Simulation Study on Borehole Sealing Effect of Gas Extraction Drilling Based on Adaptive Active Sealing Technology

With the increasing depth of coal mining, optimizing the sealing effect of boreholes has become a key technological challenge to enhance the efficiency of gas extraction. This study proposes an adaptive active sealing technology and designs a coupled experimental platform for borehole sealing and gas extraction. Sulfur hexafluoride（SF6） is used as a tracer gas to systematically investigate the impact of three sealing materials（polyurethane, cement slurry, and flexible material） and key parameters of the flexible material on the sealing effectiveness. The main conclusions are as follows: Analyzing the negative pressure decay curve of the pipeline,the flexible material exhibits the highest initial negative pressure and the slowest decay rate, indicating better pressure retention compared to polyurethane and cement slurry. A larger water-cement ratio of the flexible sealing material leads to higher initial negative pressure but faster decay. The use of adaptive active sealing technology significantly enhances the negative pressure value and prolongs the decay time. Analyzing the SF6 concentration change curve in the pipeline, the flexible material achieves the highest average concentration and the lowest decay rate, resulting in optimal extraction efficiency. A higher water-cement ratio leads to higher SF6 concentration and greater extraction rate. Increasing grouting pressure enhances gas concentration and extraction rate. The best sealing effect was achieved by following the process sequence of initially injecting a low water-cement ratio slurry followed by subsequent injection of a high water-cement ratio slurry. In summary, the adaptive active sealing technology achieves proactive filling of dynamic fractures, and optimizing sealing parameters significantly enhances extraction efficiency. This provides a new perspective for borehole sealing in coalbed gas drilling.