Simulated weathering of oil shales from Rundle, Julia Creek and Green River: Effects on oil yields and kerogen composition

Abstract

An attempt has been made over 60 weeks to simulate experimentally the weathering of Rundle, Julia Creek and Green River oil shales. Finely-ground shales were subjected to three types of ‘weathering’: 1. (1) 22 °C in air without water or sunlight (‘internal’ conditions) 2. (2) 10–35 °C under water with sunlight (‘external’ conditions) 3. (3) 100 °C in air without water or sunlight (‘extreme’ conditions). All shales exhibited decreases in oil yields by Fischer assay, the highest loss being 90 wt % for Julia Creek shale under extreme conditions for 60 weeks. Solid-state 13C n.m.r. spectra of kerogens before and after weathering under extreme conditions for 60 weeks confirm increased aromaticity and greater concentrations of oxygenated functional groups. Elemental analyses show that, for these kerogens, H/C ratios decreased by ≈ 30% and O/C ratios increased by ≈ 300%. The results are important when considering natural geological weathering of shale seams, oxidation of stockpiled shale and prolonged drying of shale at elevated temperatures.