Extensional rheological data from ex-situ measurements for predicting porous media behaviour of the viscoelastic EOR polymers

In this article, extensional rheological data of various polymer solutions, to be used in Azad Trivedi viscoelastic model (AT-VEM) for predicting the viscoelastic behavior of synthetic polymer in porous media are provided. Extensional rheology measurements are performed for different polymer solutions using Capillary breakup extensional Rheometer (CaBER) to obtain the filament diameter with respect to time. Extensional rheological parameters, such as the extensional relaxation time, maximum elongational viscosity at the critical Deborah number and strain hardening index are determined from observed filament diameter with time-based on the Upper Convected Maxwell model, the finite extensible non-linear elastic model, and the power law model.


Figures and
The data is available within the article Related research article This data in brief article is submitted as a companion paper to Azad and Trivedi [1].

Value of the data
These data are valuable for the flow of polymer through porous media The data presented here shows, for the first time, the direct measurement of extensional rheological parameters of viscoelastic enhanced oil recovery (EOR) polymers.
The data presented here shows the effect of salinity, concentration and molecular weight on the extensional rheological parameters of high molecular weight synthetic polymers, mainly hydrolyzed polyacrylamide.
The data of extensional relaxation time, maximum elongational viscosity at the critical Deborah number and strain hardening index obtained from filament drainage as a function of time can be used to screen polymers for EOR as well as fracturing applications.
The presented data validates the Azad-Trivedi Viscoelastic Model (AT-VEM) and compares with Unified Viscosity Model (UVM) for predicting the viscoelastic onset and shear thickening for polymer flow through porous media using only bulk rheology.
The data presented can be used to predict the injectivity behavior and oil recovery potential of viscoelastic polymers using AT-VEM, independent of core flood experimental parameters.

Data
The extensional rheological data of different EOR polymers, measured using CaBER at various conditions of concentration and salinity are provided in this article. Initially, the reduction in filament diameter as a function of time was monitored using the inbuilt laser micrometer. Extensional parameters such as extensional relaxation time (τ ext ), maximum elongational viscosity at critical Deborah number (μ max @De cr À 0:66 ) and strain hardening index (n 2 ) are determined from filament diameter with respect to time data using upper convected Maxwell (UCM) model, finite extensible non-linear elastic (FENE) model, and the power law model. These parameters are used in the AT-VEM for predicting the viscoelastic characteristics (such as onset, shear thickening) of EOR polymers [1]. The predictability of core flood independent AT-VEM is compared with UVM and Carreau model [1]. The details about UVM and Carreau model can be found elsewhere [2,3].

CaBER experimental procedure
HAAKE CaBER (Thermo Scientific, USA) was used for characterizing the extensional properties of EOR polymers. The details about the CaBER experimentation can be found elsewhere [1,[4][5][6]. The typical filament drainage schematic [4] during CaBER experimentation is shown in Fig. 1. The filament drainage (filament diameter decreases with time) for the polymer solutions used are shown in the Figs. 2(a)-15(a). Theories used to determine the extensional rheological data are briefed here, however, more details can be found in our previous publications [1,[4][5][6].  Table 1.

FENE theory for maximum elongational viscosity
The axial force balance, strain rate and strain pertinent to filament drainage in CaBER experiments are represented by the Eqs. (2)-(4).
where, ε ¼ Hencky strain, dimensionless _ ε ¼ Strain/Elongation rate, s À 1       η app e where, η¼ Newtonian viscosity, Pa s τ zz Àτ rr ¼ Normal stress difference ε t η app e ð Þ ¼ Apparent extensional viscosity, Pa s X ¼ Correction factor for axial variation -0.7127 As per the FENE theory, fluid relaxes at the rate 2/3 of its strain rate representing the critical Deborah number to be around 0.66 [7,8]. The maximum extensional viscosity around 0.66, indicating the elastic limit [8,9] will be used as μ max @De cr À 0:66 in the AT-VEM. Critical strain rate is determined by dividing the critical Deborah number by the relaxation time. The sharp increase in the elongational viscosities around the critical strain rate for the polymer solutions, used in each experiment is shown in the Figs. 2(b)-15(b). Values of μ max @De cr À 0:66 for each polymer samples are shown in Table 1.

Power law theory for strain hardening index
Power law is fitted to extensional viscosity vs strain values around the critical Deborah number for determining the n 2 values. The power law fits for all the experiments are shown (Figs. 2(c)-15(c)). The n 2 values determined using the power law fit are reported in Table 1.