Gas generation from coal: taking Jurassic coal in the Minhe Basin as an example
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Gas generation from coal: taking Jurassic coal in the Minhe Basin as an example Deliang Fu1,2 Yu Ma3
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Guosheng Xu2 • Li Ma1 • Fu Yang1 • Dan He1 • Zhonghui Duan1
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Received: 23 May 2019 / Revised: 15 September 2019 / Accepted: 2 April 2020 Ó The Author(s) 2020
Abstract The gas generation features of coals at different maturities were studied by the anhydrous pyrolysis of Jurassic coal from the Minhe Basin in sealed gold tubes at 50 MPa. The gas component yields (C1, C2, C3, i-C4, n-C4, i-C5, n-C5, and CO2); the d13C of C1, C2, C3, and CO2; and the mass of the liquid hydrocarbons (C6?) were measured. On the basis of these data, the stage changes of d13C1, d13C2, d13C3, and d13CO2 were calculated. The diagrams of d13C1–d13C2 vs ln (C1/ C2) and d13C2–d13C1 vs d13C3–d13C2 were used to evaluate the gas generation features of the coal maturity stages. At the high maturity evolution stage (T [ 527.6 °C at 2 °C/h), the stage change of d13C1 and the CH4 yield are much higher than that of CO2, suggesting that high maturity coal could still generate methane. When T \ 455 °C, CO2 is generated by breaking bonds between carbons and heteroatoms. The reaction between different sources of coke and water may be the reason for the complicated stage change in d13 CCO2 when the temperature was higher than 455 °C. With increasing pyrolysis temperature, d13C1–d13C2 vs ln (C1/C2) has four evolution stages corresponding to the early stage of breaking bonds between carbon and hetero atoms, the later stage of breaking bonds between carbon and hetero atoms, the cracking of C6? and coal demethylation, and the cracking of C2–5. The d13C2–d13C1 vs d13C3–d13C2 has three evolution stages corresponding to the breaking bonds between carbon and hetero atoms, demethylation and cracking of C6?, and cracking of C2–5. Keywords Jurassic coal Pyrolysis Gas generation d13C Stage evolution
1 Introduction The natural gas generated from different origins provides its formation characteristics during its evolution (Behar et al. 1992, 2008, 2010; Wang et al. 2013). Coal-formed gas has been an important field of natural gas and plays an
& Deliang Fu [email protected] 1
Key Laboratory of Coal Exploration and Comprehensive Utilization, Ministry of Nature and Resources, Shaanxi Coal Geology Group Co., Ltd., Xi’an 710021, China
2
College of Energy, Chengdu University of Technology, Chengdu 610059, China
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Ningxia Institute of Geological Survey, Yinchuan 750000, China
important role in China’s natural gas resources (Dai et al. 2014). The heterogeneity of coal is strong, and the evolution features of coal-formed gas are more complex than those of other source rocks (Sun et al. 2013). The kinetics of hydrocarbon generation extend the hydrocarbon generation of coal under laboratory conditions to geologic history (Butala et al. 2000; Ping’an et al. 2009; Shuai et al. 2006), which simplifies the gas evolution of the coal. d13C is one of the most important properties of natural gas. The d13C of coal-formed methane has obvious evolution stage feature
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