Hydrolyzed polyacrylamide effects

Anionic and nonionic polyacrylamides effectively remove suspended soHds such as silt and clay from potable water. SuppHers provide special grades which meet EPA/FDA regulations for residual acrylamides. A recent pubHcation (102) states that hydrolyzed polyacrylamides with narrow interchain charge distributions provide better performance in flocculation of clay. These polymers were prepared by alkaline hydrolysis. (See Flocculating agents.)... 

The effect of water soluble polymers on the phase behavior of the anionic mlcroemulslon system was studied as a function of surfactant H/L properties. The cloud point temperatures for the neat mlcroemulslons and those containing 1500 ppm HPAM, partially hydrolyzed polyacrylamide, and 1000 ppm Xanthan gum are given In figure 4. The addition of either xanthan blopolymer or HPAM results In an Increase In the cloud point temperature of the mlcreomulslon. Both polymers have similar Interactions with the mlcroemulslon. Again one observes a lipophilic shift of the mlcroemulslon system Indicative of a repulsive interaction between the polymer and these anionic surfactants. 

Divalent Effect In the brine of low to medium sahnities (monovalent content), the viscosity of polyacrylamide solution increases as hydrolysis proceeds (increases). However, in the presence of divalents, the viscosity behavior will be determined largely by the divalent metal ion concentrations. As hydrolysis increases, more acrylic acid exists in the solution. Hydrolyzed polyacrylamides (negative carboxyl groups) interact strongly with divalent metal cations such as Csi and Mg ". This phenomenon is commonly associated with reduction in solution viscosity, formation of gels or precipitates. 

Ouibrahim and Fruman (47) in 1980 found dilational flow in three distinct flow situations, which each involve an extensional component capillary tube flow, orifice flow, and pitot tube flow. They examined extensively hydrolyzed polyacrylamide (HPAA) and found that the dilatant effect was greatly reduced in the presence of excess salt. This finding was attributed to the effect of the salt ions in screening the charges on the polyelectrolytic HPAA and thus causing the contraction of the highly expanded molecule. 

Once any type of salt is added to a partially hydrolyzed polyacrylamide (PHPA) solution, the ions will generate an adverse effect on the viscosity of the polymer solution. 

Solution preparation is a complex problem and not very well understood. Recent experiments by Chang and Darby [1] and Oliver and Bakhtiyarov [2] indicate that the drag reduction effectiveness of partially hydrolyzed polyacrylamides increases with mixing time. At Arizona State University we have obtained similar results especially when the solvent is deionized water. On the other hand freshly mixed poly (ethylene oxide) (PEO) solutions give the most drag reduction. Impurities and ions present in v/ater also affect the polymers. In addition agglomerates of molecules may be present in the solution or can be formed by the flow. These solution difficulties are present in both aqueous and nonaqueous solutions. 

Examples of comparative gel tests with a hydrolyzed polyacrylamide are presented below. The screening experiment discussed above indicated that polymer molecular weight and salinity are important in the gel reaction. The comparative tests are used to define the magnitude of these variable effects. In addition, the results demonstrate the usefulness of the simple beaker tests described earlier. 

The polyelectrolyte acrylamide copolymers poly(acrylamide-cosodium acrylate), poly(acrylamide-co-acrylic acid), and hydrolyzed polyacrylamide were used to study the effect of charge density and charge distribution. The non-polyelectrolyte acrylamide copolymers N,N-dimethylacrylamide and N,N-diethylacrylamide, were prepared to study the effect of N-substituted monomers. 

PART II PARTIALLY HYDROLYZED POLYACRYLAMIDE, 622 Polymer Viscosity in Deionized Water, 623 Effect of Sodium Chloride on the Viscosity of HP AM, 624 Effect of Cation Type on Polymer Viscosity, 627 Effect of Alkali Type on Polymer Viscosity, 629 Effect of Surfactants on Polymer Viscosity, 634 Effect of Surfactants and Alkalis on Polymer Viscosity, 635... 

Shupe examined the effect of anionic surfactants (petroleum sulfonate) on the viscosity of partially hydrolyzed polyacrylamide (Dow Pusher 500) [69], The viscosity decreased by 22% as a result of adding the surfactant at 3 wt%. Nasr-El-Din et al. examined the influence of Neodol 25-3S on the viscosity of Alcoflood 1175L [41], Figure 19 depicts the flow curves of 1,000 ppm polymer solutions obtained at various surfactant concentrations (up to 10wt%). Unlike the results obtained with Triton X-100, Neodol 25-3S had a dramatic effect on the flow curves of the polymer solutions. This effect is similar to that obtained with simple salts. 

Muller, G., J. P. Laine and J. C. Fenyo, High Molecular-Weight Hydrolyzed Polyacrylamide. I.Characterization. Effect of Salts on the Conformational Properties, J. Polymer Science 17, 659-672 (1979). 

When an electrolyte, such as NaCl, is added to a polymer solution, the repulsive forces are screened by a double layer of electrolytes and extension is reduced. As the electrolyte concentration increases, the extension of the polymer chain decreases and the solution viscosity declines. Fig. 5.1533 illustrates the effect of salinity on the relative viscosity (apparent solution viscosity/solvent viscosity) of 250-ppm solutions of Pusher 700 , a partially hydrolyzed polyacrylamide.34 Chain extension also is controll by the... 

Table 5.3 summarizes some polymer retention data from displacement experiments for partially hydrolyzed polyacrylamides. Retention varies from 35 to about 1,000 Ibm/acre-ft over a wide range of fluid and rock properties. Information on converting retention values from pounds per acre-foot to micrograms per gram of rock is given as a footnote in Table 5.3. Several trends are present in the limited amount of retention data in the literature. Fig. 5.22 shows the variation of polymer retention with brine permeability at ROS. The retention at low permeabilities is large and is probably a result of excessive mechanical entrapment of polymer molecules in small pores. Another possible explanation is high clay content. Polymer concentration appears to have little effect on retention for the data shown in Fig. 5.22. The weak concentration dependence in Fig. 5.22 is reinforced by data from Shah for the retention of partially hydrolyzed polyacrylamide on Berea core material shown in Fig. 5.23. Retention at 50 ppm polymer concentration is 77% of the retention at 1,070 ppm.

Flow Characteristics. Permeability Reduction. Polymer retention reduces the apparent permeability of the rock. Pemiea-bility reduction depends on the type of polymer, the amount of polymer retained, ttie pore-size distribution, and the average size of the polymer relative to the pores in the rock. Permeability reduction is determined experimentally by first displacing polymer solution through a porous medium and then displacing die polymer with brine and measuring the permeability to brine after all mobile polymer has been displaced. Fig. 5.28 illustrates the effect of initial rock permeability on the permeability reduction of Berea sandstone cores by partially hydrolyzed polyacrylamide in 3 % NaCl. The trend in permeability reduction in Fig. 5.28 is consistent with the trend of increased retention as permeability decreases shown in Fig. 5.22. 

Partially hydrolyzed polyacrylamide/Cr(lll), carboxylate increase Increase Increase Increase Increase Increase Increase at low concentration, little effect at high ccncentraticn... 

The search for a low-cost, effective mobility control agent is currently focused on dilute aqueous solutions containing partially hydrolyzed polyacrylamides or polysaccharides. Rheological properties have been studied, including the effects of polymer concentration, shear rate, electrolyte concentration, and type of electrolyte. 

Investigatorsstudying partially hydrolyzed polyacrylamide solutions observed apparent viscosities 5 to 20 times the values measured in a conventional viscometer at the shear rates believed to exist in the porous media. These viscosity increases were not anticipated from the rheological behavior of the fluids. Pye introduced the concept of the resistance factor to quantify this effect. Burcik observed a decrease in the mobility of brine in a Berea sandstone disk that had been previously contacted with partially hydrolyzed polyacrylamide. The mobility reduction persisted even after 100 PV of brine had been flushed through the disk. Burcik concluded that polymer molecules retained in the pore structure by adsorption or mechanical entrapment were hydrophillic and restricted the flow of water. 

Muller, G., Laine, J.P., and Fenyo, J.C. High-Molecular-Weight Hydrolyzed Polyacrylamides. I. Characterization. Effect of Salts on the Conformation Properties, J". PolymerSd., chem. ed. (1979) 17, 659-72. 

Muller, G., Fenyo, J.C., and Selegny, E. High-Molecular-Weight Hydrolyzed Polyacrylamides. HI. Effect of Temperature on Chemical Stability, J. Appl. Polymer Sci. (1980) 25,627-33. 

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