Rheology and Flow Characteristics of Xanthan in Calcium Chloride Brine

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 (CaCl 2 ) 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.

Influence of Formate Concentration on the Rheology and Thermal Degradation of Xanthan Gum

“…Its pseudoplastic characteristics and high resistance to shear degradation [ 1 , 2 ] cover the desired requirement of high viscosity at a low shear rate, which is necessary for maintaining drill cutting in suspension when the flow is stopped, avoiding settling to the bottom hole. At the same time, these characteristics cover the desired requirement of low viscosity at a high shear rate, which facilitates pumping circulation [ 3 , 4 , 5 , 6 , 7 ]. Particularly, formate salts have been used successfully since the late 1990s as completion fluids due to their high solubility in water and the ease with which one can prepare formulations with the required density to compensate the formation pressure [ 8 , 9 ].…”

Polymer-FLR for Mud Fluid Loss Reduction

“…Breakdown of fluid loss control agents causes a large increase in the fluid loss accompanied by an increase in a filter cake thickness. This condition triggers excessive drag, high-pressure surges, differentialpressure sticking, and reduction in production-zone permeability as well as increases in shale sloughing [5][6][7][8].…”