Sandstone and shale are sedimentary rocks sometimes used as horizons to retain and redirect water. However, their use is not always the same. Despite the similarities in characteristics between these two sedimentary rocks, their differences determine how they can be used in water-bearing horizons.
Sandstone has a relatively high porosity and permeability, while shale has the opposite characteristics. Porosity and permeability are essential features of the rock that play a big role in its ability to absorb and transmit water. Sandstone’s porosity and permeability are determined by its composition, which mainly consists of free sand, as well as the density and size of the sand. Thus, sandstone has a more porous structure, so it can better absorb and transmit water than shale.
Shale has less porosity and permeability than sandstone. This is due to its composition, which mainly consists of large particles of roots, minerals, and shale. This composition has far more particles than in sandstone, and the particles are much denser and larger than in sandstone. Thus, shale has a less porous structure, so its water absorption capability is less than that of sandstone.
Therefore, we can conclude that sandstone is often an excellent water-bearing horizon because it has a more porous and permeable structure, while shale might be used as a water barrier because it has a less porous structure. The following concepts of porosity and permeability, as well as how the composition and characteristics of sandstone and shale affect porosity and permeability, make sandstone more suitable for water-bearing horizons than shale.
In general, sandstone and shale are different sedimentary rocks, and their composition and characteristics determine their use in water-bearing horizons. Sandstone has a higher porosity and permeability than shale, so it is more often used as a water-bearing horizon, while shale is more often encountered as a water barrier.