液态CO_(2)驱替煤体CH_(4)的渗流特性及机制分析  

Seepage characteristic and mechanism during liquid CO_(2) displacing CH_(4) in coal seam

作　　者：李珍宝 王凤双 梁瑞[1] 赵海章 马吉昊 魏高明 LI Zhenbao;WANG Fengshuang;LAING Rui;Zhao Haizhang;MA Jihao;WEI Gaoming(College of Petrochemical Technology,Lanzhou University of Technology,Lanzhou,Gansu 730050,China;College of Safety Science and Engineering,Xi'an University of Science and Technology,Xi'an,Shaanxi 710054,China)

机构地区：[1]兰州理工大学石油化工学院,甘肃兰州730050 [2]西安科技大学安全科学与工程学院,陕西西安710054

出　　处：《采矿与安全工程学报》2022年第6期1265-1271,共7页Journal of Mining & Safety Engineering

基　　金：国家自然科学基金项目(51904138);甘肃省自然科学基金项目(20JR10RA194);兰州理工大学“红柳优青”计划项目(02-062001)。

摘　　要：煤层瓦斯抽采效率低是造成高瓦斯及突出矿井采掘接续困难和瓦斯事故频发的重要原因。液态CO_(2)具有低温致裂增透和相变置换驱替促抽瓦斯效应,可有效提高煤层渗透性。采用自主研发的三轴多相CO_(2)促抽煤层CH_(4)平台,分析了不同温度下的煤体抽真空-CH_(4)吸附-CO_(2)驱替全过程应变、驱替浓度、流量及渗透率的变化,揭示了液态CO_(2)驱替煤层CH_(4)过程机制。结果表明:在吸附CH_(4)及CO_(2)驱替阶段,煤体均表现为膨胀应变,各阶段应变分为快速膨胀和缓慢膨胀变形阶段,CO_(2)驱替阶段的应变量显著大于CH_(4)饱和吸附阶段的应变量,温度越低,应变差异性越大;驱替过程不同驱替阶段的主导控制效应分别为裂隙游离CH_(4)驱赶、CH_(4)自解吸及CO_(2)-CH_(4)竞争吸附,驱替流量先快速增加,后缓慢降低并趋于稳定;温度越低,煤体稳态渗透率越大,低温下煤基质收缩裂隙扩容和热应力损伤增透效应远大于煤体吸附膨胀作用;液态CO_(2)驱替CH_(4)过程的低温裂隙扩容与孔裂隙损伤发育效应,大于CO_(2)-CH_(4)竞争吸附膨胀作用,是改善煤层渗透性的关键。为提高注CO_(2)的经济性,在技术应用过程不同驱替阶段应优化设计注入流量参数。The low efficiency of gas extraction is the main factor causing gas accidents and difficulties in extraction in coal mines. Liquid CO_(2)is capable of elevating fracturing at a low temperature and displacing CH_(4),which can effectively improve the coal permeability and promote CH_(4)desorption. The self-developed triaxial and multiphase platform was used to study the features of the coal strain,CH_(4)/CO_(2)concentration,flow rate,and permeability during the process of coal vacuuming,CH_(4)absorbing and CO_(2)displacing under different temperatures. The mechanism of CH_(4)in the coal seam displaced by the liquid CO_(2)was also proposed. The results show that:The strain of coal samples represented a swelling deformation during the CH_(4)adsorption and CO_(2)displacement periods,and the strain curves experienced a rapid expansion and then a slow swelling. The strain in the CO_(2)displacing period is significantly larger than that in the CH_(4)adsorption period,which shows a greater difference when the temperature is lower. During the displacement process,the dominant control effects in different displacement stages are fracturefree CH_(4)driving,CH_(4)self-desorption and CO_(2)-CH_(4)competitive absorption. The displacement flow increases rapidly at first,and then decreases slowly and tends to be stable. A lower temperature leads to an increasing steady permeability of coal. Under a low temperature,the contributions of coal matrix shrinkage and thermal stress damage were greater than the coal adsorption swelling. During CO_(2)displacing CH_(4)process,the permeability improvement of fracture expansion and pore damage at low temperature is distinctly greater than the permeability inhibition of coal swelling during CO_(2)-CH_(4)competitive adsorption,which is the key to enhancing the coal seam permeability. To improve the economic efficiency during the CO_(2)injection,the flow parameter should be optimized at the different displacing stages when applying the proposed method.

关 键 词：置换驱替 瓦斯抽采 膨胀变形 驱替浓度 渗透率 

分 类 号：TE377[石油与天然气工程—油气田开发工程]