摘要
海洋环境中天然气水合物的形成除了合适的温压条件外,还必须有充分的甲烷供给.本文介绍了甲烷-水体系的甲烷饱和溶解度、水合物体系中甲烷水合物溶解度计算方法.在气-液二相平衡甲烷饱和溶解度计算中,关键在于状态方程的选择和合适的混合规则的运用,Duan的计算模型在温度、压力和盐度变化上都具有很大的适用性,且易于应用.在含水合物的相平衡体系中,在已知组分和假定可能存在相的前提下,可利用模拟退火算法优化总吉布斯自由能,确定是二相还是三相体系,并求解甲烷水合物溶解度.在海水环境下盐的存在使平衡发生移动,利用德拜—休克尔理论或Pitzer电解质溶液理论校正盐度对于海水活度的影响,求解海水环境中甲烷水合物溶解度.基于气-液二相平衡理论的K-K方程,在临近水合物生成条件下实验或计算确定亨利常数等参数后,可计算三相平衡甲烷水合物溶解度,且简单易用.
Within gas hydrate stable zone in marine sediments, where pressure and temperature are suitable for gas hydrate formation, gas hydrate crystallizes only when dissolved methane concentration exceeds methane hydrate solubility. The calculation methods of methane saturation solubility in water-methane equilibrium system and methane hydrate solubility in hydrate system are introduced in this article. The key of calculating methane saturation solubility in vapor-liquid equilibrium system is the choice of equation of state and application of mixing rules. Duan＇s model has broad applicability in variation of temperature, pressure and salinity, and is easily to be applied. In phase equilibrium system containing gas hydrate, total Gibbs free energy is optimized using simulated annealing to determine existent equilibrium phases and methane hydrate solubility in liquid phase. This algorithm relies heavily on the initial guess about which phases exist and their approximate composition. In the pore water go marine sediment, however, the equilibrium is shifted by salts, Debye-Huckel or Pitzer electrolyte solution theory is employed to correct the influence of salt on water activity and on methane hydrate solubility. The K-K equation that is based on the theory of vapor-liquid equilibrium is also used to calculate methane solubility in three-phase equilibrium hydrate system. The parameters in this K-K equation, like Henry law constant, are experimentally determined under incipient clathrate hydrate formation condition or empirically computed.
出处
《地球物理学进展》
CSCD
北大核心
2007年第1期239-246,共8页
Progress in Geophysics
基金
中国科学院知识创新工程重要方向项目(KZCX3-SW-224)
中国科学院知识创新工程前沿领域项目(GJGCX-04-03)
国家自然科学基金项目(40572071)联合资助
关键词
相平衡
天然气水合物
甲烷饱和溶解度
甲烷水合物溶解度
phase equilibrium, gas hydrate, methane saturation solubility, methane hydrate solubility
