不同矿化度水对煤储层吸附性能的影响

为了探究水分及其矿化度对煤样吸附甲烷能力的影响,以准噶尔盆地南缘玛纳斯矿区侏罗系西山窑组块状煤样为例,采用矿化度水配制—样品制备—样品大气压下水浸—高压下注水—等温吸附实验的实验步骤,开展煤样干燥、饱水及含不同矿化度水条件下煤的等温吸附实验,探讨不同矿化度水对煤储层吸附性能的影响。研究结果表明:干燥煤样的兰氏体积显著大于注蒸馏水煤样的兰氏体积,注蒸馏水煤样的兰氏体积大于注10 000 mg/L矿化度水煤样的兰氏体积,但后者与注20 000 mg/L矿化度水煤样的兰氏体积相差不大。其主要原因为注蒸馏水煤样中水分子比甲烷分子更容易占据煤基质内表面或微孔内表面的吸附位,从而使得兰氏体积降低,而含矿化度水使得煤基质表面的吸附位进一步减少,从而造成了煤样对甲烷的吸附能力降低,但这也存在着一个极限值,大于20 000 mg/L矿化度水已不能明显降低煤样的兰氏体积。因此可推断,在地下水径流区或弱径流区,煤层水的矿化度不断增大至10 000 mg/L时,煤层中处于动态平衡的游离气含量会增加,而吸附气含量会减少,当煤层水矿化度超过10 000 mg/L,煤层中吸附气与游离气的含量比例趋于稳定。实验从研究创新的角度出发,以低煤阶煤样为例,对比分析了含不同矿化度水条件下煤样对甲烷的吸附能力的差异,并且进行了相关的理论分析和机制解释,认为地下水矿化度影响煤储层对甲烷的吸附能力。

Influence of water with different salinity on the adsorption performance of coal reservoir

In order to explore the influence of water and salinity on the methane adsorption capacity of coal samples, the isothermal adsorption experiments of coal samples with water saturation and water with different salinity were carried out using the coal samples from the middle Jurassic Xishanyao formation block in the Manas mining area of the southern margin of Junggar basin. The results show that the Langmuir volume of dry coal sample was significantly larger than that of distilled water injection sample,and the Langmuir volume of distilled water injection sample was larger than that of water injection coal sample with salinity being 10 000 mg/ L,but the latter is close to that of water injection coal sample with salinity degree of 20 000 mg/ L. The main reason is that the distilled water molecules can be more easily adsorbed on the surface of the coal matrix than methane molecules,which makes the reduction of Langmuir volume. The salinity water further reduces the adsorption sites of coal matrix surface,resulting in the reduction of methane adsorption capacity of coal samples. However,there is a limit salinity value,and the water with salinity degree greater than 20 000 mg/ L cannot significantly reduce the Langmuir volume of coal samples. Therefore,it can be inferred that in the groundwater runoff area or weak runoff area,when the salinity degree of coal seam water increases continuously to 10 000 mg/ L,the content of free gas in the coal seam will increase,while the content of adsorbed gas will decrease. When the salinity degree of coal seam water exceeds 10 000 mg/ L,both the content ratios of adsorbed gas and free gas in coal seam tend to be stable.