Magneto-rheological fluids: Tele-manipulation of ferromagnetic particles with external magnetic field for flow control and zonal isolation

A suspension of ferromagnetic particles in a viscous liquid carrier can transform into a gel- or solid-like substance when subjected to an external magnetic field. This property makes magnetorheological fluids suitable for zonal isolation and remote fluid loss control, especially when traversing large-aperture fractures where conventional treatments fail; however, most previous studies have focused on magnetorheological flow control in small channels under low flow velocities. This study uses experimental and numerical techniques to investigate magnetically-induced particle-particle and particle-chain interactions involved in fluid-flow control and clogging using magnetorheological fluids in centimeter-size flow channels. Experiments involve iron particles suspended in bentonite mud within a transparent pipe that runs between the poles of an air gap electromagnet. Normalized discharge mass-time signatures gathered under constant pressure gradient collapse onto a single trend and exhibit two distinct regimes: a gradual decrease in fluid flow rate as iron particles assemble into chains and form the granular plug, followed by a diminishing yet persistent discharge as additional particles are captured through particle-chain interactions and filtration while liquid leaks off. The time that characterizes the transition between these two regimes depends on the imposed pressure gradient and the field strength. Numerical simulations resolve the evolving magnetic field topology and explain particle-particle interactions. Particle chains accelerate as they migrate from the far-field to the magnet poles, and slow down near the poles until they arrest; this velocity profile creates a rarefaction zone away from the poles, and a concentration zone near the pole edges where chain aggregation and coarsening take place, enhanced by particle size poly-dispersity.