51st U.S. Rock Mechanics/Geomechanics Symposium,
San Francisco, California, USA
2017. American Rock Mechanics Association
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ABSTRACT: Experimental and numerical results are presented for hydraulic fracture interactions with a discontinuity (representing a natural fracture, fault, or bedding interface) in a 2D configuration where viscous dissipation is dominant. A 2D boundary element code (MineHF2D) is used to simulate hydraulic fracture interaction using experimental parameters such as interface friction, injection system compressibility and fracture toughness. Crossing and arresting (blunting) hydraulic fracture behaviors have been observed in experimental and numerical results for orthogonal and inclined interfaces. Optical analysis of video records allows tracking of fracture pathways, growth rate and opening (fracture width). The experimental results are presented using the Renshaw-Pollard criterion and compared to numerical simulation outputs. The numerical predictions of crossing behavior, fracture pathways including offsets and crossing fracture re-initiation delay compared well with measurements.
Interaction between a growing hydraulic fracture (hereafter also called HF) and discontinuities within the rock (such as a natural fracture, fault, or bedding plane, hereafter called NF or discontinuity) can have a significant impact on hydraulic fracture growth and the resulting treatment effectiveness (Kresse, Weng, Chuprakov, Prioul, & Cohen, 2013). This HF-NF interaction problem has been studied using modelling (Zhang & Jeffrey, 2006, 2008), laboratory experiments (Blanton, 1986; Bunger, Kear, Jeffrey, Prioul, & Chuprakov, 2016; Gu et al., 2012; R. G. Jeffrey et al., 2015; Kresse et al., 2013; Warpinski & Teufel, 1987) and field studies (Robert G. Jeffrey et al., 2009; Warpinski & Teufel, 1987; Weng, 2015; Weng et al., 2014) with the intent of developing a greater understanding of hydraulic fracture growth behavior in a naturally fractured rock mass.
The HF-NF interaction mechanics are complex, and two main effects are considered critical to this interaction. Firstly, local stresses at the discontinuity are changed by the stress and displacement influence of an approaching HF. Through this process, the tensile stress induced ahead of the fracture tip (process zone) can cause local sliding on the discontinuity. Alternatively, if the friction coefficient of the discontinuity is large enough to resist sliding, the applied forces can be transferred across the discontinuity and cause the creation and growth of a tensile fracture on the far side of the discontinuity.
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