phase and
the liquid phase of the suspension. This is based on several mechanisms:
Contact between the particles and the retention site, fixing of particle sites
and finally the break off of formerly retained particles (Fallah et al., 2012).

6.5 PERMEABILITY DAMAGE MODELS

Several theoretical and empirical models have been developed to
estimate permeability as a function of porosity (Pape et al., 2000; Civan,
2001; Zheng et al., 2016). It is well known that effective porosity can
decrease owing to pore volume shrinkage and leading to permeability
reduction. However, permeability can be also altered because of hydraulic
conductivity/connectivity loss (coordination number reduction) owing to
the pore plugging mechanism. In the extreme case where significant pore
blockage occurs, the porosity may not even significantly decrease. As it
will be discussed later in detail, when the rock has a large fraction of
pores with the diameter comparable to the size of particles, pore throats
can be easily plugged and blocked; this will lead to severe permeability
reduction even when the large fraction of pore space yet remains intact.
Thus, it is crucial to study asphaltene deposition in porous media via new
permeability models which consider both porosity reduction and pore
connectivity loss, especially for reservoirs with small size pores that are
comparable to the particle size.
One of the fundamental permeability models is the Kozeny Carmen
(KC) equation that considers porous medium as a bundle of cylindrical