Rocks containing organic material have some properties that set them aside from normal rock.
The approximate composition of the coal and shales may be determined by moisture and proximate analyses.
In the case of coal, its structure is often very important to the way in which it conveys fluid. The structure refers to the low small-scale fractures within the coal which are often termed cleats. These are examined by cutting the coal in orthogonal directions, polishing the faces and examining these for their frequency and infill.
While many rocks contain carbonates, the presence of carbonates in joints or cleats of coals has a dramatic effect on their permeability. Determining the presence of such carbonates may lead to the use of acid to improve permeability by the use of an acid hydrofracture or simple wellbore treatment.
Coals and, to a lesser degree, organic shales have the property that they shrink as they desorb gas. This can change the level of stress within them quite significantly.