Polymer mobility control

Comparison of Solution Properties of Mobility Control Polymers... 

This paper will address itself exclusively to the first of the above mentioned steps, namely, the solution properties of mobility control polymers. The polymers investigated cover quite a spectrum Kelzai - XC (xanthan gum), Pushei -700, Colloic XH0 and XH3, and Natrosol 250 HHR. The brief descriptions of these polymers are given below ... 

The literature on mobility control polymers includes many over-simplifications concerning the behavior of these polymer solutions such as polysaccharides are insensitive to salt, and polyacrylamides easily degrade in a shear field. This study will show that the differences between solutions are a matter of degree and the basic behaviors and the mechanisms are common to all mobility control polymers. 

The block of data concerned with this area generally does not consider the developments concerning the solution behavior of nonmobility control polymers which has been reported in the polymer literature. Implicitly, one is led to believe that the mobility control polymer solutions are unique and have little in common with more conventional polymer solutions. This study will show that there is a direct qualitative correlation between the behavior of mobility control polymer solutions and other solutions of macromolecules. In particular, it is demonstrated that the viscous properties are directly related to the hydrodynamic size of the polymer chain and the influence of system characteristics such as salt concentration, shear rate, etc., can be correlated with the effective size of the polymer molecule in solution. Consequently, this study suggests that more emphasis should be placed on the measurement of the molecular size of mobility control polymers in solution if a fundamental understanding of these solutions is to be developed. 

The dominate factor which controls the solution properties of mobility control polymers is the configuration (and hence size) that the molecule assumes in a given environment. Although the viscosity of a polymer solution is related to the hydrodynamic size of the polymer molecules, it is difficult to determine the unique relationship between viscosity and size. However, exten-... 

The intrinsic viscosity (hence the molecular size) of the mobility control polymers is a strong function of the environment or the electrolyte concentration of the solution and the temperature. The size is also affected by mechanical degradation. As shown in Table 2, increasing the salt concentration leads to a smaller size in polyacrylamides. This effect is more drastic at low salt concentrations. 

Salt Sensitivity. The viscosity of mobility control polymers is a strong function of their environment. The ionic composition of a petroleum reservoir determines the conformation that the polymer chains assume in it. This very fact is one of two reasons why the salt sensitivity of the polymer solutions need to be studied. The second incentive for an investigation of this kind is the possibility of using the water produced from a flooded field in making the new polymer solution. Since the produced water contains many salts and minerals, knowing how the viscosity changes as a function of ion concentration is important. 

Effect of Temperature on Viscosity. The viscosity of mobility control polymers decreases with increasing temperature and an Arrhenius type relationship is obeyed ... 

In this paper the solution properties of a spectrum of mobility control polymers have been compared. Polysaccharides, polyacrylamides, and hydroxy ethyl cellulose show vastly different solution behavior. Despite this, the properties investigated can be correlated by noting one molecular characteristic of these polymers, namely molecular size. 

Unsal, E., Duda, J. L., Klaus, E. E., and Liu, H. T., "Solution Properties of Mobility Control Polymers", Eastern Regional Conference of the Society of Petroleum Engineers of AIME, SPE Paper 6625, Pittsburgh, PA (1977), 1-5. 

Above the overlap concentration, a significant enhancement in solution viscosity was observed along with an increase in viscosity with salt concentration. In addition, the solution viscosity could exhibit Newtonian, dilatant, or pseudoplastic behavior depending on the shear rate, polymer composition and concentration. While considerable further research needs to be done, it appears that the use of hydrophobic groups on water soluble polymers provides an attractive approach to improved mobility control polymers for chemically enhanced oil recovery. 

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