LAUSR

Abstract In the past several decades, Gemini viscoelastic surfactant has been applied for many cases due to its specific properties, including clean fracturing fluid. As we know that counter-ions can greatly promote the micelle aggregation of VES and show important effect on its heat resistance. Potassium chloride, as a normal additive for fracturing fluids to control the clay swelling, was investigated as such counter-ions in the context. Thus, a clean fracturing fluid with good heat resistance could be obtained by studying the viscosity reduction of the fluid prepared from a novel Gemini VES. The results of molecular structure characterization showed that potassium chloride has no effect on the surfactant molecular structure in rheological tests at high temperature. Based on the rheological tests, it can be concluded that the viscosity reduction at the test conditions is mainly of the micelle dissociation. Analysis results, such as microstructure comparison and the dynamic light scattering, suggested that potassium chloride can facilitate the micelles aggregation and entanglement, especially making the micelles tighter. In this way, the fluid could keep higher viscoelasticity at higher temperature and certain shear rate. Based on this mechanism, an improved VES fracturing fluid could be achieved via iterative formation adjustment, whose final viscosity could be maintained about 40 mPa s at 160 °C during 120 min.