ABSTRACT: In this paper, the ability of a circular notch to reduce hydraulic fracture initiation pressure (FIP) from an openhole completion is validated by a series of laboratory experiments. We report six experiments conducted inside a large true-triaxial load frame in 0.61×0.46×0.46 m (24×18×18-in.) Indiana limestone block samples to simulate fracture stimulation of the well drilled in the minimal stress direction. In each experiment, the moment of hydraulic fracture initiation was identified using acoustic emission data acquired during the injection. All baseline tests with open hole without a notch revealed nonplanar tortuous fractures that initiated longitudinally. However, in notched cases, planar transverse fractures initiated at the notch location and at significantly lower pressure. This experimentally observed reduction of FIP caused by the circular notch justifies its application to address the significant challenge posed by high breakdown pressure in multistage fracture stimulation in tight reservoirs. Further, the nonlocal fracture initiation model has been improved toward explicit generalized Hubert-Willis FIP formulas for the notched open holes and validated using the obtained experimental data. These explicit FIP formulas provide useful estimations that can be applied in well stimulation design.

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