Apparent Viscosity Of Polymer Solutions Research Articles

The Thermoviscosifying Behavior of Water-Soluble Polymer Based on Graft Polymerization of Pluronic F127 with Acrylamide and 2-Acrylamido-2-methylpropane Sulfonic Acid Sodium Salt.

A new concept of thermoviscosifying polymers is proposed to address the problems about decreasing viscosity of polymer solution under high temperatures. However, existing thermoviscosifying polymers have complicated synthesis processes and high costs, and both of them restrict the wide practical applications of thermoviscosifying polymers. Although polyethers have the characteristics of thermal gelatinization, they just display thermoviscosifying behaviors only under extremely high concentrations (>15 wt %). Therefore, the graft copolymerization of the commercialized Pluronic F127 (PEO100-PPO65-PEO100) with acrylamide and 2-acrylamide-methylpropionic acid sodium salt was studied here. A series of graft modified polyether polymers were prepared and it was expected to get thermoviscosifying polymers with high molecular weights and low association temperatures. Several factors on thermoviscosifying behaviors were investigated, such as polymerization condition, polymer concentration, hydrophilic monomer, molecular structure and molecular weight. It was also proven that the apparent viscosity of polymer solution is influenced by polymer concentration, molecular weight of polymer, and content of anion groups.

Novel viscoelastic model for predicting the synthetic polymer’s viscoelastic behavior in porous media using direct extensional rheological measurements

High molecular weight, flexible polymers used for heavy oil recovery exhibits viscoelasticity that causes the thickening of apparent viscosity which could not be predicted by the conventional shear thinning rheological models. Unified apparent viscosity model (UVM) developed at UT-Austin based on the postulation that the apparent viscosity of polymer solutions is the sum of shear and elongational viscosity accounts for the viscoelastic thickening in the extensional part through relaxation time, maximum elongational viscosity and strain hardening index. Although UVM addresses the other limitation of the previous viscoelastic models, its dependence on the core flood data to predict maximum elongational viscosity and strain hardening index limits its commercial independent usage for preliminary screening.These limitations are addressed in our novel viscoelastic model named as Azad Trivedi Viscoelastic Model (AT-VEM), which could predict the apparent viscosity in the shear thickening region using the extensional parameters measured by capillary breakup extensional rheometer (CaBER) through the combination of Upper Convected Maxwell (UCM), finite extensible nonlinear elasticity (FENE) and power law theories. CaBER set up uses a step-strain to stretch the drop of polymeric liquid placed between the two plates and monitor its midpoint diameter during filament drainage. The relaxation time is determined by fitting the filament diameter from the region representing the balance between the elastic stress and surface tension into UCM. As per FENE theory, fluid relaxes at the rate two-third of its strain rate and the extensional viscosity around the critical Deborah number of 0.66 corresponds to the maximum elastic limit and would be the maximum elongational viscosity. Filament during drainage gets strained and the corresponding increment in extensional viscosity is fitted with power law to determine the strain hardening index.A series of core flood data (performed using partially hydrolyzed polyacrylamide (HPAM) polymers) from the UT-Austin that validated the UVM model was used extensively. Other reported literature data were also used. Extensional rheology was performed on those polymers at the similar conditions to determine the relaxation time, maximum elongational viscosity, and strain hardening index. These parameters along with the shear parameters were used to match the reported apparent viscosity. All the experiments fairly match well with the average downscaling power factor of 0.35 to the maximum elongational viscosity and subtrahend of 1.2 to the strain hardening index. Downscaling and subtrahend factor is essential to scale down the pure elongation in the extensional bulk field to the combination of shear and elongation experienced in the porous media.AT-VEM can be incorporated into commercial numerical simulators for predicting the injectivity and recovery due to viscoelastic thickening independently and thereby assist in quick screening polymers for oil recovery applications.

Research on Configuration of Polymer Molecular Aggregate and Its Reservoir Applicability

This article researches the effect of configuration of polymer molecular aggregate on the performance of polymer solution and its reservoir applicability, taking configuration of polymer molecular aggregate, first normal stress difference, resistance coefficient, residual resistance coefficient, and oil recovery as the evaluation indexes, guided by physical chemistry, polymer materials science, and reservoir engineering, by means of chemical analysis, instrument detection, and physical simulation. Results show that the apparent viscosity of polymer solution is closely related to the configuration of molecular aggregate. However, that reflects neither the transporting and migrating ability of molecular aggregate in porous media nor the applicability of polymer solution for reservoir core pore. Compared with “linear-branched chain” polymer, network polymer has a regional “laminated-net” structure, which has a stronger ability to adsorb and wrap hydrone, when deformation occurs, internal friction of which is larger, and apparent viscosity of which is higher with isoconcentration. Changing the configuration of molecular aggregate can enhance the tackify performance of polymer, but crosslinking or association degree must be controlled properly. Otherwise, the applicability of polymer solution for reservoir core pore will become poor, thus influencing the oil incremental effect of polymer flooding.

Solution properties of thermothickening copolymers bearing hydrocarbon end‐capped oxyethylene units

AbstractNovel thermothickening copolymers composed of acrylamide and a macromer bearing hydrocarbon end‐capped oxyethylene units were synthesized. Influences of polymer concentration, salt content, shear rate, and temperature on the solution behavior were investigated. The polymer solution exhibited shear‐thickening behavior at low‐to‐moderate shear rates (<50 s−1), and the shear‐thickening behavior was dependent on polymer concentration, NaCl content, and temperature. With the increase of salinity, apparent viscosity of polymer solution increased dramatically (especially at low shear rates). At higher NaCl content (>20 wt %), polymer solutions became physical gel, and the apparent viscosity increased by several orders of magnitude. The polymer solutions exhibited excellent thermothickening behavior, even at the low concentration of 0.15 wt %. The results of rheological measurements showed that the storage and loss modulus were successfully fitted to a single Maxwell element at low temperature (<60 °C). © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1799–1808, 2010

Synthesis and solution properties of temperature‐sensitive copolymers based on NIPAM

AbstractA kind of temperature‐sensitive water‐soluble polymers P(NIPAM‐HEMA‐AM) of N‐isopropylacrylamide (NIPAM), hydroxyethyl methacrylate (HEMA) and acrylamide (AM) were synthesized by free radical aqueous solution copolymerization. The polymers were characterized by Fourier transform infrared spectrum (FTIR) method. Solution properties, such as the influences of monomer ratios and additives on the low critical soluble temperature (LCST) of the polymer solutions as well as the viscosity‐temperature properties were studied. The results show that the polymer concentrations have no significant influence on the LCST of polymer solutions. The incorporation of HEMA units leads to a lower LCST, while AM units to a higher LCST. The additions of small molecules such as salt and surfactant also have significant effect on the LCST, the addition of NaCl decreases the LCST, while the addition of sodium dodecylbenzenesulfonate (SDBS) increases the LCST. The apparent viscosity of polymer solutions depends on temperature. The 1.5 wt % aqueous solutions of P(NIPAM‐HEMA‐AM) exhibits good thermo‐thickening behavior over 55°C, whereas the 0.8 wt % aqueous solutions do not show this behavior during the heating process. The aqueous solutions of P(NIPAM‐HEMA‐AM) are viscoelastic fluids, and the viscoelasticities mainly depend on temperature. Both the storage modulus (G') and loss modulus (G'') of 1.5 wt % polymer solutions increase with temperature. Over 55°C, G' exceeds G'', and the polymer solutions are elasticity‐dominated. In contrast, below 55°C, G'' is larger than G', and the polymer solutions are viscosity‐dominated. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010