Abstract
Petroleum gas has been stored successfully in unlined caverns in Norway for more than 25 years. Air cushion surge chambers with compressed air have been in use since 30 years ago. The main containment principles are hydrodynamic control of the groundwater and permeability control of the rock mass. The groundwater level often needs to be secured by water infiltration through �curtains� of drill holes from the surface or designated galleries. Permeability reduction by systematic pre-excavation grouting may be necessary to limit water ingress during operation. Propane/butane and ammonia are stored both at natural rock temperatures at high pressures and chilled at lower pressure. The storage caverns are all unlined. Rock support by rock bolting and sprayed concrete is performed for stabilisation only. Experience shows that with the right combination of methods, it is possible to obtain safe operation without leakage, or with acceptable leakage in the case of compressed air storage. Some storage facilities did not achieve the wanted tightness at first, but remedial measures rectified the situation. The principles are applicable in a range of rock formations, and provide significant advantages compared to surface storage.