Structure Parameters Optimization and Feasibility Tests of the Organ-Pipe Nozzle to Improve Near-Wellbore Reservoir Permeability

The structure parameters of the organ-pipe nozzle served as the cavitation generator to improve near-well reservoir permeability are optimized by simulation, and a feasibility test is carried out to verify the improvement of the permeability of sandstone and shale with the structure-optimized organ-pipe nozzle. With the gas content as the evaluation standard, numerical simulation results show that the outlet shrinkage ratio \(\left( {\Phi_D /\Phi_d } \right)^2\)  = 4–9, length diameter ratio of diffusion section \(S/\Phi_D\)  = 3.3–4.6, and diffusion angle α = 60°–80° are the optimal parameter ranges of organ-pipe nozzle flow passage. The feasibility tests show that the influences of cavitation effects produced by the nozzles whose flow channel parameters are within the optimal ranges on the permeability only have little difference. However, after the treatment of the sandstone cores and shale cores by the nozzle whose flow channel parameters are not within the optimal ranges, permeability improving rates decrease significantly compared to those treated by nozzles whose flow channel parameters are within the optimal ranges. The feasibility tests verified the rationality of numerical calculation, and show that the fluid cavitation effect is suitable for the permeability improvement of low-permeability sandstone but not for the ultra-low permeability shale. This study reveals that the fluid flow cavitation effect has the ability to improve the near-wellbore sandstone reservoir permeability and the structure-optimized organ-pipe nozzle could be used as the cavitation generator.