The interaction between natural fractures and hydraulic fracture was observed in multiple naturally fractured blocks by a series of physical model tests. The effect of natural fractures and in-situ stress on fracture geometry was revealed. Three types of fracture geometry were observed due to a change of in-situ stress contrast. Besides, pressure profiles could also reflect different characters of propagating behaviour. Random small natural fractures could lead to high frequency of pressure fluctuating during fracture propagation. Also natural fractures with strong network could lead to more smooth pressure during injection. Hydraulic fracture tended to be a dominating fracture with random multiple branches at high differential horizontal stress. It tended to be partly vertical (one wring), planar fracture with branches at a lower difference of horizontal stresses. Random natural fractures could dominate fracture geometry alone in condition of extreme low in-situ stress difference. In present of random natural fractures, mini-fracturing is still reliable if fracture geometry is a partly vertical, dominating one (even one wing).

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