Physical controls on water migration in elemental sulphur blocks

Abstract

Elemental sulphur (S⁰) is produced from processing bitumen from the oil sands region, Alberta. Long term storage of this S⁰ is under consideration. The objective of the current study was to determine the controls on water migration in variably saturated S⁰ blocks. Based on visual observations of S⁰ blocks, they were characterized as a hydrophobic fractured porous media. Thus, measurements of the hydraulic characteristics, including porosity (n) and hydraulic conductivity (K) of the matrix and the fractured media, were undertaken. These data were used to create characteristic relationships of unsaturated K (Kunsat) and volumetric moisture content (θ) change with change in positive injection pressure (Ψ). Analyses showed that the mean total matrix n (nₘ) was 0.094 ± 0.035 (n = 280), the mean n available for water migration (nₐ) was 0.065 ± 0.044 (n = 8) and the mean (geometric) K for the matrix was 2.0 x 10⁻⁶ ± 2.1 x 10⁻⁶ ms⁻¹. In the case of vertical fractures, the aperture frequencies were measured to be 2.5, 10.0 and 21.0 m⁻¹ for fractures with apertures > 1.4, 1.4 to 0.6 and < 0.6 mm respectively while the frequency of horizontal fractures, were measured to be 1.7 and 3.7 m⁻¹ for with apertures > 1.4, and < 1.4 mm respectively. The fracture n (nᶠ) was determined to be 0.0135. θ – Ψ relationships were determined for both the fractured and non fractured media. From these plots, water entry values of 9 mm and 1 m were determined for the fracture pore space and the matrix pore space, respectively. Simulations of packer tests resulted in a bulk saturated Kᵇ) values ranging from 8.5 x 10⁻⁵ to 2 x 10⁻⁴ ms⁻¹ above 9 m depth and 3 x 10⁻⁶ to 1.5 x 10⁻⁵ ms⁻¹ below 9 m depth. Coupled Kunsat – Ψ and θ - Ψ relationships were used to conceptually describe water migration in S⁰ blocks under different precipitation and mounding conditions. These plots also showed that the Kᵇ is dominated by the fractures.