As an alternative to hydraulic fracture for shale gas recovery, high temperature treatments such as combustion and pyrolysis are being used to remove organic matters and decompose minerals from shale to increase shale rock permeability for gas recovery. In this study, shales obtained from Shang Gu Basin, Shangxi, China, were burned in an air environment at a temperature of 800 °C for 45 min to oxidize the organic matters to improve shale physical properties. Energy dispersive spectrometer (EDS), scanning electron microscopy (SEM), and Fourier transform infrared (FTIR) tests were conducted to identify minerals and functional group inside the shale samples. The shale samples were also tested in a thermogravimetric analysis FTIR (TGA-FTIR) experiment to study the combustion characteristics and gas emission. The TGA curve shows that two weight loss peaks existed in the combustion process. The first peak occurring between 400 and 500 °C was found to be caused by oxidization of organic matter, and the second peak appearing between 600 and 800 °C was due to the decomposition of carbonate minerals and oxidization of organic matter. CO 2 was the main emission gas generated during the combustion process. The low temperature nitrogen adsorption method was employed to study the pore structure changes before and after the combustion. It was found that the diameters of the raw shale pores were mainly in the range of 4−8 nm. After combustion, the volume of small pores decreased and large pores increased; the mean pore diameter of the shale samples increased from 5 nm to greater than 10 nm after combustion. Scanning electron microscopy (SEM) images also show the volume of pores increased on shale surface. As a result, high temperature combustion not only resulted in oxidization of organic matters but also led to decomposition of carbonate minerals. Combustion may be one of the effective ways to increase shale permeability for gas recovery.

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As a result of the low matrix permeability of shale formation in China, the extraction of shale gases from the rocks becomes difficult. Recently, combustion and other thermal treatment methods were employed to remove organic matter from the shale to increase the permeability of the rock. In this study, geothermal properties of two shale samples were tested and analyzed. It was found that shale 1 has higher methane adsorption capacity, reflectance, and porosity than those of shale 2. Because the shale has low permeability, the two samples were heated in a thermogravimetric analysis (TGA) instrument in inert (N 2 and helium) and non-inert environments (air and CO 2 ) to increase shale permeability by removing the organic matter. From TGA weight loss curves, it was found that the weight loss rates were higher in a helium environment compared to CO 2 and air because helium has a higher thermal conductivity, which can promote organic matter cracking. However, organic matter was not oxidized with air, and some still remained inside the samples at the end of the experiments. As a result, pure air may not be a suitable combustion agent to burn the organic matter. Furthermore, the experiment revealed that carrying gases with high thermal conductivity was beneficial for the organic matter cracking.