天然气水合物二次生成及渗透率变化对降压开采的影响

在 考虑天然气水合物二次生成及渗透率变化的基础上,建立了实验室尺度下的天然气水合物降压开采数学模型。利用该数学模型,对天然气水合物降压开采过程中的水合物二次生成进行了模拟,并分析评价了水合物二次生成及渗透率变化对水合物分解产气的影响。模拟结果表明:水合物二次生成主要局限于降压产气出口附近,二次水合物现象会引起局部水合物饱和度及温度、压力等发生明显变化;同时,水合物二次生成会导致产气速率大幅降低、产气持续时间延长和系统压力急剧增加,但累积产气量不受其影响。研究发现,不同于纯降压产气过程,在水合物二次生成的情形下,产气受出口压力的影响较大,而初始温度对产气的影 响较小。

Influences of gas hydrate reformation and permeability changes on depressurization recovery

In the consideration of natural gas hydrate reformation and its permeability changes, a mathematic model was built for the laboratory-scale depressurization recovery of natural gas hydrate, so as to simulate gas hydrate reformation in the depressurization recovery process of natural gas hydrate and analytically evaluate the influences of gas hydrate reformation and its permeability changes on hydrate decomposition for gas recovery. The simulation results indicate that hydrate reformation mainly occurred in the vicinity of depressurization recovery outlet, leading to significant changes in local hydrate saturation, pressure and temperature. Meanwhile, hydrate reformation will result in a great reduction of gas recovery rate, the prolongation of gas recovery duration and abrupt increase of system pressure, but the cumulative gas output will not be affected. Research results indicate that it is different from pure depressurization recovery that under the case of hydrate reformation, gas recovery rate is greatly affected by outlet pressure, while initial temperature has less impact on gas recovery.