Study On Borehole Layout And Gas Drainage Sealing Technology Of Soft Coal

With the continuous increase of coal seam mining depth in our country,the gas disaster is becoming more and more serious.Gas drainage is the fundamental measure to solve the gas problem.Because of the soft coal quality in high gas soft coal seam,the layout and sealing of hole spacing has always been the key and difficult point of gas control in coal mine.In the mainstream research,the reasonable arrangement of borehole spacing in soft coal often uses a single gas flow method or pressure drop method as the basis of borehole spacing arrangement,and several measuring methods are rarely put into one roadway for comprehensive test and analysis.Therefore,trying to combine several methods to determine borehole spacing may greatly reduce the error caused by a single determination method,so as to improve the rationality of borehole spacing arrangement in soft coal.The special coal quality condition of soft coal seam puts forward higher requirements for borehole sealing material than ordinary borehole sealing.while ensuring good sealing performance of borehole sealing section,sealing material is required to have a good consolidation and supporting effect on borehole.Therefore,in order to improve the gas drainage effect of boreholes in high gas soft coal seam,it is of great significance to carry out the research on the reasonable arrangement of borehole spacing in soft coal and the new sealing material for boreholes.This paper takes Yuwu Coal Industry of Lu'an Group as the research object.First of all,based on the relevant national regulations on coal mine gas extraction up to the standard,such as "Coal Mine Safety regulations","interim provisions on Gas extraction Standard" and"provisions on Prevention and Control of Coal and Gas outburst",and determine the basic parameters and occurrence law of coal seam gas in the test area to understand the occurrence of coal seam gas.In this paper,the situation of substandard gas drainage in Yuwu coal industry is compared and analyzed,and the main reasons affecting the substandard of borehole gas drainage are found out.Secondly,the stress of coal around boreholes in high gas soft coal seam is analyzed,and the stress and displacement of borehole instability on coal fissures around holes are discussed based on the theory of elastic-plastic deformation,which puts forward new requirements for the reasonable arrangement of borehole spacing and sealing materials.Thirdly,in order to determine the reasonable spacing of boreholes in soft coal,the development of cracks around boreholes during drilling disturbance is preliminarily known based on the microseismic monitoring system,and it is obtained that the crack development range of drilling disturbance is 0.85-0.95 m.With the help of gas flow method,the hole spacing in different pre-extraction periods is determined,and the reasonable hole spacing in different pre-extraction periods is reduced to 1mm,and the hole spacing greater than 4m does not meet the requirements of drilling standards.Finally,combined with the pressure drop method,the reasonable spacing of boreholes in different pre-extraction periods is further determined,and the effective influence radius of gas with different extraction time is obtained.Then,according to the special geological conditions of drilling in high gas soft coal seam,a new sealing material with high strength and micro expansion matching with high gas soft coal seam is developed.The effects of key factors on the expansion and compressive strength of reinforced materials were explored by single factor analysis,and the interactive effects of key factors on expansibility and compressive strength were further determined by response surface analysis((RSM)).The optimal experimental conditions were obtained:aluminum powder and quicklime 0.52%,gypsum 2%,water-material ratio 0.6.Finally,a new type of seal with compressive strength of 15.6 MPA and expansion rate of about 10%was obtained.at the same time,the mechanical properties of the new sealing material and mine sealing material were compared and analyzed.Finally,on the basis of the above research,by optimizing the distance between boreholes and selecting a new type of borehole sealing material for field test,compared with the unoptimized hole in Yuwu Coal Industry,the gas concentration of the optimized hole is about 10%higher than that of the ordinary hole.The optimized drilling hole can effectively improve the efficiency of gas drainage and ensure that the gas extraction reaches the standard.