Storage of oil sand waste in sub-surface salt caverns: a feasibility analysis based on experimental rock mechanics and geological setting

Abstract

In order to reduce the environmental impact of heavy oil production operations in East-Central Alberta, hydrocarbon energy companies have been disposing production-related waste in solution mined sub-surface salt caverns. These caverns are situated in two bedded salt layers separated by approximately 150 m of mudstones and a thinner salt layer. In order to optimize well usage and improve project efficiency, two salt caverns per well are proposed, one in each salt formation. This study aims to provide a feasibility analysis for the proposed sub-surface storage based on a study of the geological setting combined with rock mechanical experiments. Analysis of the local and regional geology of the proposed cavern operation reveals a simple stratigraphy and tectonic stability. This implies that the project area is suitable for a salt cavern operation from a geological perspective. A total of 59 geomechanical laboratory experiments were performed on core samples to constrain the geomechanical properties of the formations involved in the salt cavern operation. These results were implemented in a FLAC3D (Fast Lagrangian Analysis of Continua in three dimensions) numerical model to investigate cavern stability, creep rates and surface subsidence. The results from this model imply that surface subsidence will be minimal (<12.1 mm over 50 years), shear stresses around the cavern will be low (<5MPa) and that failure will not occur.