Geology and Rock Properties Correlation: Outcrop Analogue Study of a Cretaceous Reservoir, United Arab Emirates

Hamdan Al-Menhali¹*, Sandra Vega², Mohammed Ali², and Manhal Sirat^2
1ADMA-OPCO
²The Petroleum Institute, UAE
*[email protected]

Geological and petrophysical investigation has been performed in an outcrop located at the northeast of Ras Al Khaimah, where Lower Cretaceous rocks of the Thamama Group dip gently into the subsurface. The area is of stratigraphic significance because it can be used as an analogue model for the Thamama reservoirs of the United Arab Emirates. The aim of this study is to better characterize and correlate the geology and rock properties of the exposed rock, and use it as an analogue for Thamama Group. This work combined the results of the following methodologies: (1) geological analysis, which included description, stratigraphic column and mapping of the outcrop; (2) rock properties analysis, which included porosity, permeability, porosity type, and mineralogy of 17 outcrop samples; and finally (3) correlation between outcrop and reservoir field properties. Our preliminary results indicated that the studied outcrop consists of mudstone-wackestone that has been crystallized with no major lateral changes. Seven main lithological units have been recognized on the basis of their depositional and/or horizontal continuous fractures. In addition, the outcrop samples display a considerable number of vertical joints filled with calcite. Horizontal open fractures are clearly present, which affect permeability. Few units have small burrows (1.0–2.0 mm) that slightly increase the porosity. Some of the lower and intermediate units contain relatively high concentrations of iron, which reduces resistivity. Finally, our observations showed that, in contrast with the subsurface Thamama reservoirs, the exposed units have very low porosity as a result of local cementation.

AAPG Search and Discovery Article #90077©2008 GEO 2008 Middle East Conference and Exhibition, Manama, Bahrain