Challenges and development direction of deep fragmented soft coalbed methane in China

Developing deep fragmented soft coalbed methane (CBM) can significantly enhance domestic natural gas supplies, reduce reliance on imported energy, and bolster national energy security. This manuscript provides a comprehensive review of commonly employed coalbed methane extraction technologies. It then delves into several critical issues in the current stage of CBM exploration and development in China, including the compatibility of existing technologies with CBM reservoirs, the characteristics and occurrence states of CBM reservoirs, critical desorption pressure, and gas generation mechanisms. Our research indicates that current CBM exploration and development technologies in China have reached an internationally advanced level, yet the industry is facing unprecedented challenges. Despite progress in low-permeability, high-value coal seams, significant breakthroughs have not been achieved in exploring other types of coal seams. For different coal reservoirs, integrated extraction technologies have been developed, such as surface pre-depressurisation and segmented hydraulic fracturing of coal seam roof strata. Additionally, techniques like large-scale volume fracturing in horizontal wells have been established, significantly enhancing reservoir stimulation effects and coalbed methane recovery rates. However, all of these technologies are fundamentally based on permeation. These technologies lack direct methods aimed at enhancing the diffusion rate of CBM, thereby failing to fully reflect the unique characteristics of CBM. Current CBM exploration and development theories and technologies are not universally applicable to all coal seams. They do not adequately account for the predominantly adsorbed state of CBM, and the complex and variable gas generation mechanisms further constrain CBM development in China. Finally, continuous exploration of new deep CBM exploration technologies is necessary. Integrating more effective reservoir stimulation technologies is essential to enhance technical adaptability concerning CBM reservoir characteristics, gas occurrence states, and gas generation mechanisms, ultimately achieving efficient CBM development. We conclude that while China possesses a substantial foundation of deep fractured CBM resources, industry development is constrained and requires continuous exploration of new CBM exploration and development technologies to utilize these resources effectively.