oa Early and Charge Related Diagenetic Controls from Rock Types (Arab C and D Reservoirs, South Rub' Al Khali Basin, Saudi Arabia)

The South Rub ‘al Khali Company Ltd (SRAK) is an Incorporated Joint Venture between Shell Saudi<br>Ventures Limited (50%) and Saudi Arabian Oil Company (50%) and was set up in order to explore for<br>non-associated gas in the South Rub ‘al Khali Basin as part of the Natural Gas Initiative in the Kingdom of Saudi Arabia.<br>The Arab C and D reservoirs in the Kidan Field of the South Rub ’al Khali Basin have recently been the<br>targets of a well drilled by the SRAK Venture. A total of 350 ft continuous core was obtained to<br>characterize reservoir properties and interpret key processes controlling their distribution across the<br>field. Depositional environments and early diagenetic patterns provided the template for burial and<br>charge-related modification of rock properties. Distinct reservoir rock types have been differentiated<br>based on petrographic observations, core porosity, core permeability and MICP (mercury injection<br>capillary pressure) data.<br>This presentation focuses on the results of the detailed diagenetic and geochemical study that allows<br>the interpretation of the key processes controlling the differentiated rock types in Arab C dolostone<br>units and Arab D ooid grainstone units. Dolostone reservoir properties in the Arab C are mainly<br>controlled by the presence/absence of late calcite and / or late anhydrite plugging of intercrystalline<br>porosity. The key diagenetic processes recorded in rock types from Arab D grainstones are: early<br>cementation, compaction, burial cementation (including calcite, fluorite and anhydrite), late leaching<br>and late charge-related cementation (calcite and saddle dolomite).<br>The rock types are mostly stratigraphically defined units, in spite of the recorded complexity of<br>diagenetic processes, associated diagenetic products and pore size distributions. The stratigraphic<br>arrangement of the rock types in the studied core responds to depositional and early diagenetic<br>controls. The late diagenetic products follow the early diagenetic template, nevertheless understanding<br>the impact of late diagenesis has proven key to predict the rock properties across the field and<br>construct new reservoir models.