Mechanism Of Infiltration Evolution And Seepage Of Coal Seam Water Injection With Surfactants

Coal seam water injection technology is an important means of coal mine dust control and gas disaster prevention.With the application of chemical dust reduction technology,additive coal seam water injection technology has also received widespread attention.Additives are wetting agents composed of one or more surfactants to promote the wettability of coal water.However,at present,the research on the infiltration and seepage law of coal seam water injection with surfactant lacks consideration of the interfacial wettability in the flow process,which is not conducive to the optimization and selection of coal seam water injection parameters.Most of the researches on the wetting effect of surfactants are surface wetting and pulverized coal wetting,but the uniform degree and distribution of wetting have an important influence on the dust reduction effect of the flow in the dual medium of coal seam water injection pores and fractures.For this reason,this paper studies the internal wetting and seepage law of water injection in coal seam with surfactant by means of theoretical analysis,laboratory experiment and numerical simulation.Firstly,the solid-liquid contact characteristics of surfactant solution and coal and the multi-scale pore structure of liquid percolation were studied.The micro-mechanism of surface wettability of coal samples was analyzed by means of industrial analysis,Fourier transform infrared spectroscopy and 3D morphology tester.The indirect antennae,contact angle decay rate and capillary rise factor of different concentration of surfactant solutions and different coal samples were measured by the contact angle measuring instrument.The results show that the contact angle and capillary rising factor of anthracite,bituminous coal and lignite decrease in turn,and the decay rate of contact angle reflects the dynamic change of solid-liquid interface wetting.It is found that the surfactants of OP-10,JFC and AES have stronger wetting ability.The multi-scale characteristics of pore fracture structures of anthracite and bituminous coal samples were studied by scanning electron microscope(SEM),industrial CT,nuclear magnetic resonance(NMR)and low temperature liquid nitrogen adsorption experiments.It is found that some fracture surfaces are interlaced and some are relatively discrete,forming different pore fracture structure characteristics.Through induction and summary,it is combined into four kinds of characteristic models according to fracture continuity and pore connectivity.The above two parts provide wettability parameters and pore fracture structure parameters for follow-up research.In order to study the influence of self-absorption of coal on coal seam water injection,the short-term and long-term imbibition experiments of different surfactants were carried out by using complex resistivity method and weighing method.The imbibition coefficient was calculated based on Lucas-Washburn-Darcy model,and the permeation water distribution law of water and surfactant solution was obtained by nuclear magnetic resonance technology.The results show that the better the wettability of the liquid is,the greater the absorption coefficient is.The higher the porosity is,the higher the osmotic coefficient and mass growth rate are.In addition,the distribution of fluid in the coal sample is obviously non-uniform in the process of imbibition,which is related to the heterogeneity of coal pore and fracture structure.The main distribution range of fluid in coal sample under the action of imbibition is 0.002μm～0.2μm pore diameter.In order to study the seepage law of water injection in coal seam containing surfactant,the water injection experiments with different water pressure,surfactant and concentration were carried out by using the self-built liquid phase triaxial seepage experimental system of cylindrical coal core.Based on the dynamic apparent permeability coefficient model,the effects of capillarity and pore fracture characteristics on permeability coefficient are analyzed.The law of water distribution in the process of water injection and surfactant injection is analyzed by nuclear magnetic resonance imaging(NMR).Finally,based on the seepage model of double porous media,a differential equation considering imbibition effect is constructed to simulate and study the water seepage distribution law of specific pore fracture characteristics.The results show that the apparent permeability coefficient model can better describe the unsaturated flow process,especially for the seepage process of low permeability coal samples,the permeability coefficient tends to constant when the pore connectivity is good,and the permeability coefficient is relatively large when surfactant is injected.Compared with the imbibition experiment,the pressurized water can penetrate into the nano-scale pores,and the wetting peak of the surfactant solution moves at a higher speed.The change of water saturation of the through fracture-low pore permeability characteristic model is close to that of the non-through fracture high pore permeability characteristic model,indicating that the pore permeability plays an important role in the change of water saturation during water injection.The increase of capillary force and pore diameter is beneficial to improve the imbibition efficiency.The research results are expected to enrich the research on the seepage law of additive coal seam water injection and provide help for predicting the wetting effect of coal seam water injection.The dissertation includes 140 figures,34 tables and 198 references.