Rock engineering problems related to underground hydrocarbon storage

AbstractOil and gas can be stored underground by a variety of means, such as in depleted oil and gas fields, in aquifers, in rock salt caverns, in unlined mined rock caverns, in lined shallow caverns and abandoned mines. Different types of underground storages require different geological and hydrogeological conditions and are associated with different rock engineering problems. However, the common issue is to ensure the gas- and oil-tightness of storage caverns. In other words, the stored oil and gas must not escape from the storage caverns. This may be realized by different means according to the types of storages and the sites geological conditions. There are basically two approaches of gas leakage control, i.e. permeability control and hydrodynamic containment. The latter involves the use of a water curtain system in many cases, which creates an artificial hydraulic boundary condition and helps to establish the required groundwater condition when needed. In addition to the common problems, the underground storage of liquefied petroleum gas (LPG) requires special attentions to the opening of rock joints, which result from the tensile thermal stress induced by the low storage temperature. Great care must be taken in choosing abandoned mines for oil and gas-storage since it is quite rare that the natural site conditions can meet the usual requirements, in particular for the gas tightness. The paper provides a general description of the gas leakage control for underground oil and gas storage projects, and addresses various rock engineering problems associated with selected types of storages in detail