Insights on spatial variography and outcrop-subsurface relationship of sandstone reservoir properties: A case study from the Late Triassic Minjur Formation, central Saudi Arabia

Understanding the variography of outcrop properties may give a guide for predicting the subsurface reservoir quality, more significantly for the more stable and resistant reservoir rocks such as sandstones compared to the carbonates. This study was planned to investigate the lithofacies and reservoir properties of different sandstone lithofacies of the Late Triassic Minjur Formation outcrop, and attempted to develop a relationship between these aspects in outcrop and subsurface settings. Based on the field and petrographic analyses, sandstone lithofacies of Minjur Formation were categorized into five types upon their textures. These lithofacies were intensively investigated for porosity and permeability. Variography analyses were applied on composite outcrop lithofacies, and also on porosity and permeability data. A good relationship was observed between porosity and permeability, which coincides with the univariate statistics of each and confirmed by variography analysis. Combination of outcrop and subsurface reservoir properties showed an acceptable correlation between outcrop reservoir properties and data from central Saudi Arabia and Rub' Al-Khali Basin in southern and southeastern Saudi Arabia. This correlation was further highlighted by the global sense of subsurface sandstone reservoir properties. In general, the current study reflects the possibility of sandstone outcrop data to act as a representative analog for its equivalent subsurface reservoir. This possibility, which is mainly controlled by the similarity in depositional setting, can be also attained for reservoir properties and quality. Obtaining more qualitative and quantitative data is always advantageous to get better and more robust correlation.