Effects of thermal maturation on stable organic carbon isotopes as determined by hydrous pyrolysis of Woodford Shale
Effects of thermal maturation on stable organic carbon isotopes as determined by hydrous pyrolysis of Woodford Shale
复制标题
DOI：
10.1016/0016-7037(83)90306-x
复制
发表时间：
1983-08
影响因子：
5
通讯作者：
M. Lewan
中科院分区：
文献类型：
--
作者：
M. Lewan
在自然系统中，获取从同一岩石单元在不同热成熟程度下排出的原油目前是不可行的。这防止了源岩中保留的有机物质与其在不同热成熟程度下排出的原油之间的成分变化直接相关。要缓解这一研究自然系统的不足，需要使用实验室实验。伍德福德页岩中无定形II型干酪根自然生成石油的过程可以通过水合热解来模拟，即在亚临界温度(<；374°C)下加热碎石与水接触。研究了热成熟对伍德福德页岩干酪根、沥青和排出类油热解产物δ~(13)C值的影响。与自然系统相似，从热解岩石中分离出的干酪根在δ13C上没有明显变化。这表明干酪根的δ~(13)C值在干酪根分型和油源岩对比中可能是有用的。从热解岩中提取的沥青的δ~(13)C值在生油初期呈下降趋势，在生油初期和生油后期呈下降趋势。这种反转不利于地球化学对比或成熟度评价。随着热成熟度的增加，沥青的饱和组分和极性组分显示出最大的δ13C变化。这两个组分的δ13C之间的差异给出了一个单向的趋势，作为热成熟度的总指标，被称为沥青同位素指数(BII)。排出的热解产物的δ13C值随着热成熟度的增加呈现单向增加的趋势。随着热成熟度的增加，排出的热解产物和沥青中芳香族组分的δ13C值的稳定性和相似性鼓励了它们在石油-石油和石油-烃源岩对比中的应用。排出的热解产物的同位素类型曲线表明，它们在石油-石油对比中可能有用，但在石油-烃源岩对比中的应用有限。
Acquiring crude oils that have been expelled from the same rock unit at different levels of thermal maturation is currently not feasible in the natural system. This prevents direct correlation of compositional changes between the organic matter retained in a source rock and its expelled crude oil at different levels of thermal maturation. Alleviation of this deficiency in studying the natural system requires the use of laboratory experiments. Natural generation of petroleum from amorphous type-II kerogen in the Woodford Shale may be simulated by hydrous pyrolysis, which involves heating crushed rock in contact with water at subcritical temperatures (<374°C). Four distinct stages of petroleum generation are observed from this type of pyrolysis; (1) pre-oil generation, (2) incipient-oil generation, (3) primary-oil generation, and (4) post-oil generation.The effects of thermal maturation on the δ13C values of kerogen, bitumen, and expelled oil-like pyrolysate from the Woodford Shale have been studied through these four stages of petroleum generation. Similar to the natural system, the kerogens isolated from the pyrolyzed rock showed no significant change in δ13C. This suggests that the δ13C value of kerogens may be useful in kerogen typing and oil-to-source rock correlations. δ13C values of bitumens extracted from the pyrolyzed rock showed an initial decrease during the incipient-oil generation stage, followed by depletion during the primary- and post-oil generation stages. This reversal is not favorable for geochemical correlation or maturity evaluation. Saturated and polar components of the bitumen show the greatest δ13C variations with increasing thermal maturation. The difference between the δ13C of these two components gives a unidirectional trend that serves as a general indicator of thermal maturation and is referred to as the bitumen isotope index (BII).δ13C values of the expelled pyrolysates show a unidirectional increase with increasing thermal maturation. The constancy and similarity of δ13C values of the aromatic components in the expelled pyrolysates and bitumens, with increasing thermal maturation, encourages their use in oil-to-oil and oil-to-source rock correlations. Isotopic type-curves for expelled pyrolysates indicate that they may be useful in oil-to- oil correlations, but have a limited use in oil-to-source rock correlations.