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Summary: Flowback analysis recently has been considered as a potential tool for assessing induced fractures through corresponding pressure analyses and rate transient analysis. In this paper, we study fracture closure mechanisms during the flowback of fracturing fluid after hydraulic fracturing treatments. Although it is known that flowback can be significantly affected by the geometry of the fractures and closure stress, there has not been any effort to understand the problem from the geomechanical point of view; rather, available studies assume that a fracture closes uniformly with constant fracture compressibility. The coupled geomechanics and fluid flow model presented in this paper help to elucidate how geostresses may affect fracturing fluid recovery under different conditions. We perform a scaling analysis to formulate the occurrence of different fracture closure modes and then use numerical analyses to verify our scaling parameters. The factors governing the flowback process include the mechanical and petrophysical properties of the rock as well as preexisting discontinuities such as natural fractures. Three different closure modes for fracture networks are described and numerically verified. The occurrence of each mode can dramatically affect fracturing fluid recovery. The role of fluid leakoff into the formation, fractures conductivity, and drawdown strategy are examined for each fracture closure scenario. [ABSTRACT FROM AUTHOR]

Knowing correct values of the rock mechanical properties is crucial for many engineering applications in subsurface. Rocks may show two failure modes during cutting: ductile and brittle. In the ductile mode, rock deforms plastically, and the debris is powdered ahead of the cutting face. On the other hand, chips are the major cutting characteristics for the brittle failure during rock cutting. The critical depth of cut represents the transition point between these two models, so knowing this value helps better predict the failure mechanism of rock. In this paper, a new method is introduced based on measuring the roughness of the groove for determining the transition point of failure modes for every rock sample after the scratch test. The graph depicting the average change in the surface roughness ( R t ) versus the scratched surface roughness ( Δ R ) can be used to identify the rock failure mode and determine the transition point for the cutting process. The value of this slope increases until the depth of cut reaches the transition point, and then the slope reaches a constant value. The main purpose of this paper is to estimate the critical depth of cut of different rock specimens employing the new surface roughness model. [ABSTRACT FROM AUTHOR]