含夹层盐岩储气库气体渗透规律研究

RESEARCH ON GAS SEEPAGE LAW IN LAMINATED SALT ROCK GAS STORAGE

盐岩储气库气体密封性能是储气库的一项重要技术和安全指标,层状盐岩储气库极可能会使天然气沿着岩层逃逸,造成天然气的外部渗漏。含软弱夹层盐岩储气库的气体渗透机制十分复杂,含软弱夹层的渗流力学模型与数值计算方法是解决评估储气库气体渗透范围的关键。考虑夹层与盐岩层之间存在层面,假设软弱夹层和盐岩为多孔介质,建立了等效边界气体渗流模型,该模型既克服了等效介质模型不能正确反映层理面渗流问题,又克服了双孔双渗裂隙介质模型计算量大的缺点。结合金坛储气库建设,数值仿真了储气库在注-采气不同循环压力作用下5a内围岩气体压力分布;研究了软弱夹层与盐岩的层理面渗透系数、采气速率和腔体群不同时注-采气等工况对储库围岩气体压力分布的影响。研究结果表明:层理面渗透系数对储气库压力分布有着至关重要的影响,溶腔群的采气速率和注-采方法对相邻矿柱的气体压力分布影响明显。研究结果为含夹层废弃盐腔储气库的设计和合理注采参数的确定提供了科学依据。

The sealing performance is an important technique and safety index for salt rock gas storage. For the salt rock gas storage containing weak interlayer, it is very possible that the natural gas will escape along the rock layer if appropriate measures are not adopted, which will lead to external permeability of natural gas. Gas permeability mechanism for the laminated salt rock gas storage is very complex. It is key problems to establish the permeability mechanical model and to put forward corresponding numerical method which is suitable for salt rock with weak interlayer based on seepage theory in porous media. It is assumed that the weak interlayer and salt rock are isotropic porous media. The interface between salt rock and weak interlayer is assumed as a fracture with a certain thickness. Based on the related theory, the equivalent-boundary model of the gas permeability is established. This model can reflect the fracture flow which is different from the equivalent medium model, and its computational complexity is less than that of double-permeability model. Combining with the field situation of Jintan gas storage, the pressure distributions of storage with different cyclic pressures for gas filling and gas recovery in five years are studied. The effect of permeability of interface between salt rock and weak interlayer on pressure distribution is analyzed. It is concluded that the effects of permeability on gas pressure distribution are very important. The scientific basis is provided for the design of salt rock gas storage with weak interlayer and reasonable choice of operating pressure.