There are 2 basic types of natural fractures that need to be studied when characterising naturally fractured reservoirs - whether it be a geothermal or hydrocarbon reservoir. These are extension and shear fractures.
Deformation bands (permeability reducing) and open fractures (enhancing) can co-exist in a sandstone reservoir but owing to timing (the d-bands form early during burial), the open fractures can still assist or provide essential reservoir permeability.
Deformation Bands can drastically impact the permeability of otherwise good quality reservoir sandstones. This example is from Permian Sandstones, N of Oslo in Norway. Here we look at some of it's key structures.
Any info on the structure/d - bands of this outcrop would be appreciated.