Polymers In Porous Media Research Articles

Entropy-induced separation of star polymers in porous media

We present a quantitative picture of the separation of star polymers in a solution where part of the volume is influenced by a porous medium. To this end, we study the impact of long-range-correlated quenched disorder on the entropy and scaling properties of f-arm star polymers in a good solvent. We assume that the disorder is correlated on the polymer length scale with a power-law decay of the pair correlation function g(r) approximately r-a. Applying the field-theoretical renormalization group approach we show in a double expansion in epsilon=4-d and delta=4-a that there is a range of correlation strengths delta for which the disorder changes the scaling behavior of star polymers. In a second approach we calculate for fixed space dimension d=3 and different values of the correlation parameter a the corresponding scaling exponents gammaf that govern entropic effects. We find that gammaf-1, the deviation of gammaf from its mean field value is amplified by the disorder once we increase delta beyond a threshold. The consequences for a solution of diluted chain and star polymers of equal molecular weight inside a porous medium are that star polymers exert a higher osmotic pressure than chain polymers and in general higher branched star polymers are expelled more strongly from the correlated porous medium. Surprisingly, polymer chains will prefer a stronger correlated medium to a less or uncorrelated medium of the same density while the opposite is the case for star polymers.

Saturation and entropic trapping of monodisperse polymers in porous media

We investigate the effect of polymer concentration on the diffusion and localization (entropic trapping) of linear polymer chains in a two-dimensional model system of small obstacles and large pores. Three distinct regimes are identified: the entropic trapping regime, a reptation regime where the larger pores are polymer saturated and the untrapped polymers reptate, and finally a crowding regime where intermolecular interactions dominate. In this model system, the entropic trapping, reptation, and crowding mechanisms compete and lead to a characteristic maximum in the diffusion coefficient for intermediate polymer concentrations.

Numerical analysis of layer and bridging adsorption of flexible polymers in porous media

We report a study of the flow of polymers solutions through porous media using traveling wave and numerical analysis. We consider flow regimes where layer adsorption of (short) undeformed chains and bridging adsorption of (long) stretched ones occurs either separately or simultaneously. The model for polymer transport taking into account these phenomena was found earlier to reduce to a system of four partial differential equations, describing respectively polymer mass conservation, bridging probability conservation, layer adsorption kinetics and bridging adsorption kinetics. In this study, we show that at short times the above quantities are concave-upward decaying functions of distance which develop to traveling wave for sufficiently long times. This corresponds to a progressive saturation of adsorption towards the inlet of the porous sample. In the case of simultaneous layer and bridging adsorption, the concentration profile exhibits an unusual superposition of traveling waves, consistent with a slower propagation of the bridging adsorption wave with respect to the layer adsorption one. This shows that flow induces a separation of short and long chains.

Unsteady-State Flow of Flexible Polymers in Porous Media

In this paper we report an investigation of the unsteady-state flow of polymer solutions through granular porous media. The experiments were performed using high-molecular-weight nonionic and anionic polyacrylamides dissolved in water containing NaCl and model porous media obtained by packing silicon carbide (SiC) grains having a narrow grain size distribution. Before injection in porous media, the polymer solutions were carefully filtered according to a method that was proved to be efficient in removing any possibly remaining microgels. The SiC grain surface was passively oxidized by a controlled thermal treatment in order to obtain a surface partially covered by a thin silica layer having adsorption properties similar to those of quartzitic sand. By packing SiC grains of different sizes, porous media having identical adsorption properties and well-known pore throats sizes can be obtained with a good reproducibility. Parameters investigated include pore size, velocity gradient, polymer concentration, and adsorption energy. A striking unsteady-state flow behavior (pressure build-up at constant flow rate) is observed when three conditions are fulfilled: (a) the velocity gradient is larger than that known to be able to induce a coil–stretch transition, (b) the polymer adsorbs on the pore surfaces, and (c) the length of stretched macromolecules is larger than the effective pore throat diameter. When one of these conditions is not satisfied the flow remains steady. These observations are interpreted by a mechanism involving the adsorption and bridging across pore restrictions of elongated chains. We propose to refer to this peculiar mode of polymer adsorption as bridging adsorption.

Transport of H + ions across a polymeric porous media

Transport of H + ions across a capillary system (a microporous polymeric membrane) is studied for different HCl concentrations. From electrokinetic measurements, information about membrane properties (resistance and transport number) and membrane/solution interactions (streaming or zeta potentials) are obtained. Results show a decrease of these parameters when concentration increases. The effect of mixed salts (HCl+NaCl) on concentration and zeta potential values is also studied. Changes in the membrane charge related to the pH of solutions are obtained.

Reptation dynamics of semirigid polymers in porous media

A theory of the dynamics of a semirigid polymer molecule in a porous medium is formulated on the basis of the reptation theory. First, the statics, i.e., the dimensions and conformation of this polymer in a straight cylindrical pore is considered. The partition coefficient of the chain between solutions in the interior and the exterior of the pore is also discussed. Then the statics of the semirigid chain in a random network of pores in three dimensions is discussed. The dynamics is discussed subsequently. The motion of the primitive path is formulated in analogy to the reptation theory. The mean-square displacement of a point on the primitive path in the pore network is calculated and the long-time diffusion constant is obtained as a function of chain length, pore size and pore structure

The Solution of the Riemann Problem for a Hyperbolic System of Conservation Laws Modeling Polymer Flooding

The global Riemann problem for a nonstrictly hyperbolic system of conservation laws modeling polymer flooding is solved. In particular, the system contains a term that models adsorption effects.

Development and Evaluation of EOR Polymers Suitable for Hostile Environments—Part 1: Copolymers of Vinylpyrrolidone and Acrylamide

Summary This paper describes the properties of synthetic water-soluble polymers that are stable for extended periods of time in hard brines at very high temperatures. Several copolymers of vinylpyrrolidone (VP) and acrylamide (AM) were prepared and evaluated in our laboratories for EOR application in hostile environments. VP in the copolymer composition protects AM against extensive thermal hydrolysis, which otherwise will result in loss of viscosity and precipitation. A range of VP/AM copolymer compositions was found to tolerate the harsh conditions of 250°F [121 °C] in seawater for extended periods of time and to be suitable for EOR application under these conditions. The performance of these polymers in porous media was evaluated by extensive coreflood experiments in Berea sandstone at 250°F [121 °C] with synthetic seawater. The results indicate that these copolymers can easily be injected into porous media and that they can be effective polymers for EOR application in hostile environments.

An Experimental Study of the In-Situ Gelation of Chromium(+ 3)/Polyacrylamide Polymer in Porous Media

Summary Gelled polymers are being used increasingly as reservoir flow control agents to improve the water-to-oil ratio (WOR) in waterflooding. To date, little has been published in the literature on the in-situ gelation of polymers in porous media. This work was undertaken to study the process of in-situ gelation of a gel system consisting of a polyacrylamide polymer, sodium dichromate, and thiourea. The experiments consisted of continuous injection of gel solutions into 1-ft [0.3-m] unconsolidated sandpacks. Pressure distributions along the flow direction were used to interpret the nature of gelation in the porous media. We found that gelation occurred much earlier than anticipated from beaker tests where gel solutions were under conditions of no shear-e.g., a gel solution with a nominal 10-day gel time in a beaker gelled in 85 hours in a porous-medium run. Shear was considered one of the major factors affecting the in-situ gelation rate, and we determined that gelation times decreased with increasing in-situ shear rates. Under the same in-situ shear rate, the in-situ gelation times were approximately equal in sandpacks prepared from different grain sizes. The order in which in-situ gelation occurred along the flow direction indicated that the shear history affected gelation time. Effluents from displacements with gel solutions were analyzed to evaluate die change in the properties of a gel solution as it moved through the porous media. The chemical analysis indicated that the retention of polymer was marked after the in-situ gelation developed.

Viscoelastic behavior of molten polymers in porous media

AbstractThe modification of the Blake‐Kozeny equation for porous media flow using the power law has been shown to hold for molten polymers as well as for the previous cases for polymer solutions. The present work extended the correlation of friction factor with Reynolds number an additional three decades.It was also shown, however, that the modified Blake‐Kozeny equation broke down when bed shear rates were in the range of excessive curvature on the polymer flow curves (shear stress‐shear rate). In such cases it is suggested that the Newtonian Blake‐Kozeny equation, together with apparent viscosity data, could be used to correlate such porous media flow of non‐Newtonians.Appearance of viscoelastic effects at the critical Deborah number value of 0.05 predicted earlier were not found to hold. The data of the present investigation show that such a critical value must be at least 0.19 or even higher. This result helps to resolve partially the anomalous results obtained by previous investigators.