Experimental and numerical study of coal mechanical properties during coalification jumps

The mechanical characteristics of coal reservoirs are important parameters in the hydraulic fracturing of coal.In this study,coal samples of different ranks were collected from 12 coal mines located in Xinjiang and Shanxi,China.The coal ranks were identified with by the increased Maximum vitrine reflectance(Ro,max)value.The triaxial compression experiments were performed to determine the confining pressure effect on the mechanical properties of coal samples of different ranks.The numerical approaches,including the power function,arctangent,and exponential function models,were used to find the correlation between coal elastic modulus and the confining pressure.The fitting equations of compressive strength and elastic modulus of coal ranks were constructed under different confining pressures.The results showed that the coal compressive strength of different ranks has a positive linear correlation with the confining pressure.The coal elastic modulus and confining pressure showed an exponential function.Poisson’s ratio of coal and confining pressure show negative logarithmic function.The stress sensitivity of the coal elastic modulus decreases with the increase of confining pressure.The coalification jump identifies that the compressive strength,elastic modulus,and stress sensitivity coefficient of coal have a polynomial relationship with the increase of coal ranks.The inflection points in coalification at Ro,max=0.70%,1.30%,and 2.40%,are the first,second,and third coalification jumps.These findings provide significant support to coal fracturing during CBM production.

Influence of tectonic stress on coalification:Stress degradation mechanism and stress polycondensation mechanism

The function of pressure for coalification is a long-term controversial issue, and the main cause is that the strata pressure and the tectonic stress were confused, which are two different actions of "pres-sure" . The former benefits the physical coalification but retards the chemical coalification, whereas the latter may not only affect the physical structure of coal but also promote its chemical composition changes. In accordance with the organic molecule evolution of coal, there are two kinds of basic mechanisms of the influence of the tectonic stress on the chemical coalification: the tectonic stress degradation and the tectonic stress polycondensation. The stress degradation mechanism is a process of that, when the tectonic stress acted on the large molecule of coal in the form of mechanical force or kinetic energy, some chemical bonds of low decomposed energy, such as aliphatic side-chain and oxygenic functional groups, were broken up and then were degraded into free radicals of less mo-lecular weight, and finally escaped from coal in the form of liquid organic matter (hydrocarbon). The stress polycondensation is considered that, under the control of the anisotropic tectonic stress, the condensed aromatic nucleus trend to be parallel arranged and to be enhanced through rotating or displacing of aromatic rings, the basic structural unit of coal (BSU) increases by directional develop-ment and preferential stack. X-ray diffraction (XRD), Fourier transformation infrared microspectroscopy (FTIR), and rock pyrolysis analysis (Rock-eval) were employed to study the deformed coal series and the non-deformed coal series. The results showed that, compared with the non-deformed coal, the de-formed coal exhibits particular characteristics: weaker aliphatic absorbance peak and stronger aro-matic absorbance peak, lower pyrolysed hydrocarbon yield, and more increscent BSU. The concepts of stress degradation mechanism and stress polycondensation mechanism presented here would not deny the dominant function of the temperature in coalification, but emphasize the "catalysis" of the tectonic stress in coalification.

Spectral narratives of microstructural restyling and their controls on hydrocarbon generation potential from coal

The low to medium-rank Tertiary coals from Meghalaya,India,are explored for the first time for their comprehensive micro-structural characterization using the FTIR and Raman spectroscopy.Further,results from these coals are compared with the Permian medium and high-rank coals to understand the microstructural restyling during coalification and its controls on hydrocarbon generation.The coal samples are grouped based on the mean random vitrinite reflectance values to record the transformations in spectral attributes with increasing coal rank.The aliphatic carbon and the apparent aromaticity respond sharply to the first coalification jump(R:0.50%)during low to medium-rank transition and anchizonal metamorphism of the high-rank coals.Moreover,the Raman band intensity ratio changes during the first coalification jump but remains invari-able in the medium-rank coals and turns subtle again during the onset of pregraphitization in high-rank coals,revealing a polynomial trend with the coal metamorphism.The Rock-Eval hydrogen index and genetic potential also decline sharply at the first coalification jump.Besides,an attempt to comprehend the coal microstructural controls on the hydrocarbon poten-tial reveals that the Tertiary coals comprise highly reactive aliphatic functionalities in the type I-S kerogen,along with the low paleotemperature(74.59-112.28℃)may signify their potential to generate early-mature hydrocarbons.However,the presence of type II-II admixed kerogen,a lesser abundance of reactive moieties,and overall moderate paleotemperature(91.93-142.52℃)of the Permian medium-rank coals may imply their mixed hydrocarbon potential.Meanwhile,anchizonal metamorphism,polycondensed aromatic microstructure,and high values of paleotemperature(~334.25 to~366.79℃)of the high-rank coals indicate a negligible potential of producing any hydrocarbons.

Action of Coal on Metal Corrosion in Coal Mines

Electrochemical corrosion behavior of metals under a variety of coal condition bas been studied in this paper. The corrosion dynamics and electrochemical parameters of metals have heen measured and the micrograph of metals corrosion has been analyzed. The results show that in the neutral electricity medium solution the metal corrosion rate varies greatly when metals contacted with different kinds of coal. The coal exerts an important action on corrosion of metal contacting with coal.In this case the deciding factors of this action are the coalification of coal and the relative electrode potential of metal. The effect of higher coalification coal with higher electroconductivity such as anthracite coal is vary noteworthy while the low coalification coal with low or without any electrocondutivity such as brown coal and coking coal produces little influence.

Enigmatic Glass-Like Carbon from the Alpine Foreland, Southeast Germany: A Natural Carbonization Process

Unusual carbonaceous matter, termed here chiemite, composed of more than 90% C from the Alpine Foreland at Lake Chiemsee in Bavaria, southeastern Germany has been investigated using optical and atomic force microscopy, X-ray fluorescence spectroscopy, scanning and transmission electron microscopy, high-resolution Raman spectroscopy, X-ray diffraction and differential thermal analysis, as well as by δ13 C and 14 C radiocarbon isotopic data analysis. In the pumice-like fragments, poorly ordered carbon matter co-exists with high-ordering monocrystalline α-carbyne, and contains submicrometersized inclusions of complex composition. Diamond and carbyne add to the peculiar mix of matter. The required very high temperatures and pressures for carbyne formation point to a shock event probably from the recently proposed Holocene Chiemgau meteorite impact. The carbon material is suggested to have largely formed from heavily shocked coal, vegetation like wood, and peat from the impact target area. The carbonization/coalification high PT process may be attributed to a strong shock that instantaneously caused the complete evaporation and loss of volatile matter and water, which nevertheless preserved the original cellular structure seen fossilized in many fragments. Relatively fresh wood encapsulated in the purported strongly shocked matter point to quenched carbon melt components possibly important for the discussion of survival of organic matter in meteorite impacts, implying an astrobiological relationship.

Discovery and implication of Late Pleistocene soft brown coal from Tengchong Basin, Western Yunnan

The Tengchong Basin, aboat 35 km^2 in area, is a dammed-by-lava type of theintermoniane basin with peat and soft brown coal. The sedimentation in the basin startedbefore 380 ka B. P., and the maximum thickness of the strata is about 250 m, in which

THE DISCOVERY AND SIGNIFICANCE OF BENZENE VAPOUR FROM COAL SEAMS, CHINA

Ⅰ. SAMPLES AND EXPERIMENT To study the composition of the coaibed gas, 139 coal samples containing gas from some important coalfields in China were analysed. They were taken from newly driven and mined faces. Since it is generally considered that as much as 80—90% of coalbed