块状甲烷水合物分解动力学特征及其影响因素

与冷泉相关的块状甲烷水合物是非常规天然气资源开发的重点目标之一。为了了解其分解动力学特征以便于制订合理的开发方案，利用高压差示扫描量热仪实验测试了块状甲烷水合物的生成与分解过程，将分解的吸热效应与分解速度相关联，分析不同环境下块状甲烷水合物分解瞬时速度和平均速度的变化特征，然后，基于实验结果采用经典的甲烷水合物分解动力学模型计算得到不同压力下甲烷水合物分解活化能，进而评价分解表面积、温度、压力和矿化度等因素对甲烷水合物分解速度的影响。研究结果表明：①随着压力升高，甲烷水合物分解活化能逐渐增大，在此次实验测试条件下其数值介于27.5～28.5 kJ/mol；②在去离子水溶液中，甲烷水合物的分解瞬时速度呈现先增加后减小的趋势，在分解早中期其累计分解物质的量随时间的变化关系呈指数函数形式增长，后期则呈缓慢线性增长；③在孔隙水溶液中，甲烷水合物的分解瞬时速度也呈现先增加后减小的变化趋势，但较之于去离子水溶液，孔隙水溶液中甲烷水合物的分解瞬时速度峰值出现的时间较晚，孔隙水溶液矿化度对水合物分解速度的促进作用弱于温度的影响；④对影响去离子水溶液中块状甲烷水合物分解速度的因素按照影响程度由大到小排序，结果依次为分解表面积、温度、压力。结论认为，在储层改造的基础上，热激法是块状甲烷水合物开采的合理方式。

Dissociation kinetics characteristics of nodular methane hydrates and their influence factors

Nodular natural gas hydrates related to cold seep is one of the important development targets of similar unconventional natural gas resources. In order to understand the hydrate dissociation kinetics characteristics for a reasonable development scheme, this paper studied the formation and dissociation process of nodular methane hydrates by using the high pressure differential scanning calorimetry. Accordingly, the endothermic effect of dissociation and the dissociation velocity were correlated, and the change characteristics of instantaneous dissociation velocity and average dissociation velocity of nodular methane hydrates under different environments were analyzed. Then, based on the test results, the dissociation activation energy of methane hydrates under different pressures was calculated in the classical methane hydrate dissociation kinetics model. Finally, the influences of dissociation surface area, temperature, pressure and salinity on the dissociation velocity of methane hydrates were evaluated. And the following research results were obtained. First, the dissociation activation energy of methane hydrates increases gradually with the increase of pressure. And in this test, it is in the range of 27.5–28.5 kJ/mol. Second, the instantaneous dissociation velocity of methane hydrates in deionized aqueous solution presents a trend of increasing first and then decreasing. The cumulative amount of dissociation substances increases exponentially over the time in the early and middle stages of dissociation, but in a slow linear pattern in the late stage. Third, in the pore water solution, the instantaneous dissociation velocity of methane hydrates also presents a trend of increasing first and then decreasing. Compared with the deionized aqueous solution, however, its peak instantaneous dissociation velocity occurs later. The salinity of pore water solution has weaker promotion action on the hydrate dissociation velocity than the temperature. Fourth, the factors that influence the dissociation velocity of nodular methane hydrates in deionized aqueous solution are ranked as dissociation surface area ＞ temperature ＞ pressure. In conclusion, based on reservoir reconstruction, the thermal stimulation method is the reasonable production mode of nodular natural gas hydrates.