Stress relief cracking and permeability improvement by high-pressure water jet slotting to enhance coalbed methane extraction

Abstract

Extracting coalbed methane (CBM) is important for energy development. Improving coal seam permeability is the key to high-efficiency CBM extraction. High-pressure water jet (HPWJ) slotting is an effective method for improving permeability. However, the mechanism by which this technology improves coal seam permeability is unclear. Therefore, in this paper, the mechanism by which HPWJ slotting causes stress relief cracking and permeability improvement to enhance CBM extraction is studied in terms of the stress relief effect and the changes in fracture field and flow field induced by HPWJ slotting. Significant changes occur in facture field and flow field. The process, coal mass stress relief → fracture development → permeability improvement → CBM extraction enhancement, is triggered by HPWJ slotting. A field experiment indicates that after HPWJ slotting, the total CBM production and its average pure quantity are 4.41 and 4.20 times those under traditional drilling conditions, suggesting that HPWJ slotting can effectively improve permeability and enhance CBM extraction. The study results have important significance for revealing the mechanism by which HPWJ slotting improves permeability and for achieving high-efficiency underground CBM extraction.