US Patent 10125594 Pressure exchanger having crosslinked fluid plugs

A method includes introducing a proppant slurry into a first end of a hydraulic energy transfer system, introducing a clean fluid into a second end of the hydraulic energy transfer system opposite the first end, operating the hydraulic energy transfer system to retain a portion of the proppant slurry in the hydraulic energy transfer system while transferring pressure of the clean fluid to the proppant slurry, and forming a fluid plug that separates the proppant slurry and the clean fluid, the fluid plug being formed by increasing a viscosity of the portion of the proppant slurry to be higher than a viscosity of the clean fluid and a viscosity of the proppant slurry in the hydraulic energy transfer system.