| China is a political and economic power,and a high resource-consuming country,whose energy source consumption highly depended on coal resource.China is rich in coal resources and coal-bed methane resources,but gas-related disaster has became one of the most serious disasters in coal mine.Therefore,the exploitation and utilization of coalmine gas is conducive to eliminating gas disaster and safety production,alleviating energy shortage situation,and reducing greenhouse gas emissions.The research of gas seepage development low is the basis of gas efficient extraction and utilization,thus,the research on gas low of solid/gas coupling were taken as study main line,the outburst coals of Songzao coal mine were used as research object,the coal microstructure was considered as study basic,and the theoretical modeling,experimental analysis and numerical analysis were taken as study method.The influence of moisture on coal microstructure is analyzed by high performance ESEM,and based on the above influence and porosity mathematical model,the permeability model considering moisture was developed.The effect of liquid wettability on gas flow was discussed and then the influence of different improving fluid on coal wettability and surface features were analyzed by experimental research.Based on the above research and experimental research on the influence of moisture on adsorption,the solid-gas coupling model considering moisture content was developed and also was verified by seepage experimental data.Moreover,the gas flow law under cycling loading and unloading of axial stress and confining pressure was experimented based on the protected coal seam stress developing law obtained by numerical analysis of FLAC3 D.Furthermore,the dual medium model contained fracture and matrix were build based on random fracture network,and then the gas flow law of gas-solid fracture network was analyzed.Therefore,based on the above researches and analyses,the conclusions and progresses were obtained as follows:(1)The dividing characteristic of rock uniaxial compression process can be obtained based on complete stress-strain rule,sample volume strain change law and fracture volume strain change law.The uniaxial compression process can be divided into five stage: fracture compressed stage,elastic stain stage,fracture stable initiation stage,fracture unstable initiation stage and structure failure.there exist some difference in fracture volume strain and sample volume strain of fracture stable initiation between hard rock and soft rock,and hard rock shows the continuously increase and soft rock shows an increase and the decrease.The main reason is that the matrix compression rate and the fracture volume expansion rate of hard and soft rock are different.This dividing characteristic can provide reference for the deformation law of soft and hard rock mass.(2)Using the high performance ESEM,the dynamic process of moisture infiltrates and regression in pore and fracture of coal have been obtained.Based on the chamber pressure,chamber humidity and fractal feature of the scan image,the dynamic influence process can be thought as five part as follow: environmental condition preparatory phase,moisture initial formation phase,moisture sharp formation phase,moisture fade-away and moisture rapid fade-away phase.In addition,the mathematical porosity model was proposed based on the occupied form of moisture in pore,and then the permeability model contained moisture content was developed and verified by previous research data,which show a good consistency with proposed permeability model.(3)The relations between the maximum contact height and contact angle were obtained based on wettability assumption of equal volume droplet.It can be obtained that the contact angle decreased due to the increase of fluid wettability under equal volume droplet,which can result in the increase of contact surface radius of solid-fluid,thereby increasing contact surface area of solid-fluid.Therefore,for the permeability-improving of reservoir,the less of improving fluid volume was used with better wettability of improving fluid for the same wetting area,which can save the cost of reservoir reform to some extent.In this,the coal wettability change law with different wetting phase under the effect of soaking of different improving fluid were discussed and analyzed.The research results have certain guiding significance for the selection of the improving fluid of reservoir reform.(4)Based on the permeability considering moisture content and the influence model of moisture on deformation-induced by absorption,the gas flow control equation contained the strongly coupled variable and the moisture influence.Based on the influence of the pore gas pressure and absorption-induced deformation considering moisture content on solid deformation,the solid deformation control equation can be developed.The developed gas-solid coupling model has the better prediction precision to describe the seepage experimental data compared with classical model.(5)The seepage experiments under change axial stress and confining pressure of circling loading and unloading were implemented based on the stress development route obtained from the numerical simulation of FLAC3 D.The seepage flux can be increased by confining pressure circling loading and uploading.The step-increase axial stress of circling loading and uploading can decrease gas flow flux to some extent.Moreover,the gas flow flux can be decreased about 60% by increase 1 MPa of confining pressure,and the gas flow flux can be decreased about 21% by step-increase axial stress.Therefore,it can be concluded that gas flow is more sensitive to the stress,which is vertical to gas flow direction,that is to say,the stress loading and uploading of vertical to gas flow direction can be one of the reason to trigger gas disaster.(6)The random fracture network can be built based on Monte-carlo random principle,and then the dual porosity medium considering matrix and fracture structure can be developed based on random fracture network and IM function imbedded in COMSOL Multiphysics.Then,the dual porosity medium has been set as computational domain,and the computational domain for gas extraction with single borehole has been simulated based on the developed solid-gas coupling model considering moisture content.Furthermore,the influence of moisture on porosity,permeability,volume strain,gas pressure distribution and gas flow flux were discussed in detail.This can provide a new method for study the gas flow characteristic of water-contained reservoir. |
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