Propagation of fluid driven fractures in transversely isotropic material

Laboratory Investigation of Hydraulic Fracture Growth in Zimbabwe Gabbro

“…There is a partial loss of transmitted pressure due to the contact conditions between the flat jacks, spacers, and specimen surfaces (due to friction). Finite element simulations of the overall geometry (accounting for the platens transmitting the pressure and the finite specimen) have shown that for a hydrostatic loading condition σ 1 = σ 2 = σ 3 = 20 MPa, a stress attenuation of around 15% (σ 3 ≈ 17 MPa) in an area around 60 mm is reported in the center plane of the sample (Moukhtari, 2020). Taking directly the flat jack pressures, we thus use an upper bound for σ 3 here, such that the reported apparent toughness is probably underestimated.…”

“…The boundaries of the specimen likely have a stronger influence on the volume estimated via Equation A2 (and thus underestimate fracture volume in the presence of finite boundaries). In addition, the applied minimum stress σ 3 is also lower closer to the boundary due to the geometry of the loading system (Moukhtari, 2020). As a result, the estimated fracture volume when the fracture front comes close to the specimen boundary is likely severely underestimated for GABB-005 as shown in Figure 5.…”