Research and application of “mining-gob”surface well extraction under repeated disturbance in coal mines

In order to overcome the technical problem that the repeated disturbance of the ground in coal mining leads to more easily deformed and damaged surface wells, the paper analyzed the movement law of strata, the deformation mechanism of surface well, as well as the failure mode and characteristics, and found that the direct cause was excessive deformation of surface well. As a result, the identification conditions for failure of surface well were summarized as follows: ① the casing shear displacement exceeds the inner diameter of the pipe; ② The minimum tensile safety factor of the casing is less than the threshold value “1”. On the basis of this understanding, the five major surface well protection technology concepts such as “avoiding, resisting, yielding, dredging and protecting”were put forward, which can effectively reduce the repeated disturbance of the ground in terms of well location selection, well structure, drilling and completion technology and safety protection device. The research team used the results in designing five surface wells in Yuecheng Mine, all of which achieved “mining-gob” long-term continuous extraction, bringing about 52.4 million m3 pure gas volume in standard condition, which not only ensured the safe production of coal mine, but also improved the utilization of gas. Further analysis of the drainage data showed that the influence radius of surface well in the mining area after five years of continuous operation exceeded 800 m.