Abstract
The influence of mechanical stratigraphy on natural and induced deformation is well established for unconventional or self-sourced hydrocarbon reservoirs. Although drill-through and coring experiments show the complexity of hydraulic fractures, most conceptual models of hydraulic stimulation are predicated on the development of large planar opening-mode fractures or swarms. In this study, we use numerical geomechanical models to investigate the role of mechanical stratigraphy in controlling deformation modes and patterns and containing the vertical growth of hydraulic fractures. The two-dimensional simulations consider initial normal-faulting stress states at 3000-m depth and moderately overpressured conditions. Strata are represented by elastic-plastic-damage constitutive relationships, with mechanical layering simulated by variations in material properties, with and without slippable layer interfaces. Simulations show that mechanical stratigraphy strongly influences stress and pore pressure evolution in response to fluid injection. Induced deformation includes complex networks of tensile, hybrid, and shear failure, with localization and dimensions strongly influenced by mechanical stratigraphy. Shear deformation dominates, with tensile deformation concentrated near injection sites. Simulations with uniform mechanical properties exhibit greater vertical fracture growth, whereas mechanically layered configurations show upward and/or downward retardation of fracture growth. The most effective containment of vertical fracture propagation occurs at transitions from relatively weak-ductile to relatively strong-brittle intervals and at weak bedding-slip surfaces.
