Regional Facies Relationships and Sequence Stratigraphy of a Super-Giant Reservoir (Arab-D Member), Saudi Arabia

C. Robertson Handford, Strata-Search LLC, Austin, TX 78726, and Dave L. Cantrell and Thomas H. Keith, Saudi Aramco, Dhahran, Saudi Arabia

Abstract

The Late Jurassic (Kimmeridgian) Arab-D member consists of complex facies associations and clinoform units that make up the intrashelf Arabian Basin and associated platform. A ramp bordered the Arabian Basin, which extended >300 km from Abu Safah and Berri fields (offshore) in the north to the interior of Saudi Arabia. This basin encloses the largest field in the world (Ghawar) as well as several other super giant fields (Qatif, Abqaiq, and Khurais), all of which produce from the Arab-D member.

From bottom to top, the Arab-D member consists of numerous mud-, organic-, and grain-dominated facies associations, which generally record an overall shallowing upward history and a long-term base-level fall. Numerous high-frequency sequences, however, are recognizable from stacking patterns and regional correlations. Lime mudstones, which are common in the lower Arab-D represent a sub-wave base (~100 ft), outer ramp setting. Overlying intraclastic and oncolitic rudstones represent storm-dominated tidal channel and algal bank environments. Thick, amalgamated rudstones record base-level fall and storm-wave erosion of the firm-ground substrates. The upper Arab-D reservoir mainly consists of open marine buildup limestones and grainstones. Coral-stromatoroid facies have accumulated as sheets and local buildups (10-20 ft of relief) during a major base-level rise that culminated in a bank margin centered in Abqaiq and northern Ghawar fields. These organic-rich facies have been laid down as backstepping, northward thickening buildups. Subsequent base-level fall has led to the deposition of several seaward stepping (southward), skeletal, peloid, and ooid grain shoal complexes having shingled, or clinoform geometry. The youngest clinoforms step southward as base-level falls and are followed by lowstand to transgressive, onlapping anhydrite units that formed in a subaqueous to desiccated salina, which extended across the remnant Arabian Basin.