A rigorous model that describes the transient flow of a polymer solution displacing a reservoir fluid was developed as a means to account for leakoff phenomena and net pressure during frαc&pαck treatments. An exact solution with a moving interface problem was derived in terms of the pressure profiles from the fracture face into the reservoir, in turn determining the fluid leakoff rate. The results show that the leakoff rate is dependent on the fracture net pressure, fluid and rock properties and injection conditions. The concept of a constant bulk property such as the leakoff coefficient is no longer necessary (or physically meaningful) in high-permeability reservoir stimulation. The developed leakoff model has been incorporated into a fracture propagation model to predict fracture dimensions, net pressure and the interactions between leakoff and created fracture during the propagation, packing stage and fracture closing. The variation of the slope behavior of the net pressure with time at a constant injection rate suggests a new method to diagnose fracture tip screenout.

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