高阶煤煤层气生产机理探究

Exploration of the CBM Production Mechanism of High Rank Coal

根据沁水盆地南部高阶煤煤层气的地质特征和生产特征,归纳了高阶煤煤层气生产变化规律,基于前人对煤层气生产特征的研究,探究了高阶煤煤层气生产机理,并通过数值模拟方法进行了验证。研究表明高阶煤煤层气生产机理为:排采过程中,近井带地层压力首先降低,但受到井控范围内远井带地层水补给,导致近井带含水饱和度下降缓慢;远井带由于无水补充,见气后含水饱和度降低,并向近井带推进,孤立气泡发展成连续气相;近井带含水饱和度高,气相渗透率低,形成"水锁效应";近井带含水饱和度降低到一定程度后,气相渗透率升高,突破"水锁效应",产气量明显增加。

According to the CBM geological characteristics and production features of high rank coal in the southern Qinshui Basin,the variation of CBM production is summarized.Based on previous analysis in gas production characteristics,the CBM production mechanism of high rank coal is explored and verified by numerical simulation.Studies have shown that CBM production mechanism of high rank coal is as follows：in the drainage process,the near-wellbore pressure drops first,but it is supplied by water far from wellbore within the well control,resulting in slow decrease of near-wellbore water saturation;due to no water supplement far from wellbore,water saturation decreases after gas appears,isolated bubbles develop into continuous phase,and drives to near-wellbore zone;because of high water saturation of the near wellbore zone,and low gas permeability,a ＂ water lock effect＂ appears;when the near-wellbore zone water saturation reduces to a certain extent,gas permeability increases,and gas production increases significantly,makes a breakthrough to ＂water lock effect＂.