不同应力和孔隙压力作用下致密煤岩渗透率演化规律

Study on Permeability Evolution of Tight Coal Under Different Stress and Pore Pressure Conditions

针对煤岩渗透特性非常复杂且存在显著的应力敏感性这一问题,利用自主研发的恒温超低渗透率测量系统,采用压力脉冲法对贵州龙凤井田的致密煤岩开展了气体渗透试验,系统研究了渗透率的演化规律及影响因素。结果表明:静水压力不变时,煤岩渗透率受有效应力和孔隙压力的共同影响呈现先降低、后升高的趋势,有效应力与孔隙压力之间存在明显的耦合效应;煤岩渗透率随有效应力增加或者孔隙压力升高均呈现幂函数形式降低,下降速率逐渐减小,呈现较高的应力敏感性,但有效应力和孔隙压力的作用机理有所区别;煤层气抽采过程中可通过适当降低储层有效应力的方法增大储层渗透率,提高煤层气抽采效率。

The coal permeability is very complex with significant stress sensitivity. A self-developed constant temperature ultra-low permeability measurement system combined with pulse decay method was used to carry out the gas permeability test on the tight coal in Longfeng coal mine, Guizhou province. The evolution law and influencing factors of permeability were studied systematically. Results show that: under constant hydrostatic pressure, the coal permeability is affected by effective stress and pore pressure, which tends to decrease first and then increase, there is a significant coupling effect between effective stress and pore pressures;the coal permeability decreases with the increase of effective stress or pore pressure in the form of a power function, and the decline rate gradually decreases, showing higher stress sensitivity, but the mechanism of effective stress and pore pressure is different;in the process of coalbed methane(CBM) extraction, the reservoir permeability can be increased by reducing the effective stress of reservoir to improve the drainage efficiency of CBM.