Study On Structure And Gas Characteristics Of Tectonically Deformed Coal With Ductile Deformation

Taking Suzhou coalfield(mainly include Zhuaxianzhuang coal mine and Taoyuan coal mine where strongly deformed coal is well developed)as the research area,we collected some tectonically deformed coal samples with different ductile deformation after systematically analyzed the structural characteristics of the coalfield and coal mines.With the analysis on the macro and micro deformation characteristics,pore structure(using mercury intrusion method and low temperature liquid nitrogen method),permeability and methane isothermal adsorption,we analyzed the pore-fracture systems of different ductile tectonically deformed coal and their gas characteristics.Control of pore-fissure systems of tectonically deformed coal on gas behaviors was discussed as well.Some of main conclusions and knowledges are summarized as follows.(1)Macro and micro deformation characteristics of different kinds of tectonically deformed coal are studied.Based on deformation degree,the tectonically deformed coal of Suxian coalfield can be classified into three types,namely scaly coal(brittle-ductile series),crumpled coal,mylonitized coal(ductile series).There are some ductile deformation characteristics of different degree in different kinds of ductile tectonically deformed coal.In specimen scale,ductile tectonically deformed coals are characterized by some macro deformations,such as primary structure being not visible,secondary linear and planar structures developed in coal,directional arrangement of lens and twisted coal blocks,wrinkle formed by coal block,appearance of strong sliding friction surfaces.As to microscope scale,ductile tectonically deformed coals are characterized by some micro deformations,such as wrinkle deformation of coal macerals,circular shear fracture groups developed and combined to be scaly and lenticular,coal blocks directionally arranged or combined to be wrinkle.Scaly coal is characterized by developing scaly structure,which is formed by the intersecting of arc-shaped friction surfaces.Crumpled coal is characterized by developing wrinkles,secondary lineation,and secondary foliation.And with the increase of deformation degree,wrinkles incline to be smaller,more compressed,and more complexed.Mylonitized coal is mainly characterized by largely developing mylonitic particles and particle flows.(2)The pore structure of ductile tectonically deformed coal and its evolution law are revealed.There is a sharp increase of total pore volume(Vt)in the ductile tectonically deformed coal when compared with primary structure coal.With the increase of deformation degree and from scaly coal to mylonitized coal,Vt changed with the rule of “sharply increase after a slow decrease”,and there is a sudden big rise in mylonitized coal.The main pore of different ductile tectonically deformed coal is respectively “big hole”,“mesopore and big hole”,and “mesopore and small hole”.The aperture section of pore volume increase appeared to be smaller during the ductile deformation.Total specific surface area(St)of ductile tectonically deformed coal also increased significantly and the increase mainly occurred in pores with radium of 2 to 40 nm.St also gradually increased with the increase of deformation degree,and reached its maximum in the crumpled coal with strong deformation or in the mylonitized coal.Moreover,from scaly coal to mylonitized coal,pore structures of tectonically deformed coal seemed to be more and more complicated with the increase of deformation degree,which was illustrated by the fractal dimension of pore volume and coefficient curvature of pore increased obviously.There is lots of pore throats and flask hole emerged in coal,which resulted into increasingly obvious phenomenon including mercury retentions and nitrogen adsorption loops.(3)The adsorption characteristics of ductile tectonically deformed coal are discussed.Maximum methane adsorption capacity(Langmuir volume VL,daf)of ductile tectonically deformed coal is slightly larger than primary structure coal,with the maximum value appears in the strongly deformed coal.The data of Langmuir volume(PL,daf)was dispersed and there was a clear decrease in mylonitized coal.There is a good positive correlation between VL,daf and pore parameters such as pore volume,specific surface area of micro pore and small pore,and complexity of small pore.There are negative correlations between PL,daf and parameters such as fracture development,total volume,and total specific area of pore,while a positive negative correlation between PL,daf and the proportion of coal particles with a radium of bigger than 100μm.(4)The permeability of ductile tectonically deformed coal is systematically analyzed.The permeability of ductile tectonically deformed coal is obviously smaller than primary structure coal and decentralized,and has an apparent heterogeneity.The permeability,during the loading and unloading process,changed in the law of “scaly coal > crumpled coal with weak deformation > primary structure coal > crumpled coal with strong deformation > mylonitized coal”.The damage rate of permeability showed the law of “crumpled coal with weak deformation > primary structure coal > crumpled coal with strong deformation and mylonitized coal”.There seemed to be a negative correlation between permeability and development of micrometer-scaled fracture,the proportion of particles ranging from 10 to 100μm,total pore volume(mainly including small pore and mesopore),while a negative correlation between permeability and coefficient of pore curvature,replacement pressure,stage pore volume fractal dimension.Meanwhile,the change rate and damage rate are mainly influenced by fracture system(in both micro and macro scale),fragment characteristics coal,volume characteristics of small pore and medium pore.