Analysis of productivity impact factors for coalbed methane drainage by remote pressure relief of surface well in mining area

The objectives of this paper were to analyze impact factors and the characteristics of gas productivity for remote pressure relief of coalbed methane by surface wells in mining area.Production trends and their impact fac-tors have been studied for 9 wells on 3 longwall panels in Huainan coal mining area.The results indicated that the gas productivity of remote pressure relief of CBM drainage could be divided into two obvious stages.Well which can accomplish the first stage in short time would get better gas production.Strata structures and mining activities greatly influenced the gas production of surface well.It was favourable to gas drainage by surface wells while the average coal extraction volume was less than 3 898 tons per day and the average mining height was less than 2.2 m if the strata structure around the well was that thickness of loose bed was less than 406 m,the ratio of the bedrock thickness to loose bed thickness was over 0.74,the interval between protective seam and protected seam was on the range of 66⁷0 m.Whereas it was unfavourable to remote pressure relief of CBM drainage while the strata around the well was that loose bed thickness was larger than 430 m,the space between protective seam and protected seam was more than 74 m,the ratio of the thickness between loose bed and bedrock was less than 0.7.But the gas pro-duction can be improved by changing well location and optimizing wellbore structure.