ABSTRACT:

Six true tri-axial laboratory experiments were conducted to investigate fracture propagation behavior in tight formation. Meanwhile, the effects of perforation parameters on fracture initiation and propagation under different horizontal stress differences were discussed. The experimental results showed that: induced fractures would like to initiate at the base of perforation, and then propagate along the maximum horizontal stress direction. Main fracture morphologies were divided roughly into three different types in our experiments: a single flat fracture, multiple-parallel fracture, and spiral-shape fracture. Moreover, high perforation density preferred to create spiral-shape fracture, and large perforation phase was keen on generating multiple-parallel fracture. In addition, a high horizontal stress difference prevented induced fractures from interacting and linking up with each other, resulting in obvious complex fractures near wellbore. However, it reduced fracturing pressure and the roughness of fracture surface effectively. Ultimately, low perforation density, 12 holes/m, with perforation phase of 60° should be used in a low horizontal stress difference for a simple flat fracture. However, high perforation density as 18 holes/m with perforation phase of 60° should be adopted in a high horizontal stress difference for a low fracturing pressure.

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