Reactive transport in 3D models of irregularly fractured rock masses

Abstract:

Reactive transport through irregularly fractured rock masses is a key phenomenon in ore-forming hydrothermal systems, geothermal systems, and many other geological processes and will affect the mechanical properties and hydraulic apertures of fractures. Realistic representations of such systems have so far been hampered by technical limitations of most hydrothermal reactive transport codes, namely the ability to represent discrete fracture networks in a porous rock matrix. We present the first three-dimensional simulation results obtained from coupling a combined finite element – finite volume scheme of the revised CSMP++ flow simulation platform (1) with the GEMIPM3K (2) chemical equilibration code. In these, we represented fracture zones as thin, porous zones of higher permeability. The simulations demonstrate the effects of fracture zone orientation relative to the pressure field and fracture zone intersections on the differential advance of reaction fronts. We outline our numerical approaches for testing and comparing the effect of various ways of representing fractures and fracture zones in irregular meshes, namely the possibility of using layers of prism elements to represent fractures of finite thickness with internally varying properties and the possibility to represent thin fractures as lower dimensional (=2D) elements. We intend to make use of the “split node” capabilities of CSMP++ (3) to maintain sharp interfaces at material boundaries in order to be able to study the transient influence of reactive flow on fracture and matrix permeability in irregularly fractured rock masses.