ABSTRACT:

The study of fracture propagation and its potential interaction with bedding interfaces is essential to investigate whether vertical fractures induced by deep subsurface injection operation penetrate into seal formation and provide potential pathways for contaminated fluid to migrate upward into the drinking water formation. The major factors that affect the fracture containment during fluid injection include in-situ stress condition and geomechanical properties of the rocks. In order to address this issue, our experimental study utilized two rocks: sandstone and mudstone. We performed a series of laboratory triaxial experiments to determine the geomechanical properties and fracture mechanical properties of intact rocks. Experiments were also conducted on rock specimens prepared with precut failure shear planes bonded with epoxy. Comparison was conducted between the intact and bonded rocks. The friction angle and cohesion of the intact mudstone evaluated using Mohr-Coulomb failure criterion are 47.8° and 10 MPa, respectively. Using the Hoek-Brown failure criterion, for normal stresses from 0 to 400 MPa, the cohesion of the intact sandstone ranged from 8.5 to 113.8 MPa and the friction angle ranged from 69.2° to 28.7°. Bonded rocks have lower Young’s moduli and maximum shear strength. The geomechanical properties of bonded samples were governed by the confining pressure-dependent strength of the epoxy.

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