黏土矿物对煤储层吸附能力影响研究

Minerals in coal are dominated by clay minerals, which are composed of certain amounts of ammonian illite, ammonian illite/smectite, rectorite, corrensite, etc, besides kaolinite, illite and chlorite commonly identified in shales. Clay minerals in coal have some adsorptive capacity of coal seam gas, and have some effects on adsorptive capacity of coal reservoir and then influence coal seam gas exploration and evaluation on its potential exploitation. However, studies of the effects of clay minerals in coal on adsorptive capacity of coal reservoir are relatively weak. Yangquan District in Shanxi Province is chosen as research area in this project, and associated methods with coal geology and coal seam gas geology are to be used to determine the composition of clay minerals in coal and analyze their pore characteristics and specific surface areas. Due to the results of isothermal adsorption tests, the adsorptive capacity of clay minerals under different temperature, pressure and water content will be found out, and differences between clay minerals in coal and their coupling effects will be discussed. According to the analysis results above, multiple linear regression is to be used to reveal the effects of clay minerals on adsorptive capacity of coal reservoir, and corresponding mathematical model will be established and degree of influence of different clay minerals will be further analyzed.

煤中矿物以黏土矿物为主，其组成较为复杂，除页岩中常见的高岭石、伊利石、绿泥石外，还含有一定量的铵伊利石、铵伊利石/蒙脱石间层矿物、累托石、柯绿泥石等。煤中黏土矿物具有一定的煤层气吸附能力，这对煤储层吸附能力具有一定的影响，进而影响到煤层气资源勘探及开发潜力评价。目前，煤中黏土矿物对煤储层吸附能力影响的研究比较薄弱。本项目以山西阳泉地区煤层为研究对象，采用煤地质学以及煤层气地质学相关方法，定量测定煤中黏土矿物的组成，分析不同类型黏土矿物的孔隙特征和比表面积。根据等温吸附试验分析结果，查明煤中黏土矿物在不同温度、压力和水分条件下的吸附能力，探讨不同类型黏土矿物吸附能力的差异以及它们在吸附过程中的耦合作用关系。依据上述分析结果，采用多元线性回归分析方法，揭示煤中黏土矿物吸附能力对煤储层吸附能力的影响并建立相应的数学模型，分析不同类型黏土矿物的影响程度。

黏土矿物是煤中矿物的重要组分，因黏土矿物对CH4具有一定的吸附能力，因此，煤层中黏土矿物的存在对储层煤层气吸附能力影响不可忽视。本文以阳泉矿区石炭系太原组15号煤为研究对象，采用煤地质学、矿物学、煤地球化学和煤层气地质学相关理论和方法，分析和研究煤层中黏土矿物成因、孔隙结构特征、CH4吸附能力以及对煤储层吸附能力的影响。结果表明，阳泉矿区15号煤层中主要黏土矿物为高岭石和铵伊利石，其次为伊蒙间层矿物。高岭石为陆源碎屑成因，铵伊利石属于成岩矿物，主要由高岭石在成岩过程中转化而来。高岭石、铵伊利石和伊蒙间层矿物对CH4的吸附能力分别为5.81 cm3/g、2.08 cm3/g和4.47 cm3/g。黏土矿物孔径主要集中在< 6 nm的范围内，高岭石、铵伊利石和伊蒙间层矿物具有不同孔径分布特征，三者对应的特征孔径分别为1.38 nm、1.31 nm和1.06 nm。其中，铵伊利石的特征孔径明显低于高岭石，这主要是由高岭石向铵伊利石转化过程中，Si、Mg、Fe、NH4、K等进入矿物晶格，导致部分孔隙变窄或者堵塞所致，进一步导致铵伊利石对CH4的吸附能力低于高岭石。煤中黏土矿物除本身具有一定的吸附能力外，其存在对煤储层具有一定的堵塞相应，约为-3.50 cm3/g。高岭石、铵伊利石和伊蒙间层矿物对煤储层吸附能力的综合影响分别为2.31 cm3/g、-1.42 cm3/g和0.97 cm3/g，高岭石和伊蒙间层矿物对煤储层吸附能力有利，而铵伊利石则产生不利影响。