Abstract
Abstract Crosslinking of guar and hydroxypropyl guar (HPG) with metal ions is used extensively in the oilfield to increase the viscosity and thermal stability of solutions made from these polymers. Guar and HPG molecules have cis-hydroxyl groups that can react with metal ions or metal ion agglomerates to form crosslinks between polymer molecules. Crosslinking results in a viscous, gel-like solution that is difficult to characterize rheologically. In this study, data generated with a cone and plate rheometer equipped with a special flow-through test fixture is used to demonstrate how the reaction rate and order change with shear rate. These data are used to develop a model for the reaction that explains not only the observations made in this laboratory, but also the observations made in a number of other research studies. In general, the reaction is fast at low shear rates and almost stops at high shear rates. Reaction rates and orders are a function of shear rate and the reaction product is also shear rate sensitive. Experimental evidence points to a shift from inter- to intramolecular reactions at high shear rates.
Published Version
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