Hydrolyzed polyacrylamide viscosity

Compared with solutions of partially hydrolyzed polyacrylamides, viscosities of xanthan solutions are much less affected by changes in salinity or divalent-ion content. Figs. 5.17 and 5.1836 illustrate this by plotting the solution viscosity at various shear rates vs. salinity and divalent-ion content. 

Compared to partially hydrolyzed polyacrylamide, xanthan gum is more expensive, more susceptible to bacterial degradation, and less stable at elevated temperatures (1). However, xanthan gum is more soluble in saline waters, particularly those containing divalent metal ions generally adsorbs less on rock surfaces and is substantially more resistant to shear degradation (1,34). The extensional viscosity of the semi-rigid xanthan molecule is less that that of the flexible polyacrylamide (263). 

Electrostatic repulsion of the anionic carboxylate groups elongates the polymer chain of partially hydrolyzed polyacrylamides increasing the hydrodynamic volume and solution viscosity. The extensional viscosity is responsible for increased resistance to flow at rapid flow rates in high permeability zones (313). The screen factor is primarily a measure of the extensional (elonga-tional) viscosity (314). The solution properties of polyacrylamides have been studied as a function of NaCl concentra-tion and the parameters of the Mark-Houwink-Sakaruda equation calculated... 

Kowblansky et A1 (19) have also measured the intrinsic viscosity of hydrolyzed polyacrylamide of a given molecular weight as a function of r for a - 1 and their results can be fitted by the expression ... 

Mannich polymers Cationic, solution polymer flocculants with MW of 5 to 8 M. Very high viscosity and only 4 to 8% active strength solution liquid. A hydrolyzed polyacrylamide, it is very useful for general municipal wastewater treatment. Dose rate normally 200 to 300 ppm or more. 

Assuming a typical oil reservoir containing medium heavy crude oil and employing a reservoir flow rate of 0.26 m/day. The solution viscosity could be increased to 30 mPa s by adding about 1000 pg/rril (0.1%) partially hydrolyzed polyacrylamide polymer (at pH 8.5). The interfacial tension could be reduced to 0.1 mN/m by adding 1% sodium carbonate, which reacts with the crude oil to produce natural surfactant. The interfacial tension could be further reduced to 0.03 mN/m by adding 0.1% ethoxylated alcohol sulfate cosurfactant. 

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. 

In packed beds of particles possessing small pores, dilute aqueous solutions of hydrolyzed polyacrylamide will sometimes exhibit dilatant behavior instead of the usual shear thinning behavior seen in simple shear or Couette flow. In elongational flow, such as flow through porous sandstone, flow resistance can increase with flow rate due to increases in elongational viscosity and normal stress differences. The increase in normal stress differences with shear rate is typical of isotropic polymer solutions. Normal stress differences of anisotropic polymers, such as xanthan in water, are shear rate independent (25,26). 

The presence of polymers at the interface between oil and water makes for excellent stabilization of emulsions (1,4). Figure 13 shows the interfacial shear viscosity of the interfacial film between a model oil and NaOH solution or polymer solution at 45°C. The model oil consisted of 20% Daqing crade oil injet fuel. The contents ofNaOH, ORS41, and a biological surfactant in the NaOH solution were 1.2, 0.5, and 0.15%, respectively. The concentration ofpolymer hydrolyzed polyacrylamide (HPAM) in the solution was 150mg/L. It can be seen that the interfacial shear viscosity of the system with the polymer is three times higher than... 

Electrically charged (hydrolyzed) polyacrylamide molecules, on the other hand, tend to expand, similar to the unhydrolyzed polymer molecules, only in good solvents which must be free of salt, such as distilled water. Therefore, a high viscosity would be offered by the polymer solution. ... 

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. 

The viscosity of the partially hydrolyzed polyacrylamide polymers decreases continuously in caustic media, and levels off after a long time. The time required for the viscosity to become constant, which could be in the order of several hours or several days, depends on the initial hydrolyzation degree and the nature of the polymer used, and the concentration of salts and caustic in the solution. 

The role of ionic polymers in enhanced oil recovery is well recognized (1). Partially hydrolyzed polyacrylamide is the most widely used ionic polymer for this purpose as it produces a high viscosity in fresh water at a reasonable cost. However anionic polyacrylamide rapidly looses its viscosity in solutions containing added electrolyte. In addition, polyacrylamides are sensitive to shear degradation. 

Fig. 5. Intrinsic viscosity of partially hydrolyzed polyacrylamides in 1.5% NaCl solution.

Fig. 6. Relative viscosity change of partially hydrolyzed polyacrylamides in water and brine at 30 C as a function of copolymer composition, (M = 5.5 x 10 ).

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... 

It is well known that the rheological properties of partially hydrolyzed polyacrylamide depend on the stresses associated with a given flow field. In a simple shear flow, the apparent viscosity is constant at low shear rates (Newtonian behavior). At a critical shear rate, the apparent viscosity decreases as the shear rate is increased, i.e., a shear thinning behavior [48]. The viscosity shear-rate data of water soluble-polymers are commonly fitted using the Carreau viscosity model [49]. According to this model, the apparent viscosity, p, is a function of the shear rate, Y, as follows ... 

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. 

Water-soluble polymers have been reviewed with particular emphasis on their application in improved oil recovery. These polymers have potential for use in mobility control, drilling fluids and profile modification. Partially hydrolyzed polyacrylamide and xanthan gum are the most commonly used water-soluble polymers in oil field applications. The apparent viscosity of these polymers depend on polymer type, molecular weight, charge density, concentration, shear rate, salt concentration, and pH, as follows ... 

An 18-20% hydrolyzed polyacrylamide was used in all tests. In all 300 ppm polymer solutions a radioactive C14 tagged polyacrylamide was used. At higher polymer concentrations (600 and 1200 ppm) a commercial product called Calgon Polymer 454 was added to the base 300 ppm radioactive solution. A special study was conducted to develop a radioactive polymer which has properties identical to the commercial product. Several experiments were run on both polymers to check these properties such as, viscosity measurements, friction reduction flow tests, and flow tests in porous media. These special studies showed that performance of the radioactive product was equivalent to that of the commercial product. A typical result of these tests is shown in Figure 1. The small differences in the polymer flow resistance factors are due to small differences in the textures of different sandpacks, rather than to differences in the chemical structures of the polymers. Friction reduction, viscosity, and retention experiments showed even closer agreements between properties of the radioactive and commercial product. 

In drilling fluid applications, several types of viscosity modifiers can be used to enhance foam stablity. These include partially hydrolyzed polyacrylamide (PHPA) clays, such as bentonite xanthan gum guar gums starches cellulosic polymers, such as hydroxy ethyl cellulose (HEG) and sodium carboxy methyl cellulose (SCMC). In Table 8, base fluid viscosities and drainage times for one-half and four-fifths of the base fluids are recorded in a foam system consisting of an anionic foamer, sodium lauryl sulfate (SLS) and a nonionic foamer, TXlOO - ethoxylated octyl phenol. It can be seen that in these systems base fluid viscosity alone... 

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... 

Fig. 5.16—Relative viscosity of hydrolyzed polyacrylamides In NaCI waters. 4...

The viscosity of a 5,000-ppm solution of partially hydrolyzed polyacrylamide was measured at several shear rates with a cone-and-plate rheometer. Table 5.59 gives experimental data as a function of shear rate. Plot the viscosity vs. shear rate on log-log paper and determine the power-law exponent, n, and the power-law constant, K, from the experimental data using least-squares analysis and correlate the viscosity as a function of shear rate. Compare values of the viscosity from the correlation with experimental data. 

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