Experimental and molecular dynamics investigation on the pyrolysis mechanism of Chang 7 type-II oil shale kerogen

Abstract

In the present study, molecular characteristics of type-II oil shale kerogen of Chang 7 in Changqing Oilfield in Ordos Basin are acquired by pyrolysis-gas chromatography-mass spectroscopy (Py-GCMS), solid-state 13 C nuclear magnetic resonance ( 13 C NMR) and X-ray photoelectron spectroscopy (XPS). Its pyrolysis mechanism is investigated by reactive force field molecular dynamics at 2000–3000 K. The optimal temperature for oil and organic gas yield of Chang 7 type-II oil shale kerogen are obtained. Bond breakage sites for Chang 7 type-II oil shale kerogen are proposed. Cross-linking at the optimal temperature is investigated. Formation mechanism of typical gas molecules is revealed by explaining HS and HO radical competition. The results show that the molecular structure of Chang 7 oil shale kerogen is highly aromatic based on the results of Py-GCMS, solid-state 13 C NMR and XPS. For decomposition of Chang 7 oil shale kerogen, the sequence of the bond breakage is determined by the bond order. For cross-linking of Chang 7 oil shale kerogen, H radical is the dominated factor of the formation of thiophene. The number of H 2 O molecules is more than those of CH 4 and CO 2 molecules at the same temperature. Compared with HS radicals, HO radicals capture more H radicals to generate H 2 O molecules. The results are useful for highly efficient development of shale oil in Ordos Basin, China. • Pyrolysis mechanism of Chang 7 type-II oil shale kerogen is investigated. • The study is based on experimental and molecular dynamics results. • Chang 7 oil shale kerogen structure is highly aromatic. • The optimal temperature of oil and organic gas yield is at 2400 K.