--> --> Outcrop-Scale Geometry and Architecture of the Reservoir Units from an Analog to the Early Triassic Khuff-A Reservoir, Central Saudi Arabia

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Outcrop-Scale Geometry and Architecture of the Reservoir Units from an Analog to the Early Triassic Khuff-A Reservoir, Central Saudi Arabia

Abstract

The Permian-Triassic Khuff Formation in Saudi Arabia and other Middle East countries is considered to contain about 40 % of the natural gas reserves in the world. One of the producing reservoir units in this formation in Saudi Arabia is the Early Triassic Khuff-A reservoir. This unit has an analog cropping out in central Saudi Arabia, named Upper Khartam Member of Khuff Formation. The understanding of the heterogeneity and architecture of the Khuff reservoir units is vital and of great importance to enhance the hydrocarbon production. Outcrop analog studies have been improved and evolved nowadays because it helps a lot in the reservoir correlation and modeling approaches, which are difficult to obtain from the subsurface. In this study, five outcrop sections (exposed as road cut in Qasim Area) are sedimentologically described and also analyzed in term of outcrop gamma ray pattern. Then, the results combined with the sequence-stratigraphic scheme originally established for the whole Khartam Member in the same area. The aim of this study is the delineation of the textural variation and spatial continuity of grainstones as potential reservoir facies on an outcrop scale. The composite sequences of the shallowing-upward Upper Khartam Member consist of five high frequency sequences distributed from marine transgression to supratidal flat in an ascending order. Stratigraphic correlations were made on the studied section between the potential reservoir units within the second and third high frequency sequences. Five potential grainstone units were traced laterally along the outcrop between distinct marker beds. The occurrence of these units is strongly ruled by their stratigraphic position. The stratigraphic architecture is highly influenced by the layer-cake type of carbonate platform during the deposition of Khuff Formation. This resulted in a good degree of continuity on the lateral scale and lesser in the vertical one. The thickness of the potential reservoir units increases upward while the thickness of the barrier muddy beds decreases. The outcomes of this study can be utilized by petroleum geologists and engineers, by providing better understanding and prediction of the lateral facies continuity for the reservoir units and by increasing the degree of confidence on the direction of drilling to enhance or increase the economic hydrocarbon production of a reservoir.