Study On The Sand-carrying Mechanism Of Viscoelastic Surfactant Fluid

Viscoelastic surfactants with longer carbon chains can form micron-sized worm-like micelles under the action of counter ions.When the concentration of the surfactant exceeds its critical micelle concentration,the micelles will be entangled with each other,showing good viscoelasticity macroscopically similar to macromolecule polymers.Compared with polymers,the advantage of viscoelastic surfactant is that its viscoelasticity can recover after a high shear rate,also known as living polymer.In addition,the viscoelasticity of VES can also change with changes in environmental factors such as temperature and pH.Therefore VES is also a new type of intelligent fluid.When the VES is used as a fracturing fluid,it can flow back to the ground without any gel breaker.This fluid has good drag reducing and little pollution to the formation as well as strong sand carrying capacity.It is a new type of environmentally friendly fracturing fluid.However,settlement and migration of proppants in VES is complicated because its viscoelasticity and microstructures.In this thesis,the sedimentation and migration of proppants in surfactants formed by OTAC and NaSal were studied through experiments and simulations.First,the rheological properties of OTAC/NaSal were studied,including the relationship between the shear viscosity of VES and the shear rate,the relationship between the viscosity modulus and the elastic modulus with the angular frequency,Based on the Giesekus constitutive equation,the rheological data of fluids with different formulations were fitted.Secondly,The sedimentation process of single particles and two particles in VES was studied,based on numerical simulation and visual experiment.The fluid elasticity has an important influence on the particle sedimentation process.The shear thinning effect and elasticity work together to make the particle tail produce a negative wake.At the same time,the negative wake leads to a larger particle settling resistance.The particles are arranged in a line in the flow direction in the viscoelastic fluid.The frequency of particle collisions decreases and the total particle group resistance decreases.Finally,the sand-carrying flow of VES in the fracture is simulated using Euler-granular multiphase flow model.The results show that when VES is regarded as a general power-law non-Newtonian fluid,the effect of shear thinning of VES on sand-carrying capacity can be obtained.By changing the consistency index K and the rheological index n to change the rheology of the fracturing fluid,the effect of different K and n on the shape of the sand embankment in the fracture was studied.When cross constitutive equation is used to simulate the sand carrying flow of VES fluid,the sand carrying capacity of the fluid increases with the increase of?₀ and n,and decreases with the increase of?v.compared with the power law fluid model,the Cross fluid model can better describe the rheology and sand carrying performance of the VES fluid.