Proppant settling in viscoelastic surfactant (VES) fluids

Polymer-free viscoelastic surfactant-based (VES) fluid systems have been used to eliminate polymer-based damage and to efficiently transport proppants into the fracture. Current models and correlations neglect the important influence of fracture walls and fluid elasticity on proppant settling. This report presents an experimental study that investigates the impact of fluid elasticity and fracture width on proppant settling in VES fluid systems. Proppant settling experiments are performed in shear-thinning VES fluids. Experimental data is presented to show that fluid elasticity plays an important role in controlling the settling rate of the proppants. It is shown that elastic effects can increase as well as reduce the settling velocities depending upon the rheological properties of the fluid and properties of the proppants. Data is presented to show that the settling velocity reduces significantly as the proppant size becomes comparable to the fracture width. The reduction in settling velocity due to the presence of the fracture walls depends on the rheological properties of the fluid, ratio of particle diameter to fracture width as well as the diameter of the particle.