  The mechanical behavior of fractures in solids, such as rocks, has strong
implications for reservoir engineering applications. Deformations, and the
corresponding change in solid contact area and aperture field, impact rock
fracture stiffness and permeability thus altering the reservoir properties
significantly. Simulating contact between fractures is numerically difficult as
the non-penetration constraints lead to a nonlinear problem and the surface
meshes of the solid bodies on the opposing fracture sides may be non-matching.
Furthermore, the challenging geometry of the arising constraints requires to
solve the problem in several iterations, adjusting the constraints in each one.
Here we present a novel discrete implementation of a dual mortar method and a
non-smooth SQP solver, suitable for parallel computing, and apply it to a two
body contact problem consisting of realistic rock fracture geometries from the
Grimsel underground laboratory in Switzerland. The contributions of this
article are: 1) a novel, parallel implementation of a dual mortar method and
non-smooth SQP method, 2) realistic rock geometries with rough surfaces, and 3)
numerical examples, which prove that the dual mortar method is capable of
replicating the nonlinear closure behavior of fractures, observed in laboratory
experiments.
