A refined numerical solution method for effective extraction radius based on gas pressure around drilling
In view of the unclear representation of the effective extraction radius of coal seam drilling,the critical value of gas pressure corresponding to the effective extraction radius was first determined,and then the gas pressure variation rule around the drilling was cal-culated using the expression of the radial flow field gas pressure of the drilling.The reliability of the calculation results was verified by the field measurement data.Then,the sensitivity of negative pressure in extraction,permeability coefficient,drilling radius and adsorp-tion constant to gas pressure distribution in coal seam was analyzed.Finally,the effective extraction radius was determined according to the critical gas pressure index,which is verified by the field gas content detection data,and the functional relationship between the effec-tive extraction radius of drilling and different original gas pressure under different pre extraction time was discussed and deduced.The results show that the gas pressure calculated by theory and the effective extraction radius are basically consistent with the field measured data.The gas pressure is inversely proportional to the extraction time and proportional to the distance from the drilling.negative pressure in extraction,permeability coefficient,drilling radius and adsorption constant b are negatively correlated with gas pressure,while adsorp-tion constant a is positively correlated with gas pressure.The effective extraction radius increases with the increase of extraction time,which conformed to the logarithmic function type.Through the deduced effective extraction radius,pre extraction time and original gas pressure function relation,the corresponding effective extraction radius can be easily and quickly calculated,and the reasonable drilling spacing can be determined,which has certain theoretical significance for the fine design of coal seam gas extraction drilling.
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