不同变质变形煤储层吸附/解吸特征及机理研究进展

Study on characteristics and mechanism of adsorption/desorption on different metamorphic-deformed coal reservoirs

不同变质变形煤储层包括低煤级、中煤级和高煤级变质变形环境中的脆性变形煤、韧性变形煤和过渡型变形煤,不同变质、变形程度和机制对煤层气的吸附/解吸影响较大。干燥煤和平衡水煤的甲烷吸附量随变质程度的增强呈现出不同的变化趋势,干燥煤呈横"S"形且易于解吸,而平衡水煤呈倒"U"字形且吸附/解吸强度皆低于干燥煤样,且解吸过程较干燥煤滞后。构造变形导致煤的大分子结构和纳米级孔隙发生不同程度的改变,进而影响气体的吸附/解吸能力,脆性变形主要增加煤的大、中孔,其基本结构单元堆砌度略有增大,甲烷吸附/解吸程度有所增强;韧性变形主要增加煤的微孔-超微孔,其基本结构单元堆砌度增加较快,煤层气吸附能力增强,降压时韧性变形煤比脆性变形煤具有较高的瞬时解吸速率。由此可见,不同变质变形环境中的煤储层吸附/解吸能力差异较大,这主要是由煤储层内部结构及其影响因素对其制约所决定的。

Metamorphic-deformed coal reservoirs include brittle deformation series, ductile deformation series and brittle-ductile transition series under the condition of low coal rank, mediate coal rank and high coal rank. Different metamorphic-deformation mechanism and degree have significant effects on coalbed methane （CBM） adsorption/desorption process. The adsorption curves of CBM in dry and moisture-equilibrated coals take different shapes of horizontal ＂S＂ and inverted ＂U＂, respectively. It is easier and quicker for methane desorption in dry coals than that in moisture-equilibrated coals. Tectonic deformation changed the macro- molecule structure and nano-pores of coals to varying degrees, resulting in the variation of CBM adsorption/ desorption characteristics： brittle deformation mainly increased the macro- and meso-pores of coals, slightly increased the stack degree of basic structural units （BSU）, and consequently enhanced the adsorption/ desorption capacity of coals. While ductile deformation principally increased micro- and ultra-micropores of coals, rapidly increased the stack degree of basic structural units （BSU）,and enhanced the adsorption capacity. The instantaneous desorption rate of ductile-deformed coals was higher than that of brittle-deformed coals when pressure is release＆ Therefore, different metamorphic-deformed coal reservoirs possess different adsorption/ desorption capacity,which is determined by internal structures and influence factors of coal reservoirs.