Rheology and Flow Characteristics of Xanthan in Calcium Chloride Brine

Abstract

Abstract Xanthan gum and other naturally obtained polymers have been used extensively in the petroleum industry as a "viscosifier" in drilling, completion, workover and hydraulic fracturing fluids. Other than the effects of shear rate, pH and temperature, the performance of various polymers can be greatly affected by salinity, due to their sensitivity to metal ions of different salts contained in the commonly used solvents. In today’s oilfield operations, it is not uncommon to combine polymers with sea water or brine of a known salt concentration in order to generate certain desired fluid properties. Consequently, the importance of understanding the compatibility and shear properties of polymer fluids in brine solvents for coiled tubing operations cannot be underemphasized. However, while there are several existing literatures on the various methods of viscosifying brine solutions with polymers, only a handful have attempted to describe the flow properties of viscosified brine. In order to bridge this knowledge gap, the present experimental study examines the compatibility and flow characteristics of Xanthan gum at various polymer loadings with different concentrations of Calcium Chloride (CaCl2) brine. An unprecedented set of flow data was acquired using an experimental flow-loop comprising of ½ in. straight and coiled tubing sections. The data demonstrated a continual decrease in drag reduction and increased friction pressure loss with increasing brine density. A comparison of those data with predicted data show that the hydraulic properties of viscosified brine can be fairly estimated using existing friction factor correlations. Nevertheless, additional flow data must be acquired with various brines and polymers to develop correlations with better accuracy.