Some problems concerning measuring shale gas content of rocks with gas desorption method

The measurement of shale gas content using isotherm desorption method for the complex Jurassic shale-mudstone-sand-stone-coal rock system was conducted with cores from the Chaiye-1 well drilled in Qaidam Basin. According to the data achieved, methodology for measuring shale gas content of rocks with isotherm desorption method was discussed based on practice. First, the shale gas desorption curve of rocks commonly exhibits multiple desorption peaks, due to the fact that the shale gas in rock represents not only adsorbed gas but also physically bound gas, and it desorbs when the micro physical structure in the rock is altered by the desorption process. Second, the lost shale gas portion of the rocks should be restored with the desorption data achieved at the early stage, which represents desorption of adsorbed gas at a stable manner. Third, residue gas of the rocks should only be measured by cracking the rocks to powder, since it is physically enclosed in the rocks. Fourth, shale gas in cores can be measured with isotherm desorption method later after the cores are canned and sealed in the desorption chamber without unreasonably data discrimination within 30 days.