Page 24 - Formation Damage during Improved Oil Recovery Fundamentals and Applications

Overview of Formation Damage During Improved and Enhanced Oil Recovery 7

injected fluids dissolve clays and other matrix minerals. Moreover, the
necessity for high-salinity conditions to promote interactions between
alkaline fluids and oil can lead to oil blockage of the flow paths (Ge et al.,
2012); (2) the formation of carbonate scale, hydroxyl scale, silicate scale,
or sulfate scale due to the incompatibility of alkaline with formation
water, depending on formation water composition and temperature
(Moghadasietal.,2004; Sheng,2011), which can result in significant
damage to permeability; (3) precipitate formation due to the reactions
among alkaline fluids and divalent or multivalent ions, which reduces
permeability and also sometimes improves sweep efficiency by facilitat-
ing preferable flow of alkaline solutions into high-permeability zones
(Sarem, 1974).
The synergistic effects of combinations of chemical flooding, such as,
alkaline-surfactant flooding (AS), alkaline-polymer (AP), surfactant-
polymer (SP), and alkaline-surfactant-polymer (ASP) are well known and
documented. In addition to the benefits of combination flooding, one
essential requirement is that the different chemicals must be compatible
and stable in their mixture, otherwise, severe formation damage is likely
to result significantly impairing the efficiency of chemical flooding
(Sheng, 2016).
The potential formation damage mechanisms associated with
alkaline-surfactant (AS) flooding include: (1) the addition of surfac-
tant into the alkaline can generate more stable emulsions, which, on one
hand, should carry more oil in the flowing water, but is adversely prone
to block the pore-throats with the accumulation of emulsions (Rudin
et al., 1994); (2) the detachment of sulfonate is likely to be enhanced
and adversely lead to the damage of reservoirs, with the addition of alka-
line as the charges of minerals become more negative (Hanna and
Somasundaran, 1977).
Although the addition of polymer into alkaline should help improve
mobility control by increasing the viscosity of displacing phase, formation
damage can be induced during alkaline-polymer (AP) flooding by the
increase of the alkaline concentration that can reduce polymer hydrolysis
and polymer viscosity (Green and Willhite, 1998).
The addition of surfactants into polymer flooding can further reduce
the interfacial tension and increase the viscosity of displacing phase by the
surfactants forming chelation structures with polymers. In addition, as sac-
rificial agents, polymers react with the divalent ions on rock surfaces to reduce