Three kerogen samples(JJZG-1,JJZG-2 and JJZG-3)isolated from the Permian Lucaogou shales of varying biodegradation levels(BLs≈0,3 and 7,respectively)were subjected to sequential stepwise pyrolysis combined with on-li...Three kerogen samples(JJZG-1,JJZG-2 and JJZG-3)isolated from the Permian Lucaogou shales of varying biodegradation levels(BLs≈0,3 and 7,respectively)were subjected to sequential stepwise pyrolysis combined with on-line detection of gas chromatography-mass spectrometry(GC-MS).Occluded fractions(bitumenⅡ)released at low-temperature steps(≥410℃)show consistent biodegradative signatures with that reported for solvent-extracted fractions(bitumenⅠ)of the original shales,e.g.,broad range of abundant n-alkanes,isoprenoids and regular hopanes for the non-biodegraded JJZG-1;trace n-alkanes and abundant hopanes for the moderately biodegraded JJZG-2;and no n-alkanes but still prominent hopanes including the microbially produced 25-nohopanes for the severely biodegraded JJZG-3.This consistency between bitumenⅡand bitumenⅠfractions indicates the biodegradability of the kerogenoccluded bitumenⅡwith limited protection from host kerogen.A minor level of protection was suggested by the trace distribution of n-alkanes in the bitumenⅡof JJZG-2,whereas the bitumenⅠhad no nalkanes.The kerogen itself was more resistant to biodegradation as reflected by the persistence of high abundances of both n-alkanes and hopanes in the high temperature(≥460℃)products of all three kerogen samples.However,the relative abundances of these product groups did show some evidence of biodegradation alteration,e.g.,ratios of n-C_(15)alkene/C_(27)hop-17(21)-ene at 510℃pyrolysis decreased by order of magnitude from the non-biodegraded(JJZG-1=27.4)to highly biodegraded(0.3 for JJZG-3)samples.The reduced biodegradation impact on the kerogen fraction(Cf.bitumen fractions)was also evident by the absence of 25-norhopanes in the high-temperature analysis of the JJZG-3 kerogen.展开更多
基金supported by the National Natural Science Foundation of China(grants No.41972163 and 42173055).
文摘Three kerogen samples(JJZG-1,JJZG-2 and JJZG-3)isolated from the Permian Lucaogou shales of varying biodegradation levels(BLs≈0,3 and 7,respectively)were subjected to sequential stepwise pyrolysis combined with on-line detection of gas chromatography-mass spectrometry(GC-MS).Occluded fractions(bitumenⅡ)released at low-temperature steps(≥410℃)show consistent biodegradative signatures with that reported for solvent-extracted fractions(bitumenⅠ)of the original shales,e.g.,broad range of abundant n-alkanes,isoprenoids and regular hopanes for the non-biodegraded JJZG-1;trace n-alkanes and abundant hopanes for the moderately biodegraded JJZG-2;and no n-alkanes but still prominent hopanes including the microbially produced 25-nohopanes for the severely biodegraded JJZG-3.This consistency between bitumenⅡand bitumenⅠfractions indicates the biodegradability of the kerogenoccluded bitumenⅡwith limited protection from host kerogen.A minor level of protection was suggested by the trace distribution of n-alkanes in the bitumenⅡof JJZG-2,whereas the bitumenⅠhad no nalkanes.The kerogen itself was more resistant to biodegradation as reflected by the persistence of high abundances of both n-alkanes and hopanes in the high temperature(≥460℃)products of all three kerogen samples.However,the relative abundances of these product groups did show some evidence of biodegradation alteration,e.g.,ratios of n-C_(15)alkene/C_(27)hop-17(21)-ene at 510℃pyrolysis decreased by order of magnitude from the non-biodegraded(JJZG-1=27.4)to highly biodegraded(0.3 for JJZG-3)samples.The reduced biodegradation impact on the kerogen fraction(Cf.bitumen fractions)was also evident by the absence of 25-norhopanes in the high-temperature analysis of the JJZG-3 kerogen.
