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Li W.,China University of Mining and Technology | Li W.,Key Laboratory of Coalbed Methane Resource and Reservoir Formation Process | Li W.,University of Queensland | Zhu Y.,China University of Mining and Technology | Zhu Y.,Key Laboratory of Coalbed Methane Resource and Reservoir Formation Process
Energy and Fuels | Year: 2014

Vitrinite samples inserted into a furnace at room temperature and heated at a rate of 10 °C/h were subjected to X-ray diffraction analysis, Fourier transform infrared spectroscopy (FTIR), and solid-state 13C nuclear magnetic resonance spectroscopy (13C NMR) to characterize the macromolecular structure of vitrinite of different ranks of coal, which was discussed with respect to changes in its chemical structure. The results demonstrate that the relationship between average reflectance of the vitrinite and temperature is linear. The structural parameters of vitrinite separated from the coking coal sample collected from the Lujiatuo mine (LJTV) (d002 = 3.56 Å, Lc = 11.62 Å, La = 10.99 Å) were obtained. The FTIR spectra include bands characteristic of aliphatic C-H stretching, with the ratio of aliphatic oxygen-containing compounds decreasing with increasing rank of the vitrinite samples. The C=O stretching contribution is lower than the aliphatic C-H stretching contribution, whereas the aromatic carbon contribution is high in all of the samples. The vitrinite structural parameters, e.g., the A factor, C factor, CH2/CH3, A ar/Aal, Al/OX, Al/C=C, and C=O/C=C, were calculated. The intensity of the aromatic carbon peak is considerably greater than that of the aliphatic carbon peak. The 13C NMR spectra reveal that the aliphatic carbon content decreases progressively with increasing thermal maturity for the replacement of aromatic hydrogens by condensation. The CCH3 groups are removed more slowly than are the C(CH2)C groups. The coalification progress was divided into two stages based on the CH 2/CH3 ratio, which first decreases and later increases. As revealed by the structural parameter fa, the aromaticity of vitrinite increases during pyrolysis. © 2014 American Chemical Society. Source


Zou M.,China University of Mining and Technology | Zou M.,Key Laboratory of Coalbed Methane Resource and Reservoir Formation Process | Wei C.,China University of Mining and Technology | Wei C.,Key Laboratory of Coalbed Methane Resource and Reservoir Formation Process | And 3 more authors.
Energy Exploration and Exploitation | Year: 2013

Based on the geological data and drainage parameters of QN01 coalbed methane (CBM) well which is located at the southern Qinshui Basin, by using CBM reservoir numerical modeling technology, 15 years' gas recoverability is predicted and the dynamic variation of reservoir pressure is studied for both QN01 well and an assumed 300 x 300m well net group by using the same parameters as QN01 well. The results show that for single well, within the first 300 days, gas recoverability is similar everywhere in the gas supply area and the dropping rates of reservoir pressure are all below 1 KPa/d. Further more, the region more than 120 m away from the well bore hole is not beneficial for gas recoverability. For well net group, dropping rates of reservoir pressure are higher than 1 KPa/d. With the increase of the distance to the well bore hole, gas outcomes more and more in the gas supply area. Similarly, the "secondary reservoir pressure dropping" caused by the well interference in the well net group has a positive correlation with the distance to the well bore hole, and the dropping rates of reservoir pressure of the well net group are approximately twice as large as those of the single well. © 2008 IOS Press and the authors. All rights reserved. Source


Li W.,China University of Mining and Technology | Li W.,Key Laboratory of Coalbed Methane Resource and Reservoir Formation Process | Li W.,University of Queensland | Zhu Y.,China University of Mining and Technology | And 4 more authors.
Energy and Fuels | Year: 2014

An energy barrier mechanism exists in the hydrocarbon generation of vitrinite. Traditional coal geochemistry is unable to explain the mechanism of the macromolecular structure evolution in the process of hydrocarbon generation. This paper studies the hydrocarbon generation characteristics by thermal simulation experiments to obtain the control mechanism of the vitrinite macromolecular structure evolution control on hydrocarbon generation. The vitrinite structure characteristics were studied by Fourier transform infrared spectroscopy (FTIR) and carbon-13 nuclear magnetic resonance (13C NMR), and the structural parameters of vitrinite were calculated. On the basis of building the model of the macromolecular structure in a vitrinte sample, the coupling mechanism between hydrocarbon generation and the evolution of the vitrinite structure was determined through quantum chemistry. These results are important and practical for the coalification theory and coalbed methane (CBM), shale gas, and other unconventional gases. The results showed that the hydrocarbon production rate increased along with increasing maturity. Gaseous hydrocarbon consists of methane and heavy hydrocarbon alkanes and alkenes. The C2-5/C1-5 ratio decreases linearly with increasing maturity. The intensity of the vitrinite functional group absorption peak decreases. Aliphatic hydrocarbons have an absorption peak before 430 C, which then declines to periodic variation characteristics. The intensity of the absorption peak because of the Cî - O moiety of aromatic hydrocarbons (1600 cm-1) decreases. The response of the intensity of substituted aromatic hydrocarbons is weak. A polyester reaction occurs at 450 C. The aromatic carbon rate change is divided into three stages. The average molecular potential energy decreases with the pyrolysis process. Vitrinite removed the methyl macromolecular structure first and then the aliphatic hydrocarbons, aliphatic chain rings, and other bonds. © 2013 American Chemical Society. Source


Zou M.,China University of Mining and Technology | Zou M.,Key Laboratory of Coalbed Methane Resource and Reservoir Formation Process | Wei C.,China University of Mining and Technology | Wei C.,Key Laboratory of Coalbed Methane Resource and Reservoir Formation Process | And 5 more authors.
Arabian Journal of Geosciences | Year: 2014

Drainage of formation water controls pressure dropping behavior of coalbed methane wells. Different behaviors indicate that formation water can be classified into two types. The first type is ineffective water, representing the water from aquifers of strong, extremely strong water yield property, or phreatic water. It is difficult to generate pressure dropping when this type of water is pumped. The other type is effective water, representing the water from aquifers of middle or weak water yield property. Pressure decline will occur if this type of water is pumped. Based on the modified Duipt equation, the production of effective water and the production percentage of ineffective water for well QNPN01 are calculated considering the variations of influence radius, absolute permeability, and relative water permeability. The results show that in the single water flow stage, the production of effective water and the production percentage of ineffective water drop in the zigzag way at first and then keep stable roughly. In the water-gas flow stage, the production of effective water decreases firstly and then keeps stable, while the production percentage of ineffective water increases firstly and then keeps stable. Furthermore, the production of effective water in unit pressure decline indicates that the process of pressure dropping can be divided into four stages. The first one is a single water flow stage in which pressure dropping completely depends on effective water. The second one refers to the beginning of a water-gas flow stage. In the stage, pressure dropping strongly depends on effective water. Pressure dropping caused by effective water drainage starts to be replaced by gas desorbing in the third stage, and completely replaced in the fourth stage. © 2013 Saudi Society for Geosciences. Source


Li T.,China University of Mining and Technology | Li T.,Key Laboratory of Coalbed Methane Resource and Reservoir Formation Process | Wu C.,China University of Mining and Technology | Wu C.,Key Laboratory of Coalbed Methane Resource and Reservoir Formation Process | And 2 more authors.
Journal of Natural Gas Science and Engineering | Year: 2015

Micro-fractures and macro-fractures are abundant in coal reservoirs, and the formation of such fractures depends on the coal-bearing environment. In addition to the development of fractures, the gas content and coalbed methane productivity are also controlled by the coal-bearing environment. Research on micro-fracture characteristics is conducted through microscopic observation, and research on macro-fracture characteristics is conducted by investigating coal cores. The method of quantitative statistics is adopted for the measure of the submaceral, and the coal facies parameters are calculated. The coal structure is explained using logging data. Then, the coalbed methane productivity controlled by the coal facies is examined. The results show that Type D micro-fractures are well developed, followed by Type C micro-fractures. The micro-fractures are primarily tensional fractures, implying that the formation of micro-fractures is controlled by external stress. Micro-fractures pass through the macropores and effectively link with other micro-fractures, whereas macro-fractures are primarily developed in clarain bands and cataclastic texture coal. The gas content increases with the gelatification index (GI) and ratio of vitrinite to intertinite (V/I) in the coal reservoir, which are favourable coal facies geological conditions for coalbed methane production. However, whereas the production of the coalbed methane wells is in its initial stage, the methane produced is mostly free and strongly desorbed gas. The coal structure primarily contributes to the permeability of the coal reservoir. The development of Type II coal can increase the production of methane, whereas the development of Type III coal has the opposite effect. © 2015 . Source

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