Abstract:

With the development of gas hydrate exploitation in the deep sea, there is an urgent need to solve basic problems, such as the reformation of hydrate and sand production in the wellbore. At present, there are few research reports on the reformation of hydrate in a stirred system containing fine-grain sands. By selecting fine-grain sand with size of 3.7—10.3μm, changing the sand concentration (0.6%, 1.6% and 5.0%), salt concentration (0.1%, 0.6% and 1.0%) and sand salt ratio, the influence of sand and salt on the secondary formation kinetics of methane clathrate under high pressure (8MPa) was studied. The results show that: ① compared to the primary induction period, the shortened time of the secondary induction period increased with the decrease of sand particle size within the range of 3.7—10.3μm; ② The fine-grain sand at concentrations of 0.6% and 1.6% promoted the secondary nucleation of hydrates; ③ In the range of 0.1% to 1.0% salt concentration, the higher the salt concentration, the closer the final gas consumption and maximum gas consumption rate of the primary and secondary generation of hydrates were, and the more significant the inhibitory effect of salt on the "memory effect" of hydrates was; ④ Under the conditions of low (0.6%∶0.1%), medium (1.6%∶0.6%), and high (5.0%∶1.0%) salt sand concentration ratios, as the sand salt ratio increased, the induction period for primary hydrate formation shortened, and the induction period for secondary hydrate formation increased. All systems had shorter induction periods for secondary formation than the induction period for primary formation, and as the ratio increased, the difference between the two induction periods decreased. It was concluded that sand particles could promote reformation kinetics in the stirring system, while salt would inhibit reformation kinetics. However, the effect of the concentration proportion of fine-grain sand and salt on the kinetics of secondary hydrate formation depended on the concentration.

Key words: gas hydrate, reformation, fine-grain sand, induction time, formation kinetics

摘要：

随着深水浅层天然气水合物试采工作的开展，亟需解决井筒含砂条件下水合物二次生成的问题，目前鲜见针对含粉砂及盐体系内水合物二次生成动力学的研究报道。本文选取粒径3.7~10.3μm粉砂砂粒，通过改变粉砂浓度（质量分数0.6%、1.6%和5.0%）、盐浓度（质量分数0.1%、0.6%和1.0%）以及砂盐配比度，研究高压条件下（8MPa）粉砂和盐对甲烷水合物二次生成动力学的影响规律。结果表明：①在砂粒粒径3.7~10.3μm范围内，相较于初次生成诱导期时间，二次生成诱导期缩短的时间随着砂粒粒径的减小而延长；② 0.6%和1.6%质量分数下的粉砂对于水合物二次成核具有促进作用；③在0.1%~1.0%含盐质量分数范围内，盐浓度越高，水合物初次和二次生成最终的气体消耗量以及最大气体消耗速率越接近，盐分对水合物“记忆效应”的抑制作用越明显；④在盐砂质量分数配比分别为低（0.6%∶0.1%）、中（1.6%∶0.6%）、高（5.0%∶1.0%）条件下，随砂盐配比度的增加，初次水合物生成诱导期逐渐缩短，二次水合物生成诱导期逐渐增长，所有体系二次生成诱导期均比初次生成诱导期短，且随配比度的升高，两次诱导期差值减小。结论认为，搅拌体系内水合物二次生成过程中，粉砂能够促进甲烷水合物的二次生成动力学，盐分则具有抑制作用，但两者的配比对水合物二次生成动力学的影响则取决于两者的浓度。

关键词: 水合物, 二次生成, 粉砂砂粒, 诱导时间, 生成动力学