Experimental investigation on tension zone in front of mode-Ⅰ fracture under in-situ stresses
The stress distribution characteristics ahead of the hydraulic fracture under in-situ stresses will affect the fracture propagation and stimulation effect.In this paper,the mechanical behaviors and the tension-compression stress distribution ahead of the Mode-Ⅰ fracture under in-situ stresses were studied using a self-designed visual fracturing experimental device.Based on the digital image correlation,a method to identify the boundary of the tension-compression zones ahead of the Mode-Ⅰ fracture tip was proposed,from which the positive linear correlation was found between the tension zone length and the fracture tip opening displacement.Before fracture initiation,the range and length of the tension zone will increase with the stress intensity factor.During the fracture propagation,the range and length of the tension zone remain constant.With the increase of in-situ stress,the length of the tension zone will decrease,and the influence of in-situ stress on the tension zone will decrease.The boundary of fracture process zone and elastic zone in tension zone was investigated,and the position of fracture process zone and the tension zone was described.The concept of process zone index in the tension zone was proposed,which was found increase with in-situ stress,indicating that nonlinear fracture is dominant in the tension zone under high in-situ stress.
rock mechanicshydraulic fracturingdigital image correlationfracture mechanicsfracture process zonein-situ stress
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