Experimental study on the hydraulic fracture behavior when meeting large particle, layer interface and natural fractures

To understand the behavior of hydraulic fracture in the rocks with heterogeneous particles, layer interface and natural fractures, this study carried out a series of experiments of hydraulic fracturing, utilizing a transparent device and an optical microscope for observing. The whole process of rock deformation during the fracturing had been record automatically and the digital image correlation method was used to analyze the deformation and strain of rocks. Several hydraulic fracturing experiments were conducted on difference stress state and rock features. The results showed that large particles had much influence on the fracturing path which could over the stress restriction and make the fracture divert, bifurcate or stop. The interface between two layers with different particle size may make fractures deflect like light refraction. The strain analysis showed that before the final fractures generated represented by a pressure drop, much deformation along the final fracture path had already occurred. That meant that the fracture path had been determined before the pressure drop, and the fracturing fluid influence the fracture path mainly by the penetration. This study can help know the law of hydraulic fracturing in real rocks and optimize numerical fracturing models.