Achieving optimal fluid performance with biopolymer viscosifiers, xanthan and welan, depends on reaching or exceeding a minimum or critical polymer concentration (CPC). CPC is affected by a variety of fluid and wellbore conditions, including: temperature and salinity, average shear rate, shear history, velocity gradients, hole angle, polymer configuration and rigidity, and the size, density, and concentration of suspended solids. The suspension and transport properties of xanthan and welan correlate directly to low-shear-rate-viscosity (LSRV) and elasticity (G'), properties which cannot be quantified with a conventional field viscometer. LSRV and G' are qualitatively related to a polymer's molecular rigidity and configuration, and quantitatively to the number of physical and chemical polymer chain associations, referred to as polymer networks and structures.

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