Directional long borehole segmented fracturing and permeability enhancement technology and its application in thick and hard coal seams

QIN Fengyuan; WU Wenbin; LI Liangwei; Pan Xuesong

doi:10.11799/ce202501014

Abstract：In response to the problems of small impact range,low extraction quality,and long treatment duration for drilling in thick and hard coal seams,the targeted coal body is physically modified and the fracture network is rebuilt using the directional long drilling segmented fracturing and permeability enhancement technology along the coal seam.In response to the problems of packer damage and fracturing fluid leakage during the hard coal setting process,based on the fracturing characteristics of hard coal and the mechanical parameter characteristics of the packer,an active pressure bearing"pressure ring to internal wedge"structure improvement is carried out at end part.The thick and hard coal seam open hole setting combination tool string is selected,and after laboratory pressure testing,the sealing effect is good,meeting the requirements of multiple pressure relief and expansion.We have developed a complete set of equipment for segmented fracturing in thick and hard coal seams,as well as a reverse segmented fracturing process for directional long boreholes.Two directional long boreholes and eight fracturing tests are conducted in No.3 coal seam of Yamei Daning Mine,Shanxi,with a cumulative drilling depth of 975 m and a cumulative water injection of 596 m3.The results showed that the gas extraction concentration in the experimental area is all above 75%.The actual impact radius of fracturing is determined by ground microseismic monitoring,transient electromagnetic in the hole,and comprehensive determination of regional seepage volume,which is 22.5～32 m.The average pure gas extraction volume in DY-1 and DY-2 boreholes are 1.36 m3/min and 1.22 m3/min,respectively.After fracturing,the maximum and minimum pure gas extraction volume in a single borehole are increased by 49%and 16%,with an average increase of about 30%.