盐穴储气库垫底气利用方案研究

Research on the withdrawal of cushion gas in salt cavern gas storage

为保证盐穴的安全,盐穴储气库运行过程中留有垫底气,这是盐穴储气库的特点之一,也是盐穴储气库的缺点。为充分利用盐穴储气库的垫底气,首先介绍了紧急工况下的最小运行压力概念,并给出基于屈服-扩容-破坏复合强度理论的设计准则,该方法能够采出部分垫底气;其次,为了置换出全部的垫底气,提出饱和卤水置换盐穴储气库垫底气的技术方案,该方案能够置换出全部的垫底气,但该方案需要大量的饱和卤水;然后,提出采用高压空气置换盐穴储气库垫底气,利用饱和卤水作为隔离介质,高压空气推动饱和卤水,饱和卤水推动天然气来置换出全部垫底气,该方案仅需一口溶腔的饱和卤水作为隔离介质,就可以用空气置换出全部的垫底气,但置换效率受制于液体的流动速度;最后介绍了一种内胆式盐穴储气库,该型储气库为无垫底气式储气库,能够高效采出全部的天然气,并能保持盐穴内压在一个较高的压力水平,有利于盐穴的稳定,能够延长其使用年限。

The prevailing cushion gas in underground gas storage(UGS)in salt caverns during the withdrawal period can ensure the safety of salt caverns,which is both a characteristic and a shortcoming of UGS in salt caverns.To withdraw the cushion gas in the natural gas salt caverns,the concept of minimum pressure in emergence(MPE)is introduced initially and the design criteria based on the yield-dilation-failure(YDF)strength theory is also given,with which part of the cushion gas could be withdrawn.Afterwards,to withdraw all the cushion gas,a technique proposal on replacing the cushion gas with saturated brine is proposed.However a mass of saturated brine is required for the replacement.To avoid this limitation,the replacement of cushion gas with high pressure air was then proposed.The high pressure air may drive the saturated brine that was used as quarantine medium,which may drive the natural gas to replace all the cushion gas.This method could withdraw all the cushion gas,but the replacement rate was restricted by the brine flow velocity.Finally,an UGS salt cavern with inner container is proposed,which is a non-cushion gas salt cavern,from which all the cushion gas could be withdrawn and whose average pressure could be kept at a higher level,thus bringing significant benefits to the stability and lifetime of salt caverns.