High efficiency gas drainage technology of hydraulic fracturing with directional long drilling in underground coal mine

In order to improve the gas drainage effect of a single coal seam with low permeability in underground coal mines, based on the shortcomings of the gas fracturing technology of ordinary medium and short borehole hydraulic fracturing, combined with the geological conditions of coal reservoirs and the characteristics of directional drilling technology, a high-efficiency gas drainage technology of directional long borehole hydraulic fracturing is put forward, and the overall pressure of long borehole is summarized.Two hydraulic fracturing modes-integral fracturing and comb-shape borehole fracturing in surrounding rock are introduced.The construction technologies and key technologies are analyzed.Taking Yangquan mining area as an example, the directional long borehole hydraulic fracturing test was carried out and its effect was investigated.The results show that the fast fracturing technology based on the principle of expandable packer can be used for integral fracturing of long boreholes, and the fast setting of combination of sealing tools can be realized within 10 minutes.The slip sleeve fracturing technology of bare-hole packer was adopted in the section fracturing of comb hole, and the slip sleeve of all levels was opened in turn by the way of hole opening shot, thus the water injection fracturing operation of each branch of comb-shape borehole was completed.With the increase of the distance from the borehole, the total water content of the coal in the influence range of hydraulic fracturing first increases and then decreases, and the gas content of the coal seam has the opposite distribution characteristics to the total water content of the coal body.During the fracturing process, the stress and deformation of the roadway were obvious.In the initial stage of the ejection, the water flow carried a large amount of powder, and the powder discharge amount reached 6.5 t.The maximum influence radius of integral fracturing with long boreholes and sectional fracturing with comb-shape boreholes are 58 m and 60 m respectively, which are 2.32 times and 3.53 times larger than that of conventional fracturing boreholes.The average gas drainage volume is 1.51 m3/min and 0.25 m3/min, which are 24.40 times and 13.89 times higher than that of conventional fracturing boreholes.The analysis shows that there was a water flooding effect in the fracturing process, and there was a spatial imbalance in the effect of fracturing on the coal reservoir transformation..The phenomenon of volume expansion and softening occurs after water absorption of coal and rock mass, which changes the distribution of stress field around boreholes, and leads to the deformation of roadway under compression damage.During the staged fracturing of comb holes, the fractures in the surrounding rock communicate with the fractures in the coal seam through traction, thereby forming a new coal reservoir fracture network system, which is conducive to improving the gas drainage effect.