| Diffusion plays an important rolein the process of gas migration output,but now the study of the diffusion regularity of tectonically deformed coal mostly adopt particle coal and desorption diffusion method,which cannot objectively reflect the physical properties and reservoir conditions of original coal seam,diffusion controlling mechanism is short of the coupling analysis of internal and externalfactors,and especiallyexisting diffusion model have great disadvantages of highly-idealized degree,low accuracy and unclear suitable conditions.To solve the above problems,starting with actual occurrence state of underground coal seam,by gas chromatography diffusion method and desorption diffusion method,the experiments on gas diffusion law of tectonicallydeformed coal were carried out,the factors such as confining pressure,air pressure,temperature,coal quality,coal body structure,microstructure that affect the gas diffusion law and coupling controlling mechanism are discussed,tectonicallydeformed coal gas diffusion model that reflect different stratum conditions are set up,and the new model is validated and applicable.The results show that,(1)Four types of pillared sampling methods are used to process raw coal,and difficulty of sampling fragmented-mylonitic coal is solved.An isostatic pressing specimen of tectonically deformed coal is prepared.(2)The experiments such as mercury injection,nitrogen adsorption,small Angle X-ray scattering and scanning electron microscope are used to analyze the microscopic pore and crack features of tectonically deformed coal,and fractal dimension quantitative characterization method for the whole aperture of tectonically deformed coal is put forward,which lay the foundation forrevealing gas diffusion controlling mechanism of tectonically deformed coal.?The pore volume of anthracite and meagre coal are mainly distributed in micro and transitional pore,while fat coal transitional pore and mesopore,but the distribution of specific surface area are all in micro pore.The total pore volume,specific surface area and mercury ejection efficiency of the three types coals increased as the damaged degree increased,while the median aperture and expulsion pressuredecreased as the increase of damaged degree,but the rates of increase or decrease were not same atdifferent stages.?In the same aperture,pore specific surface area tested by SAXS was obviously greater than the experimental results by liquid nitrogen adsorption,about 1.7~8.8 times higher,and the biggest increase was anthracite.This is caused by the increase of closed pore.?The calculation methods of whole aperture fractal dimension of tectonically deformed coal was defined and put forward,and the effective unification of whole aperture fractal dimension was realized,whichprovided a convenient for the quantitative characterization of heterogeneities in tectonically deformed coal.?Total numbers of microscopic cracks of anthracite,meagre coal and fat coal present a rule that increased first and then decreased as the increase of damaged degree,in which the microscopic cracks of cataclastic coal developed best.(3)The diffusion coefficients were respectively tested by methods of gas chromatography to pillared coal sample and desorption method to particle coal sample,difference and applicability of the two methods to reflect the tectonically deformed coal gas diffusion law were studied,and the factors such as confining pressure,air pressure,temperature,damaged degree that affected gas diffusion law of tectonically deformed coal were discussed.?A gas chromatography experiment platform to test gas diffusion coefficient by simulating the conditions of original stratum was set up.?The method of gas chromatography to test diffusion coefficient,by exerting confining pressure,air pressure and temperature on raw pillaredcoal sample,while desorption method only exertair pressure and temperature,no considering confining pressure.Both the diffusion coefficient determination methods can reflect the gas diffusion law of tectonically deformed coal,but the stratum occurrence state of samples isdifferent,which cannot simplyreplace each other.The former is mainly used to predict and evaluate gas diffusion rate in original coal seam,the latter is mainly applied to calculate lossesin the process of gas content determination.?In gas chromatography experiment,the diffusion coefficients of four types coal structure in anthracite,meagre coal and fat coal present an exponential relation decreased as the increase of confining pressure,but as the increase of air pressure and temperature,the diffusion coefficients of them increased by exponential relation.At the same conditions of confining pressure,air pressure and temperature,the diffusion coefficients of four types coal structure in anthracite,meagre coal and fat coalpresent a rule that first increased and then decreased as the increase of damaged degree,and diffusion coefficientsof the same damaged degree samples first increased and then decreased as the increase of metamorphic degree.?In desorption experiment,the diffusion coefficients of four types coal structure in anthracite,meagre coal and fat coalpresent an exponential relationincreasedas the increase of air pressure,and as the increase of temperature,the diffusion coefficients of them increased by linear relation.At the same conditions of air pressure and temperature,the diffusion coefficients of four types coal structure in anthracite,meagre coal and fat coal increased as the increase of damaged degree,and diffusion coefficients of the same damaged degree samples also increased as metamorphic degree increased,which were markedly different from the results determined by gas chromatography method.The two methods reflect the gas diffusion law of tectonically deformed coal in the different stratum condition.(4)The internal and external factors such as confining pressure,air pressure,temperature,coal quality,coal body structure,microstructure that affect the gas diffusion law and controlling mechanism are analyzed,tectonically deformed coal gas diffusion model that reflect different stratum conditions are set up,and the new model is validated and applicable.?The influence of temperature on the gas diffusion law of tectonically deformed coal from different stratum conditions are basically identical,and the diffusion coefficients increase as the temperature rise,the control mechanism of which is the root-mean-square speed and mean free path of gas molecules were changed.?At macro-scale,the influence of pressure on the gas diffusion rules of tectonically deformed coal present the diffusion coefficient increase as the pressure rise,but the control mechanism is different.There are two situations: first,when put the confining pressure on coal sample,the diffusion law is controlled by mechanical functions and adsorption,and the main controlling factor is the effective stress,and diffusion coefficient of tectonically deformed coalhas a negative effect to the effective stress.Second,when there is no confining pressure on coal sample,that is a unloading state,and the air pressure is mainly to change the concentration grads of adsorption gas and the root-mean-square speed and mean free path of gas molecules.Pressure relief has an important influence on microscopic pore structure of coal sample,which may lead some closed and semi-closed pore to open.?Under the same condition of temperature and pressure,diffusion coefficientdetermined by gas chromatography method first increased and then decreased as the increase of metamorphic and damaged degree,mainly controlled by microscopic pore and microscopic crack,while diffusion coefficient determined by desorption method increased as the increase of metamorphic and damaged degree,mainly controlled by original pore structure characteristics and the distribution featuresof original microstructure changed by external environment,and micro pore,flask pore,and some closed poreplay a leading role.Both the diffusion coefficient determination methods can reflect the gas diffusion features of tectonically deformed coal,but the key control factor and application conditions are different,which cannot simply replace each other.?According to main factors affecting the tectonically deformed coal gas diffusion law,different modeling tools and principle were selected,and tectonically deformed coal gas diffusion model that reflect different stratum conditions were set up.Tectonically deformed coal gas diffusion coupling mode based on gas chromatographic methodis mainly used to predict and evaluate gas diffusion rate in original coal seam,and tectonically deformed coal Fractal – Time related-Fick diffusion model based on adsorption methodis mainly applied to calculate losses in the process of gas content determination.The precision of new model was validated by theory and practice,which meets the requirement of production. |
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