Page 284 - Formation Damage during Improved Oil Recovery Fundamentals and Applications

Formation Damage by Organic Deposition 255

reservoir rock (heterogeneity or homogeneity, deposits and fractures).
Knackstedt et al. (2011) imaged and studied the pore scale crude oil brine
populations to quantify the residual oil phase and to estimate wettability
alteration. For that purpose, several imaging techniques were applied,
such as surface chemical techniques (SEM and SEM-EDS) and X-ray
microCT. Using microCT, 3D images were obtained with a voxel size
down to about 1.5 mm resolution (Seifried, 2016).

6.4.4 Porous media studies
Asphaltene deposition problems encountered deep down in rock reser-
voirs are extremely problematic, and very challenging to tackle, as
opposed to production tubing deposition problems, which is typically the
focus of many asphaltene studies. Minssieux (1997) studied various core
samples with different rock characteristics in core-flooding experiments,
with regards to porous media. He concluded that porous sample plugging
only seemed to occur after enough oil had flowed through the sample,
and that damage at earlier times was only observed in samples with a
lower initial permeability (Seifried, 2016).
Behbahani et al. (2013) developed a new model based on multilayer
adsorption kinetics and Pak et al. (2011) studied asphaltene deposition
in a core holder containing a sandstone, in which asphaltene deposi-
tion was assessed through pressure drop measurements across the
vessel. The amount of deposited asphaltenes within the core was eval-
uated through the difference of asphaltene content in the inlet and
outlet stream. This indirect method was applied to study asphaltene
deposition caused by three different processes: Recycled gas injection
(most damage), CO 2 injection and natural depletion (least damage)
(Pak et al., 2011). They have also observed that porosity reduction
occurred mostly in the core inlet. A combined theoretical and
experimental study was carried out by MendozaDeLaCruz etal.
(2009), where the main mechanisms identified as significantly causing
permeability reduction were: (1) The asphaltene deposits are
significantly smaller than the size of pores and throats, leading to a
gradual reduction of pore throat radii and (2) the deposition of aggre-
gates are larger than the size of a given throat, hence leading to a
reduction in the fluid flow area. However, this model fails to describe
the deposition process under dynamic conditions because it doesn’t
account for entrainment of particles.