Physical and hydraulic characterization of fractured, hydrophobic sulphur within above-ground sulphur blocks

Abstract

Volatility in the price of sulphur has resulted in the temporary storage of sulphur in large, surface blocks at oil sands properties in northern Alberta, Canada, that are subject to oxidation which produces acidic effluent. Characterization of water storage and migration within these blocks is required to assess potential environmental impacts. Investigation of the elemental sulphur (S0) blocks at Syncrude’s Mildred Lake site included fracture mapping and laboratory testing of core samples for density and permeability to air and water. Internal porosity was mapped with X-ray tomography, and water-intrusion porosimetry was used to define saturation–pressure relationships. The blocks have regular polygonal fractures with a porosity of approximately 1.4%. The mean total and water-available porosity of core samples was 9% and 6%, respectively. The water-entry pressure head was 1–2 m for matrix pores, but only 1–2 mm for fractures. Estimated functional relationships for volumetric water content versus water pressure of the fracture and matrix system are used to illustrate how infiltration is likely to occur rapidly along fracture pathways but with insufficient pressure to allow water to penetrate the matrix, suggesting that acid production occurs by flushing of the fracture surface with little influence from the matrix.