Large underground unlined rock caverns for storage of crude oil or liquid hydrocarbons are very often designed to operate with a gaseous phase maintained to a pressure range above atmospheric pressure(>1 bar abs.).To maintain the pressure of the gaseous phase in a cavern above atmospheric pressure it is necessary to inject a compensation gas(gas in)during the cavern emptying phase.The reverse operation(gas out)must be carried out during product filling to avoid overpressurization in the cavern.The management of this compensation gas requires a dedicated industrial unit for production,recovery,and treatment.In case of large underground caverns with net capacity of several million tons,the construction and operation costs for such a unit become prohibitive.To limit the need for compensation gas,the permissible pressure range in operation must be extended.Whereas the maximum gas pressure is mostly limited by the tightness issue,the minimum pressure is mainly governed by stability aspects.In this paper,the possibility of lowering the minimum pressure in operation below the atmospheric pressure is investigated,focusing on the cavern stability aspects.During construction at atmospheric pressure,for the large cavern section and rock mass quality expected,long-term stability can be achieved by conventional spraying of shotcrete and rockbolt installation.During operation,minimum pressure in the storage cavern close to vacuum is investigated and its impact on reinforcement need is reviewed using results of two distinct approaches: homogeneous continuum as well as wedge stability.The particularities regarding the required reinforcement for caverns operated at atmospheric pressure are also investigated.
展开▼
