储层条件下煤岩应力敏感性及对气井产能的影响

Stress sensitivity of coal reservoir and its influence on coal bed methane well productivity under reservoir condition

为深入研究煤层气井开采过程中煤岩储层产生的应力敏感性,通过自主研发的煤岩力热耦合渗流实验装置,开展了回压应力敏感实验。此实验在模拟煤储层原位地质条件下进行,通过下游出口端回压不断降低导致的渗透率变化反映整个开采过程中由于孔隙流体压力下降而产生的储层应力敏感性。借助实验数据拟合公式,在考虑煤储层应力敏感性条件下,推导了气体稳定流动的气井产能方程,并通过实例分析了应力敏感性的存在对煤层气井产能带来的影响。研究表明:考虑应力敏感时的气井产量比无应力敏感的气井产量有大幅降低;如果井底流压过低,产生的应力敏感性较强,会对地层产能造成浪费;井底流压过高,但产气量又会较低,因此为保证煤层气井在较高产量下生产,须建立合理的生产压差。

In order to further study the stress sensitivity of coal and rock reservoirs in the coal-bed gas well mining process,the back-compressive stress sensitivity experiment was carried out through the coal-rock thermal coupling seepage experiment device independently developed.The experiment was carried out under the simulated in-situ geological conditions of the coal reservoir,and the permeability change caused by the continuous decrease of the downstream outlet back pressure reflected the reservoir stress sensitivity caused by the decrease of pore fluid pressure during the whole mining process.With the help of experimental data fitting formula and considering the stress sensitivity of coal reservoir,the productivity equation of gas well with stable gas flow was derived,and the influence of the stress sensitivity on the productivity of coalbed gas well was analyzed through an example.The results show that the production of gas well with stress sensitivity is lower than that of gas well without stress sensitivity.If the bottom hole flow pressure is too low,the stress sensitivity will be strong,and the formation productivity will be wasted.The flow pressure at the bottom of the well is too high,but the gas production will be low.Therefore,in order to ensure the production of coalbed methane(CBM)wells at a high yield,a reasonable production pressure difference must be established.