A New Model of Stereoscopic and Combined Coalbed Methane Drainage by Both Surface and Underground Boreholes

Through the study of combined coalbed methane (CBM) drainage theory, method and field test by both surface and underground boreholes, according to drainage theory of CBM by both surface and underground boreholes and the characters of three zones (caving zone, fractured zone, and bending zone) above goaf, a new model for stereoscopic and combined CBM drainage by both surface and underground boreholes is proposed. The transition zone between fractured zone and bending zone should take butt joint by horizontal well and vertical well. Horizontal section is set appropriately near the return airway. Taking large diameter drainage pipe more than 200 mm and using the technology of segmented seal and graded negative pressure drainage to drain CBM choosing different drainage wells at different coal mining stages. After coal mining for this model, it can achieve synchronous drainage in different zones and stereoscopic drainage on the space. At the same time, it can drain shale gas or tight sandstone gas above the coal seam, which achieves combined gas drainage for different types of gas and "one gas well with multi applications".