Key Takeaways & Executive Findings
- •• • 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.
Abstract
This study systematically investigates the synergistic drag reduction mechanism of surfactants and porous media in coal seam water injection. Four surfactant types—cationic CTAB, anionic SDBS, amphoteric BS-12, and nonionic OP-10—were tested with five porous media pore sizes (3–12 mm) using a custom-built all-in-one drag reduction test system. The effects of surfactant type, mass concentration, driving frequency, and pore diameter on drag reduction efficiency were evaluated. Results show that in an empty tube, drag reduction efficiency increases with mass concentration. As driving frequency increases, drag reduction first rises then falls, peaking at 35 Hz. With porous media, drag reduction exhibits pore size dependence, reaching a maximum at 8 mm and decreasing thereafter. The composite surfactant-porous media system achieves synergistic enhancement over single systems. At 0.05% mass concentration, all surfactants attain maximum drag reduction, with CTAB showing the highest efficiency. Optimal conditions (0.05% CTAB, 35 Hz, 8 mm pore size) yield a drag reduction rate of 66.14%, a 1.4-fold improvement over 20 Hz. These findings demonstrate that tailoring surfactant and porous media parameters can significantly optimize coal seam water injection efficiency, offering a practical approach for dust control in mining.
1. Introduction
Coal seam water injection is a key technique for dust suppression in mines, yet its efficiency is often limited by poor water wettability and high flow resistance in coal beds. Conventional approaches using water alone fail to penetrate micro-pores effectively, leading to inadequate dust control and increased operational risks. Surfactants have been proposed to reduce interfacial tension and enhance wetting, but their drag reduction performance in porous media under dynamic conditions remains poorly understood, hindering the design of effective injection protocols.
This study addresses this bottleneck by systematically evaluating four surfactant types across a range of concentrations, driving frequencies, and porous media pore sizes. By identifying optimal combinations—specifically, CTAB at 0.05% concentration, 35 Hz frequency, and 8 mm pore size—the research provides actionable parameters that maximize drag reduction efficiency. This experimental framework enables engineers to tailor injection systems for specific coal seam conditions, potentially reducing energy costs and improving dust suppression outcomes.
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LIU Kaixin, CHEN Guoliang, WANG Pengfei (2026). Experimental Study of Drag Reduction with Surfactants in Porous Media for Coal Seam Water Injection. Environmental Chemistry. https://doi.org/10.7524/j.issn.0254-6108.2025050803
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Frequently Asked Questions
What is the optimal surfactant concentration for maximum drag reduction, and does it vary with surfactant type?
All four surfactants (CTAB, SDBS, BS-12, OP-10) achieve maximum drag reduction at a mass concentration of 0.05%. At this concentration, CTAB exhibits the highest drag reduction rate of 66.14% under optimal conditions (35 Hz, 8 mm pore size). Concentrations above 0.05% do not further improve performance, suggesting a saturation effect.
How does driving frequency affect drag reduction, and what is the underlying mechanism?
Drag reduction increases with frequency up to 35 Hz, where it peaks, then declines at 40 Hz. At 20 Hz, flow is predominantly laminar, and surfactant micelles remain coiled, failing to form effective viscoelastic networks. At 35 Hz, the flow transitions to turbulent, allowing micelles to stretch and form networks that suppress turbulence. At 40 Hz, shear stress exceeds the critical threshold, causing micelle breakage and reducing drag reduction.
What is the role of porous media pore size in drag reduction, and why is 8 mm optimal?
Pore size significantly influences drag reduction, with a maximum at 8 mm. Smaller pores (3–6 mm) may restrict surfactant micelle formation or flow, while larger pores (10–12 mm) reduce the surface area for interaction, diminishing the synergistic effect. The 8 mm pore size likely provides an optimal balance between surface contact and flow dynamics, enhancing the drag reduction efficiency.
How does the composite surfactant-porous media system compare to single systems in terms of drag reduction efficiency?
The composite system achieves synergistic enhancement, meaning the combined drag reduction is greater than the sum of individual contributions from surfactant alone or porous media alone. This is attributed to the porous media promoting micelle network formation and increasing effective surface area, thereby amplifying the surfactant's turbulence-modifying effects.
What are the practical implications for coal seam water injection operations?
The findings suggest that using CTAB at 0.05% concentration with a porous medium of 8 mm pore size and a driving frequency of 35 Hz can maximize drag reduction, improving water penetration and dust suppression efficiency. This can lead to reduced water consumption, lower energy costs, and enhanced safety in coal mines.
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