Study and Application of Water Production Characteristics and Drainage and Mining Control Methods in Different Drainage and Mining Stages of CBM Wells

This paper, through the mechanism analysis and data analysis, studies the different characteristics of water supply in the one-phase water flow stage, critical desorption stage, and water-gas two-phase flow stage, during the overall CBM development procedure and proposes a whole set of elaborate control methods for bottom flow pressure. The results show that the water supply from coal seams to the bottom of wells in single-phase flow stage increases continuously with the increase of time, so that the increase of the pumping units with the drainage time can maintain the constant pressure drop rate. Due to the frequent change of phase state, the water supply of coal seam fluctuates greatly, so it is necessary to pay close attention to the changes of water volume and bottom hole pressure in order to prevent the flow pressure dropping sharply. In two-phase stage, slow down the pumping units in advance for the first time of gas releasing and start from the tiny amount gradually. In steady output stage, the principle of slight and frequent gas release should be followed to guarantee the stability of bottom hole pressure and water production with the steady rising of gas production.