The presence of preexisting fractures and the need to place multiple hydraulic fractures in relatively close proximity from each other make stimulating unconventional formations a challenge. This paper experimentally reviews the geomechanical factors governing the hydraulic fracture interactions with the formation's preexisting fractures and the fracturing completion's simultaneous hydraulic fractures. The methodology followed in this study uses a series of laboratory fracturing tests. The experimental tests used rock samples made of synthetic, gypsum-based cements, such as hydrostone and plaster, and were performed in a number of experimental settings to investigate some geomechanical factors of relevance. Among such factors, the preexisting fracture's cementation, aperture, and relative height as well as the design of the fracturing stage completion were examined in the course of the experimental portion of the work. As a result of the laboratory experiments, it has been found that a hydraulic fracture crossing the preexisting fracture is largely dictated by the preexisting fracture's cement fill type relative to the matrix of the host rock. Likewise, the height of the hydraulic fracture relative to the preexisting fracture may govern their intersection mode, however, there seems to be an insignificant impact of the preexisting fracture aperture on the intersection outcome. Moreover, the fracturing stage completion design was found to have considerable impact on the hydraulic fracturing outcome. Stress interference between the fracturing sources in a stage highly affects the outcome of each fracturing source. Middle fracturing sources tend to result in inhibited hydraulic fracture propagations while outer fracturing sources achieve hydraulic fracture propagations with outward curvatures. Overall, the experimental data and findings enable us to validate some theories, calibrate numerical simulators, and answer some pressing questions. The results discussed in this paper provide very useful insights into fracturing unconventional formations.

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