粉土中二氧化碳水合物分解过程的核磁试验研究

A NMR-based analysis of carbon dioxide hydrate dissociation process in silt

多孔介质中天然气水合物的相变条件及分解过程是研究水合物开采的核心问题.本文基于核磁共振技术探测了粉土中二氧化碳水合物分解过程中液态水的含量与分布并计算了水合物饱和度.实验结果表明在水合物分解过程中随着温度的升高小孔隙中的水合物先分解,随后大孔隙中的水合物开始分解;由分解过程中试样表面弛豫率并没有发生变化,可以排除水合物在土颗粒表面形成的现象,推断水合物应该赋存在粉土孔隙中间位置;粉土中二氧化碳水合物的相平衡条件为P-T-S_h空间中的一条曲线,代表了具体的试验路径;试验前后粉土T_2分布曲线变化较大,说明水合物生成与分解过程中试样微观结构发生了变化,主要表现为小孔隙体积变少,相应的大孔隙体积变多;在4°C时随着二氧化碳的消耗,水合物饱和度反而有轻微降低的现象,表明试验过程中水合物水合数变小.

It is necessary to determine the equilibrium condition and dissociation process of natural gas hydrate in porous media in the evaluation and recovery of natural gas hydrate as an energy resource. Based on the NMR technique, the liquid water content and distribution during hydrate dissociation process in the silt were detected and the hydrate saturations were calculated. The results showed that the hydrate in the small pores dissociated first as the increase of temperature, and then the hydrate in the macropores began to dissociate. Since the surface relaxivity of sample kept unchanged during the hydrate dissociation process, it was inferred that the hydrate cannot coat soil particles and hydrate grown in the middle of pore. The phase equilibrium condition of carbon dioxide hydrate in silt was a curve in P-T-Sh space, which indicated the specific experimental path. Variation of T2 distribution curves of silt before and after hydrate formation/dissociation verified the microstructure alteration during the test and small pores decreased and correspondingly large pores increased. As the temperature increased to 4°C, hydrate saturation decreased with carbon dioxide consumption, which indicated that hydrate number decreased during hydrate dissociation process.