The use of nanoparticles has been demonstrated to enhance the rheological properties of the viscoelastic surfactant (VES) fluid. However, their influence on the rheological properties as a function of temperature is not well known. In this study, a detailed analysis of improved rheological properties and thermal stability of the VES fluid beyond their optimal working temperature was conducted. The effect of nanoparticles was also studied.

A base VES fluid was prepared with the required amount of surfactant along with an ionic strength agent dissolved in sea water. The desired type of nanoparticles in required amounts were added to the base VES fluid and homogeneously dispersed. Different types of nanoparticles were added to prepare corresponding nano-VES fluid. Rheological properties of the base VES fluid and different nano-VES fluids were measured against variable shear rate. The fluids were tested at a temperature at which the base fluid shows highest gelling behavior, and at temperatures above and below that value.

Results, Observations, Conclusions: The initial thermo-viscosifying effect and eventual thermo-thinning effect with temperature havebeen widely observed for viscoelastic surfactants based fluids. The effectshavebeen attributed to the effect of temperature on the structural changes of wormlike micelles. Nanoparticles being of the dimensions that are comparable with the thickness of these wormlike micelles are readily able to incorporate themselves into these structures and influence their rheological behavior. These interactions change both with respect to temperature and shear rate applied on them. Further, these interactions differ depending on whether the fluid is in the thermo-viscosifying region or the thermo-thinning region with respect to the temperature. Based on the kind of nanoparticle used, significant improvements in rheological behavior from a fracturing fluid perspective have been observed. In addition, shear rates at which a shift from Newtonian to non-Newtonian behavior with respect to shear rate occurs, has also been observed to change.

A greater insight into the effect of nanoparticle additives on temperature related rheology of VES fluids has been provided. This understanding is crucial for the optimization of a VES fracturing fluid based on the well-to-well changes in temperatures.

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