关键词: 黏弹性表面活性剂流体, 颗粒沉降, Giesekus模型, 松弛时间, 负尾迹

Abstract: As a novel smart fluid, wormlike micellar fluids (WLMFs) have been used in the oil and gas enhancement and other process industry engineering. However, this fluid has an entangled wormlike micellar network and demonstrates complex viscoelastic rheology such as shear banding, extensional hardening and shear induced structure in flowing. It is urgent to investigate the particles settling and transport behavior in the complex flow of WLMFs. Amazingly, the negative wake may occur as the particle settling in this complex fluid, which means the fluid can flow at the opposite of particle settling direction. The negative wake of sphere particle settling in the WMFs plays an important role in the interaction between the fluid and particle. In this work, sphere particle settling behavior in viscoelastic surfactant (VES) wormlike micellar fluid was investigated by POLYFLOW based on the Giesekus constitutive equation. The effects of relaxation time and migration factor on the flow velocity and stress distribution around particles were analyzed. Furthermore, the mechanism of the negative wake in the rear of the particle and the effects on particle drag were investigated. The results showed that the Giesekus model could correctly interpret the behavior of non-linear shear thinning and extensional stress in the process of particle settlement in WLMFs. More extensional strain at the rear of particle was caused by the fluid elasticity. Furthermore, the negative wake occurred at the rear of particle for the interaction of fluid elasticity and shearing thinning. It can extend the downstream of particle settling with increasing the fluid elasticity (De number) and decreasing the ratio of extensional viscosity to zero shear viscosity (Tr, Trouton number). The negative wake promoted drag reduction and resulted in the increasing of particle setting velocity. The results can develop the theory of the multiphase flow of complex fluid and promote the application of viscoelastic surfactant wormlike micellar fluid.

Key words: viscoelastic surfactant fracturing fluid, particle settling, Giesekus constitutive model, relaxation time, negative wake