注热CO_(2)增产CH_(4)过程数值模拟研究

Numerical simulation of heat CO_(2)injection to increase CH_(4)

通过建立二元气体扩散场—渗流场—传热场的耦合方程,利用COMSOL模拟了不同温度和压力下CO_(2)驱替CH_(4)过程中驱替效果、CO_(2)储存量、CH_(4)产量及煤体渗透率等的变化规律。结果表明:CO_(2)驱替作用会导致煤体部分区域出现CH_(4)压力上升高于原始储层压力的现象。随着驱替压力的增大,CO_(2)储存量与CH_(4)产量增加,当驱替压力由2 MPa增高到6 MPa时,驱替比由2.85增大到4.38。而当注入温度从20℃增高至100℃时,驱替比由4.38降低至4.34。在驱替开采过程中,驱替压力是影响驱替效果的主要因素。随着驱替的进行,CO_(2)影响范围逐渐增大。在CO_(2)影响区域,CO_(2)的注入对煤层渗透率影响较大,煤基质对CO_(2)的吸附使煤层渗透率迅速下降;而在CO_(2)未影响区域,煤体渗透率随着CH_(4)的解吸而增大。

In this study,the coupling equation of binary gas diffusion-seepage-heat transfer field was established.COMSOL was used to simulate the change laws of displacement effect,CO_(2)storage,CH_(4)production and coal permeability during CO_(2)displacement of CH_(4)at different temperatures and pressures.The results show that CO_(2)displacement will lead to CH_(4)pressure rising higher than the original reservoir pressure in some area.CO_(2)storage and CH_(4)production increase with the increase of displacement pressure.When the displacement pressure increases from 2 MPa to 6 MPa,the displacement ratio increases from 2.85 to 4.38.However,when the displacement temperature increases from 20℃to 100℃,the displacement ratio decreases from 4.38 to 4.34.In the process of displacement mining,displacement pressure is the main factor affecting the displacement effect.With the displacement,the influence range of CO_(2)gradually increases.In the area affected by CO_(2),the CO_(2)injection has a great influence on the permeability of coal seam,the adsorption of CO_(2)by coal matrix makes the permeability of coal seam decrease rapidly.In the area unaffected by CO_(2),the coal permeability increases with the desorption of CH_(4).