  Simulations of fluid flow in naturally fractured rocks have implications for
several subsurface applications, including energy storage and extraction, and
waste storage. We are interested in flow in discrete fracture networks, which
explicitly represent flow in fracture surfaces, but ignore the impact of the
surrounding host rock. Fracture networks, generated from observations or
stochastic simulations, will contain intersections of arbitrary length, and
intersection lines can further cross, forming a highly complex geometry. As the
flow exchange between fractures, thus in the network, takes place in these
intersections, an adequate representation of the geometry is critical for
simulation accuracy. In practice, the intersection dynamics must be handled by
a combination of the simulation grid, which may or may not resolve the
intersection lines, and the numerical methods applied on the grid. In this
work, we review different classes of numerical approaches proposed in recent
years, covering both methods that conform to the grid, and non-matching cases.
Specific methods considered herein include finite element, mixed and virtual
finite elements and control volume methods. We expose our methods to an
extensive set of test cases, ranging from artificial geometries designed to
test difficult configurations, to a network extruded from a real fracture
outcrop. The main outcome is guidances for choice of simulation models and
numerical discretization with a trade off on the computational cost and
solution accuracy.
