Dynamic oscillatory rheological measurements may be used as a diagnostic tool for the characterization of microstructure (e.g. crosslink density of a gel or degree of association for a dispersion). The petroleum industry has historically used steady shear viscosity measurements to characterize completion fluids because these measurements can be made to mimic shear flows believed to exist in the well bore and reservoir. However, steady shear measurements are limited in the information they provide because it is difficult to deduce information about fluid structure or the evolution of structure from steady shear data alone. An understanding of the contributions of viscosity from steady shear measurements and elasticity from dynamic oscillatory measurements is critical to:

  1. predicting suspension capabilities of a fluid

  2. evaluating the effects of chemical modification in developing improved fluid systems and

  3. identifying those factors which are necessary for accurately predicting flow properties in the field.

This paper presents the interpretation of dynamic oscillatory shear data on well completion fluids, including water soluble polymers, crosslinked polymers, and gelled hydrocarbons to demonstrate the utility of these measurements in different applications. Data show that gel formation and degradation can be monitored by observing the frequency and strain dependence of the viscous and elastic components of stress Data also show that shear and temperature decrease crosslink density and as a result affect the fluids ability to transport particles. The effects of sample preparation, chemical modification, or the addition of chemical additives, such as crosslink delayers, on fluid structure will be discussed.

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