The aim of this paper is to investigate the fracture aperture behavior when secondary cracks occur on the main fracture surface. This phenomenon has not been analyzed in the literature. The investigation shows that the aperture profile of a hydraulic fracture with secondary cracks is no longer a smooth elliptical shape as it used to be when there is no secondary crack, but an irregular shape containing discontinuities (also called jumps). The jump keeps on growing with time when the secondary crack propagates into the formation. The investigation also reveals that the aperture profile of the hydraulic fracture with secondary cracks can be larger or smaller than the one without secondary cracks depending primarily on following factors: permeable (leakoff) or non-permeable (no leakoff) media, locations of secondary cracks and pressurization on the secondary crack surfaces. With the existence of secondary cracks, the location of the maximum fracture aperture is no longer at the centre of the fracture. The study has led to two main conclusions: (i) The effects of secondary cracks on the hydraulic fracture geometry emphasize the important role of geomechanics when simulating a hydraulic fracturing problem. Without considering geomechanics, the jumps in the aperture profile can never been seen; (ii) Abnormal changes in the profile of the main hydraulic fracture with secondary cracks can strongly influence the fracturing stimulation process.

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