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从描述天然气水合物系统的动力学模型出发,利用拟解析方法将纯甲烷气水合物系统的稳态模型推广到包含盐度的情况.基于包含盐度的这种新稳态模型,通过数值方法来确定甲烷气水合物稳定带(MHSZ)和甲烷气水合物实际存在区(MHZ)的顶界和底界、以及游离气存在区的顶界.数值结果表明,甲烷气水合物实际存在区的厚度随盐度的增大而变薄;盐的存在降低了气体水合物的稳定性,引起MHSZ的底界上移,进而导致水合物稳定带的厚度比纯水情况下的厚度变薄.另一方面,由于降低溶解度会减少形成水合物所需气体的数量,所以海水中盐的存在可能会促进更多天然气水合物在稳定带的形成.数值模拟结果也表明,对于盐水情况,在天然气水合物稳定区甲烷气的存在并不能充分保证气体水合物的生成,只有当溶解于盐溶液中的甲烷气浓度大于盐水中的甲烷气溶解度,并且甲烷气通量大于相应的甲烷气扩散传输率的临界值时,甲烷气水合物才会生成.为了保持海洋沉积物中气水合物的存在或形成甲烷气水合物,甲烷气源源不断的供给是必需的,只有这样,才能补偿因甲烷气扩散和对流所引起的损失,这些源源不断的甲烷气可能是源于微生物或者地热过程.
Based on the description of the kinetic model of gas hydrate system, the steady-state model of pure methane gas hydrate system is generalized to include salinity by quasi-analytical method.Based on the new steady-state model including salinity, To determine the top and bottom boundaries of the MHSZ and the MHZ of the methane gas hydrate and the top boundary of the free gas zone.The numerical results show that the methane gas hydrate in the actual zone The thickness decreases with the increase of salinity; the presence of salt reduces the stability of gas hydrate and causes the bottom of MHSZ to shift upward, which leads to the thickness of hydrate stability zone becoming thinner than the case of pure water. On the one hand, the presence of salt in seawater may promote the formation of more gas hydrates in the stable zone due to the reduced solubility of hydrates, which reduces the amount of gas required to form hydrates. Numerical simulations also show that for brine conditions, The presence of methane gas in the stable zone does not adequately ensure the formation of gas hydrates, only if the concentration of methane gas dissolved in the brine solution is greater than the methane gas solubility in the brine and the methane gas Methane gas hydrates will only be formed if the flux is greater than the corresponding critical value for methane gas diffusion rates. A steady supply of methane gas is necessary to maintain the presence of gas hydrates in marine sediments or to form methane gas hydrates , The only way to compensate for the methane gas diffusion and convection caused by the loss of these continuous methane gas may be derived from microbial or geothermal processes.