Page 75 - Hybrid Enhanced Oil Recovery Using Smart Waterflooding

CHAPTER 4 Hybrid Chemical EOR Using Low-Salinity and Smart Waterflood 67

has shear rate-dependent viscosity, i.e., the viscosity synthetic polymers of Flopaam 3330s, Flopaam
changes corresponding to the shear rate. As the polymer 3630s, and AN-125, in the laboratory experiments.
EOR deployment uses the polymeric solution at low The study matched the Carreau model, which is the
concentration of polymer, the pseudoplastic or shear- shear-thinning part of the mechanistic model, as a func-
thinning behaviors are applicable to the vast majority tion of polymer concentration, salinity, hardness, and
of polymeric solution in diluted homogeneous regimes. temperature to the measured data in the shear-
Generally, the shear-thinning polymer shows the thinning regime (Fig. 4.1). Kim, Lee, Ahn, Huh, and
decreasing viscosity with an increase in shear stress or Pope (2010) developed the shear-thickening part of
shear rate. The analytical form of the power law, the mechanistic model to correspond the rheology of
described in Eq. (4.6), commonly describes the shear- synthetic polymers as a function of the same parameters
thinning behavior between the viscosity of polymeric (Fig. 4.2).
solution and shear rate (Bird, 1960). The two-
parameter equation of the power law is also known as
the Ostwald-de Waele model. The model is applicable Retention
to the pseudoplastic regime, not to the high and low There are three types of polymer retention: adsorption,
shear rate regimes. mechanical trapping, and hydrodynamic retention.
Although the adsorption occurs in both stagnant and
n 1 (4.6)
hð _ gÞ¼ K _ g transport regimes, the mechanical trapping and hydro-
dynamic retention only occur in the transport regime
where _ g is the shear rate; K is the flow consistency index;
within the porous media. The mechanical trapping de-
and n is the flow behavior index. scribes the larger molecules to be stuck in the narrow
The Carreau equation of Eq. (4.7) describes the channels or pores. Therefore, it highly depends on
shear-thinning behavior more accurately in the whole the pore size distribution. The hydrodynamic reten-
regime (Bird, Armstrong & Hassage, 1987; Carreau, tion is easily thought to be trapped temporarily in
1972).
the stagnant flow region, i.e., close to the porous me-
n 1
a (4.7) dia, because of the hydrodynamic drag force. Because
hð _ gÞ ¼ h N þ ðh 0 h N Þ½1 þ ðA _ gÞ Š a
of the hydrodynamic retention, higher concentration
where h 0 is the viscosity at very low shear rate; h N is the of polymer can exist in this region compared with
viscosity of limiting value at high shear rate; A and n are that in the bulk of the injecting solutions. The mechan-
the polymer-specific empirical constants; and a is gener- ical trapping can be avoided through screening test.
ally equal to 2. The hydrodynamic retention is relatively minor and
There are other models to describe the pseudoplastic can be ignored in the practical applications. Because
rheology of polymeric solution. Often, the polymeric the adsorption of polymer is significant compared
solutions show an increasing apparent viscosity in with the mechanical trapping and hydrodynamic
high shear stress condition. This relation of an retention, adsorption is the major interest in the poly-
increasing apparent viscosity with an increase in shear mer retention. The adsorption occurs by the interac-
stress or shear rate is shear-thickening or dilatant tion between polymer molecules and solid surface.
behavior. A couple of mechanisms have been proposed The main contribution on the interaction is the phys-
(Clarke, Howe, Mitchell, Staniland, & Hawkes, 2016; ical adsorption by van der Waal’s and hydrogen
Delshad et al., 2008; Seright, Fan, Wavrik, de Carvalho bonding rather than chemisorption. The solid surface
Balaban, 2011), and they explain that viscoelastic of with a larger surface area leads to the more adsorption
polymer improves the displacement efficiency reducing of polymer and the significant removal of polymer
residual oil. The research team from the University of from the bulk solution. Although the hydrodynamic
Texas at Austin developed the mechanistic model, retention is conventionally considered as a reversible
which incorporates the Carreau equation for shear- process, the polymer adsorption is assumed to be,
thinning behavior, to represent viscoelastic behavior. mostly, an irreversible process. The isothermal adsorp-
The proposed model is the summation of shear- tion is generally nonlinear to the polymer concentra-
thinning and thickening behaviors of polymeric tion, and it can be described by the Freundlich or
solution (Delshad et al., 2008). Incorporating the visco- Langmuir models. The general form of the Freundlich
elastic model and experiments, the rheology database of isotherm model is described in Eq. (4.8).The general
the synthetic polymers has been constructed. Lee, Kim, form of the Langmuir isotherm model is shown in
Huh, and Pope (2009) measured the viscosity of three Eq. (4.9). Gupta and Greenkorn (1974) reported the