不同降压速率下天然气水合物垂直井分段降压开采特性试验研究

Experimental study on natural gas hydrate production characteristics in stepwise depressurization with vertical well at different depressurization rates

认识分段降压法对天然气水合物储层开采特性的影响规律,能够为提高天然气水合物开采的效率和可控性提供科学依据。为此,利用自主研发的大尺寸二维天然气水合物开采模拟试验装置,开展了3种不同降压速率下的天然气水合物单一垂直井分段降压开采模拟试验,研究了降压速率对降压开采过程中储层的压力响应、温度响应、产气量、瞬时产气速率以及平均产气速率等的影响情况。结果表明:压力变化速率的异常峰值现象的产生与回压阀密切相关,且其持续时间之比约等于降压速率的反比;相同降压幅度下,降压速率越小时,降压持续的时间越长,外部热量传递越多,促使更多的水合物在降压阶段发生分解,使得总产气占比越高;随着降压速率减小,峰值产气速率在第2次降压阶段内出现的时间越来越晚,水合物分解速率达到最大值的时间逐渐推后。

The study aims to investigate the impact of stepwise depressurization on the production characteristics of natural gas hydrate reservoirs to enhance the efficiency and controllability of hydrate production.A self-developed large-scale two-dimensional simulation test system was utilized to conduct stepwise depressurization experiments on a single vertical well of natural gas hydrate at three varying rates.The research focused on analyzing the effects of different depressurization rates on pressure response,temperature response,gas production,instantaneous gas production rate,and average gas production rate at the reservoir’s planar scale.The results indicate that abnormal peak phenomena in pressure change rate are closely associated with the back-pressure valve.The duration ratio is approximately inversely proportional to the depressurization rate.With the same depressurization magnitude,a lower depressurization rate results in a longer duration,enhancing external heat transfer and promoting greater hydrate decomposition during depressurization.This leads to a higher total gas production ratio.A decrease in depressurization rate delays the peak gas production rate in the second stage and shifts the time for maximum hydrate decomposition rate.