Integral hydraulic fracturing gas drainage technology for directional drilling in gob-side entry under influence of mining

Abstract

For the difficulties in the construction of the directional drilling along the coal seam adjacent to the goaf under the influence of mining, such as the difficulty in hole formation and the inability of conventional measures to implement hydraulic fracturing, this paper takes the hydraulic fracturing drilling in the goaf adjacent to the 2# coal seam of Huangling No.2 Coal Mine as the research object, and puts forward the drilling layout idea of “entering the roof before entering the coal seam”. The comprehensive determination method of main key parameters is obtained, and the minimum value of opening point to coal point （Ｌ value） is 71.6 m; the stepwise release packer and matching in-hole fracturing tool combination suitable for the integral hydraulic fracturing of directional drilling are determined. The engineering practice has been carried out in the affected area of mining in the 209 working face, and the directional drilling and overall hydraulic fracturing construction of three “first entering the roof and then entering the coal seam” boreholes have been successfully implemented. The directional drilling length is 240-270 m, the rock hole section （Ｌ ｖａｌｕｅ） is 105-117 m, the single-hole fracturing section length is 126-165 m, the pumping pressure is 15.2-19.0MPa, and the fracturing fluid consumption is 248-315 m3. The measured influence radius of hydraulic fracturing is 36-54 m. The average gas drainage concentration and volume of fracturing boreholes has increased by 4-16 times and 3-8 times compared with that before fracturing. The gas drainage volume of pre-pumping boreholes in the fracturing area is twice that of the unfractured site, and the number of boreholes with gas drainage concentration greater than 60% is 5.1 times that of the unfractured area.

Keywords

• gas drainage
• double lane driving
• gob-side working face
• directional drilling
• hydraulic fracturing