Stylolites

This chapter provides a reference for the increasing number of geologists who have little or no experience in the interpretation of natural and induced fractures in cores. Stylolites, formed by dissolution under asymmetric confining stresses and lined with insoluble materials, can be considered to be fractures in the sense that they are irregularly planar features formed during deformation of the rock. In addition, the extension fractures that form along some stylolites are important contributors to a reservoir permeability system. Each stylolite that has associated, well-developed fractures can create a permeability streak in a reservoir, and stacked stylolite-fracture systems can contribute significantly to reservoir plumbing. Stylolite-related extension fractures are typically widest at the stylolite and commonly originate at stylolite teeth. The fractures taper to blind terminations within the adjacent rock. They may be developed on one or both sides of a stylolite.