Technical system and engineering practice of coal seam permeability improvement through underground directional long borehole hydraulic fracturing

Advanced penetration enhancement in low-permeability coal seams is an effective technical support for realizing regional advanced and efficient drainag e of coal seam gas. In view of the insufficient pumping capacity and fracturing imbalance faced by hydraulic fracturing of directional long boreholes,the rapid,fixed-poin t,segmented and reusable hydraulic fracturing in-hole tool combination and complete sets of equipment in underground coal mines have been developed to achieve the transformation of underground hydraulic fracturing from traditional point fracturing to regional fracturing. Combined different coal( rock) layers with long directional bore holes,we proposed and formed the integrated/segmented hydraulic fracturing of comb-shaped holes in the top( bottom) plate of the fractured soft coal seam,the overall/ segmented hydraulic fracturing of the medium-hard coal seam through the directional hole along the coal seam,and the hard coal seam along the bedding directional lo ng borehole integral/segmental hydraulic fracturing coal seam permeability enhancement technology system. The field engineering practice of different fracturing techno logy was carried out with the fractured soft coal seam in Hancheng Mining Area,medium hard coal seam in Huangling Mining Area and hard thick coal seam in Jiaozuo Mining Area as the research objects. The results show that: the comb-shaped main hole of the roof of the fractured soft coal seam in Hancheng Mining Area is588 m fra cturing in 4 stages,the maximum isolation depth is 467 .81 m,the fracture radius is 39.6 m,and the gas drainage volume of the borehole is 4.8 times that of the conventio nal borehole. The main hole depth of the medium-hard coal seam in Huangling Mining Area is240 ~ 285 m,the length of the fracturing section is 117 ~ 216 m,the mini mum fracturing radius is 36 m,and the average gas drainage volume of the boreholes is 4 times of the unfractured borehole. In Jiaozuo Mining Area,the depth of the mai n hole along the bedding is 605 m,the isolation depth is 385.73 m,the fracturing section is 220 m long,and the fracturing influence radius is 33 m. The gas drainage volu me of the borehole is 2.3 times that of the conventional borehole. Underground directional long borehole hydraulic fracturing technology combines the advantages of dir ectional long borehole gas high-efficiency drainage technology and hydraulic fracturing enhanced drainage technology,and realizes large-area coal seam enhancement and advanced gas pre-drainage.