Porosity and Permeability Characterization within the Lithofacies Framework of A Miocene Dam Formation Outcrop, Eastern Saudi Arabia

Abstract

Modeling of reservoir geology and properties is a highly demanded topic nowadays, for better understanding of reservoir heterogeneity particularly in the inter-well spacing. Outcrop studies represent one of the main targets to fill the limitations of subsurface data. In this context, an outcrop of Miocene Dam Formation was targeted for sedimentology and petrophysical analyses. Dam Formation is a Middle Miocene Formation, which is composed of mixed carbonate-siliciclastic sediments. Stratigraphically, Dam Formation is overlain by Hofuf Formation and underlain by Hadroukh Formation. The purpose of this research is to characterize the porosity and permeability of selected lithofacies, within the overall lithofacies framework of an outcrop of the Miocene Dam Formation in Al-Nasbiyah Area, Eastern Saudi Arabia. The Methodology that have been adopted to fulfill this work includes: 1- conducting detailed sedimentology logging and petrography in order to investigate the lithofacies pattern of Dam Formation, 2- sampling of the selected lithofacies for porosity and permeability analyses, and later selecting some of these samples for XRD, SEM, and Micro CT-Scan 3- geostatistical modeling of lithofacies framework, porosity, and permeability. The lithofacies investigation revealed that Dam Formation is composed of mixed carbonate-siliciclastic deposits, of tidal flat environment, with dominance of carbonate deposits. The lithofacies selected for petrophysical investigation are, from bottom to top, skeletal oolitic grainstone, sandy fossiliferous packstone, burrowed wackestone, and stromatolite grainstone in the top of the succession. The porosity-permeability relationship exhibits poor correlation for these lithofacies. Regarding the geostatistical modeling, several realizations were generated for lithofacies, porosity, and permeability models. These models were validated qualitatively and quantitatively on the basis of comparison with input data and present day lithofacies setting. These models showed small scale heterogeneity in porosity and permeability even within the same lithofacies, these heterogeneities can be attributed to depositional and diagenetic controls on reservoir quality. The study showed that such models can be used as a guide for better understanding of the depositional setting, stacking pattern, and moreover property characterization and distribution, which might be used for prediction purposes if available subsurface models could be used for validation of such inter-well models.