| Based on the micro-deformation characteristics of tectonically deformed coal with highvolatile,this thesis reproduces the coal micro-deformation characteristics under in-situ temperature and pressure through a physical simulation experiment(high-temperature and highpressure deformation experiment).And then this thesis analyzes the influencing mechanism of the deformation environment(temperature,confining pressure,and differential stress)and the in-situ coal macro-micromechanical properties on the micro-deformation difference of high-volatile bituminous coal,revealing the response characteristics of pore structure,methane adsorption,and fracture distribution during the micro-deformation of high-volatile bituminous,as well as the effects of temperature,confining pressure,and differential stress on pore structure,methane adsorption,and fracture distribution during the tectonic deformation of high-volatile bituminous.The main achievements are as follows.(1)The control mechanisms of temperature,confining pressure,and differential stress on the micro-deformation difference of high-volatile bituminous coal.And the progressively evolutionary pattern of micro-deformation to high-volatile bituminous coal.Confining pressure and differential stress are the primary factors that cause the brittle deformation of coal,while temperature has little effect on the brittle deformation of coal.Differential stress is the main influencing factor for the ductile deformation of coal,followed by temperature and confining pressure.The temperature could be regarded as a “catalyst” for ductile deformation,and the catalyst effect is significant when the temperature is high.Confining pressure could be viewed as an “inhibitor” for coal ductile deformation,and the inhibitory effect is prominent when confining pressure is high.The ductile deformation of high-volatile bituminous coal is divided into two types:high-temperature ductile deformation and low-temperature ductile deformation.The boundary temperature for low-temperature and high-temperature ductile deformation of high-volatile bituminous is about 150 ℃ in Suxian study area.The progressive evolution of micro-deformation to high-volatile bituminous coal is as follows: primary structure,cataclastic structure,schistose structure,mortar structure,granulitic structure,scaly structure,wrinkle structure,and mylonitic structure.The brittle deformation is the basis of ductile deformation.(2)The in-situ coal macro-micromechanical properties and their effect on the microdeformation of high-volatile bituminous coal.At 100 ℃,the elastic modulus and hardness of each maceral follow the rule of exinite < vitrinite < inertinite in high-volatile bituminous coal.In inertinite,the aromatic carbon content is the highest,the aliphatic side-chain is the shortest,and the aromatic layer and stacked layers are the largest.It makes inertinite’s molecular structure stability the highest and the resistible stress the largest.Therefore,the inertinite has the largest elastic modulus and hardness.In exinite,aromatic carbon content is the lowest,aliphatic sidechain is the longest,and aromatic layer and stacked layers are the smallest.It makes inertinite’s molecular structure stability the lowest and the resistible stress the smallest.Therefore,the exinite has the smallest elastic modulus and hardness.In vitrinite,the content of aromatic carbon and the aliphatic side-chain stay middle,as well as the aromatic layer and the number of stacked layers.It makes the molecular structure stability and the resistible stress of vitrinite stay middle.Therefore,the vitrinite has the middle elastic modulus and hardness.At the scale of hand specimen,the microdeformation difference of high-volatile bituminous coal is mainly caused by the various macromechanical properties of coal.The coal with larger macroscopic elastic modulus and hardness has a greater ability to resist the deformation,which tends to generate fractures under stress,forming brittle deformation.Oppositely,the coal with smaller macroscopic elastic modulus and hardness has a weaker ability to resist the deformation,which tends to generate the curved particles under stress,forming ductile deformation.At the scale of maceral,the micro-deformation difference of high-volatile bituminous coal is mainly caused by the various micro-mechanical properties of coal(i.e.,the mechanical properties of maceral).The exinite with smaller elastic modulus and hardness is easy to produce the curved ductile deformation under stress,while the vitrinite and inertinite with larger elastic modulus and hardness are easy to produce the fragmented brittle deformation under stress.(3)The function mechanisms of temperature,confining pressure,and differential stress on the pore structure heterogeneity during the tectonic deformation evolution of high-volatile bituminous coal.Under the compression of confining pressure and differential stress,the new micro-fractures break some macropores,part of the micro-fractures transform into macropores,part of the macropores transform into mesopores,and part of the mesopores transform into micropores.Meanwhile,under the softening of temperature,the above three transformations become more significant.The volume variation of each pore is caused by the difference in their respective pore size distribution.On the other hand,the occurrence and persistence of confining pressure and differential stress strengthen the brittle deformation in high-volatile bituminous coal.The main morphology of macropores is gradually transformed into the ink-bottle pores and slit pores from the original cylinder pores under the compression of stress.The main morphology of mesopores is gradually transformed into the wedge pores and bottle-neck pores from the original cylinder pores.With the continuation of differential stress,the ductile deformation is enhanced incessantly,and the wedge pores appear and gradually increase in the macropore under the combined action of temperature softening and stress compression.The slit pores and bottle-neck pores appear and gradually increase in the mesopore.(4)The function mechanisms of temperature,confining pressure,and differential stress on the methane adsorption heterogeneity during the tectonic deformation evolution of high-volatile bituminous coal.The methane adsorption is closely related to the specific surface area of micropores in high-volatile bituminous coal.As the specific surface area of micropores increases,the Langmuir volume of methane adsorption gradually increases,and the methane adsorption capacity gradually increases.The occurrence and persistence of confining pressure and differential stress strengthen the tectonic deformation evolution of high-volatile bituminous coal from primary structure coal to brittle deformed coal.In particular,a small number of mesopores are compressed and converted into micropores,slightly increasing the specific surface area of micropores,which raises the Langmuir volume and adsorption capacity of methane slightly.However,the difference between brittle deformed coals is slight.With the continuation of differential stress,ductile deformation is enhanced incessantly in high-volatile bituminous coal.The ductile flow of fine particles and their long-time friction with each other generate heat,raising the coal temperature and softening the coal slightly.Combined with the stress compression,a small number of mesopores in coal slowly transform into micropores,which raises the specific surface area of micropores slowly and then boosts the Langmuir volume and adsorption capacity of methane slowly.(5)The function mechanisms of temperature,confining pressure,and differential stress on the fracture distribution heterogeneity during the tectonic deformation evolution of high-volatile bituminous coal.The occurrence and persistence of confining pressure and differential stress strengthen the tectonic deformation evolution of high-volatile bituminous coal.The fractures in coal gradually increase and reach the maximum at the stage of wrinkle coal.Subsequently,the fine particles in coal generate strong ductile flow under the continuation of differential stress,which fills or compresses part of fractures,condensing the coal.Thus,the fractures slightly decrease at the stage of mylonitic coal.Meanwhile,the fracture distribution shows anisotropy in various tectonically deformed coals,mainly developing along the direction of differential stress and densely developing in the stress concentration area.On the other hand,when the coal-bearing stratum is gradually lifted,the rock outcrop is slowly denuded,and the tectonic stress steadily increases,the temperature and confining pressure suffered by the coal seam slowly decrease.The differential stress slowly increases,gradually increasing the number of macro-fractures in the coal seam.This thesis has 113 figures,21 tables,and 402 references. |
