| Coal and gas outburst is one of the main geological disasters affecting deep coal mining.With the increase of mining depth year by year,the ground stress and coal seam gas parameters are increasing,which aggravates the severity of coal and gas outburst.The traditional regional outburst prevention measures under deep conditions have problems such as long construction period and low extraction efficiency,which seriously affect the safe and efficient production of coal mines.Therefore,in order to improve the efficiency of gas control,a large diameter,long distance,high efficiency and low cost area penetration technology has been developed by directional drilling.In this paper,aiming at the problems such as insufficient theoretical basis for borehole parameter design,difficult determination of coal seam gas parameters,and inaccurate evaluation method of coal seam outburst elimination in the outburst prevention aspect with directional boreholes,a lot of ways are used to establish the dual-permeability gas-solid coupling model of gas migration in coal body under considering matrix and fracture strain to make sure the directional borehole layout parameters by studying the gas extraction under the condition of negative pressure continuous attenuation in borehole,build a mathematical model for inversion of original gas pressure and content of coal seam to analyze regional difference characteristics of coal seam gas parameters and put forward efficient dynamic method to evaluate the effect of coal seam outburst elimination,which is verified in Xuehu coal mine.The main results were as follows:(1)The effect mechanism of negative pressure on gas emission is discussed.The differential equation of pressure drop is established when gas fluid with variable mass flows in the borehole to obtain the unsteady distribution model of extraction negative pressure along the direction of borehole length by studying the mechanism of extraction negative pressure on gas emission.The attenuation law of negative pressure of borehole extraction is analyzed.Results show that the negative pressure attenuation in the borehole changes in exponential function under the condition of known drilling parameters.(2)By putting forward mechanical compression coefficient and adsorption coefficient,the dual-permeability gas-solid coupling model of gas migration in coal body under considering matrix and fracture strain is established basing on elastic theory of porous media,effective stress law and adsorptive strain theory.Then,the evolution process of gas gushing in the large-bore multi-branch directional drilling under the unsteady distribution of negative pressure extraction is simulated to determine the spacing of the directional borehole.Results show that effective influence radius of each branch hole for gas extraction is decreasing along the direction of hole length,and the optimal spacing of directional drilling in test coal seam is determined.(3)An inversion model of coal seam gas parameters is established based on the gas emission quantity from borehole by analyzing the law of gas emission from coal cuttings and coal walls during drilling.Then,the inversion method of coal seam gas parameters while drilling is proposed,which is applied in the field.Results show that the gas parameters of coal seam are not uniformly distributed and have obvious regional difference characteristics,and the data are normally distributed.The inversion calculation error is between 5.35% and 18.18%,which proves the accuracy and reliability of the inversion model.(4)Based on the fine distribution of gas pressure,the evolution process of coal seam gas drainage and total amount of gas drainage,an efficient dynamic evaluation model for coal seam outburst elimination is established,and on-site verification is conducted.Results show that traditional gas extraction evaluation method for coal area in the calculation amount of coal seam gas,standard gas extraction,extraction rate and extraction time have bigger error,it is impossible to ensure that all coal seam extraction reaches the standard within the specified time,while the new model calculation results and the actual closer to,higher reliabilityThe research results of this paper are of great theoretical significance and practical value for strengthening the research on the precision and visualization of coal seam gas parameters,perfecting the theory and technology of the regional outburst prevention with boreholes,and realizing the precise prevention and control of coal and gas outburst.The dissertation contains 221 pictures,17 tables and 221 references. |
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