Page 23 - Formation Damage during Improved Oil Recovery Fundamentals and Applications

6 Bin Yuan and David A. Wood

1.4 CHEMICAL FLOODING

Among various techniques of EOR, chemical enhanced oil recov-
ery (CEOR) has drawn increasing interest from oil companies. CEOR
includes surfactant flooding (S), alkaline flooding (A), polymer flooding
(P), alkaline-surfactant flooding (AS), alkaline-polymer (AP), surfactant-
polymer (SP), and alkaline-surfactant-polymer (ASP). The performance
of CEOR depends on the interaction efficiency among the injected
chemicals, crude oil, formation water, reservoir conditions, and other
stringent requirements, such as reservoir retention levels, compatibility,
and thermal and aqueous stability of the injected chemicals.
The associated formation damage mechanisms with surfactant flood-
ing include: (1) emulsion blockage and water-in-oil emulsion (Feng et al.
2011) tends to increase the viscosity in comparison to clean oil, produced
by mixing surfactant and crude oil, which even with oil-in-water emul-
sions can improve the mobility ratio and sweep efficiency (Xu et al.,
2011); (2) wettability alteration from oil-wet to water-wet; (3) phase
trapping caused by the multiphase fluids transport with high capillary
force (Nelson and Pope, 1978); (4) excessive adsorption and retention of
surfactants leading to the decrease of porosity and permeability, and less
efficiency of surfactant adsorption along oil-water interfaces for enhancing
oil recovery (Hirasaki et al., 2011); (5) surfactant precipitation, viscous
microemulsions, complexes, gels, and liquid crystals with increase of
salinity that can damage permeability (Stellner and Scamehorn, 1986).
The damage issues caused by polymer flooding consist of: (1) poly-
mer retention and plugging that reduce permeability caused by adsorption
(Tang et al., 2001), mechanical trapping (Garti and Zour, 1997) and
hydraulic retention (Bhardwaj et al., 2007); (2) incompatibility of polymer
with formation fluids and rocks leading to both inorganic precipitation
and organic deposition (Fletcher et al., 1992); (3) the mitigation of fines
or sands caused by the strong adsorption of polymer onto clay particles
(Borchardt, 1989). Consequently, before polymer is applied for IOR
purposes, first, it should be subjected to a number of laboratory screening
tests, including polymer injectivity, adsorption, and brine-compatibility
tests. In addition, its microbial, mechanical, and chemical degradation
characteristics should be established.
The formation damage mechanisms caused by alkaline flooding
consist of: (1) migration and blockage of fine particles after alkaline