Experimental Study of Drag Reduction with Surfactants in Porous Media for Coal Seam Water Injection

• • At 0.05% mass concentration, CTAB achieves a maximum drag reduction rate of 66.14% at 35 Hz and 8 mm pore size, a 1.4-fold increase over 20 Hz, indicating optimal operating conditions for industrial coal seam water injection. • • Drag reduction efficiency increases with surfactant mass concentration in empty tubes, but peaks at 0.05% for all tested surfactants, beyond which no further improvement is observed, guiding cost-effective dosing strategies. • • Porous media pore size critically influences drag reduction: maximum efficiency occurs at 8 mm, with performance declining for larger pores, highlighting the need for precise media selection in field applications. • • Driving frequency modulates drag reduction: efficiency peaks at 35 Hz, corresponding to the laminar-turbulent transition, where surfactant micelles form effective viscoelastic networks; at 40 Hz, shear-induced micelle breakage reduces efficiency, defining operational limits.