含天然气水合物沉积物分解过程的有限元模拟

FEM-based simulation of decomposition process of gas hydrate-bearing sediments

温度和压力的变化会引起含天然气水合物沉积物的分解,其过程伴随着相态转换、孔隙水压力和气压力耗散、热传导、骨架变形等过程的相互耦合作用。基于多孔介质理论建立了描述含天然气水合物沉积物分解过程的数学模型,考虑了水合物分解产生的水、气流动、水合物相变和分解动力学过程、热传导、骨架变形等过程的耦合作用。基于有限元法,建立了模拟水合物分解过程的数值模型,并编制了计算机分析程序。通过对降压法和升温法开采过程的数值模拟,揭示了在水合物分解过程中沉积物储层的变形、压力、温度等因素的变化规律。结果表明:降压法和升温法都会导致储层变形以及产生超孔隙压力,但两种方法作用效果不同;同时,水合物分解过程包含渗流及热传导作用。

The variation of temperature and pressure may lead to decomposition of gas hydrate in a hydrate-bearing sediment（HBS）;meanwhile,several coupling processes are induced,including phase transition,pore water and gas pressures dissipation,heat transfer and skeletal deformation.A mathematical model is developed to describe the decomposition process of gas hydrate-bearing sediments based on the theory of porous media.The model properly considers the coupling effect among pore water/gas flow,phase transition,the kinetic process of hydrate dissociation,heat transfer and the skeletal deformation.Based on the finite element method,a numerical model describing the process of gas hydrate decomposition is developed and a computer program is compiled.Through numerical simulation of both depressurization-based and heating-based production processes,variation of displacement,pore pressures,temperature and other parameters in gas hydrate bearing sediments reservoir are analyzed.The results indicate that reservoir deformation and excess pore pressure are induced by depressurization and heating method with varying degrees,meanwhile,the seepage and heat conduction are contained in the gas hydrate dissociation process.