DEPOSITIONAL AND DIAGENETIC BARRIERS, BAFFLES AND CONDUITS: PERMIAN CARBONIFEROUS UNAYZAH RESERVOIR, NUAYYIM FIELD, CENTRAL SAUDI ARABIA

The Unayzah Formation is one of the most important Palaeozoic reservoir systems in Saudi Arabia. In the Nuayyim field, Central Saudi Arabia, it produces light, sweet crude oil and consists of three main reservoir units, in descending stratigraphic order: Unayzah A, B and C. These reservoir units include a wide range of depositional facies deposited under a variety of climatic conditions, from high-latitude glacio-fluvial to more temperate playa/ lacustrine, floodplain and braided-fluvial to hot-arid aeolian environments. Together with the diagenetic changes superimposed on the various depositional facies, this has produced complex reservoir heterogeneity. The effects of this diagenetic and sedimentologic complexity on reservoir quality and compartmentalization are the subject of this paper. Approximately 816 ft of core and 611 core plug samples were examined from three wells which penetrate, completely or in part, the Unayzah reservoir. We combine petrographic and scanning electron mic