深部中－高煤级煤储层孔隙结构与吸附性

摘要

为了探讨中－高煤级深部煤层孔隙结构特征和吸附性，以陕西宜川和山西柿庄地区埋深100～1800 m 的中－高煤级样品为研究对象，对样品进行了煤岩煤质分析以及压汞法、核磁共振、低温液氮和等温吸附等测试，结果表明：（1）随着深度的增加，煤层吸附孔含量增多，渗流孔含量减小，渗透性降低，储层物性变差。（2）比表面积和总孔体积在1000 m 附近出现高值区域，随后才出现如前人所述的随深度逐渐降低的趋势，这与小孔的贡献率一致，可见比表面积和总孔体积并非完全由微孔决定，小孔作用显著。（3）深部煤层吸附性是压力的正效应与温度的负效应共同作用的结果，随着压力的增高，吸附量明显增加，温度每升高1℃，吸附量平均减少0.25 cm3／g；兰氏压力并不是简单地随温度递增而递增，而是存在随温度变化的拐点（35℃），大于拐点温度时，兰氏压力才呈现增高趋势。%The exploration and exploitation of coalbed methane have gradually turned into deep coal seams. Taking Yichuan of Shaanxi and Shizhuang of Shanxi as the study area,collecting shallow and deep coal samples and integrating with some experiments,this paper analyzes the difference of pore structures between shallow coal seams and deep coal seams and the adsorption characteristics of deep medium-high rank coal reservoirs.Mineral and lithotype test,mercury intrusion method,NMR,low-temperature nitrogen adsorption test and isothermal ad-sorption test had been used for this study with those coal samples (1 00 -1 ,800 m).The results with the in-crease of the depth are as follows:(1 )The percentage of adsorption pore shows a trend of increase while the number of seepage pore decreases.The mercury injection curve has a trend toward type Ⅲ.The main peak area of low NMR T2 relaxation is gradually increasing and even can be up to 90% of all peak areas when the depth is more than 1 ,700 m;the zero signal sections among main peaks show that the ability of connectivity between mi-cropores and mesopores is worse.The curves of low-temperature nitrogen adsorption have a trend from typeⅠto typeⅡ.The above results show that the abilities of pore connectivity,permeability and physical properties of reservoirs are becoming worse.(2)Coal reservoir surface area and pore volume have their high-value ranges near 1 ,000 m.Then,they decrease just as the predecessors’point of view,which is due to the small pores. (3)The adsorption ability of deep coal seam is influenced by positive effect of pressure and negative effect of temperature.The maximum adsorption capacity increases when the pressure becomes high,but the adsorption capacity has a decrease of 0.25 cm3 /g while the temperature rises 1 ℃.The effect of temperature on Langmuir pressure is different from predecessors’views.There is an inflexion point in temperature (35 ℃)and Langmuir pressure will not rise until the temperature reach it.