Study on three-dimensional horizontal well exploitation, directional gathering and transportation and utilization of coalbed methane in high gas mining areas

High gas mining areas are crucial sources of coalbed methane （CBM） which is vital for mine safety. Conventional CBM production methods in high gas mining areas primarily involve surface drilling, exploitation, and transportation systems. However, these surface-based approaches face challenges including complex operations, high costs, and safety risks, which also hinder the construction of CBM processing facilities and long-distance transportation networks in rugged terrains, resulting in difficulties in widespread adoption and poor economic returns. Considering the geological conditions of Baode Coal Mine, including its mining faces and gas power plant facilities, a coalbed methane extraction process from ground-drilled spoon-shaped well group has been developed. This system includes two three-dimensional horizontal wells to extract gas from working faces, while a large-displacement directional well reinjects the extracted gas and production water into the mine shaft. The gas is then transported to the gas power plant via underground pipelines within the mining area, which forms a closed-loop system for extraction and utilization. This innovative approach ensures efficient construction, significantly reduces costs, enhances the safety of gas collection, transportation, and utilization, and solves the problem of surface water pollution. Through research and experimentation, four key technologies have been developed: ①a three-dimensional horizontal well guidance drilling technique is built for shallow, wide-offset wells in rock strata with multi-layered coal seams and interbedded gangue structures. ② A nitrogen piercing layer fracture technology is formed for isolation walls in multi-bedded gangue formations, creating vertical interconnected fracture networks between thin coal seams and interbedded gangue layers. ③ A four-stage gas extraction and five-parameter control gas production process is optimized for uniform gas production, achieving initial success in at high-gas mine faces. ④A closed-loop system is established for three-dimensional horizontal well producing gas in a well group, a large displacement directional well reinjecting gas and water while underground pipeline transportation and utilization. According to the field test of Baode Coal Mine, the three-dimensional horizontal well technology for coalbed methane exploitation, directional gathering and utilization in high gas mining areas is feasible, and the economy and safety can meet the demand of coalbed methane exploitation in high gas mining areas.