Drilling induced fractures in coal core from vertical exploration well: a method to determine cleat azimuth, and the angle between cleat and maximum horizontal stress, and its application

Drilling induced fractures that have been described from cored sandstone, mudstone and limestone, also occur in many coal cores. This paper outlines a method of using petal and related fractures in coal core to determine the angle between face cleat and the principal horizontal stresses. The method also enables determination of the azimuth of cleat, in wells in which the apparent dip of cleat on a scanner image is vertical. As the angle between face cleat and the principal horizontal stresses can have a major influence on initial permeability, the method has application in coal bed, coal mine, and enhanced coal bed methane.