Water saturation in shale rocks is an important factor for the flow of gas in a porous medium and for maintaining the flow of fracturing fluids. Furthermore, an assessment of gas resources in place is not limited to the volume of free gas and adsorbed gas. Water contained in the pores should be considered, too.
In shale rocks that are rich in organic matter, the water occurs solely in inorganic pores.
Gas contained in organic pores is free of water as kerogen is hydrophobic, i.e. it repels water particles. As a result, a low rock water saturation coefficient correlates with a high content of organic matter in the rock.
The situation is just the opposite in the pores of inorganic origin, wherein the water is attracted by hydrophilic clay minerals. The volume of the water contained in the inorganic pores tends to decrease during compaction of sediments, their diagenesis and as a result of void filling with the migrating hydrocarbons.
author: Ireneusz Dyrka