热处理提高煤岩渗透率的机理

Mechanism exploration on improving coal rock permeability by heat treating

为了探索煤岩渗透率与温度的关系及其机理,通过加热实验研究了二者在200℃以内的关系,通过X衍射分析、电镜扫描等手段,并从煤化学、煤地质学等角度对其机理进行了分析。结果表明:初始渗透率在0.5 mD以内的煤岩,经加热处理后其渗透率可显著增至15 mD以上。分析认为:煤岩热处理后渗透率提高的机理为:煤岩脱水以及部分挥发组分的逸散会产生新的渗流孔隙;甲烷分子的解吸以及基质凝胶化组分脱水,导致煤基质收缩;煤岩中碳氢原子发生氧化生成气态产物并逸散,形成了微小裂缝并降低了煤岩的致密程度;热应力作用下煤岩内部变形不均产生了微小裂缝。最后提出可以对煤层注入热CO2提高采收率。

This paper investigated the relationship between coal rock permeability and heating temperature in less than 200 °C through laboratory experiments. And by means of X-ray diffraction analysis and Scanning Electron Microscope, the influence of heat on coal rock permeability was analyzed from perspective of coal chemistry and coal geology. The results shows that coal rock permeability could be significantly increased from less than 0.5 mD to 15 mD by heat treating. Analyzing results indicate that mechanisms may be explained as follows： Firstly, dehydration of coal rock and partly volatile components releasing of coal rock will form new pores. Secondly, desorption of methane molecules and dehydration of gelatinous micro-component in the matrix lead to the shrinkage of coal matrix. Thirdly, coal rock generates hydrocarbon gases after oxidizing reaction of carbon and Hydrogen atoms, and the gas releasing forms tiny cracks and reduces the degree of coal rock compaction. Fourth, coal rock encounters inhomogeneous deformation under thermal stress, and produces uneven small cracks. Finally, the paper proposes a new mode of coal bed methane （CBM） exploitation to enhance CBM recovery by injecting thermal CO2. Above researches may be of great help to the exploitation of CBM reservoirs with low permeability in China.