Modelling the geomechanics of gas storage: A case study from the Iona gas field, Australia

Abstract

This paper presents a 3D geomechanical modelling study of the Iona gas storage facility in the state of Victoria, Australia. The results provide important information pertaining to gas storage, which can then be used to understand certain geomechanical aspects of CO2 storage. A key finding in this paper is that significant changes to the horizontal stress magnitudes are imparted by changes to the fluid pressure due to gas injection or withdrawal. This effect, known as the reservoir stress path, significantly influences fault stability by counteracting the changes to effective stress. In the case of Iona, pressurisation of the field results in a stress path which is parallel to the failure criterion rather than towards it, as would be expected in a classical treatment which does not incorporate complex poro-elastic effects. Another output of interest relates to reservoir deformation, which would be manifested at the ground surface as heave or subsidence. During periods of peak gas withdrawal and injection, surface ground movement is predicted to be on the order of −9mm and +2.5mm, respectively. These numbers are similar to the surface deformation observed at the In Salah CO2 injection project, but much smaller than the subsidence observed in some producing hydrocarbon fields.