Acoustic and strength characterization of Upper Cretaceous dolostones from the Bahariya Oasis, Western Desert, Egypt: The impact of porosity and diagenesis

Abstract

The Western Desert of Egypt has huge reserves of good-quality natural stones such as limestones, travertines and dolostones. In this paper we assess the dolostones of El Heiz and Ain Giffara formations exposed at the Bahariya Oasis by investigating their lithological, textural, acoustic, and strength properties, and accordingly their economic significance and potential contribution to the national economy of Egypt. Representative dolostone rocks were collected at carefully-selected field sites. The microfacies analysis revealed that three main facies are recognized in the collected rocks: vuggy dolostone, marly dolostone, and sandy dolostone. The measured density and porosity of the studied rocks have been largely affected by the sediment composition, depositional setting, and the diagenetic alterations which, in turn, influenced the acoustic properties and strength of the rocks. Results of the uniaxial unconfined compressive strength (UCS), tensile strength (σt), point load strength (IS50), and the Schmidt Hammer rebound (SHR) number of the studied samples indicate generally high-strength rocks. Various interrelationships between the acoustic and strength properties were obtained using the regression analysis and have been interpreted in light of the rock microfacies and the observed diagenetic processes. Significant relationships have been obtained particularly between the UCS versus the acoustic velocities and the SHR. The resulting empirical relationships with the moderate/high coefficients of correlation can be used to compute important rock parameters from those that are measured on a routine basis; hence enabling a much quicker and efficient evaluation of the rocks. Results of the present study are also useful for studying the strength and acoustic properties of similar surface and subsurface dolostone sequences in the Western Desert of Egypt, as well as other areas of similar geological setting and depositional facies.