Multi-scale flow behavior in mudrocks
Abstract: Mudrocks have become of large interest in the last decades.
Their compression behavior controls the development of overpressure in the
subsurface. Additionally, mudrocks can act as seals for oil and gas or as host
rock for storage of waste material or CO2, and can even be a source
rock for shale gas. Here, I will discuss two types of mudrocks: (1) a
resedimented, deepwater, marine mudrock and (2) a gas shale. Even though both
look different on various scales, flow through both mudrocks
is multi-scale. Large preserved pores in the marine mudrock, caused by
silt-bridging, control Darcy flow and contribute to an increased permeability
in silt-rich mudrocks. In contrast, smaller pores within the clay interact with
those large pores at smaller rates and over longer timescales resulting in flow
through multi-porosity systems affecting solute and mass transport. On the
other hand, heterogeneities like microfractures in gas shales, whether natural
or induced by sampling and/or handling, have higher permeabilities than the matrix
permeability resulting in multi-scale transport through these tight systems.