Application of coalbed methane hydraulic jet-increasing permeability-nitrogen injection to increase production in Shanxi mining area

Abstract

China is rich in coalbed methane resources, but the geological conditions of coal seams are complex and variable, and gas production is generally low. Simulations are conducted using the #15 coal seam in the Qiyuan mining area as a case study to improve coalbed methane production. The coal seam has low pressure, low permeability, low saturation and strong heterogeneity. Nitrogen injection has been used in this mining area, but the target production capacity has not been reached. This paper proposes a method to increase production using hydraulic jet drilling, controllable shock wave, and nitrogen injection, and field tests are conducted. The gas production increased from 120 m3/d to 600 m3/d–700 m3/d. Numerical simulations were conducted to determine the ability of the three stimulation methods to increase production. It is assumed that a small number of jet holes are used, and the permeability of the coal seam cannot be significantly improved. The results showed that the gas production was 2–8 times higher after using hydraulic jet drilling and a controllable shock wave than without stimulation measures. The combination of hydraulic jet drilling and controllable shock wave plus general nitrogen injection increased the gas production by 13 times compared to no stimulation measures, but the gas production decreased rapidly. The gas production after one year was consistent with that before general nitrogen injection. Gas production increased faster and was maintained longer after segmented nitrogen injection, and the overall gas production increased, but its decreasing trend was consistent with that of general nitrogen injection. This study provides references for conducting production tests in low pressure, low permeability, and low saturation coal seams.