Dynamic multifield coupling model of gas drainage and a new remedy method for borehole leakage

Air leakage in borehole not only seriously restricts the development and utilization of coal bed methane (CBM) but also affects gas disaster prevention and underground safety mining. Several triaxial-seepage experiments were conducted to analyze the seepage characteristic change of raw coal under different loads in consideration of the above-mentioned problems. On this basis, a dynamic multifield coupling model, including coal permeability evolution, creep mechanical, and binary gas flow system, was proposed to describe the CBM drainage process. Based on this fully coupling model, factors influencing air leakage flux were investigated by numerical method. Findings show that the dynamic change of air leakage flux is determined by stress and permeability variation. Therefore, in practical work, grouting method can be adopted to decrease coal permeability and softening modulus as well as increase coal residual strength and support stress, so as to reduce air leaking in borehole. Furthermore, we also proposed a new remedy method, including self-developed GP material and corresponding sealing-plugging integrative device, for preventing borehole leakage. The field test results indicate that the gas concentration of the boreholes was effectively enhanced after the leakage treatment by this method, and a great drainage level was still maintained at the late period. The results in this work can provide a remedy method for improving borehole sealing and drained gas quality. Such method is important for enhancing the CBM utilization, reducing greenhouse gas emission, and ensuring mining safety.

Automated summary

This study investigates the issue of air leakage in coal bed methane (CBM) extraction and proposes grouting method and sealing-plugging device as remedies. Experimental and numerical findings show that these methods effectively reduce air leakage in boreholes and improve the gas extraction level. This is crucial for enhancing CBM utilization, reducing greenhouse gas emissions, and ensuring mining safety.