| Gas drainage is the main technical means of gas prevention and control in China's coal mines,and the effect of gas drainage in coal mines depends to a certain extent on the sealing quality of drainage boreholes.The application of high-performance sealing materials and appropriate sealing technology can significantly improve the sealing quality.Traditionally,the static sealing technology of "two blockages and one injection" is often used to plug boreholes.The solidified sealing material is difficult to plug effectively the newly developed air leakage cracks in the extraction process,which results in low gas concentration and poor effect,and the air leakage of cracks is easy to lead to coal oxidation spontaneous combustion and other disasters.Aiming at the technical problem of efficient drilling of new cracks around boreholes in the process of pumping,this paper adopts the method of combining theoretical analysis,experimental research and engineering application to analyze the wall stress characteristics of formed boreholes,and probes into the distribution characteristics of borehole stress under roadway conditions,the regional distribution law of borehole radial cracks and their development characteristics;on this basis,research and development are carried out.An internal graded granular cellulose mucus sealing material with high permeability and selfadapting fracture development characteristics was developed,and its optimum proportion and performance parameters were obtained.Based on curtain grouting method,a bag-mucus combined self-adapting dynamic sealing technology with pressure was proposed.The main conclusions are as follows:Firstly,according to the stress characteristics of coal and rock mass around the roadway,the stress variation characteristics of surrounding rock around the borehole are calculated theoretically,and the controlled conditions of crack generation are obtained.Based on the similar simulation experiment,taking the low-rank coal of 40202 mining face of Dafosi Mine in Shaanxi Province as the research object,the growth degree,width and area proportion of cracks after drilling excavation are analyzed,and the statistical distribution characteristics of three types of typical crack scales are obtained: type I cracks are deeper and wider,crack branches are more and large cracks are connected with small cracks;type II cracks are long strips,with fewer branches and their cracks are wide.The degree of fracture is narrower than that of type I,and the length of fracture is longer than that of type I.The type III fracture is caused by the connection between type I fracture and type II fracture,and the fracture area is the largest.Secondly,the stress conditions of graded particles and the formation process of plugging curtain were analyzed.Based on the fracture size distribution characteristics and particle gradation theory,the optimum amount and proportion of particles were selected.Carboxymethyl cellulose nano was used as the main material,with gelatin,sodium polyacrylate and other additives,and coconut oil fatty acid diethanolamide as surfactant.The optimum composition of graded granular cellulose mucus sealing material was obtained as follows: sodium carboxymethyl cellulose 6 phr,sodium polyacrylate 1 phr,8 phr of graded granule,3 phr of gelatin powder,0.05 phr of coconut oil fatty acid diethanolamide,160 phr of water.At the same time,the viscosity,water retention,stability and expansion of the new graded granular viscous sealing agent were measured systematically.The results show that the new type of viscous sealing material has good stability,easy grouting,high expansion rate and good contact with coal wall.Compared with the traditional sealing agent,the sealing performance of the new type of viscous sealing material has been significantly improved.Thirdly,aiming at the problem that traditional polyurethane sealing technology and "two plugging and one injection" cement mortar sealing technology are difficult to adapt to dynamic crack sealing,a bag-mucus combined pressure adaptive dynamic sealing technology is proposed,that is,the modified sealing agent injected into the combined bag,the granular graded mucus injected between the bags under adaptive pressure,and the dynamic transportation of graded particles in the crack.The "curtain sealing" of new cracks is formed by moving and stacking bridges,which realizes the dynamic sealing of the development process of new cracks.Aiming at the new regional fracture groups induced by the dense drilling field in the extraction process,the second dynamic sealing technology of regional fracture fields of hole groups is proposed,which takes the self-adaptive sealing technology as the core and implements curtain dynamic mucus between dense drilling holes.The effective sealing of regional fissures in drainage hole group is realized by adding injection.Finally,based on the above research results,the project is applied in Dafosi Coal Mine,Xianyang,Shaanxi Province.The results show that,compared with the original polyurethane borehole sealing technology,the bag-mucus combined pressure adaptive dynamic sealing technology can increase the gas extraction concentration of boreholes by more than 30%.For the regional fissure field with Dense Boreholes in the drilling field,the second dynamic sealing technology can increase the gas extraction concentration from 2% to 60%.Within 30 days,the gas extraction concentration of single borehole can be increased by more than 10 times,and the application effect is obvious.The research results provide theoretical guidance and technical support for the efficient plugging of pre-drainage gas boreholes in coal mines. |
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