Permeability evolution of a fractured, porous and permeable sandstone at simulated georeservoir conditions

Bentheim sandstone is regarded as a conventional georeservoir rock even at great depth, due to its mineral composition, homogeneity, micro- and macrostructure. Therefore it has been extensively tested for a variety of applications to understand its physical and mechanical properties under changing environmental conditions.

A recent study has shown how the simultaneous change of pressure, temperature and pore pressure, therefore recreating environmental conditions at selected depths, affects the evolution of permeability at depths, both when the rock is buried and when the rock is exhumed. The interaction between those variables has a complex effect on the permeability of Bentheim Sandstone, which could not have been identified by assessing individually the role of a variable. These results show that the permeability of such rock could be overestimated with classical studies and highlight the importance of investigating rock mechanical and hydraulic properties at georeservoir conditions. These experiments have been performed on intact samples.

However, rocks at depth contain fractures and faults, which may alter the interconnectivity of the pore space, hence the permeability of the rock itself. The deformation and failure of Bentheim Sandstone at high strain resulted in permeability loss due to the formation of comminuted material and grain crushing which lowered the pore space interconnectivity. No fractured sample has been tested under simultaneously changing environmental conditions.

To fill this gap, we replicate the experimental procedure used to test intact samples of Bentheim sandstone, both under simultaneously changing conditions and under a sequential variation of different variables, after the sample has been brought to failure. Our goal is to understand the importance of fractures on the permeability evolution at different simulated depths.