Study On Surface Wettability And Gas Desorption Characteristics Of Coal Under Surfactant Modification Effect

In the context of the"double carbon"goal,China’s energy sector is accelerating the safe,green,economic,low-carbon and high-quality development of the coal industry.However,most coal mines in our country are mainly coal seams with low permeability.After gas extraction through coal seams,there are still hidden dangers such as gas concentration exceeding the limit.The research shows that the wetting effect of coal rock surface can be improved by injecting surfactant water solution into coal rock,and the desorption performance of gas can be effectively inhibited.In this thesis,six coal samples with different degrees of metamorphism are selected to carry out wettability experiments of coal,and gas coal with low degree of metamorphism is the key research object.From the microscopic perspective of coal,the influence characteristics of surfactant aqueous solution on oxygen-containing functional groups,free radicals and pore structure of coal are explored.At the same time,the water injection test device after gas adsorption-desorption of coal was independently built,and the gas desorption test study of pre-adsorption equilibrium coal samples under the condition of injecting surfactant aqueous solution was carried out.The main conclusions are as follows:（1）The surface tension of the surfactant solution and the contact Angle with the six coal samples decreases rapidly with the increase of the concentration,and tends to be stable when the concentration reaches the critical micellar concentration（CMC）.It is believed that with the increase of the concentration of the surfactant aqueous solution,the surfactant molecules gradually form the saturated adsorption monolayer at the gas-liquid interface and reach the stability.The contact Angle between the surfactant water solution and the coal sample presents an inverted U-shaped change with the increase of the metamorphism of coal rock,and the wettability effect of Kuai-T,AEPO-9,6501 on different metamorphism of coal rock is obviously better than that of SDBS,CAB-35,APG0810.The orthogonal test showed that the optimal solution of concentration ratio of complex surfactant solution was0.02%AEO-9+0.06%6501+0.04%fast T.The wetting effect of complex surfactant solution was better than that of single surfactant,resulting in a synergistic effect of"1+1>2".（2）The total peak area of the oxygen-containing functional groups（hydroxyl,carboxyl,carbonyl and ether bonds）of coal is positively correlated with the concentration of the aqueous solution of AEO-9 surfactant,which is attributed to the hydrophilicity of the oxygen-containing functional groups.With the increase of the aqueous solution concentration,the increasing oxygen-containing functional groups improve the wettability of the aqueous solution on the coal surface.Meanwhile,Lande g factor,line widthΔH and free radical concentration N_gincreased first and then tended to be stable with the increase of the concentration of AEO-9 surfactant aqueous solution.In the range of 0～0.2%,the peak area of oxygen-containing functional group and free radical concentration N_gincreased by 67.91%and 66.90%,respectively.（3）The development degree of micropore structure of coal samples soaked in surfactant water solution is weakened,especially the specific surface area and pore volume of micropores in the range of 1-10 nm decrease obviously with the increase of the concentration of water solution.At the same time,the surface fractal dimension D₁decreases with the increase of aqueous solution concentration,and the structural fractal dimension D₂shows an inverted U-shaped trend of first increasing and then decreasing with the increase of aqueous solution concentration.（4）Under the same preadsorption equilibrium pressure,the gas desorption performance parameters（Q₁,Q_∞,V₁）of dry coal samples are the largest,followed by the coal samples with water,and the coal samples with surfactant water solution are the smallest.With the increase of the concentration of the injected surfactant aqueous solution,the gas desorption performance parameters of coal gradually decrease.When the solution concentration is greater than CMC value（0.0389%）,the degree of gas desorption capacity of coal samples tends to be stable.The analysis shows that the surfactant reduces the surface tension of water solution and the contact Angle of water solution on coal surface.At the same time,the"clusters"of water molecules block or fill micropores in the form of capillary condensation,and the adsorption of water by coal causes the expansion and deformation of the matrix to weaken the pore structure of coal,resulting in the increase of the capillary force of coal pore,thus weakening the desorption and diffusion ability of gas.In addition,the compound surfactant aqueous solution has better inhibition effect on coal gas desorption than the single AEO-9 surfactant aqueous solution.