Geological characteristics of the Lower Silurian Qusaiba Shale, Rub Al-Khali Basin, Saudi Arabia

The Lower Silurian Qusaiba Shale of Qalibah Formation is considered as the most prolific source rock for the Paleozoic petroleum system of Saudi Arabia. Additionally, it has significant potential for unconventional shale gas. This study has been conducted on about 30 feet continuous core of Lower Qusaiba hot shale, Rub Al-Khali basin, Saudi Arabia. Core description shows different lamination patterns (〈 5mm: 5-15 mm and 〉15 mm), reveals that it is predominantly composed of fine lamination of fissile hot black shale and grey shale present alternatively. Grey shale is having high silica contents. Sedimentary features including soft sedimentary deformation, bioturbation and natural fractures (both open and filled) have been observed at several locations in core samples. Thin section study reveals various grain types forming the framework of the rock samples and the pore space fillers (clay) between these grains. Grain types include detrital mineral grains (quartz, micas and heavy minerals). The rock types identified in samples are mainly argillaceous mudstones. It has very low inter-granular porosity of about 1 or <1 percent and mainly filled with cementing material clay. The fractures and micro-faults observed in core samples also attributed porosity to shale.c.