Study on the grouting diffusion characteristics and sealing mechanism of fractures under gas-bearing conditions

WANG Zhiming; LI Zhenhua; SUN Zhidong; SUN Yuning; CHENG Jianwei; WANG Meng; ZHANG Shuo; SI Leilei; ZHAO Yaoyao

doi:10.13247/j.cnki.jcumt.20250152

Abstract：Grout-based sealing of fractures is an important method for alleviating air leakage across extraction boreholes and increasing gas concentration.Gas-bearing attributes are wide-spread among surrounding rock fractures found in coal seam gas extraction boreholes.In order to analyze the diffusion behavior of the grout and sealing mechanism across gas-bearing frac-tures,the multi-step methodology for scientific research was applied.First,an individual gas-bearing fracture grouting diffusion experiment was designed to clarify the propagation law of the grout front as well as the response law of grouting pressure.Then,by using the theoretical model for the diffusion of fracture grouting,the distributions of grout front and pressure for gas-bearing fractures were analyzed,disclosing the coupling effect between the liquid(grout)phase and the gas phase.Finally,based on distribution characteristic analysis for the pre-and post-grouting fractures in gas-bearing coal,the migration characteristic for the grout within coal fractures was studied by numerical simulation,as well as the sealing mechanism under the liquid-gas coupling effect.We found that the diffusion front of the grout for the gas-bearing fractures shows an apparent"U"distribution shape,which becomes gentle by the migration for the grout.The arc angle of the front decreases with increasing gas pressure,while it in-creases with larger fracture aperture,higher grout viscosity,and faster grouting rate.Among these factors,gas pressure exerts a more pronounced influence on grouting pressure compared to grout viscosity,fracture aperture,and grouting rate.A negative-pressure environment fa-cilitates faster grout diffusion in the central part of the fracture but slows down flow near the fracture walls,thereby increasing the arc angle of the diffusion front.A sharp pressure drop is observed at the liquid-gas interface within the fracture,and the liquid-gas coupling effect weak-ens as grout migrates and fracture aperture enlarges but becomes more significant with higher absolute gas pressure,greater grout viscosity,and increased grouting rate.Post-grouting anal-ysis reveals that large-aperture fractures in gas-bearing coal are significantly reduced or elimi-nated,with some of them partially filled by grout and transformed into small-aperture frac-tures,increasing the proportion of small fractures.Negative-pressure conditions promote grout penetration into small-aperture fractures,whereas positive gas pressure hinders grout entry into branched small fractures.These findings enrich the theoretical understanding of grouting sealing in gas-bearing fractures and provide practical guidance for efficient grouting and sealing of surrounding rock fractures of underground gas extraction boreholes.