Once considered only as source rocks and seals, shale formations are now also considered as tight-porosity and low-permeability unconventional gas reservoirs. The classification as a reservoir is mainly technology- and economics-driven. Major gas (and significant oil) production from these plays is facilitated by massive hydraulic fracturing treatments that increase permeability and help to reactivate natural fractures. Natural faulting and fracturing are critical factors controlling present-day stress distribution, which in turn influences hydraulically induced fracture system development. Stimulation ultimately enhances reservoir drainage, yielding economically viable hydrocarbon production (Rutledge and Phillips, 2003; Gale et al., 2007; Miskimins, 2009). To better understand the created fracture geometry, borehole-based induced microseismicity monitoring may be used (Figure 1).

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