Flow Properties Of Polymer Solutions Research Articles

Evaporation-controlled dripping-onto-substrate (DoS) extensional rheology of viscoelastic polymer solutions

Extensional flow properties of polymer solutions in volatile solvents govern many industrially-relevant coating processes, but existing instrumentation lacks the environment necessary to control evaporation. To mitigate evaporation during dripping-onto-substrate (DoS) extensional rheology measurements, we developed a chamber to enclose the sample in an environment saturated with solvent vapor. We validated the evaporation-controlled DoS device by measuring a model high molecular weight polyethylene oxide (PEO) in various organic solvents both inside and outside of the chamber. Evaporation substantially increased the extensional relaxation time lambda _{E} for PEO in volatile solvents like dichloromethane and chloroform. PEO/chloroform solutions displayed an over 20-fold increase in lambda _{E} due to the formation of an evaporation-induced surface film; evaporation studies confirmed surface features and skin formation reminiscent of buckling instabilities commonly observed in drying polymer solutions. Finally, the relaxation times of semi-dilute PEO/chloroform solutions were measured with environmental control, where lambda _{E} scaled with concentration by the exponent m=0.62. These measurements validate the evaporation-controlled DoS environment, and confirm that chloroform is a good solvent for PEO, with a Flory exponent of nu =0.54. Our results are the first to control evaporation during DoS extensional rheology, and provide guidelines establishing when environmental control is necessary to obtain accurate rheological parameters.

Flow Enhancement of Water-Soluble Polymers through Porous Media by Preshearing

We examine the role of preshearing on the flow properties of polymer solutions containing essentially an acrylamide-based copolymer obtained from an emulsified polymer emulsion inverted by a surfac...

An Investigation of Polymer Adsorption in Porous Media Using Pore Network Modelling

Polymer injection in hydrocarbon reservoirs has been of great interest in petroleum engineering as an enhanced oil recovery method. In order to have a reliable injection plan, an accurate estimation of polymer behaviour is required to control the fluid flow in porous media. However, it is difficult to calculate the flow properties of polymer solutions—known as non-Newtonian fluids—in porous media, due to variable viscosity at different shear rates. Adsorption of polymer molecules onto the rock surface decreases the available cross-sectional area of polymer solution, therefore at a constant rate, the shear rate increases. As a result, it is important to investigate how polymer adsorption can affect the polymer solution flow behaviour in porous media. Moreover, prior to any polymer injection plan, the amount of adsorbed polymer should be calculated, due to the high cost of polymers. In the present study, pore network modelling was used to investigate the effect of polymer adsorption on flow behaviour of polymer solutions in porous media. To achieve this goal, a simple pore was constructed to adequately represent the real structure of the porous medium. It was then validated by simulation of Newtonian fluid flow in the network and comparison of the calculated flow properties with the experimental data. After validation, the pore network was used for simulation of non-Newtonian fluid flow in porous media. The experimental apparent viscosity of non-Newtonian fluid was used for verification of the procedure and the developed network. The apparent viscosity of non-Newtonian was calculated successfully using macroscopic properties of the rock sample and measured bulk properties of non-Newtonian fluid. The effect of polymer adsorption on calculation of non-Newtonian fluid apparent viscosity was then investigated. It was shown that the polymer adsorption process plays an important role in calculation of polymer solution apparent viscosity. The results reveal that polymer adsorption cannot be neglected, especially in near well-bore areas where the adsorption is high. Finally, the effect of wettability in calculating the total amount of adsorbed polymer volume was studied. The results suggest that neglecting the rock’s wettability can result in an overestimation or underestimation of the amount of adsorbed polymer.

International Workshop on Recent Advances in Flow Properties of Polymer Solutions, Melbourne, Australia, 11–12 August, 1988.

International Workshop on Recent Advances in Flow Properties of Polymer Solutions, Melbourne, Australia, 11–12 August, 1988.

ポリアクリルアミド水溶液のコア内流動性について

In this paper, we studied the effects of the chemical structure and compositions of polymer and brine on the flow properties with the aim of mobility control. Five kinds of partially hydrolyzed polyacrylamides were used as polymer samples. We used brine which contained mono-valent (Na+, K+) or divalent (Mg2+, Ca2+) ions.We measured the flow properties of polymer solutions as apparent viscosity, screen factor, resistance factor and residual resistance factor and discussed the relation between each other. The results were as follows:(1) The resistance factor, residual resistance factor and screen factor, respectively, increased with a polymer molecular weight increase. From these results, it was confirmed that the resistance factors had a positive correlation with the screen factors.(2) The resistance factor and apparent viscosity decreased with a brine concentration increase. These behaviors become extremely remarkable in divalent ion solutions. However, the screen factors decreased relatively little and the residual resistance factors were almost constant in these brines.(3) The resistance factor increased at a frontal velocity of over 5ft/day, but there was a reverse tendency at a rate less than 5ft/day.

The Effect of Ultrasonics On the Injectivity And Viscosity of Xanthan Gum For Enhanced Recovery Applications

Abstract This paper outlines preliminary studies which have indicated that the injectivities of xanthan gum solutions can be improved by ultrasonic treatment without adversely affecting formation viscosities in enhanced recovery methods. Introduction One of the major concerns in applying polymer flooding to reservoirs with relatively tight oil sands (less than 100 md) is to have good injectivity while maintaining high solution viscosities(l). If the solution is mixed well and the molecules are dispersed thoroughly without being mechanically degraded, then this optimum situation is reached. Ultrasonic waves have been used to disperse particles of the micrometre Size(2). The capability of ultrasonic waves to disperse particles or agglomerates stems from the cavitation caused by ultrasonics. Cavitation occurs in the regions of the liquid which are subjected to rapidly alternating pressures of high amplitude(3). Besides dispersion, ultrasonic waves have been utilized to break up polymer molecules. The ultrasonic degradation of polymers in solution is of a mechanical nature. The stresses set up in the polymer molecule are caused by the friction forces generated by the relative movement of the molecules of solvent and the polymer molecule as a result of the collapse of cavitation bubbles(4). The permanent degradation can be measured by determining viscosities and by chemical reactions. A recent review of the work in this area is presented by A. M. Basedow and K. H. Ebert(4). Ultrasonics were also found to be effective in liquefying gels(5). The polymer molecules that are used as- mobility control agents in enhanced oil recovery are between 0.1 µm and 0.5 µm in diameter(6). Xanthan gum molecules (Kelzan -XC) have been reported to be around 0.3-0.4 µm(7). These molecules have bonds between them that are weaker than the covalent bonds between the units of the chains. Morris suggests that these weak non-covalent associations between aligned molecules build up a tenuous gel-like network. He also proposes that this network is progressively broken down with increasing shear rate(8). These bonds lead to an increase of entanglements between the polymer chains. Moorhouse et al. characterize the bonds between the molecules as hydrogen bonds(9). If one can break the hydrogen bonds and decrease the degree of entanglement without destroying the covalent bonds, then he can increase the injectivity of the solution and still maintain the high viscosity level. It has been suggested that the larger polymer aggregates present more resistance to flow and accumulate greater shear stresses; hence they are more vulnerable to rupture than the smaller species or the dispersed molecules(4). The principle of utilizing ultrasonic waves to improve the flow properties of polymer solutions through porous media without decreasing the viscosities is examined in this investigation. Procedure In a previous study, the optimum blending of xanthan gum solutions was obtained by the shearing of the solution through several orifice plates, with 100 psi pressure drop each plate(7). Excessive pressure drops across the orifices leads to mechanical breakdown of the molecules. Some of these solutions prepared by optimum blending were subjected to ultrasonic radiation; their injectivities and viscosities were determined.

Rheological Applications of a Drop Elongation Experiment

A new method for determining the extensional flow properties of polymer solutions and melts is proposed and analyzed. The physical principle behind the method is that when a fluid drop is placed in a rotating field of a higher density fluid it will experience axisymmetrical extension or contraction when the rotational speed is varied with time. Under rather general conditions, an analysis is possible of the dynamic response of the drop in terms of measurable and controllable variables. This gives rise to a number of different steady and transient extensional flow experiments. Such experiments are described, and a specific unsteady experiment is used to verify the assumptions of the analysis and to indicate the quantitative accuracy of the method.

Flow Properties of Polymer Solutions. II. Phenomenological Relation for the Stress Following Sudden Start of Steady Shear Flow

The stress development at the start of steady shear flow was calculated from experimental data for the strain-dependent relaxation modulus of a concentrated polymer solution with the use of a constitutive equation based on the strain-dependent relaxation spectrum. Calculated results were in close agreement with those observed in the range of relatively low rate of shear, where no stress overshoot at the start of steady shear flow was observed. When stress overshoot was present, the calculated result was in close agreement with the observed up to the time at which the stress reached its maximum value. This time corresponded to a certain value sB of the shear strain, irrespective of the rate of shear, and was accurately predicted from the relaxation modulus using the strain-dependent constitutive model. At longer times the calculated result for the rate of decrease of the stress was too small, compared with the observed, so that the predicted peak of the stress overshoot was too broad. It was concluded that the strain-dependent constitutive model may be applied to polymer solutions when the shear strain is smaller than sB or when the rate of shear is smaller than sB/τm, where τm is the maximum relaxation time of the polymer solution.

Steady-State and Oscillatory Flow Properties of Polymer Solutions

Viscosities, first and second normal-stress differences, and related material functions were determined for steady-state and oscillatory shearing of polyethylene oxide and polyacrylamide solutions by use of a Weissenberg R-17 Rheogoniometer with cone-and-plate shearing geometry. Pressure transducers—located along the radius of the plate, with their 0.04-in-O.D. pressure-sensing membranes flush with the plate surface—were used to determine local values of the normal stress. The sensitivity of the transducers was 20–30 dynes/cm2 for steady-state and 10–15 dynes/cm2 for unsteady-state measurements. The ratio of the secondary to the primary normal-stress difference was negative, was as large as −0.2 for the solutions studied, and appeared to decrease with increasing shear rates over the shear-rate range investigated. Complex viscosity and displacement and amplitude functions for both the primary and secondary oscillatory normal-stress differences were determined as functions of the frequency. A significant improvement in the agreement predicted by the “analogies” between the oscillatory primary-normal-stress-difference functions and the complex viscosity functions was achieved in comparison with previous results by reduction of instrument compliance. The Spriggs four-constant and similar models, as well as the Carreau and Bogue-Chen models, were compared with our steady-state and oscillatory data, and these fit the data fairly well; but overall, the Bogue-Chen model appears to represent the data somewhat better.

Flow Properties of Polymer Solutions. I. Temperature Dependence of Stresses Following Sudden Start and Cessation of Steady Shear Flow

Following sudden start and cessation, respectively, of steady shear flow, stresses, κη(t, κ) and κη(t, κ), were measured for a 20-% solution of polystyrene in chlorinated biphenyl. Here κ is the rate of shear and t is the time after sudden change of rate of shear. Measurements were performed at every 5°C starting from 30°C up to 50°C with a rheometer of the cone-and-plate type in the range of rate of shear 1×10−4∼10−2 sec−1. Measured results included behaviors characteristic of high rates of shear such as stress overshoot as well as those characteristic of low rates of shear. The accuracy of data as examined with linear viscoelasticity relations at low rates of shear was satisfactory. A method of reduced variables with respect to temperature T, time t, and rate of shear κ was revealed to apply to stress development function η(t, κ) and stress decay function η(t, κ): η(t, κ)/η0 and η(t, κ)/η0 and obtained at various temperatures were unique functions of two variables t/aT and κaT, where η0 is the zero-shear viscosity and aT is the shift factor usually employed in the time—temperature reduction for functions in linear viscoelasticity.

Flow Properties of Polymer Solutions. III. Non-Newtonian Viscosity and Relaxation Mechanisms with Long Relaxation Times

Contributions of relaxation mechanisms with long relaxation times were examined for the shear stress κη(t, κ) after a sudden stop of steady shear flow of a 20-% polystyrene solution in chlorinated biphenyl, where κ is the rate of shear and t is the time of stress decay. The longest relaxation time τm(κ) and the corresponding strength ηm(κ) were evaluated from the slope and the intercept at t=0, respectively, of the asymptotic straight line at large t in the plot of logη(t, κ) vs. t. Those for the second longest relaxation time, τm(κ) and τm-1(κ), were obtained in a similar manner from the plot of vs. t. The relaxation times τm(κ) and τm-1(κ) were found to be independent of κ and the τm-1(κ) ratio τm(κ) was about 3. At the limit of zero rate of shear, ηm(κ) and ηm-1(κ) were approximately 30 and 45%, respectively, of the zero shear viscosity η0. As κ increased, ηm(κ) and ηm-1(κ) decreased more rapidly than the steady shear viscosity η(κ) did; the difference η(κ)−ηm(κ)−ηm-1(κ) was almost independent of κ. It was concluded that the nonlinear behavior, such as the shear-dependent viscosity of the polymer solution, is mainly due to the nonlinear behavior of the few relaxation mechanisms with long relaxation times.