不同饱和度的天然气水合物注热开采动态实验研究

Experimental Study on Heat Injection Production Performance of Natural Gas Hydrate(NGH)at Different Saturation

天然气水合物(NGH)的饱和度与水合物藏绝对渗透率(流动性)、产气能力及毛管压力存在极大的相关性,从而影响水合物分解的进程、含水合物层的温度、压力分布及产气规律。本文基于我国实际天然气水合物藏的饱和度分布情况,为减少由于水合物渗透率过小而造成的流体流动性差所产生的影响,通过室内水合物生成动力学装置,采用间歇注气方法合成20%~30%、30%~40%、40%~50%3组不同饱和度的水合物样品,并展开了注入流速为6 mL/min,注入温度为60℃的一维填砂管注热开采实验。实验结果表明,分解前缘、热前缘和注入热水前缘是3个不重叠的概念,由于热传导与对流换热的影响,以入口端为起点由前往后依次是热前缘位置、分解前缘位置、注入热水前缘位置;饱和度越大,热量损耗越大,注入热水温度较初始温度下降幅度越大,此时注入流速越接近分解前缘平均移动速率;累积产气量与完全分解所需时间随着饱和度的增加而增大,平均产气速率受两者的影响,先增大后减小,且随着饱和度的增大水合物藏渗透率减小,热量损耗变大,进而影响产气速率。

There is a great correlation between the saturation of natural gas hydrate(NGH)and the absolute permeability(fluidity),gas production capacity and capillary pressure of hydrate reservoir,which affects the process of hydrate decomposition,the temperature and pressure distribution of hydrate-bearing layer and the law of gas generation.Based on the actual saturation distribution of natural gas hydrate reservoirs in China,in order to reduce the impact of poor fluid fluidity caused by too small permeability of hydrate reservoirs,three groups of hydrate samples with the saturation of 20%~30%,30%~40%and 40%~50%were synthesized in a hydrate generation kinetic device by intermittent gas injection,and one-dimensional sand filling pipe thermal injection production experiment with injection temperature of 60℃and injection flow rate was 6 mL/min.The experimental results show that the decomposition front,heat front and injection hot water front are different concepts.Due to the influence of heat conduction and convective heat transfer,the position from front to back is heat front,decomposition front and injection hot water front.With the increase of saturation,the heat loss increases,and the decrease of injection hot water temperature increases compared with the initial saturation.At this time,the injection velocity is closer to the average moving rate of decomposition front.The cumulative gas production and the time required for complete decomposition increase with the increase of saturation.Affected by both,the average gas production rate first increases and then decreases.With the increase of saturation,the permeability of hydrate reservoir decreases,the heat loss increases,which affects the gas production rate.