Effective Use of Depositional and Diagenetic Tools to Predict Good Reservoir Quality of Khuff Formation in Eastern Saudi Arabia, and the Gulf Countries

By

 Ibrahim A. Al-Jallal¹

(1) Saudi Aramco, Dhahran, Saudi Arabia

 The late Permian Khuff Formation, represent a part of the Tethys sea deposition over the Arabian Plate, located, paleogeographically, in southern hemisphere at the same latitude as it is now. The Formation in Saudi Arabia consists of several packages of cyclic sediments. There are five major units, the Khuff- E, D, C, B, and A members from bottom to top. The Khuff-E is mostly very shallow marine deltaic clastics, with some lenses of dolomudstones and shales in the east and with incised valley-fill clastics in central Arabia to the west. The Khuff-D is mostly dolomudstones, with lenses of anhydrites and shales. In this unit, there are two layers of nodular anhydrite that are very prominent markers called the Khuff-D markers; they can be correlated regionally in almost all of Saudi Arabia, the Gulf countries and Iran. The Khuff-C, B and A contain the reservoir facies in Saudi Arabia, the grainier reservoir facies, subtidally deposited, are usually interbedded with mudstones and anhydrites that deposited in intertidal and supratidal environment.

Because of the importance of the Khuff as a major source of gas in Saudi Arabia, it was studied in detail. Regionally, the depositional setting was defined, the Khuff Formation isopach was mapped, lithostratigraphic units were correlated, major facies were recognized, anhydrite footage and average porosity were mapped. These tools combined were used to interpret the shelf edge and shelf break locations. Then areas of good reservoir potential with cleaner facies and less anhydrite were predicted near the shelf edges and shelf breaks. Sour gas areas were explained, in areas with more anhydrite concentration and less grainy facies. Poorer areas of reservoir facies were predicted and explained.