【作者】 梁海峰；

【导师】 宋永臣；

【作者基本信息】 大连理工大学 ， 热能工程， 2009， 博士

【摘要】 面对当前能源短缺和环境恶化的严峻形势,寻求高效、清洁能源成为人类面临的迫切任务。甲烷水合物具有储量大、能量密度高、燃烧清洁等优点,被认为是21世纪最具开发前景的能源,开展甲烷水合物的基础物性及其开采技术的研究具有重要的理论和现实意义。本论文针对多孔介质中的甲烷水合物进行降压分解实验和数值模拟研究。建立了模拟多孔介质中甲烷水合物生成和分解的实验系统,测得了多孔介质中甲烷水合物的相平衡曲线。在此基础上,系统地进行了甲烷水合物的生成和降压分解实验研究,分析了开采动态及影响因素,结果表明边界传热能极大的影响水合物的分解速率。采用通入过量气体提高水转化率的定容合成甲烷水合物实验方法,较大程度上避免了在测量过程中水合物的生成和分解,国内首次利用甲烷测量了恒温恒压恒流条件下含不同水合物饱和度时多孔介质的绝对渗透率,通过与当前通用模型的比较,发现与Masuda渗透率模型拟合较好。建立了三维立方体孔隙网络模型,研究了孔径分布对水合物相平衡的影响,模拟了水合物在多孔介质中生成导致的渗透率变化,模拟结果与实验数据吻合较好,表明了采用孔隙网络模型可以在微观尺度上模拟多孔介质中水合物的生成和分解。考虑水、气、水合物三相,水、气、水合物三组分,根据质量守恒和能量守恒原理,考虑水合物在多孔介质中的生成分解动力学和热力学,建立了基于二维轴对称的甲烷水合物分解数学模型,采用全隐式方法进行求解。通过与实验结果对比,验证了数学模型的准确性。对实验室尺度下多孔介质中甲烷水合物降压分解进行了影响因素敏感性分析,结果表明,水合物分解速度常数、渗透率下降指数、气液两相相对渗透率、岩石导热系数、水合物藏初始温度和各相饱和度、出口压力以及边界传热等均会影响多孔介质中甲烷水合物分解速率。研究结果表明：气相相对渗透率的增加较相应液相相对渗透率的增加更能提高水合物的分解速率；对高饱和度的水合物藏,需要采用降压和注热联合开采；液相饱和度对水合物分解速率的影响存在一个最优值,大约为相应的有效残余饱和度；在较强边界传热条件下,累积产气量增加有限,而耗热量增加较多,且多孔介质区域内可能同时存在水合物生成和分解。更多还原

【Abstract】 Energy shortage and environmental pollution are serious problems we have to cope with in the world. Developing efficient and clear energy source has become an urgent task to solve these problems. Since Methane Hydrate (MH) has many advantages including a vast amount of reserve, high energy capacity and less pollution after combustion, it has been viewed as a potential energy source for the 21st Century. The studies on the basic properties and production techniques of MH are very important in theoretical and practical aspects.The physical modelings of MH formation and dissociation in porous media were conducted using a self-designed apparatus. The phase equilibrium curves of MH in porous media were measured, which are very consistent with those obtained by other researchers. Under our experimental conditions, the MH formation and dissociation in porous media by depressurization were studied and the production performance and influencing factors were analyzed. The results show that higher boundary heat can increase largely MH dissociation rate.MH in porous media was formed with constant volume method by injecting excess methane gas which can improve the water conversion rate as much as possible. The permeabilities of hydrate-bearing porous media were measured with methane, which decrease the effect that MH formation or dissociation during measurement on experiment data. The experiment results were compared with existing models and it was found that they were good fitting with Masuda’s model.A three-dimensional cubic pore network model was developed to model the phase shift of MH in porous media with different pore sizes. The permeability variation of hydrate-bearing porous media was studied. The simulation results are consistent with experiment data well, which shows that pore network model can be used to study MH formation and dissociation in porous media at micro scale.An advanced 2-D axisymmetric simulator including three phase (water, gas, and hydrate) and three components (water, gas, and hydrate) was developed based on the mass and energy conservation theory. The thermodynamic and intrinsic dynamic of MH in porous media are considered in the simulator. The governing equations are dicretized with finite difference method and solved with fully-implicit manner. The data matching was conducted using the mathematical model and the experimental results, which is consistent with each other and proves the accuracy of the mathematical model. The sensitive factors were studied for laboratory-scale MH dissociation by depressurization. The results suggest that intrinsic kinetic constant, permeability reduction index, gas-water relative permeability, rock heat conductivity, initial temperature, initial phase saturation, outer pressure and boundary heat transfer are sensitive for MH production by depressurization. The increase of gas relative permeability causes higher hydrate dissociation rate than the corresponding increase of water relative permeability does; the combination of depressurization and thermal stimulation is a better technique to explore MH in the MH reservoirs with high initial hydrate saturation; The initial water saturation has an optimum value for increasing hydrate dissociation rate and the value is about equal to the effective residual water saturation; Under the condition of higher boundary heat transfer, the increase of cumulative gas production is less than the increase of cumulative heat absorbed, the formation in some regions and dissociation in other regions maybe occur simultaneously.更多还原