摘要
天然气水合物是突破世界能源瓶颈的重要潜在途径,降压法是目前公认最经济有效的开采方法。降压开采时会引起固相水合物分解、液气产生与运移、热量传递及沉积物骨架变形,表现出温度场、液气渗流场、应力应变场间强烈的热-水-力(T-H-M)耦合响应,易诱发开采井倾斜、储层塌陷等灾变。基于开源有限元平台Open Geo Sys及其已有的饱和土T-H-M耦合模型,通过嵌入水合物动力分解方程表征固相水合物分解为气液相过程,引入水气质量守恒描述液气相变特性;在此基础上采用非线性互补方法(nonlinear complementary problem,简称NCP)结合特殊主变量选取严格框定液气饱和度范围,并将水合物动力分解速率与控制方程源汇项予以关联;构建了开源的水合物开采T-H-M耦合分析模型。通过与室内降压分解试验和大尺度数值模型对比,验证了该模型的适用性和正确性,并探讨了水合物开采过程中孔隙水压缩性对沉积物T-H-M耦合过程的影响。结果表明:本模型求解水合物分解引起的固液气相变与液气相生成或消失等强非线性问题时稳定性好;降压开采过程中水合物由近及远逐渐分解,产生气液逐渐向边界处运移并逐渐达到稳定运移状态,气、液相饱和度渐趋稳定;受气相溶解的影响,气相饱和度发展滞后于液相饱和度;高孔隙压力下孔隙水压缩性对远端孔压与骨架变形影响显著。
Natural gas hydrates are considered as one of the most important potential alternatives for energy shortage,and depressurization is believed to be the most economic effectiveness for hydrate exploitation.The exploitation induces solid hydrate dissociation,liquid/gas generation and migration,heat transfer and skeleton deformation,showing strong thermo-hydro-mechanical(THM)coupling behavior of sediments.These processes will trigger geotechnical hazards,such as borehole inclination and reservoir collapse.A THM coupling numerical model for hydrate exploitation was developed based on the open-source FEM platform OpenGeoSys.In detail,the kinetic reaction equation was implemented to represent the liquid/gas generation during gas hydrate dissociation.Air and water mass balance equations were introduced to illustrate the phase change between liquid and gas phases.Besides,the nonlinear complementary problem(NCP)combined with the choice of special primary variables was adopted to strictly constrain the liquid/gas saturation,and kinetic reaction rate was connected to the source/sink terms of governing equations.The model was validated and verified through a test and a large-scale numerical model,and the effects of pore water compressibility on the THM coupling response of hydrate-bearing sediments were discussed.Results show that the model was numerically stable in dealing with the nonlinear problems of phase change among solid,liquid and gas phases,and of phase appearance/disappearance of pore fluids caused by hydrate dissociation;the hydrates dissociate from near to far regions,and the produced gas/liquid gradually migrated to the driving well and reached a steady state,where the gas/liquid saturation tended to be stable;due to the influence of air dissolution,the evolution of gas phase saturation lagged behind that of the liquid saturation;the pore water compressibility had a non-negligible effect on the dissipation of pore pressure and skeleton deformation under large pore pressure.
作者
叶智刚
王路君
朱斌
陈云敏
YE Zhi-gang;WANG Lu-jun;ZHU Bin;CHEN Yun-min(Key Laboratory of Soft Soils and Geoenvironmental Engineering of the Ministry of Education,Zhejiang University,Hangzhou,Zhejiang 310058,China;Institute of Geotechnical Engineering,Zhejiang University,Hangzhou,Zhejiang 310058,China;Center for Hypergravity Experimental and Interdisciplinary Research,Zhejiang University,Hangzhou,Zhejiang 310058,China)
出处
《岩土力学》
EI
CAS
CSCD
北大核心
2023年第11期3191-3202,共12页
Rock and Soil Mechanics
基金
中央高校基本科研业务费专项资金(No.226-2023-00083)
国家自然科学基金(No.51988101,No.52078458)。
