Water-soluble polymers are used to viscosify water-based fracturing fluids. This facilitates the growth of fractures and the placement of proppants. After placing proppants, polymers are removed to maximize productivity. To achieve optimum residual-polymer removal, it is essential to break the polymer gel to a low-viscosity fluid. Internal breakers or an acid flush are commonly used to break the polymer gels. Any insoluble or unbreakable residue can block pore spaces, leading to lower productivity. Therefore, it is very important that the polymers used for fracturing applications contain a minimum amount of insoluble residues or no insoluble residues.
In the widely used gravimetric method for determining residue, the polymer is first hydrated and then degraded before using gravimetric techniques. A standard gravimetric method takes more than 24 hr for one polymer sample. The accuracy of the results depends on consistency of laboratory techniques, such as filtration and weighing. Therefore, it was considered worth examining if a turbidity-based method could be developed to determine the insoluble residue quickly.
A linear correlation was found between turbidity and acid-insoluble residue of guar. The acid-insoluble residue, after keeping the guar sample in an aqueous fluid at pH 1.0 and 110°F for 24 hr, bears a linear correlation with the turbidity of the solution. The turbidity of guar solution after 2 hr of hydration at pH 7.0 also bears a linear correlation with the acid-insoluble residue. However, the turbidity did not bear any correlation with the total water-insoluble residue.
This study led to the development of a turbidity-based method to determine the acid-insoluble residue in guar after approximately 2 hr. This is possibly the first study to correlate turbidity with acid-insoluble residue in guar and has the potential to be used for other polymers as well.