页岩对甲烷高温高压等温吸附的热力学特性

Thermodynamic characteristics of isothermal adsorption of methane at high temperature and pressure in shale

为了研究页岩在高温高压条件下对甲烷的吸附特性,采用高压等温吸附实验仪,分析了取自贵州岑巩地区天马1井的页岩对甲烷的吸附效果,并根据lausius-Clapeyron方程和Vant-Hoff方程求得甲烷吸附的等量吸附热和极限吸附热,从热力学角度分析甲烷在页岩上的吸附特性。研究结果表明:贵州岑巩地区天马1井页岩对甲烷的等温吸附曲线形态在不同温度条件下基本一致,都存在着明显的极值点;在低压阶段,等量吸附热随吸附量的增加而逐渐增加,平均吸附热为43.59kJ/mol,表明可能发生了化学吸附;在高压阶段,等量吸附热随吸附量的减少而逐渐升高,表明随压力增加解吸更加困难;通过Vant-Hoff方程计算得到的极限吸附热为39.61 kJ/mol,表明天马1井页岩孔隙表面与甲烷气体之间的相互作用力较强。对于相互作用力较强的页岩,在页岩气开采过程中可以结合注入与页岩孔隙表面作用更强气体的方法来促进解吸,如CO_2等气体。

In order to investigate the adsorption characteristics of methane in shale under high temperature and high pressure conditions,the methane adsorption effects of shale examples,which were taken from Tianma No.1 well in Cengong area of Guizhou,were tested and analyzed using high pressure isothermal adsorption tester.Lausius-Clapeyron equation and Vant-Hoff equation were used to obtain the equal adsorption heat and limit isosteric heat of methane adsorption.The adsorption characteristics of methane on shale were analyzed based on the thermodynamics. The results show that the methane isothermal adsorption curves of shale from Tianma No.1 well in Cengong area of Guizhou are basically consistent under different temperature conditions with obvious extreme points. The thermodynamic analysis shows that the isosteric heat under low pressure increases with increasing adsorption capacity. The average isosteric heat is 43.59 k J/mol,indicating the existence of chemical adsorption.However,in the high pressure stage,with the removal of methane molecules from the surface of shale being more difficult,the amount of adsorption heat gradually increases with the decreasing adsorption capacity.The calculated limit adsorption heat through the Vant-Hoff equation is39.61 k J/mol,indicating that the interaction force between the shale surface and the methane is relatively strong in Tianma No.1 well.To promote the desorption of this type of shale with strong interaction force,the combined actions such as injecting more powerful gas that acts more strongly on the surface of shale such as carbon dioxide and other gases should be considered.