Determination of molecular structure of kerogens using 13C NMR spectroscopy: II. The effects of thermal maturation on kerogens from marine sediments

Chemical and nanometer-scale structure of kerogen and its change during thermal maturation investigated by advanced solid-state 13C NMR spectroscopy

“…It exhibits a decreasing trend with increasing thermal maturity in the order 634-1 % 472-1 > 548-1 % IL-3 > 554-1 % IL-6, see top of Fig. 11a, consistent with the findings of Patience et al (1992). The fraction of aromatic bridgehead carbons is discussed below.…”

“…Comparison with dipolar-dephased spectra shows that around 125 ppm, the signals of protonated aromatics are coincident with those of one of two nonprotonated aromatic bands. However, Patience et al (1992) and Wei et al (2005) as- signed all of this signal to (nonprotonated) bridgehead carbons and built their assessment of the degree of condensation on this assumption. Subspectra of CH 2 signals are shown in Figs.…”

“…For example, Patience et al (1992) subdivided alkyl carbons into C, CH, CH 2 (in midchain or ring), CH 2 (adjacent to a methyl group), and CH 3 (attached to alkyl or aromatic C) based on chemical shifts of carbon types of model compounds. With heavily overlapping chemical shift ranges, this was an imprecise means of making chemical shift assignments.…”

Solid state 13C NMR analysis of shales and coals from Laramide Basins. Final report, March 1, 1995--March 31, 1996

“…Basically, the NMR measurements show how the distribution of aliphatic and aromatic carbons changes with time and temperature during burial. The loss of aliphatic carbon is associated with oil and gas production because these carbons have a sufficient number of attached hydrogens to produce hydrocarbons (Patience et al 1992. Aromatic carbons, being hydrogen deficient, generate little oil or gas.…”

“…These results supported other geochemical analyses that were acquired on the suite of samples. The NMR data were combined with Rock-Eval data to estimate the hydrogen budget for petroleum generation using a recently developed methodology (Patience et al 1992 Additional NMR measurements and techniques were also employed to obtain information about chemical changes in sedimentary organic matter that occurs during artificial and natural maturation. Solid-state I3C NMR measurements were combined with elemental analysis and mass balance data to determine the amount of aromatization of aliphatic carbon moieties that occurs during hydrous pyrolysis of coals from the Washakie Basin.…”