Factors Concerning the Development, Distribution and Preservation of Reservoir Facies in Jurassic Carbonates and their Impact on Petroleum Systems in Eastern and Northeastern Saudi Arabia

By

 A/Motaleb Al-Qahtani¹, Alastair Gray², Geir K Ytreland²

(1) Saudi Aramco, Dahran, Saudi Arabia (2) Saudi Aramco, Dahran 31311, Saudi Arabia

 The Rimthan Arch is a positive feature, which existed from Bajocian until Portlandian time separating the Gotnia and Arabian intra-shelf basins throughout this period. This feature, whose lateral extent has varied considerably throughout time, significantly controls development of Jurassic reservoir facies. The distribution and quality of the most important carbonate reservoirs in the Eastern Province of Saudi Arabia appear to be controlled by a system of positive elements; tectonic and/or depositional highs. Water depth, energy and primary depositional environment created and/or modified the sediments into reservoir rocks in the vicinity of these highs.

Analysis of petrography, paleontology, core description work, core porosity/permeability analysis and integration with well logs and seismic interpretation permit a reasonable description of the Upper Jurassic Arab carbonate facies throughout the area, and are summarized into regional facies and net pore volume maps. Similarly, reservoir distribution maps for the other reservoir units from this time are presented. An attempt is made to use sequence stratigraphy and seismic stratigraphy to describe the systems, and to predict facies variation as it pertains to the development of petroleum systems and prediction of various potential stratigraphic play types such as; dolomitization as a sealing mechanism, facies variations, biohermal buildups and updip reservoir pinchouts. Recent reprocessing of seismic data indicates that such facies variations may be seismically detectable.

Saudi Aramco oil typing work indicates a distinct separation of oil families into Gotnia and Northeastern Arabian Families and enhances the prospectivity of the Rimthan Arch trend.