Polyacrylamide solution viscosity, saline

The substantial decrease of polyacrylamide solution viscosity in mildly saline waters can be uti1i2ed to increase injection rates. A quaternary ammonium salt polymer can be added to the polyacrylamide solution to function as a salt and reduce solution viscosity (144). If the cationic charge is in the polymer backbone and substantially shielded from the polyacrylamide by steric hindrance, formation of an insoluble interpolymer complex can be delayed long enough to complete polyacrylamide injection. Upon contacting formation surfaces, the quaternary ammonium salt polymer is adsorbed reducing... 

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... 

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. 

Polymer Viscosity/Concentration Relationships. A polysaccharide broth [PS(B)J, a polysaccharide powder [PS(P)J, a polyacrylamide liquid [PAA(L>], and a polyacrylamide powder [PAA(P>] were evaluated for the proposed polymer flood. Polysaccharide polymers gave substantially higher solution viscosities than polyacrylamide polymers (Fig. 2). The magnitude of the difference in viscosity between the two basic polymer types was at first surprising, in view of the relatively low-salinity brines used in the study. On the other hand, each of the brines had a relatively high ratio of divalent cations to total dissolved solids (TDS). Results from the laboratory have consistently shown that such brines act as if they were high-salinity brines. 

For polyacrylamide there are two rheological effects which can be explained in terms of its random coil structure. Firstly, it was discussed above that polyacrylamide is much more sensitive than xanthan to solution salinity and hardness. This is explained by the fact that the salinity causes the molecular chain to collapse, which results in a much smaller molecule and hence in a lower viscosity solution. The second effect which can be explained in terms of the polyacrylamide random coil structure is the viscoelastic behaviour of this polymer. This is shown both in the dynamic oscillatory measurements and in the flow through the stepped capillaries (Chauveteau, 1981). When simple models of random chains are constructed, such as the Rouse model (Rouse, 1953 Bird et al, 1987), the internal structure of these bead and spring models gives rise to a spectrum of relaxation times, Analysis of this situation shows that these relaxation times define response times for the molecule, as indicated in the simple Maxwell model for a viscoelastic fluid discussed above. Thus, because of the internal structure of a flexible coil molecule, one would expect to observe some viscoelastic behaviour. This phenomenon is discussed in much more detail by Bird et al (1987b), in which a range of possible molecular models are discussed and the significance of these to the constitutive relationship between stress and deformation rate and deformation history is elaborated. 

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