注CO_(2)提高页岩吸附甲烷采收率核磁共振实验

Nuclear Magnetic Resonance Experiment for Enhanced Recovery of Adsorbed Methane from Shale through Carbon Dioxide Injection

明确CO_(2)作用下页岩对CH_(4)的吸附解吸规律,对提高页岩气采收率具有重要意义。在明确目标页岩孔隙结构的基础上,引入核磁共振测试技术,分别开展了注CH_(4)和注CO_(2)吸附解吸实验,定量表征了CH_(4)的绝对吸附量,并研究了CO_(2)对页岩中CH_(4)吸附解吸的影响规律。结果表明:页岩中的CH_(4)以页岩表面的吸附态、孔隙中的游离态和颗粒之间的自由态赋存;核磁共振法计算的CH_(4)绝对吸附量大于热重法测定的过剩吸附量;CO_(2)能够解吸摩尔分数为21.8%~33.2%的吸附态CH_(4);吸附态CH_(4)解吸后会滞留在孔隙中成为游离态,但无法从孔隙中逸出成为自由态;注CO_(2)提高吸附气采收率的同时还应辅以二次水力压裂或CO_(2)干法压裂技术,以提高游离态CH_(4)向自由态的转化效率。研究成果可为提高页岩吸附CH_(4)采收率提供参考和借鉴。

It is very important to clarify the adsorption-desorption law of shale-adsorbed CH_(4)under the action of CO_(2)to improve the recovery of shale gas.On the basis of clarifying the pore structure of the target shale,the nuclear magnetic resonance(NMR)testing technique was introduced,the CH_(4)injection and CO_(2)injection adsorption-desorption experiments were carried out separately to quantitatively characterize the absolute adsorption amount of CH_(4),and the influence law of CO_(2)on the adsorption-desorption of CH_(4)in shale was investigated.The results show that CH_(4)in shale occurs in three states:adsorbed state on the shale surface,unbound state in pores and free state between particles;the absolute adsorption amount of CH_(4)calculated by NMR is greater than the excess adsorption amount determined by thermogravimetry;CO_(2)can desorb the adsorbed CH_(4)with molar fraction of 21.8%~33.2%;the adsorbed CH_(4)will remain in the pores as unbound state after desorption,but cannot escape from the pore space as free state;while CO_(2)is injected to improve the recovery of adsorbed gas,the secondary hydraulic fracturing or CO_(2)dry fracturing technology shall be adopted to improve the conversion efficiency of unbound state CH_(4)to free state.The research results can provide reference for improving the recovery of shale-adsorbed CH_(4).