页岩岩芯CH4吸附/解吸特性试验研究

Research of CH4 adsorption/desorption characteristic on shale rock cores

关键词:  页岩  岩心  吸附  解吸  朗格缪尔模型  吸附势理论

Key words:  shale rock  rock core  adsorption  desorption  Langmuir model  adsorption potential theory

摘要:

页岩对CH₄的解吸、吸附作用直接影响页岩气渗流规律,进而影响页岩气井的开采效率。为真实反映储层页岩的吸附/解吸特性,选用相对颗粒更能保持岩层原始地质结构的Ф50 mm×100 mm页岩岩心试样,并在恒定轴压和围压条件下,通过恒温水浴改变试验温度,开展了不同温度、不同储层压力作用下页岩吸附/解吸试验。试验结果表明:①由于页岩原始结构的微裂隙的各向异性,岩心吸附曲线表现出“阶梯状”和“负吸附”特征；②颗粒试样比岩心样品的吸附量更高,并且吸附量随围压变化更均匀,而岩心吸附过程压力与吸附量相关性差,并在极限压力点出现突增现象；③页岩岩心吸附CH₄以微孔和微裂隙填充为主,其次是大孔的单分子层吸附；④吸附势理论模型在描述岩心的吸附和解吸过程比Langmuir模型更合理。

Abstract:

The desorption and adsorption of CH₄ in shale directly affect the law of shale gas seepage, and then affect the production efficiency of shale gas wells. In order to factually reflect the rules of shale adsorption and desorption in shale gas reservoir, the study adopts shale cores (Ф50 mm×100 mm) which are capable of retaining more primitive geological structure, then exerts axial and confining pressures on shale cores, with the equipment of thermostatic water bath, then carries out the research of adsorption and desorption characteristics about shale reservoir under different temperature and stress. The results show that:(1) For the micro-fractures of shale primitive structure and its anisotropy, the adsorption isotherms of cores show “stepped” and “negative absorptive” characteristic; (2) the adsorption ability of shale particles is higher than cores, and the adsorption isotherm of it is more regular, the correlation between cores adsorption pressure and adsorption capacity is poor, which causes adsorption isotherms more complicated and sudden increase in the extreme pressure point; (3) the adsorption of methane in shale cores is priority to micropore and microfracture filling, then the macroporous monolayer adsorption is followed; (4) the theoretical model of adsorption potential is more reasonable than Langmuir model in describing the process of adsorption and desorption of cores.