Surfactant-based, SB fluids exhibit complex rheological behavior due to substantial structural changes caused by the molecules self-assembled colloidal aggregation. Temperature and salinity affect their rheology and flow properties.
In this study, both rheological and viscoelastic properties for the optimum concentration, 4%, of Aromox® APA-T viscoelastic surfactant (VES) were investigated using two brine solutions; 2 and 4% KCl and wide range of temperatures (72°F – 200°F). Flow properties were examined using a 1/2-in. straight and coiled tubing (CR = 0.019).
The results show that increasing solution salinity promotes formation of rod-like micelles and increases its flexibility. Salinity affects micelles growth and their rheological and viscoelastic behavior is very sensitive to the nature and structure of the added salt. Different molecular structures are formed; spherical micelles occur first and then increased temperature and/or salinity promotes the formation of rod-like micelles. Later, rod-like micelles are aligned in the flow direction and form a large super ordered structure of micellar bundles or aggregates called shear induced structure (SIS). Different structures implies different rheological and flow properties. Likewise, rheology improves with increasing temperature up to 100°F. Further increase in temperature reverses the effects and viscosity decreases. In addition, drag reduction and flow characteristics of SB fluids are improved by the addition of salt and/or increasing temperature up to 100°F. Results obtained are in full agreement with rheological and viscoelastic behavior of SB fluids for both salinity and temperature.