Outcrop Analog Studies of the Wasia-Riyadh and Aruma Aquifer in Kingdom of Saudi Arabia.‎

Journal Article
B, ‎7.‎ Keller, M., D., Bohnsack, R. Koch, M. Hinderer, J. Hornung, H. Al Ajmi, and Abuamarah . 2019
Publication Work Type: 
Research
Magazine \ Newspaper: 
AAPG Memoir ‎Journal
Volume Number: 
116
Pages: 
‎317–382‎
Publication Abstract: 

ABSTRACT
In recent years, outcrop analogue studies have become a powerful tool in sedimentology for the assessment of reservoirs, both in hydrocarbon and aquifer studies. Data from exploratory drilling campaigns can be augmented significantly by observations on the outcrop of the corresponding stratigraphical interval with the objective to validate the borehole information through direct observation. In addition, through the physical separation of the outcrop area and the subsurface, the increased spatial coverage of a reservoir and its equivalents provides
additional information about facies and their changes and thus on reservoir properties.
This chapter presents results of a study on the Cretaceous sedimentary aquifers in Saudi Arabia (Wasia–Biyadh–Aruma) in order to better assess the storage volume of fossil groundwater, which is of  fundamental importance for the hyper-arid kingdom. Besides the regional 3-D stratigraphic framework, the focus was on measurements of porosity and permeability of approximately 150 samples and the interpretation of reservoir quality in terms of sedimentary facies and its diagenetic overprint. In general, both porosity and permeability are varying on a high level (Biyadh: 1–36% / 2100–6500 mD; Wasia: 3–42% / 2100–6500 mD; Aruma: 1–38% / 1026–0.15 Darcy). Apparently, the storage volume and hydraulics of these regional aquifers are controlled not only by their fracturing but also by their matrix porosity. Permeability varies by about an order of magnitude among samples
or between vertical and horizontal permeability within some samples. This variation can be well explained by heterogeneity due to sedimentary facies, for example, cross-bedding and bioturbation. In some areas, the kind of cementation and its intensity have a large effect on the permeability. The data obtained enhance the quality of the hydraulic interpretations of this aquifer system.
Spectral gamma-ray logs proved to be useful for a regional correlation and the correlation of aquifers and aquicludes. This is based on the recognition of the major unconformities in the logs but also on the identification of various paleosol horizons, which regularly show high
emissions of U and Th radionuclides. Intensive weathering during the Cretaceous is responsible for dominantly kaolinitic clay mineralogy and consequently negligible K emissions.