煤中矿物质对甲烷生储特征影响的机理

Influence characteristics and its mechanism of minerals in coal on methane generation and storage

煤中矿物质对甲烷生成及储集具有不同的作用,影响机制比较复杂,为进一步阐释煤中矿物质对甲烷生成储集的影响特征,采集了国内褐煤分布典型地区内蒙古霍林河煤矿和河南义马煤矿进行脱矿前后的生气热模拟实验,分析了煤中矿物组分对甲烷生成的作用机理;同时结合国内4个代表性地区同一区同一煤层不同灰分产率(矿物含量)煤样的等温吸附实验和煤芯解吸实验,探讨了矿物组分对煤吸附储集甲烷的影响特征。研究表明:生气热模拟实验中霍林河和义马2个煤矿煤样的甲烷生成强度曲线呈高斯分布形态、累积生成强度曲线均呈双台阶的Srichards曲线形态,脱矿前生成强度和累积生成强度都远高于脱矿后煤样,认为所含矿物组分对热解生成甲烷具有正效应作用,主要原因:(1)矿物组分中黏土矿物与煤有机结构间具有类离子交联作用,加热过程中增强了生成甲烷的煤大分子结构分裂强度及化学活性;(2)加热过程中黄铁矿对煤有机结构分解具有很强的活性催化作用;吸附实验与解吸实验显示,同一区同一煤层甲烷空气干燥基的朗格缪尔吸附体积和含气量均随灰分产率(矿物含量)增加而呈显著降低趋势,矿物组分对煤吸附甲烷主要表现为负效应,其原因在于不同矿物组分对吸收态甲烷储集的煤分子结构、吸附态甲烷储集的孔隙结构和游离态甲烷储集的显微裂隙具有不同的空间分占作用。

Minerals in coal have different effects on methane generation and storage,and the influence mechanism is relatively complex.In order to further reveal the influence characteristics,the thermal simulation experiments of gas generation before and after demineralization were carried out on the lignite samples from Huolinhe Coal Mine in Inner Mongolia and Yima Coal Mine in Henan,China,and the influence of minerals on methane generation was analyzed.At the same time,combined with the isotherm adsorption experiments and coal core desorption experiments of coal samples with different ash yield(mineral content)of the same coal seam in the same area of four representative regions in China,the influence characteristics and mechanism of mineral on methane adsorption and storage were discussed.The results show that the methane generation intensity curves of coal samples in Huolinhe and Yima areas in the thermal simulation experiment are Gauss distribution,and the cumulative generation intensity curves are two-step Srichards curves.The generation intensity and the cumulative generation intensity before demineralization are much higher than that after demineralization,which shows that the minerals have a positive effect on the methane generation from coal pyrolysis.The main reasons are as follows:the first is that the clay minerals and the organic structure of coal have like-ionic-crosslinking effect,which enhances the splitting and activity of coal macromolecules generating methane during the heating process,and the second is pyrite has a strong active catalytic effect on the decomposition of the organic structure during the heating process.The adsorption experiments and desorption experiments show that the Langmuir adsorption volume and gas content of methane air drying base of the same coal seam in the same area decreased significantly with the increase of ash yield(mineral content),indicating that minerals have a negative effect on coal adsorption.It is considered that different minerals have a space-occuping effect on the coal molecular structure of the absorbed methane storage,the pores of the adsorbed methane storage,and the micro fractures of the free methane storage.