注能(以CO_2为例)改性驱替开采CH_4理论与实验研究

在简述煤层气开采技术发展历程基础上,针对煤层气抽放开采率低的问题,提出了注能改性驱替开采煤层气技术,并从有效应力与热力学原理,能量平衡理论等方面进行了可行性分析。通过自主研发系列实验设备,对大尺寸、低渗透煤样进行了不同应力与温度条件下的渗透与驱替置换实验,揭示了注CO_2驱替开采煤层气的机理、规律与特征。研究结果表明:CO_2在煤体表面的吸附势大于CH_4,CO_2吸附引起的煤体表面自由能变化和吸附热均强于CH_4,注能(CO_2)有助于煤层气采收率提高;在一定的约束应力条件下,注入压力升高,CO_2吸附引起的煤体表面自由能变化和吸附热升高,同时作用在煤体上的有效应力降低,煤体的渗透性增强,CO_2驱替置换效果提高,反之,注入压力不变约束应力增大,有效应力增加,煤体渗透率降低,驱替置换效果变差;煤体对超临界态CO_2有很强的吸附性,在较大的有效应力和较低渗透率条件下,依然能保持较高的CO_2/CH_4置换率;提高注入CO_2温度,有助于部分吸附CH_4解吸,但同时煤体对CO_2吸附能力也减弱,导致CO_2/CH_4置换率有所降低。

Theory and experimental study of CBM recovery driven by energy boosting

It is an important issue to enhance coalbed methane (CBM) recovery in the development of CBM industry.This paper systematically elaborates the method of energy boosting for enhancing CBM recovery.The model of the energy transformation was built and the feasibility of this method was analyzed by thermodynamics.Furthermore,a large number of experiments were conducted to investigate the CO2 enhanced CBM recovery.The results show that ① the adsorption potential of CO2 is greater than that of CH4 on the surface of coal matrix.The variations of surface free energy and adsorption heat of coal due to CO2 adsorption are greater than that due to CH4 adsorption.② Under constant confining stress,the increase of the CO2 injection pressure promotes the change of the surface free energy and the adsorption heat.Meanwhile,the effective stress decreases due to the progressive injection pressure,which increases the permeability,resulting in the promotion of the CO2/CH4 displacement rate.On the contrary,under constant injection pressure,the effective stress increases due to the progressive confining stress,leading to the decrease of coal permeability,which has a negative effect on the displacement rate.③ Supercritical CO2 is more adsorptive to coal than gaseous CO2,leading to a high CO2/CH4 replacement rate under great effective stress.④ Increasing the CO2 injection temperature will contribute to the desorption of some adsorbed CH4,but it has a negative effect on CO2 absorption,leading to the decrease of the CO2/CH4 replacement rate.The study provides a theoretical and technical method to improve the existing CBM extraction technology and enhance the CBM recovery.