Study on the performances of fluorescent tracers for the wetting area detection of coal seam water injection

Coal seam water injection can effectively prevent dust pollution and coal mining disasters, such as coal bumps and coal seam fires. However, the quantitative determination of the range where water can reach during the water injection remains a challenge and there is no effective method reported for the measurement yet. Herein, we introduce the fluorescent tracers widely used in oil field into the wetting range detection of coal seam water injection. Three commonly used fluorescent tracers, fluorescein sodium, calcein disodium, and fluorescein iso-thiocyanate (FITC), were examined for their performances in detecting the wetting area of coal seam water injection. Considering the two migration stages, wetting and seepage, of the water injected in coal seam, the bottom-up imbibition and seepage experiments were respectively conducted on the fluorescent tracers, and the fluorescence intensities of the tracer solutions before and after the seepage experiment were measured. The results suggest that both fluorescein sodium and calcein disodium promote, but FITC inhibits the wetting stage. Fluorescein sodium promotes the seepage, but calcein disodium and FITC only do at low concentrations. Due to the retention effect, the permeability coefficients of all of the tracers show decreasing trends as the experiment proceeded.

Automated summary

Coal seam water injection is effective in preventing dust pollution and coal mining disasters. However, the quantitative determination of the water injection range is challenging, and there is no effective measurement method available. This study introduces fluorescent tracers commonly used in oil fields into the detection of the wetting area of coal seam water injection. The results show that fluorescein sodium and calcein disodium promote the wetting stage, while FITC inhibits it. Additionally, fluorescein sodium promotes seepage, while calcein disodium and FITC only have an effect at low concentrations. The permeability coefficients of all tracers decrease as the experiment progresses, attributed to the retention effect.