Cores are defined as cutting and removing cylindrical rock samples from a wellbore. Coring provides the operator with a relatively undamaged sample or cross section of the reservoir rock. By obtaining cores, geologists can study the porosity and permeability of underground rocks. Conventional coring and sidewall coring are the two most commonly used coring methods. Conventional coring uses a component called a "core barrel" that consists of a drill string that extends to the bottom of the hole. The core tube has a hollow inner tube, and the outer tube and drill string rotate around it and remain stationary. To reduce damage to the core, the operator can use a fiberglass cover or rubber cover. Special core drill is used for cutting. The hole surface of hollow drill has natural diamond or PDC cutting surface.