Geochemical and mineralogical controls on the geomechanical properties of the Eze-Aku Shale: Implications for a potential hydrocarbon reservoir

Abstract

Oil and Gas Shales are becoming major contributors to the daily crude output in the global energy market. Due to permeability concerns, they require hydraulic fracturing to be commercially productive. Analysing their geomechanical properties and mineralogical influences is key to understanding the fracability and production optimization of shale reservoirs. To this regard, this study evaluates the geomechanical, geochemical and mineralogical properties of the Eze-Aku Shale. Twenty Eze-Aku Shale samples were collected from four locations (Onoli-Awgu, Lokpanta, Okopsi and Aboine) in the Southern Benue Trough. The samples were analyzed to determine composition of major oxides and minerals using Energy Dispersive X-Ray Fluorescence (EDXRF) spectrometry and X-Ray Diffraction (XRD) technology respectively. Parameters such as static Young's modulus and Poisson's Ratio were determined following the International Society for Rock Mechanics (ISRM) standard to define the brittleness and fracability of the shale samples. Average mechanical properties ranged from 0.07 to 0.13 GPa and 0.7–9.8 for Young's modulus (E) and Poisson's ratio (v) respectively. The ratio of Young's modulus to Poisson's ratio negatively relates with clay mineral presence (Illite, Kaolinite and Muscovite) in Okposi and Aboine while in Lokpanta and Onoli-Awgu these parameters however, relate positively with Calcite and Quartz. Good hydraulic fracture performance is linked to brittleness and high Young's moduli, which is favoured, by high silica and carbonate content. This research thus reveals that the mineralogy of the Eze-Aku Shale has prevailing effects on its geomechanical properties. In Lokpanta and Onoli-Awgu however, the shale can be compared most notably to the Barnett Formation (Shale), Eagle Ford Shale and Marcellus Formation.