TSO effect - tip-screen-out is a situation when proppant bridges in the fracture prematurely during pumping and the trading pressure rises rapidly to the technical limit of the equipment.
TSO fracture designs are specifically intended to screen-out. In this case, it is often possible to continue pumping and inflate the fracture width without exceeding the pressure limits of the equipment. Very high pressures and very high proppant loadings are applied near the end of a fracture treatment where the tip of the fracture has stopped growing due to bridging of proppant at the fracture dip because frac fluid leakoff.
TSO fracture designs are mainly done in high permeable and soft formations where high fracture flow conductivity (width) is needed.