Brittle Failure

The physical definition of brittleness and ductility
Brittleness and ductility are manipulated to illustrate the deformation behaviors when rocks are experience certain stress. A rock is considered to be ductile if it consumes a high amount energy before fracturing. Brittle rocks are unable to accommodate high strain before fracturing, resulting in open microfractures after hydraulic fracturing. In other hand, the conventional reservoirs brittleness is mainly used to evaluate the drillability in drilling operations, sawability in rock cutting analysis , and mechanical winning of coal rocks (Jin et al., 2014). Brittleness is one of the significant rock parameters in shale reservoirs. It recognizes as key information to evaluate the capability of formation to create an effective fracture network that conducts the hydrocarbons to each borehole. Thus differentiating brittle from ductile rocks has been the key to unique success in shale gas reservoirs. In the lab scale, The Brittle failure is occurred when the ability of the rock to resist load decreases with increasing deformation. Brittle failure is induced with materials that undergo little to no permanent deformation before failure and depending on the test conditions which may occur suddenly and catastrophically.
These two rock elastic parameters are combined to reflect the rocks ability to fail under stress (Poisson’s Ratio) and maintain a fracture (Young’s Modulus) once the rock fractures. Ductile shale is not a good for reservoir because the formation will want to heal any natural or hydraulic fractures. Ductile shale however, makes a good seal, trapping the hydrocarbons from migrating out of the more brittle shale below. Brittle shale is more likely to be naturally fractured and will also be more likely to respond well to hydraulic fracturing treatments (Ren et al 2014), (Wang 2008), (Rickman