Dynamic modelling of overprinted impermeable fault gouges and surrounding damage zones as lower dimensional interfaces

In the modelling of subsurface fluid flow, faults are dominant features since they can act as fluid pathways or barriers. Special emphasis is therefore placed in representing them in a numerically efficient manner and the use of lower dimensional domains has become prevalent to simulate higher permeability features like fractures. Such features, however, only represent some of the components of natural fault networks, which can also include rather impermeable fault gouges surrounded by higher permeability damage zones for instance. Here we present a numerical approach to simulate such systems at a large scale, where the thickness of those features makes it advantageous to represent them as discrete rather than continuous domains, using lower dimensional interfaces in a conforming mesh. Benchmarks show excellent agreement with equivalent continuous simulations, regardless of the fault thickness or permeability, both for flow conduits and barriers. This approach can also account for the overprinting of faults with different permeabilities, as well as their dynamic evolution, which we illustrate with an example of trap charging. This work demonstrates the applicability of the approach to simulate fluid flow in faulted environments of various permeabilities and we discuss how those results can easily be extended to account for multi-physical processes.