Mechanism exploration on improving coal rock permeability by heat treating

This paper investigated the relationship between coal rock permeability and heating temperature in less than 200 ℃ 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 ex-plained 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.