Coupling Of Coal And Water And Its Application In Gas Control Of Hujiahe Coal Mine

Due to the complex geological conditions of coal mines in China,mine gas is still the main source of mine disasters.According to statistics,in the occurrence of coal resources in China,the middle-high rank coal and low rank coal account for half of the total.Therefore,the efficient gas extraction and coal mine safety production of low rank coal reservoirs are of great significance to ensure the supply of coal energy in China.Practice has proved that gas drainage is one of the main technical means to prevent and control the gas disaster in coal mine.However,the characteristics of coal seam,the gas concentration in high gas,low permeability and low rank coal reservoir is low and the drainage effect is poor,which makes the conventional drainage technology difficult to meet the requirements of the safety production of coal mine.It has been proved that the hydraulic measures are one of the effective technical measures for gas control.Therefore,according to the characteristics of gas occurrence in low rank coal reservoirs,it is of great practical significance to study the new technology of gas hydraulic control in low rank coal seams with high gas and low permeability,so as to reduce the gas disaster of low rank coal and ensure the safe mining of low rank coal in Western China.In this paper,based on the research of Hujiahe coal mine gas,the coupling effect of coal and water in the process of high-pressure water intrusion into coal body and the law of its effect on coal body cracking,coal bed gas desorption,displacement and seepage are systematically studied by means of theoretical analysis,experimental research and field test.On this basis,a new method of low rank coal gas control is put forward,which is the combination of " highpressure water inducing coal cracking and permeability increasing and residual wate sealing gas ".The specific research results are as follows:1)the wetting characteristics and influencing factors of coal body in hujiahe mine are analyzed.It is found that the metamorphic degree of coal body in hujiahe mine is low and the wetting characteristics are poor.The wettability of coal body in hujiahe mine is affected by factors such as surfactant,pore structure,surface functional group,etc.: surfactant can significantly improve the wettability of coal body,the pore of coal body is inverted ink bottle type pore,and there are many surface pores,and the hydrophilic groups on the surface of coal body occupy a low proportion,so it is not easy to be wetted.2)the adsorption capacity of coal gas increases with the increase of equilibrium pressure.Due to the existence of water molecules,it has competitive adsorption with methane,plugging pore channels and hindering the adsorption of coal body,which makes the adsorption capacity of coal gas gradually reduce with the increase of water content under constant pressure;when the water content is 8%,the final adsorption capacity is the smallest.3)the seepage experiment of the loaded water bearing coal body is carried out on the seepage experiment platform.It is found that the permeability of coal sample decreases with the increase of water content under the condition of constant air pressure;the permeability K of coal sample decreases with the increase of confining pressure under the condition of constant water content and different confining pressure;the permeability K of coal sample decreases with the increase of confining pressure under the condition of constant water content and different confining pressure With the increase of pressure,the permeability K of coal decreases first and then increases,showing a "V" shape,and the inflection point of permeability K of coal sample is around 2.5 MPa.4)with the increase of water content,the compressive strength of coal samples decreases gradually and the peak strain increases.Under the same conditions,the yield limit in the direction of parallel bedding is obviously greater than that in the direction of vertical bedding.The hardness of Hujiahe coal is strong.During the experiment,the acoustic emission signal is less at the beginning,but at the yield stage,the stress and acoustic emission signal almost reach the peak value at the same time5)through the experiment of high pressure water acting on the water bearing coal,it is found that the crack initiation point of the water bearing coal decreases exponentially with the increase of the water content of the coal body.With the increase of water content,the peak value of compressive strength continuously shifts to the right,and the compaction interval of coal body also expands with the increase of water content.With the increase of water content,the number of adsorption holes decreased and percolation holes increased.The desorption experiments of coal samples before and after high-pressure water injection show that the desorption of coal decreases with the increase of water content;compared with the desorption law of coal samples after injection and without injection,it can be seen that the desorption gas amount after injection decreases.6)through the field test of high-pressure water injection,it is found that the gas in the highpressure water fracturing test is at a high concentration for 30 days,which indicates that the permeability enhancement effect of the fracturing test is significant;the final gas concentration of the water injection test borehole is lower than that of the extraction test,and the water injection has a retardation and slow-release effect on the gas of the coal extraction body,so the water injection can obviously inhibit the gas release of the coal.The research results have certain scientific significance for the engineering application of high-pressure water injection to increase permeability and block residual gas,which is conducive to better grasp the change law of gas adsorption and seepage in coal seam and gas extraction mechanism in Hujiahe mining area,and provides theoretical support and guidance for the establishment and Engineering application of high-efficiency gas extraction method in coal reservoir of Hujiahe mining area.The paper has a total of 81 pictures,22 tables,and 99 references.