用^(13)CNMR CP/MAS波谱表征干酪根的性质

NATURE OF KEROGEN CHARACTERIZED BY SOLID STATE C-13 NMR SPECTROSCOPY

用固体^(13)C核磁共振(NMR)交叉极化(CP)魔角旋转(MAS)波谱技术,研究大庆地区不同类型与成熟度的20个干酪根样品的性质;根据7种化学结构与干酪根有关的模型物质的化学位移数据,总结干酪根NMR谱中脂碳与芳碳谱带峰型的变化规律,提出除视芳碳率f_a外,脂碳和芳碳峰的峰高与半峰宽之比h_1/B_1与h_2/B_2,与干酪根的结构密切相关,是表征干酪根类型与成熟度的良好参数。实验表明,干酪根的芳碳率、环缩合指数,以及h_1/B_1,h_2/B_2与H/C之间有很好的线性关系。据此提出了用f_a划分干酪根类型的具体指标,并用h_1/B_1与h_2/B_2作图以表征干酪根的类型及其演化途径。

Nature of twenty kerogen samples from Daqing Oilfields different in type and degree of maturity were investigated using solid state C-13 nuclear magnetic resonance spectroscopy with cross polarization (CP) and magic angle spinning (MAS) techniques. Carbon-13 chemical shift data of seven kerogen structure related model compounds provide knowledge about general patterns of aliphatic and aromatic bands in a C-13 NMR spectrum of kerogen. For the aliphatic band, peak height of the band will be centered around 30 ppm owing to the high abundence of long chain methylene carbons, while methyl, methine, cyclic methylene and oxygen bonded carbons broaden the band width at the half-height. For the aromatic band, the chemical shifts of protonated and bridged carbons concentrate in the range of 125-130 ppm, but will be scattered to 100-160 ppm due to the contribution of alkyl and oxygen substituted aromatic carbons. The apparent carbon aromaticity(f_a), ratio of peak height to width at half height of aliphatic and aromatic bands(h_1/B_1 and h_2/B_2) derived from NMR spectra represent the chemical structure of kerogen, and are found having good linear relationships with H/C. These parameters may be used for classifying the kerogen types and measuring the degree of maturity. An immature type I kerogen has a low carbon aromaticity f_a, say less than 0.23, high h_1/B_1, ranged 16～32 and low h_2/B_2 ranged 1-2; while for a type III kerogen, f_a will be higher than 0.5, h_1/B_1 lower than 6 and h_2/B_2 ranged 7～16; the intermediate values are assigned to the type II kerogen. A diagram plotted with h_1/B_1 and h_2/B_2 is suggested to illu-strate the kerogen evolution path of different types.