Gas storage in unlined caverns - Norwegian experience over 25 years

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 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 (See Table 1). Experience confirms that: thorough geotechnical investigations are necessary; the rock cover must be sufficient to avoid hydraulic splitting; the groundwater level should be maintained during construction by water infiltration; water infiltration is an effective measure to maintain the groundwater level if used after pre-grouting; systematic pre-grouting with micro- and ultra-fine cements at high pressure is necessary if strict requirements to tightness shall be met; grouting of concrete plugs needs special attention; chilled storage has been successful down to -42 degrees C; it is important to have the water seepage under tight control and to follow proven cooling procedures to avoid leakage through the rock mass or around concrete plugs. Although a combination of methods may be needed for each plant, the hydrodynamic control applies primarily to pressurised storage, whereas permeability control is needed for chilled storage. (A). Reprinted with permission from Elsevier. For the covering abstract see ITRD E124500.