Micro-pilot test for optimized pre-extraction boreholes and enhanced coalbed methane recovery by injection of liquid carbon dioxide in the Sangshuping coal mine

The extraction efficiency of high-gas coal seams is low in China with a large number of pre-drainage boreholes. In this study, we analyze the coal seam gas displacement mechanism using liquid carbon dioxide by combining theoretical analysis, experiments, and field tests. Changes of gas displacement efficiency with time under different displacement flow and pressure conditions are determined. We propose a coalbed methane displacement method using liquid carbon dioxide and apply the model in a field test carried out in well No. 2 of the Sangshuping coal mine. The results show that the injection of liquid carbon dioxide in coal seams is a pressure swing adsorption process. The effective displacement radius from the in-situ tests reaches 20 m. The maximum CH4 extraction concentration in the test area is 65%, which is 2.41 times higher than that of the original coal seam (27%). The maximum methane extraction flux rate is 0.884 m(3)/min, which is 2.34 times that of original coal seam (0.377). Implementation of liquid carbon dioxide displacement coalbed methane technology optimizes borehole arrangement and enhances coalbed methane extraction. (C) 2020 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.