Mechanism Exploration and application on Improving Coal Permeability by Heat Treating

Abstract

The relationship between coal permeability and temperature under 200 °C was studied using a coal-heating experiment, and the mechanism of coal permeability increase was analyzed using X-ray diffraction analysis and electron microscope scanning. The results show that coal rock’s permeability could be increased from 0.5 to 15 md after heat treating. These mechanisms may be explained as follows. First, the desorption of methane molecules and the dehydration of gelatinous microcomponents in the matrix, which shrinks the coal matrix. Second, dehydration of coal rock and volatile coal, which will flow out and form new pores. Third, coal rock encounters inhomogeneous deformation under thermal stress, producing a small crack, unevenly. Fourth, coal rock generates hydrocarbon gases after oxidation, forming tiny cracks and reducing the degree of coal rock compaction. Finally, the study proposes a new mode of coalbed methane (CBM) exploitation to enhance CBM recovery by injecting thermal CO2. The above studies may be used to exploit CBM reservoirs with low permeability.