室内沉积物中天然气水合物形成数值模拟研究

室内模拟合成水合物沉积物样品是开展水合物研究的一个重要途径，但实验方式耗时且不易控制。数值模拟技术则能够比较方便定量地控制水合物形成条件，快速模拟其形成过程。据此采用实验室常用的恒容法模拟研究了水浴降温条件下，室内沉积物中天然气水合物的形成过程，进一步揭示了其形成和分布规律。研究结果表明，在混合均匀的气-盐水体系中，能够合成相对均匀分布的水合物模拟地层样品。但在体系温压条件趋于稳定后，仍需维持较长的反应时间来促使体系反应的最终完成。当体系中存在薄“夹层”(主要是指模拟介质中间区域的渗透率和孔隙度发生变化)时，薄“夹层”的渗透率和孔隙度都会对系统中水合物的形成过程产生一定的影响，但最终系统中的水合物饱和度分布与无夹层时基本相同，这可能是由于采用恒容法形成水合物，前期水合物生成速率快，多孔介质中的薄“夹层”对体系传质影响显著，后期由于反应速率变慢，其影响相对较小，在维持较长的反应时间后，趋于一致。

Numerical Simulation on Natural Gas Hydrate Formation withinPorous Media Using Constant Volume Method

Synthesizing samples of hydrate-bearing sediment in laboratories is an effective way to investigate the properties of gas hydrate occurring in nature.However,it is time-consuming and hard to manipulate.Numerical simulations can easily and quantitatively simulate hydrate formation in sediment by controlling any formation conditions.Therefore,in this work the numerical simulation method was introduced to study the formation process and distribution of gas hydrates in lab-scale sediment under the conditions of constant volume and water bath cycling.The results show that the hydrate sample with relatively uniform distribution can be produced in the well-mixed gas-brine system.However,a long reaction time is still required to ensure that gas hydrates have synthesized completely even though the system temperature and pressure tend to be stable.When an interlayer (i.e.,the permeability or the porosity in the intermediate part is different from its up and below parts) occurring in the sediment,both the permeability and the porosity of interlayer have effects on the formation of gas hydrate at the lab scale,but the final saturation distribution of gas hydrates in the medium is almost the same to that in homogeneous sediment.This could be mainly because the hydrate formation rate is rapid at the early stage,and the interlayer affects the mass transfer in the system significantly,as is opposite in the later period because of the slow reaction rate.After maintaining a long reaction time,the results tend to be consistent.