The Upper Paleozoic Coals In Ordos Basin: The Molecular Characterization And Their Kinetic Studies On The Hydrocarbon Generation

It is reported that the Upper Paleozoic coals are the major gas-source rocks in Ordosbasin, one of the most important oil-gas sedimentary basin in our country. Remarkablysuccesses have achieved in the evaluation on hydrocarbons potentials of the source rocks. However, the researches about the generation and transformation evolution of coal-derived hydrocarbons based on the new technique-kinetic of the hydrocarbon generation are limited. However, it is important for the natural gas exploration and recovery.Regarding the Upper Paleozoic coals (Taiyuan coal and Shanxi coal) in Ordos Basin, the present paper aims to discuss the geological and geochemical problems related with these coals, such as the generation and transformation evolution of coal-derived hydrocarbons by pyrolysis kinetic under constant high pressures, and these coals molecular properties by Py-GC-MS and Ruthenium-Ion-Catalyzed-Oxidation (RICO) reaction, including those of the raw coals, their covalent bond networks and non-covalentbond associated fractions. These results may supply helpful information to the mechanismon the hydrocarbons generation.The results of pyrolysis kinetic indicate that there are differences between these two coal's kinetic parameters of the hydrocarbon generation and of vitrinite reflectance. The coal-derived hydrocarbons' generation and transformation evolutions reconstructed by the kinetic of the hydrocarbon generation suggest that, large-scale secondary hydrocarbon generation is not likely during the uplifting and cooling process of Ordos basin. Compared the homogenization temperature of fluid inclusion with the maximum palaeotemperarure from the Ro kinetic, it infer that, the water-gas interfaces have migrated out of the strata driven by the natural gas in the middle and the east of Ordos basin, and the natural gas formed have not driven the water out in the north of Ordos basin. These results imply the good natural gas exploration foreground in the middle and the east of Ordos basin.The results from Py-GC-MS and RICO indicate that, there are differences in themolecular characterization between these two raw coals, their extracts and residues ofCS2-NMP mixed solvents, which is the key lead to the differences in their hydrocarbons generation behaviors. Further researches suggest the molecular structures, which are composing with abundant complex condensed aromatic fractions and a few alkyl groups attached to aromatic nuclei, are relatively constant of the residues of CS2-NMP mixture,and the differences are only in the composition of aromatic fractions. On the other hand, the molecular structure of the CS2-NMP mixture extracts, which are relatively variable, unexpectedly, have some complex condensed aromatic fractions and alkyl groups attached to aromatic nuclei.The paper discusses the possibility of hydrocarbons generation by the destroying and restraint of the associated structure and think that associated structure is important to hydrocarbons generation. A great deal of the geological and experimental facts can satisfactory explain with the existence of associated structure in coal and source rocks.