Gas generation from coal: taking Jurassic coal in the Minhe Basin as an example

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);theδ13C 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 ofδ13C1,δ13C2,δ13C3,andδ13CO2 were calculated.The diagrams ofδ13C1–δ13C2 vs ln(C1/C2)andδ13C2–δ13C1 vsδ13C3–δ13C2 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 ofδ13C1 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 inδ13CCO2 when the temperature was higher than 455°C.With increasing pyrolysis temperature,δ13C1–δ13C2 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.Theδ13C2–δ13C1 vsδ13C3–δ13C2 has three evolution stages corresponding to the breaking bonds between carbon and hetero atoms,demethylation and cracking of C6+,and cracking of C2–5.

Thermal simulation experiment of organic matter-rich shale and implication for organic pore formation and evolution

A thermal simulation experiment of diagenesis,hydrocarbon generation and evolution of the organic matter-rich shale was carried out to investigate formation and evolution of organic pores under the constraint from immature,low mature,mature,high mature to overmature geological conditions.The argon ion polishingefield emission scanning electron microscope was used to analyze microscopic features of original samples and simulated samples of various evolution stages.Results showed organic pores could be formed during hydrocarbon generation from biochemical and hypothermal processes in the immature and low mature stages,and the shale shallow-buried depth might be favorable for preservation of organic pores;the generation and evolution of organic pores were of heterogeneity,and the maturity was not a decisive factor which controlled formation and development of organic pores,while the difference in physiochemical structure of organic matter played an important role in formation and evolution of organic pores;the organic pore development was obviously related with the retained oil,and the organic pores formed in the oil generation stage were easily filled by pyrolysis asphalt;organic contraction fractures/organic marginal pores might be important storage spaces for shale gas occurrence,and their development was mainly controlled by the physiochemical structure and evolution degree of organic matters when the chemical adsorbed organic matter was converted into the physical adsorbed organic matter and the free organic matter.