Research On Expansive Fracturing And Increased Permeability Mechanism Based On The Low Permeability Coal Seam

The rapid economic and social development has led to a gradual increase in coal demand.This speeds up the extension of coal mines to deep coal seams in our country.Due to the multi-field coupling effect in the deep region and the decrease of coal seam permeability,this leads to increased difficulty in gas prevention and control around the mining area.This paper uses experimental analysis and field testing methods to measure expansive fracturing and increased permeability mechanisms.It has important theoretical and practical significance for solving the problem about the application of expansive fracturing,increased permeability and improving the gas treatment effect of the low permeability coal seam.This analyzed microstructure characteristics and basic reaction parameters of expansive materials before and after the hydration reaction experiment.The expansive pressure increased exponentially with the reaction time.The reaction temperature experienced four stages of slow rising,fast rising,reduce rising and slow falling.The composition ratio of Ca O-C₃S-C₃A was determined by mixing designed material and retarding experiment,which solved the problems of short retarding time and high temperature in the curing process of expansive materials.This leads the retarding time being extended to 175min and the reaction temperature was reduced to 100℃.It improved the pore structure of the coal,achieved the purpose of slow increased permeability,promoting gas desorption and preventing coal spontaneous combustion.Based on the full-field strain and acoustic emission of coal macroscopic crack monitoring system to analyze the expansive fracturing under the condition of surrounding rock stress combination loading strain,acoustic emission and dynamic response characteristics.The development of coal crack showed a trend of slow growth.With the increase of surrounding rock stress,it will cause the expansive pressure required to increases and the fracturing time increases.The effects of ultra-slow loading,thermal action of expansive materials on permeability and stress-strain of coal were analyzed by using THM-3 thermal-fluid-solid coupling triaxial seepage test device.The strain of coal increases and the damage degree is higher,which is beneficial to gas migration.Based on the experimental data of true triaxial coal expansive fracturing and increased permeability the dynamic evolution characteristics of seepage,stress and reaction time of coal under the condition of expansive fracturing were constructed.In the elastic compression stage,the permeability decreased with reaction time,and the expansive pressure increased with reaction time in a quadratic polynomial trend.At the stage of yield damage,the plastic deformation of coal leads to an increase of permeability.The expansive pressure decreases exponentially until the coal is completely broken.A multi-field coupled increased permeability model of temperature-seepage-stress-chemical field was constructed to reveal the spatio-temporal evolution of permeability during the process of expansive fracturing.The increased permeability effect based on the low permeability coal seam was simulated and analyzed.The dynamic evolution law of the increased permeability effect of expansive fracturing was determined with the time of extraction and the location of hole distribution.The field test was carried out with the developed insulating resin expansive device.The gas extraction efficiency of the coal seam was improved obviously after the expansive fracturing.The gas extraction volume was increased by 1.6 times and the extraction concentration was increased by 2-3 times.This research provides theoretical guidance for the field application of expansive fracturing and increased permeability technology.Figure 120;Table 18;Reference 152...