Rheology and Flow Properties of Fracturing Gels in Straight and Coiled Tubing

Abstract

This study involves experimental investigation of rheological and hydraulic characteristics of aqueous based polymeric and surfactant fluids in straight and coiled tubing. The fluids matrix includes guar, HPG, PHPA, welan, xanthan, and surfactant. Bohlin rheometer was used to evaluate rheological and viscoelastic characteristics. For hydraulic characteristics, small- and large-scale flow loops were used.     

It is observed that all fluids exhibit comparable non-Newtonian behavior and improved viscous and elastic properties. Among polymeric fluids, guar and welan provide better viscosity and suspension properties. Surfactant is significantly affected by the formation of rod-like micelles and other microstructures. Master curves for rheological and elastic properties are developed using the molecular theory approach. The foremost benefit of these curves is its dimensionless form that provides a unique technique to predict viscosity for all fluids.

For hydraulic properties, friction losses in coiled tubing are significantly higher than in straight tubing due to centrifugal forces and secondary flows. Surfactant is more sensitive to shear field applied where different microstructures are induced and thus they exhibit better drag reduction characteristics than polymeric fluids especially in coiled tubing with larger sizes. However, in straight tubing, guar shows better drag reduction characteristics than surfactant and other polymers, which diminishes as tubing size increases.  However, welan gum exhibits a comparable performance. Overall, all fluids are considered good candidates as fracturing fluids with specific features for each. Unique characteristics of each fluid is discussed and explained in more details within the context of the present paper.