Dense segmented radial jetting stimulation method of screen tube in coalbed methane horizontal well

The permeability of coal near shaft wall is low for the reservoir damage, and the space of conventional segmented hydraulic jetting is long. A method of dense segmented radial jet with pre-drilled holes as nozzles was proposed to improve the permeability of coal near shaft wall, and the spring-hydraulic packer and liquid injection nipple were designed and optimized for horizontal well completion with pre-drilled liner. The calculation model of single pre-drilled hole radial jetting and seepage increment ratio of coal breaking cave near shaft wall are established. The number of pre-drilled holes per meter, exit jetting velocity of pre-drilled hole and flow rate were optimized. The influence of permeability ratio K_γ between the solid intrusive zone and the filtrate intrusive zone and the depth of solid intrusion zone H_s on the seepage increment ratio of coal near the shaft wall is analyzed. The results show that the spring-hydraulic packer with a design of non-skeleton rubber cylinders, radial sliders, and strong tensile spring, which improves the stability of high-frequency sealing of the dense segmented radial jetting tools within the pre-drilled liner, achieving completion and reservoir stimulation in one trip for coalbed methane horizontal well. Under the conditions of H_s=3.5 cm and K_γ=0.01, the radial hydraulic jetting space of the pre-drilled liner was reduced to the pre-drilled hole space of 0.05 m, and the seepage increment ratio of coal methane horizontal well increased by 5.5% with dense segmented radial jetting. The research results provide technical guidance for solving the reservoir damage challenge in coalbed methane horizontal wells completed with pre-drilled liner, and theoretical basis for permeability enhancement operations in coal near shaft wall.