A New Stratigraphic Model for the Khuff Formation in the Sub-surface of Central and Eastern Arabia: Implications for Reservoir Geology
Kamal, Rami A. and Geraint W. Hughes
Saudi Aramco, Saudi Arabia
The Khuff Formation carbonates and evaporites in the sub-surface of central and eastern Saudi Arabia are a series of cyclic shallow marine and tidal flat carbonate and evaporite deposits, which accumulated aggradationally on a broad shelf in Later Permian time. Within the Khuff Formation, carbonates can develop three important natural-gas-bearing reservoirs. A new stratigraphic model, rooted in sequence stratigraphy, has been created to be reservoir prediction friendly. Eustatic control was utilized in an attempt to better understand the cyclicity of the intra-carbonate units and the alteration of evaporites and carbonates. The presence of absence of evaporites, dolomites or carbonates is considered to be related to catch-up and keep-up carbonate depositional regimes, which are in direct response to different rates of sea level rise and fall. Over the years, the Khuff Formation has developed a reputation for being a difficult formation for reservoir prediction. Recent studies have shown, however, that this is not the case. Lithostratigraphic interval that are prone to reservoir development can be recognized within predictable stratigraphic positions in the model, which in turn are discernible on wire-line logs traces and in rock core. The lithostratigraphy of the Khuff Formation is also simplified and standardized, in order to provide a new practical and functional model for explorationists, reservoir geologists, and reservoir engineers. Micropaleontological analysis of selected rock cores has also revealed important information on vertical and lateral variations with strong implications to reservoir prediction. Micropaleontology has also enhanced the ability to identify second- and third-order depositional cycle breaks.