Abstract: During the course of hydraulic fracturing in high permeability loose formation, the stability of fracture face will be destroyed by the shearing stress of fracturing fluid because of the formation's poor cementation and low strength, thus causing the sand grains attached to the fracture face to be moved back to the fracture tip with fracturing fluid injection to form scour fractures. Meanwhile, the back moving of sand grains by the action of hydraulic, scour is favourable to the formation of "Tip-screen-out" ( TSO) , which can also strengthen the hydraulic scour on the contrary. Such an interaction will control the size of fracture width and the efficiency of TSO-fracturing, thus having important value to scientific, research. The existent fracture width prediction models are based on elastic: theory, by which the fracture width can't be exactly predicted, because the hydraulic, scour phenomenon couldn't be considered. In the paper, in consideration of rock mechanics, fluid mechanics, fracturing fluid property and fracturing operation conditions, the mechanism of forming scour fractures is analyzed; a new model of predicting the widths of hydraulic, scour fractures (aiming at vertical fractures) is set up；the relevant calculation program is worked out；and the model is analyzed and checked up according to some actual data finally.  (Financed by the 863 Program project, No. 863-306-ZT04-03).
Key words: High permeability formation, Tip-screen-out ( TSO),  Hydraulic scour,  Elastic frature, Scour fracture, Fracture width