The Deformed Coal Structural Evolution And Its Control To Gas Properties

Deformed coal is the product of tectonic action. Deformed coal with high energy gas is the essential condition of coal and gas outburst. Following the idea of “the structure determines the nature”, three pairs nature coals and symbiontic deformed coals of different metamorphic grade of coal and 9 deformed coals in fault area from Pingdingshan No.8 Coalmine were analyzed and discussed in this paper. Textural analysis methods, such as FT-IR,13 C NMR, XRD, mercury intrusion, low nitrogen adsorption, the isothermal gas adsorption and desorption experiment were applied to selected experimental samples for determining the evolutional characteristics of deformed coal, meanwhile the related research results about coal macromolecular structure, lower weight molecule composite, pore structure and their relationship with gas properties were analyzed and summarized. The evolutional law of deformed coal structure with the help of Mechanochemistral function was revealed preliminarily, the mechanism for Mechanochemistral hydrocarbon generated was analyzed, and the structural control to gas properties of deformed coal was discussed.The main conclusions of the research are as follows:(1)Tectonic action does not only control the structural evolution of deformed coal,but also provide the energy for it. The trend of Structural evolution of deformed coal under the Mechanochemistral function is similar to temperature. The results show that the alkyl side chain shed and the aromatic system increased in deformed coals in the process of the tectonic stress, which suggests the leading effect to the structural evolution of coal.(2) Deformed structure jump in middle rank coals is the mutual competition for aliphatic side chains with aromatic system, The alkyl side chain shedding is remarkable for fat coal, and it’s possible to form the long-chain aliphatic or naphthenic hydrocarbon with methylene enriching relatively. At the same time, aromatic condensation and aromatization effect are competing each other to promote the growth of aromatic system.(3) With the increase of the coal metamorpic grade, it is showed a decrease tendency in unstable oxygen functional groups,-OH/NH; the stable groups, C-O andCH2-C=O, increased, and then decreased. The evolution of oxygen functional groups is related to the tectonic position of coal seam, which is reducing gradually in the closed system, but the hydroxyl groups of deformed coal surface is increasing and enhance the water because of slow oxidation in fault area.(4)The material origin of hydrocarbon generated is composed coal macromolecular structure and lower weight molecule composite. The periodic tectonic activity leads deformed coal structural evolution from a closed, semi closed system into a semi closed,open system, which greatly promotes organic reactions toward the direction of the increased volume, and is beneficial to hydrocarbon generation. Hydrocarbon generation and expulsion is mutually stimulative and inhibited, which forms organic unity. Meanwhile the mineral in deformed coal has a catalytic effect on hydrocarbon generation.(5)With the increase of tectonic action, the dominant pores of different damage degree deformed coal reduce and become uniform. micropores are dominant in deformed coal. Pore volume and specific surface area of all the pores are relatively more than those of undeformed coal, which macropores and mesopores increase obviouslier. The thin-neck-bottle-shaped pores enlarge further and the pore connectivity decreases in deformed coal. oal macromolecular structure determines the structural evolution of nano-scale pores and controls to gas adsorption. Lower weight molecule composite transforms pore structure and pore size distribution, and changes the gas adsorption layer. Pore structure provides space for gas adsorption, pores and fracture provide a channel for the gas diffusion and osmosis. The formation and propagation of microfractures in gas-filled coal are intermittent, non-continuous. The increasing microfractures promote the reaction of organic chemistry that contributes to produce gas.The evolution of microstructure controls to gas properties of deformed coal.