Stability Assessment of Salt Cavern Roof Beam for Compressed Air Energy Storage in South-Western Ontario

Abstract

Due to the intermittent nature of renewable energy sources, application of energy storage systems is an important part of the development in support of clean technologies. Compressed Air Energy Storage (CAES) plants can provide utility scale storage by compressing air into a reservoir during off-peak period and generating electricity by expanding the air when energy demand is high. CAES is a proven technology that offers various services to the power network and provides flexible load management; however, site selection is a critical step during the design process of a plant. Salt deposits are recognized as potentially suitable geological layers for a compressed air energy storage system. In south-western Ontario, salt beds of the Salina Group of the Michigan basin provide suitable salt deposits for the excavation of storage caverns. Only two salt beds of the Salina Group are thick enough for excavation of a cavern, these are known as the unit A2 and unit B salt beds. In the case of an underground storage system, stability and serviceability of the storage cavern must be investigated using geomechanical models. Geomechanical issues may cause serious damage to the cavern, which could stop the system from functioning. The stability of the cavern roof layer has been investigated using voussoir beam theory. This method has been widely used to model rock mass behavior around underground openings. The results of the analytical solution have been validated against an existing case and verified by using a Universal Distinct Element Code (UDEC). The stress distribution within roof beams is investigated and upper and lower limits of roof size have been determined. Based on the findings from numerical analyses, assumptions of the voussoir method iv oversimplify the problem and cause inaccurate results. Hence, the selected iterative solution has been modified using a nonlinear approach. The updated procedure significantly enhanced the consistency of the results obtained from analytical solution with numerical models. To demonstrate validity of the modifications, a systematic parametric study has been included by using a wide range of beam parameters. The impact of creep behavior of the roof beam was examined by adding the deformation due to steady state creep to the elastic response of the beam. Also, the effect of the pressure difference around the cavern roof has been examined to determine maximum and minimum pressure inside the cavern with respect to size of the roof layer.