Rheological Properties of an Amine Oxide Viscoelastic Surfactant With Application in Well Stimulation

Abstract

Abstract The use of proper fluid system is one of the most important factors in the success of well stimulation processes like hydraulic fracturing and matrix acidizing. Viscoelastic surfactant (VES) based fluids are among stimulation fluids which recently have been used with promising results. The rheological properties of a tallow amine oxide amphoteric surfactant base fluid with applications in matrix acidizing and hydraulic fracturing have been studied. To find the linear viscoelastic region, the stress amplitude sweep tests were conducted in the constant frequency of 1 Hz and the shear stress range of 0.1 to 10 Pa. The linear viscoelastic region has been found to be between 0.1 to 1 Pa. Then, the effect of stress amplitude and temperature on elastic modulus (G′), viscous modulus (G″) and complex modulus (G*) have been investigated and the results were interpreted on the basis of Cates' tube theory. The frequency sweep tests have been carried out within the frequency range of 0.01 to 4 Hz and the constant stress amplitudes of 0.1, 0.5 and 1 Pa. For the evaluation of the effects of temperature on the properties of the VES solution, the tests have been done at the temperatures of 25, 28, 30 and 35°C and constant stress amplitude of 0.1 Pa. The results of experiments at the constant temperature and different stress amplitudes showed that the increase in stress amplitude caused an increase in transition frequency and widen the viscous dominant region. In the other hand, with increase in temperature at the experiments with constant stress amplitude, the transition frequency decreased and the VES solution showed the dominant elastic behaviors. The results of frequency sweep tests in the form of Cole-Cole plots showed that the surfactant system highly deviated from Maxwell's mono relaxation model and, therefore, the stress relaxation mechanism in the fluid found to be the combination of reptation and breaking of wormlike micelles. These results can be used to better understand the rheological properties of VES-based fluids and manipulate their properties for using in well stimulation processes.