Din&ccedil / er-1 (1968) and South Din&ccedil / er-1 (1980) exploration wells are located at Sirnak Province of Southeast (SE) Anatolia. South Fields of SE Anatolia have received a significant attention after the completion of subjected wells and numerous studies have been implemented regarding this area. Many theories about the geological generation of these fields were put forward by people who studied this region.Both wells have penetrated the Arabian Plate autochthonous units. The Cudi Group, of this sequence, mainly consists of dolomites and anhydrites. The samples from the cores of this referred interval and the thin sections of these cores were examined in details by X-Ray Diffraction (XRD) Analyses and petrographic microscope. Thin sections taken from the core samples of the Cudi Group&rsquo / s Bak&uuml / k, &Ccedil / amurlu and Telhasan formations (from older to younger) stand out in the diagenetic manner. The analyses of these thin sections showed that dolomitization is the main diagenetic process along with some textural changes such as the increase in the deformation of algal structures, formation of stylolites and secondary porosity. Clay minerals, mainly illites, shows detritic behaviors rather than characters representing a diagenetic origin. Obtained results from this study showed that the dolomitization as diagenetic process plays an important role in oil and gas formations within Cudi Group. Dolomite stoichiometry studies indicated that Cudi Group formations have modern dolomites since they show poor ordering reflections. They are also younger formations which are subjected to longer periods of diagenetic effects in comparison with Uludere Formation&rsquo / s dolomites.