Study On Influence Law And Regulation Method Of Water On Gas Desorption And Adsorption Characteristics Of Coal Sample

High-gas coal seams have generally low permeability and dry coal body,and coal&gas outburst disasters are easy to occur in the mining process.Hydraulic measures can significantly improve the gas seepage and diffusion.The wettability and adsorption/desorption characteristics of the coal body modified by additives will be also changed.However,the invasion of external liquid has dual effects of displacement and water-blocking on the gas.In order to explore the coupling outburst prevention mechanism of these two effects in the process of water injection,combined with theoretical analysis and experimental research,it studies the influence of water intrusion on gas displacement and water-blocking effect under high pressure,selecting three additives to transform the structure of coal sample and expounding the relationships between the structure characteristics and adsorption/desorption characteristics of coal sample.The main results are as follows:（1）The basic physical parameters of coal samples are tested.The volatile content in coal accounts for less than 37%,with poor wettability.The ash content is more,so it has a great impact on the wettability.The contact angle is 105.98°.The porosity of coal sample is 4.12%,and the average pore diameter of micropore is 0.479nm,and the total pore volume is 0.076cm³/g,and the total specific surface area is 259.35m²/g.In a certain range,the larger the moisture content is,the smaller the△P and a is,indicating that moisture has an inhibitory effect on the adsorption/emission performance of coal.（2）Through the experiment of displacement of gas by post isobaric water injection,it can be seen that within a certain range,the water injection ratio is directly proportional to the displacement of gas,inversely proportional to the pressure relief desorption capacity,and directly proportional to the water-bocking capacity.The adsorption equilibrium pressure is directly proportional to the gas displacement,directly proportional to the pressure relief desorption and inversely proportional to the water-blocking.Increasing the equilibrium pressure can weaken the water-blocking effect.Water injection displacement can promote the gas drainage efficiency in the process of water injection,while the water lock effect can inhibit the rapid desorption and release of gas in the process of coal seam mining,because time stages of the two effects are different.（3）Through selecting 1-butyl-3 methylimidazolium tetrafluoroborate,sodium dodecyl sulfate and hydrofluoric acid to treat coal samples,it is found that when specific surface area of micropores in coal samples decreases,the average pore size increases,and micropores change into mesopores resulting in the reduction of micropore volume,the adsorption site for gas decreases,and the gas content that can be adsorbed decreases.Aliphatic hydrocarbons and aromatic hydrocarbons are hydrophobic,and oxygen-containing groups such as carboxyl and hydroxyl are hydrophilic.When the average chain length（I₁）and fat ratio（I₂）decrease and the ratio of oxygen enrichment（I₃）increases,and the carbon structure arrangement of coal becomes closer,and the crystal nucleus diameter increases,and the aromatic layer is more flat,and the condensation degree and aromatization degree of coal become higher,the contact angle becomes smaller,the wettability of coal increases,and the difficulty of external liquid entering coal decreases,that is helpful to strengthen displacement and water-blocking effect.（4）Through the experiment of displacement of gas by post isobaric additive solutions injection,it is found the wettability of coal body is the direct reason affecting whether the solution can enter the pores and fissures.The smaller the contact angle is,the stronger the wettability of coal sample is,and the less difficult it is for the solution to enter the coal,so the displacement amount and water-blocking amount of solution to gas increase.If the solution is acidic,although it will separate most minerals in coal and increase the contact angle,it also widens the pore fissure channel,so it can strengthen the displacement effect and weaken the water-blocking effect.（5）According to the experimental research,the optimization scheme of coal seam gas drainage is put forward,that is,"Pre-mining high-pressure water fracturing to increase permeability of coal seam to strengthen gas drainage+Mining medium low-pressure water injection to block residual gas".And additive solution is injected in the process of high-pressure water injection to strengthen the wettability of coal body,so that more gas can be discharged through the open pore fissure channel.In the process of face mining,additive solution is injected at low pressure to strengthen the water-blocking effect,so as to ensure there will be no sudden emission of gas during mining.There are 81 figures,15 tables and 115 references in this thesis.